Army Aviation Digest - Sep 1968

8/12/2019 Army Aviation Digest - Sep 1968

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UNITED ST TES ARMY AVIATION

DIRECTOR OF ARMY AVIATION ACSFORDEPARTMENT OF THE ARMY

BG Edwin L Powell Jr.

COMMANDANT U. S. ARMY AVIATION SCHOOL

MG Delk M. Oden

ASST COMDT U. S. ARMY AVIATION SCHOOL

COL M. H. Parson

DIGEST EDITORIAL STAFF

LTC J. R. Dome ChiefRichard K. Tierney EditorWilliam H. SmithJohn P. JonesLinda McGowan

GRAPHIC ART SUPPORT

Harold G. LinnHarry A. PickelDorothy L. CrowleyAngela A. Akin

DIRECTOR U. S. ARMY BOARD FOR AVIATIONACCIDENT RESEARCH

COL Russell P. Bonasso

USABAAR PUBLICATION S AND GRAPHIC S DIV

Pierce L Wiggin ChiefWill iam E. CarterJack DeloneyTed KontosCharles MabiusPatsy ThompsonMary W. Windham

SEPTEMBER 1968 VOLUME 14 NUMB

EDITOR'S NOTE

ROKA HELICOPTER SCHOOL, MAJ William H. Gardner

COLOR ROD GREEN, MAJ Richard A Baynard

FATIGUE AND NIGHT FLYING , MAJ Ira L Hartwell

ARMY AVIATION IN THE ANTARCTIC, John Penman Jones

ARADMAC, Ray Farley

WHAT PRICE COMPLACENCY? CPT J. O Estes

MAIL ORDER INSTRUMENT TICKET

EROSION AND YOU, CPT James M. Morris

THE FIRE TEAM, CW2 John M. Barber

FM HOMING AS AN INSTRUMENT NAVAID, CW2 John R. Fox

LET'S HIGHLIGHT NIGHT FLIGHT, CPT Frank Gall

O NO O

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WOOD THAT I COULD TALK, LTC Charles W Sills

FACT OR FICTION, MAJ Joe D Jobe

GO NO GO SENSE, MAJ Chester Goolrick

ADVANCE OF TORNADIC TURBULENCE, Fred C Bates

SYSTEM SAFETY, LTC Clement A Wyllie

PEARL 'S

THE GENTLE ART OF ORING INSTALLATION

USAASO SEZ

LSE Inside

The mission of the U. S. ARMY AVIATION DIGEST is to provide information of an operationaor functional nature concerning safety and aircraft accident prevention . training maintena.ncoperations research and development aviation medicine and other related data .

The DIGEST is an official Department of the Army periodical published monthly undersupervision of the Commandant U. S. Army Aviation School. Views expressed here in arenecessarily those of Department of the Army or the U. S. Army Aviation School. PhotosU. S. Army u n l ~ sotherwise specified. Material may be reprinted provided credit is given toDIGEST and to the author unless otherwise indicated .

Articles photos and items of interest on Army aviation are invited. Direct communicationauthorized to: Editor U. S. Army Aviation Digest Fort Rucker Ala. 36360.

Use of funds for printing this publication has been approved by Headquarters Departmentof the Army 3 Novemb . r 1967 .

Active Army units receive distribut ion under the pinpoint distribution system as outlinedAR 3101. Complete DA Form 12-4 and send directly to CO AG Publications Center 2Eastern Boulevard Baltimore Md. 21220. For any change in distribution requirements initiaterevised DA Form 12-4.

National Guard and Army Reserve units submit requirements through their State adjutantsgeneral and U. S. Army Corps commanders respectively.

For those not eligible for official distribution or who desire personal copies of the DIGEpaid subscriptions 4 .50 domestic and 5 .50 overseas are available from the SuperintendentDocuments U. S. Government Printing Office Washington D. C. 20402.


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EDITOR S NOTE: In this issue the DIGEST features the U. S. Army Aviation De -tachment which is supporting personnel engaged in antarctic studies. To free the articleof possible distractions, some interesting points about Antarctica itself were omitte d. How-ever it is felt the reader will appreciate the achievements of the aviation ection andthe people with whom it works much mQre if they have an idea of the unique barriers impo ed by the antarctic environment.

The average man knows little about Antarctica, other than that it is cold and is atthe bottom of the earth. He wants to knQw more, and that is one of the reasons the Armyhas a detachment operating there.

How cold Antarctica is depends on the location, since the continent is as large as Mexico

and the United States combined. The official low has been recorded as 126.9 below zeroFahrenheit at the Soviet Union s Vostok Station. Yet temperatures as high as 42 abQvezero have been recorded at McMurd.o Sound.

Scientists estimate that 95 percent of the world s permanent ice is located within theantarctic convergence, a hypothetical line surrounding the continent where the cold seameets the warmer water from the tropics. Seafarers who cr oss this imaginary line reporta rapid drop in temperature of some 10F, the only indication of entering the convergence.

All together there are about seven milliQn cubic miles of snow and ice piled on the continent. Scientists theorize that should it melt, the earth s seas would rise by nearly 200 feet.This would cover the entire state of Florida and much of the rest of our country. Also,they estimate the weight of the iCe to be so tremendous that if it were removed the continent itself would rise unevenly by as much as 2,500 feet.

Aside from the cold Antarctica offers the worst weather in the world. Along the GeorgeV Coast, winds of 100 mile per hour are frequent and have been reported as high as 200miles an hour. Changes in weather are frequent and zero-zero conditions are common.

Geographically Antarctica differs from the arctic in that it is a continent surroundedby seas. The arctic, on the other hand, is an ocean surrounded by land.

An.other difference is that there are no polar bears in Antarctica, and all existing lifeis either sea life or inhabits the warmer coastal regions. Animal life consists of severalvarieties of seals; seven species of penguins; Skuas and Snow Petrels, flying birds that looklike gulls; and whales, including the vicious killer whales and enormou blue whales. Thereis an abundance of sea life, which is being considered as a possible source of food to alleviatesome of the world s shortages.

Inland i the largest area void of life on earth. Unless it can be seen personally, it is

impossible to conceive travelling as far as from Maine to Acapulco, Mexico, without asingle sign of life - plant or animal.Being south of the equator, the seasons are reversed. Like the arctic region, summer is

one long day and winter is one long night. There is only one sunrise and one sunset peryear at the pole itself.

Evidence, including fossils, petrified tree trunks and geological findings, indicate Ant-arctica was at one time covered with lush rain forests and enjoyed a warm climate. Whyit has changed to a frozen land is one of the answers scientists are seeking. Abundantmineral deposits also are being explored.

Man is curiQUS by nature, and as long as he is curious there will be those who bravethe elements of this last frontier in an attempt to unlock the secrets it holds.

SEPTEMBER 968


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ROK Helicopter chool

N E A R LY 5 0 , 0 0 0 o r e a ntroops, most from the FirstRepublic of Korea Army, are nowd ployed to the Republic of Vietnam and are fighting, as the largestfore by far from any of our allies,alongside our own soldiers. Therecord of these fine soldiers hasbeen outstanding.

