This bulletin provides information informing flight crews of temporary recommended procedures for preventing high thrust surge/stall.
Five high cycle RB211-535C engines have experienced recoverable surge/stalls during takeoff. Tests conducted by the engine manufacturer reveal that the loss of high thrust surge/stall margin is related to a lack of thermal stabilization and a high number of flight cycles.
The high thrust surge/stall margin of an engine, especially one that is not thermally stabilized, decreases as a function of increased thrust. The most adverse surge/stall margin occurs about 40 seconds after takeoff thrust is set. Although the surge/stall margin is improved by reducing the level of takeoff thrust, any subsequent increase in thrust during the takeoff may induce surge/stall.
Rolls Royce has issued two Non-Modification Service Bulletins.
SB 72-8249 requires a full thrust takeoff and a warm-up procedure on high cycle engines identified in that Bulletin.
SB 72-8251 provides an engine health check and a requirement for full thrust takeoffs and/or engine warm-up as identified in that Bulletin.
Either Bulletin requires suitable placards to be installed by the operator on those airplanes requiring full thrust takeoffs and/or engine warm-up procedures to assure flight crew compliance with the operating restrictions contained in the applicable service bulletin. The placard should be located on the front instrument panel in full view of the flight crew.
The following interim operating instructions are in effect until further notice.
Non Placarded Engines:
Engines With Warm-up and Full Thrust Takeoff Placards:
Reduced thrust procedures are not permitted when an appropriate placard is installed. When required, takeoffs shall be made at maximum rated thrust with EECs ON, if operable. In the event an EEC is inoperative, the takeoff should be made with both EECs OFF and maximum rated thrust set manually. With maximum rated thrust set, advancing thrust levers farther during takeoff or initial climb, is not required. During maximum rated thrust takeoffs, flight crews should anticipate higher rates of climb.
If engine surge should occur during takeoff it is usually audible and accompanied by rapidly rising EGT, and decreasing EPR and RPM. After a safe altitude is attained and even if EGT limits were exceeded, normal engine operation can be recovered by throttling back to idle until the EGT has decreased below 500°C. Thrust may then be restored, as required, up to Max Continuous and, as long as engine parameters remain within limits, normal engine operation may be resumed.