The Ejection Site - Discussion of Airliner Ejection Seats

8/9/2019 The Ejection Site - Discussion of Airliner Ejection Seats

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The Ejection SiteDiscussion of Airliner

Ejection Seats



The Ejection Site - Discussion of Airliner Ejection Seats.docx

The Ejection SiteDiscussion of Airliner Ejection Seats

Airliner crashes cause the deaths of hundreds of people in a single incident causing them to be

one of the most publicized forms of death. Often in the wake of a disaster such as the TWA Flight

800 crash people ask my opinion as to why Airliners are not equipped with ejection seats. The

following is my personal analysis.

Concept: Passenger Survival Systems for Commercial Aircraft:

especially considering Ejection Seats

Description of system: All passenger seats to be replaced with a seat capable of being jettisoned

from aircraft ON PILOT or COCKPIT CREW COMMAND. The seats are to be outfitted with a

recovery system (parachute ) to lower the seat occupant to the ground safely. The Crew seats

would be similarly equipped.

Pro: Safe recovery of passengers in the event of a catastrophic disaster.

Con:

1. Danger to maintenance crews

2. Danger to passengers due to accidental discharge

3. Possible injuries to passengers due to use

4. Weight increase

5. Larger seat area requires fewer seats in given area

6. Egress hatch requirement requires considerable redesign of cabin fuselage

7. Cost- Ejectable seat would add costs for:

a. Redesign costs

b. Development costs

c. Seats (military seats can cost upward of $100,000 per unit)

d. Periodic maintenance

e. Replacement parts

f. Maintenance crew training/explosive certification

8. Minimal time of use




Discussion:

Ejection seats are complex devices which when used in military service have proven to be quite

successful at saving the lives of aircrew. As complex devices they require much maintenance and

training to function with a high degree of success. Even though modern ejection seats are designed

for fully automatic function after initiation, the occupant requires training to use the seateffectively and safely. Ejection seats are designed to cause an occupant to separate from the

aircraft at a high enough rate of speed to clear any part of the aircraft structure. This

requirement necessitates a high impulse force to be used to launch the seat and its occupant.

Military seats are fired with an impulse in the Z axis of between 12 and 22Gz depending on the

seat design. This impulse varies with the type of seat propulsion with the rocket/catapult seat

being the lower value, and the pure gun type being the higher. This value, however, is also

influenced by the weight of the occupant, and the values quoted above are based on a seat

occupant in the 150-200 lb weight range. With the continued influx of female pilots and crew,

the weight of the average pilot is dropping. This is leading to much research to provide a

propulsion system for an ejection seat that is usable over a much wider range of occupant weight.

Other considerations include the occupant's connection to the seat. Parachutes require more than

just a simple lap belt. At a minimum, the harness requirements include a pair of leg straps, a pair

of shoulder straps and a chest strap. These straps must be adjusted for each individual to be a

snug (read uncomfortable) fit for each passenger. In most airline trips I've been on, most

passengers unbelt the minute the cockpit crew turn off the lab belt indicator (this is confirmed by

recent news stories about passenger injuries due to turbulence). In the case of a situation requiring

a mass ejection, this would have to be delayed until ALL passengers AND crew are strapped in

securely prior to depressurizing the cabin, blowing the hatches and initiating ejection.

When the cabin is depressurized and the hatches are jettisoned, the passengers would be

exposed to the lower oxygen pressure in the upper atmosphere, the wind blast which would cause

flail injuries and injuries by loose flying objects such as handbags, cameras, camcorders, trays,

carry-on bags, and other objects.

Jettisoning a large number of hatches in the roof of an airliner will also cause significant changes

in the aerodynamics of the aircraft leading to control problems for the flight crew.

The aircraft structure would require massive modification to make ejection seats feasible, including

strengthening the cabin floor for the additional weight and the recoil of the seat firings. The cabin

roof would have to be configured with the aforementioned hatches. The fuselage would thereforeneed a major increase in supports to allow it to hold its shape when the hatches were jettisoned.

Overhead baggage compartments, and under-seat storage would have to be eliminated to give

adequate clearance above and, because of the seat depth, below. Legroom would have to be

adjusted to make sure that adequate clearance was maintained on ejection to prevent leg

injuries.




Mechanical ejection (spring/bungee) would provide inadequate thrust to ensure that passengers

would clear the empennage. Compressed gas systems that would have enough force would

provide too great of an initial force for safety. This means that pyrotechnic rocket/catapult

systems be used. These systems would necessitate significantly increased training for maintenance

personnel, cabin and flight crews. The pyrotechnics would require maintenance on a regular basis

in an explosive rated hanger with explosive rated storage.