Nevertheless, the tactics and theterrain of the war in Vietnam, as

well as increasing requir ments formore mobility in the defense ofSouth Korea itself, have precipitated the need for organic helicopters within the Republic ofK o r e a R O K ) army. K o r e a narmy pilots, many traint d at theU. S Army Aviation School atFort Rucker, Ala., have mademaximum use of their fixed wingassets predominantly 0-1 and U-6aircraft) since the end of theKorean War some 14 years ago.Their excellent ground forces nowneed the mobility and flexibilityof rotary wing aircraft.

During 1967 the ROK armyreceived the first three of a significant quantity of ob ervationtype , OH-23G Raven helicoptersthrough th Military AssistanceProgram MAP). Also, in 1967the ROK army began trainingrotary wing pilots in the UnitedStates for both service in Vietnamand to meet in-country requirements. Until that time, ther wasonly one rotary wing qualified pilotin the entire Korean army.

Initially 15 of the ROK army smost qualified pilots, both in flightexperience and in knowledge ofEnglish, were sent to the UnitedStates for helicopter qualificationand UH-l transition for eventualdeployment to Vietnam. Upon

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Major William H Gardner

th ir arrival in Vi tnam UH-IDhelicopt rs were made available tothem so th y could fly in supportof the Korean forces th reo

The Aviation School a t FortRuck er also established a specialUH-l maintenance cours to trainthe initial 15 UH-l cr wchiefs. InMarch and April 1967, an addit ional six pilots were sent toCONUS to receive the full rotary

wing qualification course includingphases I, II, and III. They completed their training in Januaryand February 1968.

More Korean pilots will receivetraining in the United States ona ch dulcd basis during FY 68.This training will produce pilotsfor both Vi tnam and to supportin-country requirements , as severalpilots will receive training to bein tructor pilots in the OH-23G.Enlisted maintenance personnel forboth UH-l and OH-23G aircraftare also programmed for trainingduring FY 68.

However, it was recognized thatthe undeterminable length of thewar in Vietnam , the extent of theROK commitment, and the needfor organic helicopters in the ROKarmy in the face of increased NorthKorean infiltration would t aterequirements for Korean armyhelicopter pilots that would quickly exce d the numbers that couldbe produced through schooling inthe United States.

The only solution lay in thee tabli hment of a Kor ean armyh licopter school where Koreaninstructors, both flight lin e andplatform, could teach their countrym en to fly and maintain helicopters. As a result, aviators ofEighth U. S Army and the U. S

Army Advisory Group, KoreaKMAG) found themselves advis

ing the third larg est army in thefree world in the stabli hment oa helicopter school and a helicopterprogram. In short, several UnitedState officers found themselves inthe perhaps unprecedented position of assisting in the creation oa helicopter training base for animportant Asian power.

One of the first considerationshad to be the training of necessary enlisted p rsonnel to maintainthose first three OH-23Gs and subsequent aircraft to be deliveredthrough the Military AssistanceProgram. t wa d cided that threeexperienced fixed wing mechanics,all senior noncommis ioned offi erswould attend a chool held at D tachment L , KMAG in F bruary1967, which would cov r theorganizational maintenance of thOH-23G. Eight oth r mechanicswere sent to the Eighth Army fieldmaintenance support units aCamp Humphreys for similar in-truction on the higher echelons o

aircraft maintenance.Of necessity, the instruction wa

primarily OJT but it was extr mely successful, as both unitshad not only capable and interested U. S maintenance personnelbu t also s vera l w qualifiedKorean civilians employed as mechanics. This latt r group helpedoffset any languag e problem andwas th key to the success of theschooling.

As evi d ence of the effectivenessof the program, at Detachment Lfor the last 3 weeks of th e 8-w eekcourse all organizational maintenance on the four OH-23Gs assigned was performed by the three

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The need for orean army helicopte r pilots exceeds thenumber being tr a ined in the U S This has resulted inthe establishment of a orean army helicopter school

Korean NCOs with a minimum ofsupervision.

The graduation of these firstOH-23G crewchiefs in the ROKarmy could only be a stopgap

m asure. Concurrent with theflight training of ROK armyaviators at the propo ed school,the establishment of a helicoptermaint nance course for Koreanaviation p rsonn 1 and el cted enlisted m n was deem d absolutelynecessary.

Again, using th facilities at Detachment L and its associated airfield, R-401, two offic rs and onesenior NCO were given th necessary guidance and

JT forpre

paring the PO I programs ofinstruction) and lesson plans forthe maintenance classes to betaught at the new sc hoo l The twoofficers, fluent in E nglish, had justreturn d from the U. S. ArmyAviation School at Fort R uckerw h ere they h ad acte d as interpret rs for the ROK army mechanics attending the special courseon UH-l maintenance.

SEPTEMBER 1968

With aircraft and qualifiedm chanics both U. S militarypersonnel and Korean civilians)available at R-401, th major problem was the stablishment of aworkable and realistic POI for theproposed courses. Two courses w reinitially envision d. The fir t wouldtrain enlisted men in the organizational maintenance of the OH-23G.The second would be concurr ntwith the flight line training of thestudent he licopter pilots and wouldnot be nearly as extensive .

A letter was sent from the commanding general of DetachmentL BG Samuel McC. Goodwin, toMG Delk M. Oden, commandantof the U. S Army Aviation School,requesting copies of the PO I andles on plans for all maintenancecour s taught in conn ction withthe OH-23 h licopter. Within twoweeks the reque ted material arrived. The three instructors sp ntthe next few w eks working withboth their sup riors an d KM AGpersonnel in analyzing the P Olsand lesson plans rec iv d .

By late August, POI for theinitial maintenance courses at thenew school had b en det rmin d.The two officers and th N C h a dscreened all training films available in-country beli ved pertin nt

to their program and had foundseveral that would be of gr atvalue. However with the e tablishment of their POI they found acomplete lack of any other training aids in Kor a to support theirPOI except the aircraft themselves.The I son plans that had beens lected for the POI were carefullyrevi w d and a list of the requiredseveral hundred slides, transparencies, and opaque projections wasprepared.

Again, the call w nt out to theAviation School at Fort Rucker,reque ting as many of th aidsas w re readily ?-vailabl. In avery short time, a package arrivedcontaining every training aid requested in 35 mm slide form, lesstwo that were no longer p rtinent.This quick response by USAA VNSwas instrumental in establishingwhat proved to be a prof ssionaland comprehensive maint nance

progra.m of instruction in time forthe op ning of the school.

With the output of qualifiedmaint nance personnel now as

ured, the next obstacle to beh urdl d was the securing an d

tocking of necessary spar parts.H r a g a i n Eigh h A rmy a ndKMAG personnel working with

th Korean army, es t a bl is h ed aworking relationship that woul dinitially permit th e use of U. S

channels but Korea M AP fu n d ing.Several perso n ne l from the R O Karmy receive d training in aviationtec h supp ly and particularly insetting up the PLL (pre cribedloa d lis t ) for the OH- 23G. Fieldmaintenance support is provi d edby the ROK army i tself, withassistance from Unite d States personnel and facili t ies only whenrequire d .

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ROK Helicopter SchoolWith the maintenance problems

associated with the birth of aKorean army helicopter programeither resolved or solutions in sight,

the primary .area for concern nowwas where to find the necessaryinstructor pilots to teach theircountrymen. Major General JamesH. Skeldon, chief, KMAG, advanced the idea that three of the15 ROK pilots presently in theUnited States receive OH-23 instructor pilot qualification at theU. S Army Primary HelicopterSchool , Fort Wolters, Texas, andthen return to Korea rather thango on to Vietnam.

