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ALERT 250-C20 CS1~1023COMMERCIAL SERVICE LETTER

Detroit Diesel AllisonIndianapolis. ndiana 46206 Page 1 of 6August 1, 1973FAA-DER Approve

Subject: Extreme Turbine Outlet Temperature Effects on TurbinesSeveral incidents of severe c rackine of the #l Turbine Wheel havebeen investigated by DDA. The items below require your urgentattention as their effect on Turbine Whee l life is significant.

PART ONEPart One contains general information on fuel shut-off during shut-down, high temperature, low power indications, and re-emphasizesthe standard practices that are to be used in dealing with these areas.

I. FUEL SHUT-OFF DURING SHUTDOWNDue to the critical effect of high temperature on the turbine wheel,and the possibility of the CECO MC-40 Fuel Control Shut-Off ValveNOT in the FULL OFF POSITION, we are repeating an excerpt from250-C20 CSL-1009.

CAUTIONTO ASSUR E THROTTLE CUTOFF, HOLD TWIST GRIPIN CLOSED POSITION UNTIL THE Nl DECELERATESTO ZERO AND TOT IS STABILIZED.

If only partial fuel cutoff is experienced (indicated by a sudden andconsiderable rise in TOT during Nl deceleration), engage the startbutton while placing the fuel valve switch to off and hold starterengaged until flame out is indicated by an appreciable drop in TOT.After the starter is disengaged, TOT mujst be monitored duringcoast-down to be sure there is no sudden reversal.II. HIGH TEMPERATUR E

Over temperature can and has been encountered during starting transientpower and shutdown.Although the maximum temperature limits refer to starting, these samelimits also apply to transient power and shutdown. Limits and requiredmaintenance action are as follows: Revision No. 4September 5, 1975

Rolls-Royce Proprietary Data Uncontrolled Printed Copy

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250-C20 (XL-1023Page 2COMMERCIAL SERVICE LETTER

During Starting and ShutdownTemp Range Time

up t0 793C. (1460~.) No limit793-927C. (1460-1700F.) Over 10 sec.928-999.C. (1700-1830F.) Not allowedovw 999C. (1830O~.) Not allowed

Maintenance Action NoneInspect Turbine.Inspect Turbine.Removed turbine forheavy maintenance oroverhaul.

During Power TransientTemp Range

Up to 777C. (1430F.)Time Maintenance Action

No limit None(transient only)777-793oc. (i430-i460~.) Until stabalized None(5 min. max. )793-843C. (1460-1550F.)

793:843C. (1460-1550F.)844-927-C. (1550-1700F.)Over 927C. (17OO.F.)

0 to 6 sec. None(intentional useof temperaturesin excess of 793C.is not recommended)Over 6 sec. Inspect Turbine.Not allowed Inspect Turbine.Not allowed Remove turbine for

heavy maintenance oroverhaul.

It is essential that the indicating system be calibrated as called out in theappropriate airframe maintenance manuals at each 300 hours or wheneversymptoms indicate a possible error in the indicating system.Revision No. 3June 12, 1974Published August 1, 1973


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250-C20 CSL-1023Page 3COMMERCIAL SERVICE LETTER

III. LOW POWER INDICATIONS:If a noticeable deterioration in power is experienced in a rather short period,a cracked first-stage turbine nozzle diaphragm may be the prime cause.Cracks in the diaphragm change the flow pattern of cooling air to the first-stage turbine wheel and this may have an effect on wheel life. It is essentialthat operators be fully aware of the engine operating characteristics. Operatorand maintenance personne l are aware that there are other causes for powerloss also. Prior to assuming that the nozzle is the prime cause, other sec-tions of the engine must be exonerated as the cause.

Followingapower loss discrepancy and the first-stage turbine nozzle dia-phragm is found cracked, replace the first-stage nozzle only if the visibledamage can be corrected with nozzle replacement. (Refer to Replacing theFirst-stage Turbine Nozzle or First-stage Turbine Nozzle Shield paragraphin 250-C20 Operation and Maintenance Manual.) If the damage extends beyondthe first-stage nozzle into the turbine assembly (or it is suspected), theturbine must be removed from service and inspected as called out in theoverhaul manual. Those parts which do not meet the criteria as establishedin the overhaul manual must be replaced.CAUTION: UNDER ALL CIRCUMSTANCES, IF THE TEMPERATURE HASEXCEEDED 999C. (1830F.) DURING STARTING OR SHUT-