The ejection sequence would have to be from the rear to the front of the cabin, with the flight

crew being the last of all to be ejected. In an airliner with 30 rows of seats, the seats would have

to be jettisoned in row sets, with separation rockets to insure dispersal of the seats and prevent

mid-air seat collisions. There would have to be a delay between rows for the same reason. This

delay in military jets is in the vicinity of .4 to .5 second. This adds up to some 15-16 seconds for a

full ejection of the aircraft. Seats that are unoccupied must be weighted to ensure that they

separate in a predictable path. While the seats are firing, the aircraft would be exposed to

forces from the catapult charges, and the center of gravity would be changing rapidly. This would

cause significant difficulty to the flight control system to maintain stability.

The above paragraph details one of the primary problems with airliner ejection systems. The

majority of airliner disasters occur at low altitude, usually during takeoff/landing which is a

section of the airliner envelope that would not be conducive to a lengthy ejection sequence.

Taking two examples: TWA Flight 800; and Sioux City: TWA 800's failure (regardless of the

cause) occurred too fast for the flight crew to have initiated the ejection before the structural

failure of the aircraft would have destroyed the firing system. If there was a cabin crew initiated

backup, the structural failure might still have been great enough to have prevented the system

from functioning (presuming that the depressurization and wind blast conditions allowed the cabin

crew to reach the actuation device and fire the system). Flight 800 also had an in-flight fire whichwould have caused casualties, and flying debris from the damage to the front of the aircraft

which would be impacting the ejecting passengers. The airflow pattern from such damage would

also affect the flight path of the ejection seats, probably causing mid-air collisions which would

cause injuries and seat malfunctions.

Sioux City's crash was one where a system failure had disabled the plane’s flight controls, but left

the engine controls active. The plane was under pilot control for some time prior to the impact. In

this case, the plane could have been controlled to altitude, the passengers strapped in, briefed on

procedure, and then command ejected. This assumes that the passengers would remain calm,

return to their seats and strap in. The pilots would then have to attempt to maintain control of the

aircraft while the seats ejected for 15 seconds behind them (if it doesn't seem like a long time, set

a timer for 15 seconds, close your eyes and wait...). When it finally got to the cockpit area, the

flight controls would have to be ejected with the crew as they would be unable to release the

grips before they would be injured by them during ejection.




The only viable solution I have seen for this problem is the concept of a parachute recovery

system for the entire aircraft, or large portions of it. I believe that a system that would jettison the

wings and engines of the airliner and recover the passenger cabin could be developed which

would allow for significant possibility of saving lives. Ballistic Parachute systems have been

developed by a company called Ballistic Recovery Systems Inc. to lower ultra light aircraft and

aircraft up to 1500 pounds. With the gross weight of a fully loaded 747 being over threequarter of a million pounds, the systems would have to be considerably larger and would be

heavy and expensive to add to an existing airframe. In future designs, a parachute system could

be designed integral with the airframe. In order to be feasible, the system would probably have

to jettison the engines and wings to lower the gross weight that could be lowered. Accordingly, If I

were the designer, I would design the craft to separate the smallest possible sections including

people. In other words, the airframe should be designed with passenger cabins that are

separable by bulkhead to break the cabin into let’s say three segments. Each segment would

have one or more parachute system to recover the segment individually. That would still be a

large segment (in some 747 aircraft there can be 510 passengers thus 1/3 would be 150

people. At an average weight of 150 lbs. that would be 22500 pounds of people. The structureweight would also have to be considered as well as carry-on baggage, and if the under floor

baggage compartment is a part of the segment, the weight of the baggage would also have to

be considered.) Even though this is viable it is not likely to be built! The costs would be very

large, the modifications to the airframe extensive, and the percent chance that it would or could

be used to positive effect so low that it is unlikely that aircraft company would find it

economically feasible.

Conclusion:

Passenger survival by separating the passengers from the aircraft prior to impact is not an optionthat could be easily or cost effectively implemented. In my opinion, crash prevention and

improving survivability of the airframe would be a better use of funds. If a plane does not

crash usually the survival rate is 100%!!! In the case where an aircraft does crash, if the

passengers are not killed or immobilized by the impact, they have a good chance of survival if

they can egress the wreckage quickly! Smoke and fire are the main killers of people after a

'survivable' impact. The trend toward smaller and fewer escape doors must not continue. The risks

to the passengers are much greater with only a few more rows between the passenger and an

emergency exit.

This document is based solely on my personal analysis of the concept of equipping Commercial

Aircraft with ejection seats. The information it is based on is public information on ejection seats

and airliners, as well as analytical discussions with other aviation enthusiasts.

For more information on Airliner safety, see either Airline Crash Research Site or the Aviation

Safety Web Pages.

Source: http://www.ejectionsite.com/eairliner.htm

http://users.aol.com/BRSchute/BRS.HTML

http://www.d-n-a.net/users/dnetGOjg/Research.htm

http://web.inter.nl.net/users/H.Ranter/


http://www.ejectionsite.com/eairliner.htm






http://www.d-n-a.net/users/dnetGOjg/Research.htm

http://users.aol.com/BRSchute/BRS.HTML

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The Ejection Site - Discussion of Airliner Ejection Seats