With the aid of both the Aviation School at Fort Rucker andthe Primary Helicopter School atFort Wolters, the necessary adjustments to the scheduled instructionfor the 15 pilots were accomplished. The one rotary wing qualified pilot then in country wastransitioned into the OH-23G andwas given the responsibility tooversee th e estab lishm ent of theschool. The three USAPHS trained

instructor pilots arrived in Kor eain August and began working withEighth Army standardizationpilots in formulating the flightPO I for the new school.

On 18 September 1967 usingtheir three OH-23G helicopters,the three instructor pilots trainedat USA PHS and the six 0 JTmechanics (four enlisted and twoofficers) who worked with Detachment L, KMAG, the ROK armycommenced rotary wing trainingin Korea for the first time. Thefirst class of four students, aftercompleting the course which consisted of 60 flight hours and afterpassing final checkrides conductedby U. S standardization pilotsfrom Eighth Army, was graduatedon 18 November 1967. The fourthclass is now underway. In the th r eeprevious classes 12 pilots have beenqu a lified.

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[Wi th the knowledge gainedfrom these class s and an increasing r quirement for qualified helicopter mechanics within the ROK

army, a course of instruction inorganization maintenance trainingwith 33 students was scheduledto begin in July. A course infield maintenance is also beingplanned.]

There were other considerations.In providing organic helicoptersto a country whose army has neverhad them before, the problem ofthe education of aviation personnel as well as commanders, especially senior commanders, to thecapabilities and limitations ofrotary wing flight could not beignored. Such areas as fuel range,special fuel considerations (ROKfixed wing aircraft use 115/145without TCP, which is required forthe OH-23G ), increased maintenanc time for both daily andscheduled maintenance, coldweather operations, flying in marginal weather, and turbulence,specially in the mountains, must

be thoroughly understood by allwho would fly and who employhelicopters for the first time inKorea ~ anywhere.

Another problem and one of themost common areas where personnel not familiar with helicopt rsare initially confused, is why helicopter pilots seldom fly direct butrather tend to follow valleys andriver bottoms. t wasn't until thehelicopter took on such great significance in Vietnam that manysenior U. S officers fully understood the forced landing capabilities and characteristics of thehelicopter.

Fortunately Eighth U. S. Armyhas had h licopters in Korea sinceshortly after the beginning of theof the war in 1950. Senior Koreanofficers have often used these air-

craft when necessary for the accomplishment of the Eighth Armymission. This fact, coupled withthe need for close helicopter support during the antiguerrilla operations of the summer of 1967 andan increased emphasis on helicopteruse by the advisors of KMAG, hasprovided the means to acquaintKorean -army officers and menwith the OH-23G in particular andhelicopters in general.

Pilots from all units withinEighth Army would and do attempt to discuss and explain totheir Korean passengers the whysand whats of helicopter flying.For example, they point out theneed for smoke both to identify

isolated helipads and to indicatewind direction and velocity. Theyattempt to explain turbulence andits effects on helicopters. In short,they have accepted the additionalmission of assisting the leaders ofthe Korean army to prepare forthe presence of organic helicopters.

Other areas of concern are inflight and ground safety peculiarto helicopters. Here KMAG advisors, in particular, are trying toacquaint Korean officers at alllevels with the increased hazardsinvolved.

The interest of all pilots withinEighth Army; the assistance ofKMAG and, in particular, theaVIatIOn advisor to the ROKarmy; the support of Eighth U. SArmy , the aviation staff and itsstandardization pilots; and the invaluable aid of the schools at FortWolters and Fort Rucker havebeen instrumental in helping theprofessional and dedicated aviatorsof the ROK army in the successfulbeginning of the R OK army helicopter program. It has a long wayto go, but it is, nonetheless, anauspicious beginning. The programand school will grow and it willnot be long before the ROK armyhelicopter school can take its place.alongside its very effective fixedwing school. a;:..'

Here was a clear case where long exper ience-and maybe a touch or two of overconfidence-

overruled good judgment and got in the way ofsound performance. There isn t a lot you can sayabout it except that it was a great pity, but nobody sfault except the pilot concerned. The passenger nevergot a chance to offer an opinion.

You can say the same thing about the pilot whomakes a hasty, by-guess-and-by-God stab at his loadcapacity and attempts to take off with more cargothan a sea captain would permit in the hold of afair-sized freighter. The pilot knows his load shouldalways be calculated precisely. He n o w s ~and chancesare good he s seen, what can happen when excessIQads are ignored or guessed at. So what happens ?He lets his experience trick him into believing he canget off with extra ammo and another passenger.

The thing is that he might be right. For a while.There ll corne a day when he will be wrong.Dead wrong, probably.

GRADE SCHOOLSimple inexperience s another matter. A young

ster fresh out of flight school s naturally as cautiousas an Arctic explorer crossing thin ice, but this cau-tion is likely to be mixed with a natural amount of

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beginner s uncertainty as to what he can or can t do.He s a ripe candidate to be tricked by what we can

call the follow-the-Ieader principle, the kind ofthing which got him a broken arm at the age of 10when he tried some daredevil stunt the bigger kidsdown the block could pull off with no strain.

To illustrate, it may be that no accident exactlylike this one has ever occurred. There have been anynumber in which the same principle was involved.Suppose you are a warr.ant officer with relativelyfew hours behind you. You are part of a flight ledby a major with more experience than Methusaleh.Okay, the major takes off in the lead aircraft withsix pcrsons aboard - and gets airborne. What aboutyou? Do you try to handle six, or do you kick off

one man because the engine of your aircraft s oldand tired and the lead aircraft has a new one?

There s another dandy follow-the-leader game,involving dust, which has only one disadvantage-the last man in always loses. The rules call for thelead helicopter to kick up a cloud of dust and land.The second chopper stirs up more dust and lands.The next one in adds to the confusion and lands. Thelast man adds to the


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-- ==::::. .: - _- -y u are the commandero your aircraft . . . youdecide the load

~ = - - - - - - - - - : :~ ~ r -

Follow-the-Ieader is like crack-the-whip. It s notalways fun if you are at the end of the line. Any

pilot, young or old, has to keep in mind the fact thatwhat another chap has just done successfully mightnot apply to him. Conditions vary. So do aircraft andso do the men aboard them. An experienced manwith his Go No-Go barricade safely in place neverforgets that a pilot is the commander of an aircraftand the sole judge of his and its operating limits.The limits applying to another aircraft are somebodyelse s business.

No matter how you earn your living in life, you vegone a long way toward success when you havelearned to keep your own nose to your own particu-lar grindstone.

INDIANS IN AMBUSH

Make no mistake about it.In Army aviation, keeping your nose on the grind

stone every second you are on the job is the one sureway of avoiding a Go No-Go violation. The Go NoGo factor is likely to be a hidden factor, one readyto trip you at any time, i you are not alert for itin all its guises.