DOWN OR 927C. (1700F.) DURING POWER TRANSIENT, THETURBINE ASSE MBLY MUST BE REMOVED FOR OVERHAULINSPECTION.PART TWO

Part Two contains the information required: To perform the special main-tenance actions required on the rigging; to make a one time rigging adjustmentand check; and to perform a one time inspection if the engine has ever beensubjec ted to an afterfire.THE FOLLOWING AIRCRAFT RIGGING CHECK IS REQUIRED FOR 250-C20 CECO-CONTROLLED ENGINES:Check fuel control quadrant reading. It must be minus 2 with throttle leveragainst min. stop when the twist grip is in FUEL OFF.reading is not minus 2, If the quadrantreadjust the minimum stop on the fuel control tominus 2 on the fuel control quadrant as follows:

Revision No. 4September 5, 1975Published August 1, 1973


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250-C20 (XL-1023Page 4COMMERCIAL SERVICE LETTER

A. The minus 2 position may be obtained by adjusting the minimumstop screw to 0, then out one-half turn from the 0 position.B. Check the quadrant to be sure the pointer is minus 2 when thetwist grip is in FUEL OFF. If minus 2 cannot be set due to thelimitations of the aircraft control system, a minimum of 0 isacceptable.

n THE FOLLOWING FUEL CUT-OFF VALV E LEVER ADJUSTMENTIS REQUIRED:A. On CECO Fuel Control P /Ns 6851506 (CECO P/L 104000A8) andprior, the following applies .

1. An adjustment of the cutoff lever link is also required. Whenthe minimum stop is adjusted to minus 2, adjust the cutofflever link, (See Figure) using an open-end wrench by firstturning the inboard (top) nut four (4) flats in the direction toshorten the effective length of the link. Then adjust outboard(bottom) nut (usua lly the same amount) so that the lever bush-ing is tight between the lock nuts.2. If the minimum stop is adjusted on ly to 0, adjust the cutofflever in the same manner except turn the nut eight (8) flatsin the place of four (4).3. When this adjustment is made (either 4 or 8 flats) and it isassured the lock nuts are tight against the bushing, the nutsmust be painted with red glyptal to identify the control asbeing adjusted and also to serve as a secondary lock.

ADJUST THESEAS REQUIRED NUTS

RIGHT SIDE VIEW(AS INSTALLEDI Revision No. 4September 5, 1975Published August 1, 1973


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B. On CECO Fuel Controls P/N 6887770 (CECO P/L 104000A9) andlater, adjustment of the cutoff lever link is not permitted. ,m. GROUND CHECK OUT OF AIRCRAFT RIGGING AND CECO MC-40FUEL CONTROL CUT-OFF VALVE:

A. A short ground run should be made and the rigging rechecked forrepeatability of the setting (0 or -2) w ith the twist grip in FUELOFF.B. After the ground run is completed and the rigging has been checked,the fuel control cut-off valve should be checked for leakage by the

following procedure:1. Disconnect the fuel hose from the fuel nozzle, place the freeend in an open container.2. Turn on the aircraft switches requ ired to provide fuel boostpump pressure to the engine and pull the ignition circuitbreaker or remove primary wire from ignition exciter. *3. Motor the engine to 10% Nl RPM using the starter. .4. If fuel flows from the open line in excess of the rate of 20drops per minute with the twist grip in fuel off, replacethe fuel control. Repeat the check before accepting thefuel control.5. If the cut-off operates satisfactorily, connect the fuel hoseand tighten the coupling to 80-120 lb. in.

Iv. INSPECTION REQUIREMENTS BAS ED ON E:NGINE HISTORY.A. It is recommended that log books, inspection records, etc.,

be reviewed for any after-fire occurance that might have beenexperienced and if an after-fire has occurred and no maximumtemperature was reported, a turbine removal and inspectionshould be made.B. If an after-fire shou ld occur, a turbine removal and inspectionshould be made, and the contents of this letter should be re-viewed to determine the appropriate corrective action.

Revision No. 4September 5, 1975IPublished August 1, 1973Rolls-Royce Proprietary Data Uncontrolled Printed Copy

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I250-c20 CSL-1023Page 6 COMMERCIAL SERVICE LETTER

SUMMARY

Again, we must stress the importance of:1. Proper Shutdown Techniques.2. Proper Throttle Rigging.3. Know ledge of Modulated Starting Procedures.4. Calibrated Turbine Outlet Temperature Indicating Systems.5. Know ledge of Eng ine Operating Characteristics with Regardto Power Versus TOT.6. Proper and Reasonable Throttle Manipulation During Starts

and Accelerations.7. On multiple engine installations, do not exceed TOT limitson single operation.

L. 0. DavidsonService ManagerGas Turbine EnginesREM/bsc


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Csl 1023