Younger pilots, for instance, might not appreciatethe fact that N 1 is as important as N 2 when i t comes

SE

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RIGHT, MISS PILKINGTON?There s no denying a fool's paradise can be an

attractive place - too attractive, as Miss Pilkingtonkeeps telling her girls. As every body who has beenin such a paradise for any length of time sorrowfully knows, the day comes when you have to pay up.

In Army aviation, the price can be higher thanmost people like to fork over - especially when theGo No-Go violations which lead to accidents don tseem very serious by themselves. When an airmanallows carelessness, indifference, ignorance, fatigue,sickness, or emotional upset to push him past thepoint of safe performance limits, he doesn't have togo mu h past the point of no return. Any distanceat all s enough to guarantee results.

The fact s that in all its aspects, Go No-Go meansexactly what it says. Violate the limits often enoughand eventually you're going to find yourself in moretrouble than you can handle.

Right , Miss Pilkington?ght Miss Pilkington

SEPTEMBER 968

If you ve beenoverlooking pressurealtitude, ignoringN I going beyond

your limitations,or don t know your-10, you ve beenliving n afool s paradise

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52/68

OME RECENT observations and studies indicatethat vortices, or tubes, of tornadic or near-tornadic intensity may be encountered in and underinnocent looking lines of clouds extending fromthunderstorms. Visible tornado (or waterspout) fun-nels may not be present to alert the unwary pilotbut it appears that these vortices may exist up to20 nautical miles from the associated thunderstorm.The precipitation of lightning, and the ambient tur-bulence in their vicinity is only light to moderate.Invisible vortices below the cloud bases may sometimes be evidenced by dust-whirls at the surface (orsworls on a water surface).

Deductions from some accidents in the vicinity ofthunderstorms indicate that these tubes may extendto great heights within the flanking cloud lines (atleast to about 18,000 feet m s and theoretically ashigh as 35,000 feet near the thunderstorm). Neitherthe tubes nor the embedding clouds appear to bereliably detectable on airborne radar, although thecloud line may be picked up by ground radar whenviewed within about 30 miles if there is no intervening heavy precipitation. The cloud line may be detected on airborne radars below 8,000 feet msl andwithin some 20 nautical miles. Typically the e.choshows a sharp first iso-echo contour with a relatively

dry interior. I t is likely that these cloud lines giverise to the longer appendage echoes sometimes seenwith tornadoes.

One important aspect of this hazard is the greatdistance from the associated thunderstorm at whichthese tubes may exist. Ten miles is an average valuefor audibility of thunder, so that a thunderstormmight not be reported at the coincident ground station. Since there are no completely reliable local indications of the existence of the vortices, avoidancemust be based upon a knowledge of the presenceof the thunderstorms with which these cloud linesand tubes are frequently associated, and flight procedures to avoid the cloud lines.

The meteorological conditions under which thehazard exists are similar to those for the tornado.Thunderstorms in tornado forecast areas should besuspected. I t also appearS that these tubes aremuch more frequent than observed and reportedtornadoes, so that thunderstorms, other than thosewell known to be of an air-mass nature, also shouldbe suspect. A good first rule for absolute safety fromthis hazard is to avoid all suspected thunderstormsby at least 2 nautical miles on any line bearing andat any altitude

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dvanceof

TornadicTurbulence

Thunderstorms in squall lines over smoother terrain are likely candidates, especially when there isappreciable windspeed change greater than about 30knots with altitude to about 20,000 feet. A preferredorientation of the cloud line is into the storm-relatedwind. To estimate this, take the storm-motion vector(as from a radar observation) and subtract the meanwind vector in the lower 20,000 feet. The resultantvector will point in the direction from the thunder-storm in which these cloud lines with related tubesfrequently tend to form. Avoid flying in or underclouds, especially lines of clouds, in the quadrantabout this vector. Under IFR conditions, build inan avoidance of 20 nautical miles up to 5,000 teetabove the surface, 5 miles at 15,000 feet, and about7 miles at 25,000 feet.

Caution is especially advised on landing and takeoff, descent and climbout, under or through theselines of clouds. Because of a possible convergence of

the tubes upward in the cloud line, the hazardtends to increase with altitude in the clouds.Effects upon aircraft encountering these tubes

may. range from a hard bump of several g's upona direct encounter with a weaker tube, through anunusual thump in grazing incidence with the circulation of the tube, and vigorous upsets in othergrazing encounters with fully developed tubes. Noaircraft has ever been built that can be expected totake the loads possible in a tornado and surviveThese fully developed tubes even with no tornado

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U L POINT PROB BILITYORN DO a TORN QIC

1953 1962 B SE

funnel to the surface below, are of such a nature andintensity as to preclude passing through unscathed.

Preliminary estimates of probability of encounterwith these tubes in random fiight (no avoidanceskill) below 35,000 feet in the United States east ofthe Rocky Mountains indicate that an air transport

might encounter a tube once ev ery 3,000 hours( approxima ely ) . The probability of this encounterbeing of a major or catastrophic nature has b en

stimated at about one chance in eight. Thus, ifno avoidance is practiced, a major or catastrophicincident may be expected in 24,000 hours of indicatedoperation. Skill in avoidance can increase this waiting time by a factor of 10 or more. No t e, howeverthat clos e avoidance of a h eavy thunderstorm echoto the south or southw est may produc e a n egativeavoidanc e skill. The old rule of out of echo, out oftrouble is definitely out for th se phenom na ( seechart above).

Some further suggestions for flight safety withrespect to these hazards ar :

1 Und r visual flight rule, do not fly below lin esof clouds extending from an intense. thunderstormand often on a common bas with the thunderstorm.

f flight is absolutely necessary, circumnavigate oroverfly with adequate clearance. R emember how farfrom the thunderstorm the hazard may ex ist and howinnocent the related airspeed may appear.

2 f inadvertently ca ught und er on e of th e selin es, watch for dust whirls (or wat r sworls on a

SEPTEMBER1968

R eprinted fromFlight Safety FoundationBulletin 68-102

Fred C Bates Ph.D.Institute of Technology

Departm ent of G eophysicsGeophysical Engineering

St. Louis University

water surface) and avoid overflying these. Get outfrom under fast.

3 Use a local ground weather-surveillance radarto best advantage in preflight briefing. The type ofthunderstorm which often produ es these tubesappears to have a typical echo (ext ensive anvil re-

turn, a scallop , sometimes an appendage coincidentwith a cloud line ) . A similar look at your airborneset before takeoff and below 8,000 feet can be helpful. Use gain settings higher than those for best de-lineation of thunderstorm echoes to bring up theweaker cloud echoes.

4. f no information is available for estimatingthe storm-relative wind vector, the most frequentorientation of the flanking cloud lin es from the as-ociated thunderstorm is from southeast through

southw st to northwest.5. Under instrument flight rules, note carefully

that the orientation of the related cloud lines maynot coincide with the orientation of the thund rstormline it elf. Use the basis of estimate given to find theprobable cloud line orientation. In using groundradar vectors, be sure the set us ed either has thecapabi lit y of detecting these cloud lin es or is backedup by such a set.

6 Close avoidance on the opposite flank of thethunderstorm is not suggested. I t must be remembered that th ere are other hazards, e.g., larg e hail,whic h must b e avoided.

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From a paper presented to the Institute of Aerospace Safety andManagement at the University of Southern alifornia by the author

HIS PAPER IS PRESENTED to introduce theuninitiat ed to th e system saf ety eff ort an d pro-

mote its co nsid er a tion through all phas es of ma -t erie l d eve lopm ent. Although safe ty has histori ca llyb ee n a consid erat ion in the d velopment of industrialand military systems, unfortunat ely it has b ee n afterthe fa c t. The evo lution of the syst ms approachwithin the safety spectrum is the first tangibleeffor t to cope with this deficiency. t is important toour military postur e that system compon ents b e pro-vid d with minimum probability of failures whichr esult in catastrophic eve nts.

Th ere is an equally important moral requirement.

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In A af e ty Policy for th e F ed eral er vice Pr sidentJohnson st a ted: Americans have always placed the

high es t value on human lif e, in accord with theworth of very indi v idual. As th e public repositoryof our orial id eas, governm nt has di r ect obligation

.to express our regard for human life in every measuren c ssary to safeguard and protect it."3

Management ta k e h ee dTh system safety concept is not n ew . Its pr ese nt

evo lution spans some 50 years. As early as 1913, aNational Safety Council was formed and 5 yearsla t er, in 1938, the Civil Aeronautics Act es tablish eda Bu r ea u of Saf ety. As far as we know , this was th

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===

L T Clement A yll ieChief Engineering Branch

US B R

first activIty of this nature specifically aligned withaerospace programs. 5

At the Fourteenth Annual Meeting of the Institute of Aeronautical Sciences in New York in January 1946, Amos L Wood presented a pap r entitl d The Organization of an Aircraft Manufacturer's Air Safety Program. 14 He emphasized theimportance of looking at design concepts and safetyanalyses.

In 1948, another paper was published by Williamr Stieglity in the Aeronautical Engineering v ientitl d Engi neer ing for Safety. 9 He, too, stressedthe need for safety in design.

SEPTEM ER1968

In 1960, the first military Systems Safety Officewas established by the USAF Missile Division inInglewood, Calif. 5

In 1962, as an outgrowth of work done by theU.S. Navy, th Ballistic Missile Division of the USAFpublished its first specification for system safety, entitled System Safety Engineering: Military Sp cification for the Development of Air Force BallisticsMissiles. 5 Later in 1963, MIL-S-38130, Gen ralRequirements for Safety Engineers of Systems andEquipment, was publish d This was the first safetyspecification that could be applied to all systems inthe Air F orce. 10

The Army monitored the Air Force effort andpublished MIL-S-58077 30 June 1964. The Armyspecification was identical to the Air Force MIL-S-38130, exc pt that it applied exclusively to aircraft. 13During Phase IB of Project Definition, the Army

formallyimplemented

MIL-S-58077 onthe

AdvancedAerial Fir Support System (AAFSS) 1 March 1965.I t is inter sting to note that, although the Air Forcewas first to publish a system safety specification, theArmy was first to implement it. However, the AirForce subsequently implemented MIL-S-38130 onthe C-5 and C-141 programs. 6

In June 1966, the Army, Air Force, and Navyjoined forces and, in a tri-service agreement, published MIL-S-38130A, entitled: General Requirements for System Safety Engineering of Systems andAssociated Subsystem and Equipment. This sp cification superseded MIL-S-38130 and MIL-S-58077.

In the near future, MIL-STD-882 , now in the proposal stage, will replace MIL-S-38130A.

Before proceeding, it is necessary to define certainterms which will be mentioned throughout this paper.The following may be considered operationally defined as indicated:

Accident - An event occurring by chance or fromunknown causes. 4 11

Hazard - Source of danger or risk.412a f e t y Freedom from those conditions which can

cause injury or death to personnel and damage to, orloss of, equipment or property.4 12

System - A system is the unification of all component parts of a whole, necessary to achieve a desired result with effective control Therefore itis incumbent for a person using the word system toprecisely defin or bind the limits in which th sys-tem operates. As an example, the earth may b asyst m when limited to th earth's bounds. However,when viewed in relation to the solar system, the earthbecomes a subsystem. 5 12

System Safety - The optimum degree of safetywithin the constraints of operational. effectiveness,time, and cost, attained through application of man-

53


56/68

SYSTEMS FETY

the Army, Air Forc e and Navy joined forcesand, in a tri-s ervice agreement, publish edMIL-S-38130A, entitl ed: General R equir em e ntsfor System Saf ety Engin eeri ng of Systemsand Associated Subsystem and Equ ipm en t

agement scientific and ngineering cr it er ia , and h -niques and pr o ce du r es, throughout all phases of system development. 8

FUNDAMENTALS OF SY _STEM SAFETYPreviously , in systems development , th e e mphasis

has been on accident pr vention af t er co mpl etio h of

the design. A review of U.s.. Army accident rates fornew aircraft disclos ed ex tremely high initial rates,which tend d to de crease and lev el off after a num-ber of years of us .6 High initial losses can be reduced by an effective system safety program , implemented early in th e c onceptual phases, and operatedthroughout the life cycle of the system.

The developm nt ost of any system will be slightlyincreased by the syste ll safety effort. However , asubstantial reduction in retrofit and training costswill more than offs e t the initial investment. T h e pr e-

5

v ntion of only one or two major accidents throughb tter design r suIting from the system safety effortcan pay for the entir e sys tem safety program.

In today's t ec hnology , mat er iel procur em nt pr oc sses normally follow a road map of manag mentpr o ce dures ca lled th " lif e cycle." This cycl s di -vided into four major phases: Co n ce ptual , D efinitionA cq uisition , and Operational. 4 They are not n ecessarily sequential and th ey may well overlap. Also,d ep ending upon the particular product the timeframe may vary 'from days to years. To further expand th ese phases into more m ea ningful steps, weca n cons ider a produ ct to follow these phases: 5

Evaluation of customer requirement.Conc eptual d esign.Prototype development.Produ ct design.



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Test and qualification.Manufacturing.Use.Ultimate disposal.Implementation of system safety principals in

volves assignment of specific safety tasks within theframework of these life cycle processes. These tasksmust be astutely planned organized staffed andcontrolled if the safety job is to be efficiently accom-plished. They must be universally accepted by man-agement as vital functions and a necessary extensionof the increasingly complex technology facing industry today.THE SAFETY TASK CHECKLIST

Unless a specific task can be clearly identified witha given objective it will present management witha difficult problem of integration with no meaningfulfunction. Listed are some fundamental tasks thathave been derived from military specifications andother sources. These have stood the test of time andconsiderable discussion since first presented. 4 5 12Common sense may imply others.

onceptual Phase1 Establish and integrate safety requirements. De -

sign checklists design handbooks milit ary specifications and experience factors are valuable sources forthese requirements.

2 Conduct gross hazard analyses and providesafety input to preliminary technical developmentplans.

Definition PhasePrepare a schedule of safety milestones in conso

nance with total system effort. This schedule shouldbe included in the Request for Proposal RFP) todevelopment contractors.

ontractor DefinitionFollowing the contract award for systems defini

tion major system safety program milestones mustbe agreed upon. Efficiency during this phase can pre-vent costly design changes and retrofit programs later.The following are considered absolute necessities:

Develop and approve system safety plan.Identify safety requirements and updat e source

documen a ion.

Compile system safety standards.Complete detail safety analyses.Review system requirements.Participate in trade-off studies.Establish maintenance safety requirements.Provide input into test plans.Establish training safety requirements.Review of detailed system specifications for safety

requirements.Identify safety documentation requirements.Provide inputs to final reports.

SEPTEM ER 968

the prevention of only one or twomajor accidents throughbetter design resultingfrom the system safetyeffort can pay for the entiresystem safety program


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SYSTEM S FETY

ystem safety is not intended tobe a replacement for any of theother system effectivenessdisciplines it must be recognized

s a separate discipline whichequally bears on systemeffectiveness

6

S FETY T SK CHECKLIST

conceptu l ph sedefinition ph secontr ctor definition

cquisition ph seoper tion lph se

ccidentinvestig tion

Acquisition PhaseIn this phase systems elements are developed

against end item detailed specifications resulting

from the Definition Phase. Here again system safetymilestones must be established:Modify and approve system sa fety plan as required.Complete design reviews.Approve test plans for safety.Complete ECP reviews.Complete facility design reviews.Complete safety analyses.Approve safety documentation.Validate safety items in Technical Orders.Complete safety requirement reviews.Review test reports.



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Operational PhaseThis phase overlaps the acqUIsItIOn phase and a

gradual transition from one to the other occurs.During this phase, it is particularly important thatspecial attention be given the customer/contractorrelationship. As user problems occur, corrective actionis taken and its effectiveness measured. Both partiescan contribute from previous experience gained during earlier development phases.

ccident Investigationt may seem superfluous to cite accident investiga

tion as a separate safety task. Unfortunately, experience has proven otherwise. The preparation andimplementation of an effective accident investigationplan is essential to the system safety effort. Whena catastrophic event occurs, future prevention effortscan be seriously hampered by inaccurate or premature actions from inadequate investigation planning.Provisions for the use of contractor technical personnel most knowledgeable about the system concernedare essential to investigation teams. The recordingand maintenance of accident investigation recordsare especially important to the system safety feedback loop. Appropriate corrective action to preventrecurrence of similar accidents is largely dependent

on the adequacy of accident investigation reportingprocedures.

MG Joseph D. Caldara (USAF, Ret), presidentof the Flight Safety Foundation and past Directorof Aerospace Safety, USAF, said: I think it's mandatory that there is no single key for safety - nogrand or magic formula to insure that everyone involved in any activity does what he is supposed to dothe way he is supposed to do it. Safety must be theproduct of many people, dynamic - not static, thesum of many activities."

To my way of thinking, General Caldara has expressed the premise upon which system safety mustevolve. It is an assuring function of management andcertainly the sum of many activities.

System safety is not intended to be a replacementfor any of the other system effectiveness disciplines(i.e., reliability, maintainability, human factors, quality assurance, etc.). On the contrary, it must be recognized as a separate discipline which equally bearson system effectiveness. System safety assures management that sufficient consideration is given to impending failures.

SEPTEM ER 968

REFERENCES1 Caldara, MG (Ret) J.D., What's Up Front

Still Counts," Flight Safety Foundation, New York,N.Y., SETP Cockpit, January 1965.

2 Griffith, MG Perry B., The Safety of CombatPotential," ir University Quarterly R e v i e w ~reprinted by AF SBAMA, October 1962.

3 Johnson, L. B A Safety Policy for the Federal Service," The White House, Federal RegisterDoc. 65-2096-7, pp 2517-8.

4. Lee, Gordon E., "Does System Safety Fit Intothe AFSCM 375 Management System '?," 30 October1967 (paper presented to faculty of University ofSouthern California).

5. Miller, C. 0. The Role of System Safety nAerospace Management, August 1966.

6 Newton, CPT R. W. and COL R. H. Hamilton,The Army Evaluation of MIL-S-58077, and Those

Agencies Involved in Its Implementation, U.S.Army Board for Aviation Accident Research, 1966.

7 Ruff, G. G., The System Safety EngineeringPlan (SSEP), and Integration Considerations in theImplementation Process," nnals of Reliability and

a i n t a i n a b i l i t y ~Vol. 4, (Washington: Spartan Books,July 1965).

8. Ruff , George F., "Systems Approach and theSafety Concept," Hazard r e v e n t i o n ~Vol. 3, No.3,Bulletin of the Aerospace Systems Safety Society,December 1965.

9 Stieglity, I., Engineering for Safety," ero-nautical Engineering R e v i e w ~February 1948.

10 U.S. Air Force, General Requirements forSafety Engineering of Systems and Equipment,MIL-S-38130, Hq., U.S. Air Force Systems Command, Washington, D.C.

11. U.S. Air Force, "System Safety Management,AFSCM 127-1, Washington, D.C., 1 January 1967.

12. U.S. Air Force, "Syste;ns Engi neeri ng Management Procedures," AFSCM 375-5, Washington,D.C., 14 December 1964.

13. U.S. Army Safety Engineering of AircraftSystems? Associated Subsystems and Equipment;General Requirements for, MIL-S-58077 (MO) ,30 June 1964.

14. Wood, Amos L., The Organization and Utilization of an Aircraft Manufacturer's Air Safety Program, The Boeing Company, Seattle, Washington.Presented at the Institute of the AeronauticalSciences Meeting, New York, January 1946.

7


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8

Pearl spersonal

equipmentand

rescue/ survivallowdown

If you have a quest ion about persona lequ ipment or rescue and surv iva lwrite Pearl U S Army Board forAviation Accident ResearchFort Rucker Alabama 36360



61/68

NEW BRAIN BUCKET

A NEW PROTECTIVE helmet s in the offingfor Army aviators.The helmet-tentatively called the SPH-3B Mod

i f ied)-wil l offer a number of distinct advantagesover the helmets presently in use, according to LTCRobert W. Bailey, commanding officer, U.S. ArmyMedical Research Unit, Fort Rucker, Ala.

Distinctive advantages the new helmet offers are: Greater noise attenuation. Lighter weight. Improved boom microphone. Improved helmet-to-head attachment.LTC Bailey said the new helmet evolved from

U.S. Navy SPH-3 helmet which was originally designed for use by Navy helicopt r pilots. The Navydesigned the original helmet with two prime goalsin mind: crash protection and acoustic attenuation toprevent hearing loss in a high noise environment.

USAARU improvements over the Navy version in

c ude beefing up the primary shell of the helmet from0.065 inches to 0.10 inches, a move which will significantly increase both the crash and acoustic protectionoffered by the helmet.

The new helmet weighs significantly less than boththe APH-5 used by Army aviators in the U.S., and agreat deal less than the AFH-1 ballistic helmet issuedto Army aviators in Vietnam. The lighter weight isexpected to significantly reduce helmet fatigue onaviators.

Although the new helm t weighs 1 ss than anypr sently in use, LTC Bailey reported that its bal

listic characteristics were nearly as good s the specially d signed and heavy AFH-l. This is attribut dto the us of Epoxy One r sin in the primary shell.

The old commo harness common to the APH-5was scrapped in favor of a direct mike positioned infront of the wearer's lips. The new mike offers a

SEPTEM ER 968

low r noise-to-human speech ratio as compared withthe old mike whos hollow boom indiscriminantlypi ked up and amplified noise.

The h e l m ~ t t o h e a dattachment suspension of theSPH-3B Mod) consists of a fire-resistant, syntheticfabric web which is easily adjustable. Aside fromaffording the wearer venti la tion - which was unheard of in the APH-5 - the web suspension isdesigned to keep the helmet on the aviator's head athigh impact forces to giv maximum crash protection.

USAAR U plans also call for the use of th shatterproof, nonbreakable polycarbonate visors with thenew helmet to give aviators greater face and eyeprotection.

LTC Bailey said also that logistic groundwork forthe introduction of the helmet was laid in consonance with Army Materiel Command. He alsopointed out that, while USAARU was the proponentof the new h lmet, U.S. Army Board for Aviation

Accident Res arch, AMC, and the U.S. Navy AeroSpace Research Laboratories all worked closely onth project.

LTC Bailey also paid tribute to the U.S. ArmyCombat Development Command Aviation Agency atFort Rucker for th ir swift development of the necessary Qualitative Materiel Requirement QMR) topave the way for speedy helmet procur ment.

Forty new helmets were recently received byU AAR U for testing. Tw nty are earmarked foruser testing by the Department of Rotary Wing andthe Department of Tactics at the U.S. Army Aviation School. The balanc will be laboratory tested bya civilian contract agency.

Pending modifications which may arise as a resultof testing, the new helm ts are expected to be introduced into the Army supply system around the turnof the year. Issue is expected to be on a one-for-oneexc hange basis.

9


62/68

rom e ll Heli c opt e r ROTOR BREEZE

he Gentle Art of

O -RINGS from a maintenance standpoint involve problems of hydraulic gland leakage andpneumatic gland lubrication. Maintenan ce inspectionof O-ring seals presents two questions: 1 ) Howmany drops of fluid must seep past hydraulic O-ringbefor e an obj ec tionable l eak is indicated? 2 ) H ow

much air must s ep past a pneumatic O-ring beforeth ere is an indication of a damag ed O -ring or of aneed for lu brication to re d uce wear by fri c tion?

To understand the hy d raulic problem of lubrication, it is n ecessa ry to study the general purpose, design, and fun tion of O-rings, and to consider separately the sp ial featur es of hydrauli c and pneumaticsystem O-rings. With this background , th e mechaniccan tell th difference betwe en a seep and a lea k

The principal purpo e of th e O-ring is to act asa seal. The O-ring depends primarily upon its re

siliency ability to adjust by deformin g and sp r inging ba ck ) for ac complishing its sealing action.

Th e simplest O-ring installation is a static seal.Figur 1 shows an O-ring on a bolt , which could bea hydraulic tank plug. Gen erally, the d esign of thegroove, into which the O-ring fits , is such that th eO-ring is squeez d approximately 10 pe r c nt to effectsealing action. Thu , when the surfaces to be sealedare brought tog e ther th ey compress th e O-ring andit serves as a gasket. Th e resilien cy of th e O-ring ~ s o

60

r ing

Installation

allows it to stretch out under press u re so that thering contacts the out r face of its confining gro ovto provid e a dd itiona l sealing action . It is importa nto no t e that the under surface of the bolthead fittightly on the boss . Any crack will allow the O- ringto ex trude.

In the static typ an d , for that matter in aO-ring ~ s t a l l a t i o n sit is important that just thproper size O-ring b used , that the O-ring an d thparts contact d b smooth and free of irregularitiesand that all of th e parts be clean . Slight imperfections an d / or contamination can b e instrumental icausing leakage. An im p erf c tion or a bit of foreignmatter can crea te an opening past the O-ringthrough which fluid can flow.

Th O-ring must also be of a material that is com

patible with the particular fluid in the syst m. f thwrong material is used , the O-ring may sw exce iv ly and d e teriorat e

A fr h O-ring when in talled may normally sweas much as 10 p erc nt when exposed to th e fluiand working operation. Allowance is made for thiin th e design of the O -ring groove. Ex cess ive sweling , ho w eve r, indi ates that the O-ring and fluimay not be compatible. In components that must rmain at very low friction values to prop erly functionexcessive swelling of O-ring seals may increase fric



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NO T E T H A T O R I N G C R O S S S E C T I O N

I S T H I C K E R T H N D E P T H O F S E A T I N G G R O O V E

S E A TONG G R O O V E O E P T H

FIGURE 1

P O S S I B L E L E A K A G E

Static seal no moving parts

tion m a n y tim es b eyond th e maXImum allowabl evalue.

A prop er O ring installation generally results in adiam e tr a l squ ee ze of approximately 1 p ercent ofthe O ring cross s ec tion. Th e volum e of the O ring isalso slightly less than th e v olum e of th e groov e. The

initial squ eezingis

to fa cilitat e a prop er seal: th eslight left-over area in th e groove is to ac commodat e slight normal swellin g and to p e rmit a sliding ,rolling , and kneading action of the O rin g un d erpr essur e and mov em ent . The rolling aids in workingfluid un d er the O ring and thus k ee ps it lubricat ed.

A simple O -ring installation involving m ov in gparts ( running seal ) is shown in figure 2 . This is acommon type of appli cation used wh ere the pressures to be r estrained run from z ero to about 1500psi.

Wher e mov em ent is involv ed , th e installation specifi cation ge nerall y d efin es an amount of l eakag e thatis p ermissibl e. A slightly moist surfa ce is an indicationthat th e syst em flui d is lubri cating th e O -ring asnecessary. The spe cification will gen erally stipu latthat there sh a ll be no leakage w h en the assembly is

static, an d will allow a few d rops of fl ui d to formp er min u te d ur ing o p erat ion . P ermiss ibl e leakage w illvary, d ep en d ing on wh ther the sea l enco u nters interm i t tent or co n ti nu ou s m o tion.

SEPTEM ER 968

O R IN G

FIGURE 2unning seal with single backup ring

S P L I T T Y P E S P I R A L T Y P E

FIGURE 3unning seal with dual backup rings

6


64/68

W I T H O U T

B A C K U P

he Gentle Art ofO ring Installation

O R I N G T E N D S T O

E N T E R C L E A R A N C E

FIGURE 4Installation of backup rings

T Y P I C A L

R I N G O F T E F L O N

F O R L O W B R E A K O U T

A N D R U N N I NG F R I C T I O N

62

U S H A P E D S L I P P E R

R I N G F O L D E D B A C K

O N I T S E L F F O R

I NS E R T I O N

/

R IN G IS ST R A I G H T E N E D

I N I NS E R T G R O O V E W I T H

O N E P O I N T E D N Y L O N T O O L

FIGURE 5InstallaJion of U s h a ~seal

More than the specified maximum number ofdrops per minute, however, indicates (1) a fault inth e installation , ( 2 ) nick d or scratched sealing surfaces, (3) foreign particle ontamination , or (4 )worn or damaged O-rings.

Wh re the high er pr essures are b eing sealed off

with O-rings (operating pr essure gen era lly above1500 psi ) , backup rings may be used with O-rings.Two typ es of ba ckup rings are shown in figurth e s plit washer and spiral types.

Bac kup rings provid e a firm surface against whi chthe O-ring ca n pr ess to avoid bein g ex trud ed , un d erhigh pr essur es into th e clearance betw een the surfa ces being s aledo I f th ese back up rings w re notprovid ed, th high pr essur es co uld squeeze out , orex trude , som of th e O -r in g into the clearance spac e.Any movement b tw een the surfaces, wh en the O-ringis thus deform d , would result in a high ra t e ofO-ring wear, and th e ability of th e O-ring to providean effective seal is soon lost (see fig. 4 ) .

With O-rings properly fitt ed , th e br eak out force(eff ort n eeded to start movement ) is not generallylarge. Br ea kout fri ct ion or force is high er than running friction , and is th largest factor th a t must beco n id ere d in th e d esig n of O-ring seals.

To prevent grabbing or seizing of smooth surfacesun d er high pressur e, slipper rings ar provided.Th ese, in cross section , may be U -shap ed, L-shaped ,or plain bands, and th ey are usually ma d e of T eflon(see fig . 5 and 6 ) .

Th e T eflon material has a very low coefficient of

fri ction which means that it will s tart out with alow breakout for ce and run with relatively no fri tionun d er load , eve n in th e abs nc e of lubri ca tion. Th efree -sliding slipper rings thus adopt the sealing re-silience of th e O-rings to th e high er working pressur e

A differ ent techniqu e is r quired for installingslipper rings b cause th e T eflon material does not

deform as easily. I t is sometimes necessary todouble check th e Teflon portion of the high

pr essure O-ring assemb ly, as shown in figure 5. Oncpositione d , it requir es working or ironing the Teflon ring back into its orig inal shape in the O-ringgroove . This is accomplished with a smooth nylontool to preclude scratching an d marring of the metaland th e slipper rings.

Parti cular care must b take n wit h all O-ring , installations to avoid d amaging the rings. All partswith which the O-ring is likely to come in contactduring a ssembly should b e smooth to prevent cuttingor shearing of any parts of the O- ring . The too lused to aid in positioning the O-ring shoul d be ma d eof nylon or similar mat rial so th a t th e ring and itsmating groov e are in no way scratc h ed or nicked.

U S . ARMY AVIATION DIGEST


65/68

This practically rules out the use of metallic tools.Lubricating the O-ring with the system fluid or witha grease compatible with the system will assist insliding the O-ring into place.

Pneumatic seal lubrication is more difficult to control than is hydraulic seal lubrication. The pressur

ized air that enters the pneumatic seal from the system does not lubricate; in fact, it dries out the sealand any lubricant that may be on the packing.

To maintain an effective seal with a pneumaticsystem O-ring, lubrication is usually provided by afelt wiper. -During overhaul, this wiper is servicedwith MIL-L-4343A lubricating grease. The wiper isthoroughly impregnated with this grease, not superficially smeared. Tests to date indicate that, in pneumatic systems, grease is a better lubricant thanhydraulic fluid, both in dynamic and static seals.Service experience indicates that a unit can be operated 50,000 continuous cycles without additionallubrication.

In some installations it is necessary that the O-ringsbe passed over sharp edges, such as screw threads. Insuch instances, it has been found practical to coverthese raw edges tightly with a thin plastic tape, thento lubricate the O-ring and work it into position,after which the tape is removed see fig. 7).

O-rings in service undergo a slight swelling andsoftening and may be subjected to wear that is notalways apparent to the eye; these O-rings are proneto inadvertent damage upon reinstallation. I t isrecommended , therefore, that only new rings be usedupon reassembly of a unit. This can do much topreclude and eliminate difficulties.

In summary, proper O-ring maintenance necessitates periodic inspection and keen observance. Theline mechanic must determine. these things:

Is the dripping fluid hazardous damaging anothercomponent) or creating a fire danger?

Is the drip rate excessive?Has there been any increase in the rate of drip

since the last inspection? Since an increase mayindicate the beginning of trouble, the componentshould be carefu lly checked at frequent intervals.)

Is the drip rate normal for this type of installation?

Is any air escaping from the pneumatic system?I f so, is the hourly leakage rate high enough to require a closer check on all seals?

I f the line mechanic understands the purpose ofthe O-ring and if he realizes that it is not a perfectseal, he will have little trouble making a practicalappraisal of how many drops of fluid must leak pasta hydraulic seal before the seep becomes an objectionable leak - and he will also know how importantit is to replace pneumatic system components thathave dry O-rings.

SEPTEMBER 968

proper O ring maintenancenecessitates periodicinspection andk n observation . . .

rail;- . /

/ .> ./ FlIJtl.- .. /. ' . '. ,, / ,. ' . ,.

FIGURE 6L shaped se l on left: pl in on right

FIGURE 7Tape protects O ring during installation

63


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*************

U S S O e zi i i i i miml * i i i i i m :i : mi i i i : m i m :i i ii i i i i i i i i i i i i i i i i i i i i i i i i i i i m :i i : mi : mi i i i i i i i i i i

64

The U S Army Aeronautical Service Office discusses**********

what to look for on t he NOTAM tapesi f you really are shor t of air t raff ic controllers

the air t raff ic control MO S changes

On flight information: We have had a near overboost condition of rumbling about NOTAMidentifiers associated with Army airfields. However, the situation is in the green now. t seems that mostCONUS Army airfields do not have their own identifiers on the various FSS NOTAM circuits.So how do you know what to look for on the NOT AM tapes? The quick fix is to check page 2of the 10 July Flight In ormation Bulletin The identifiers for all CONUS AAFs are all listed there.

What's the Flight In ormation Bulletin? Thought some of you might ask. t was that white,brief (two to four pages or so) letter size bulletin that you have usually not been able to locatein the flight planning room, because it so effectively blended in with all the other white flightplanning publications. We've solved the camouflage problem though, so now it should stand out -Army green, all the way.

In case you haven't missed it, you might have a look at it. Basically, the bulletin is a weeklycompilation of NOTAM information of relative permanence, which gets the word out in onehandy document in advance of FLIP changes. The item on NOTAM identifiers, for example, will bedropped when the FLIP IFR and VFR supplements are revised to incorporate this information.On air traffic controllers: Say you're short air traffic controllers? This is not an uncommon conditionlately, but are you really? Short, that is. USAASO found 130 qualified air traffic controllersin one Army area alone who were not being used in A TC positio ns. t may be an attestation to theunlimited flexibility of our Army air traffic controllers that they can also serve capably as mechanics,grass cutters, cooks, drivers, etc., but i t 's no consolation to the aviator who has to figure out thetraffic pattern, avoid the construction on short final and make the right turnoff after rollout,all on his own.

So, the next time You see a particularly busy, bright-eyed young latrine orderly, you might dowell to stop and question him. He might be an air traffic controller - demonstrating hisflexibility.

More on controllers: f you haven't seen OPO letter, OPOMO, dated 14. May 1968, subject:Revision of AR 611-201 (MOS 93B, Air Traffic Controller), it is recommended reading for air trafficcontrol supervisors and airfield operations o f f i ~ r sand commanders. What it does is shred outthe 93B MOS into four MOSs:

93H A TC Tower Operator93J ATC Ground Control Approach (GCA) Specialist93K ATC En route Specialist93L Air Traffic Control Chief

Although not effective until 1 January 1969, it requires some serious thought and planning now,some training and retraining soon, and some extensive TDA revision eventually. We might addthat the air traffic controller personnel career potential is greatly enhanced by the shred out.Implementing instructions will be forthcoming soon.



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f b