The changes outlined in this bulletin have been incorporated into the QRH.
Boeing has determined that the existing LOSS OF THRUST ON BOTH ENGINES non-normal checklist is not the optimal method for resolving a dual engine failure or flameout from a high power setting when ground contact is a factor. The revised procedure provided with this bulletin improves start capability in this situation. The checklist contained in this Bulletin has been coordinated with all 757 engine manufacturers.
Boeing The difficulty in obtaining a rapid restart from a dual engine failure or flameout at high power settings is residual heat in the engine. The engine may restart into a stall, which may result in a hot start. Placing the Fuel Control switch to CUT OFF if the engine appears stalled or approaches the EGT start limit, clears the stall. Returning the switch immediately to RUN "reschedules" the engine control and allows the start to continue. EGT drops rapidly when the Fuel Control switch is placed to CUT OFF. "Cycling" the Fuel Control switch is more effective than waiting for the engine to cool with the Fuel Control switch in CUT OFF while engine RPM decelerates. By cycling the Fuel Control switch, higher N2 (or N3), and high pressure compressor (HPC) airflow may be sustained during the start attempt. This cycling increases HPC cooling, minimises RPM loss, and may reduce the overall time required for a successful restart.
The revised recall portion of the checklist includes positioning the Fuel Control switches of both engines to CUT OFF, and then returning the Fuel Control switches to RUN. If EGT rises rapidly approaching the placarded EGT limit on the Standby Engine Indicator (SEI), or the engine appears to be stalled during start (EGT increasing with RPM not increasing), the flight crew should position the associated Fuel Control switch(es) to CUT OFF, then immediately return the Fuel Control switch(es) to the RUN position. With a hung or stalled engine start, cycling the Fuel Control switch(es) in this manner is repeated until one engine is successfully started.
The new recall steps are most applicable in the unlikely event of a dual engine failure when the engines are operating at a high power setting. The subsequent checklist steps of alternately placing the Fuel Control switch in CUT OFF for 30 seconds and RUN for 30 seconds have not changed from previous checklists. They address the more likely scenario of having low fuel pressure during restart attempts while drifting down from higher altitudes.
When one engine is successfully restarted, the flight crew should accomplish the ENGINE FAILURE/SHUTDOWN checklist. If an engine start is desired after engine shutdown (with no fire or apparent damage) accomplish the ENGINE INFLIGHT START checklist.
Dual engine failure is an emergency situation that demands prompt action regardless of altitude or airspeed. It is important to accomplish the recall steps and fly the appropriate airspeed during the start attempt. There is a higher probability that a windmill start will succeed if the restart attempt is made as early as possible (or immediately after recognizing engine failure) to take advantage of the residual high engine RPM. Use of higher air speeds, and altitudes below 30,000 feet, will also improve the probability of a successful restart. Loss of thrust at higher altitudes may require drift down to lower altitude to establish adequate fuel feed pressure.
The engine inflight start envelope defines the region where windmill starts were demonstrated during certification. It should be noted that this envelope does not define the only areas where a windmill start may be successful. The LOSS OF THRUST ON BOTH ENGINES checklist is written to ensure that flight crews take advantage of the high RPM at engine failure regardless of altitude or airspeed. A subsequent APU start may be initiated as soon as practical for electrical power and to obtain air pressure for starter assisted start attempts. Complete the checklist recall steps before attempting an APU start for the reasons identified above.
If electrical power is restored, do not confuse APU generator power with airplane engine generator power at idle RPM; do not advance the thrust lever prematurely.
During restart attempts with both engines failed, use the SEI takeoff EGT placard limit even if EICAS remains powered. EGT during rapid restart may exceed the limit displayed by EICAS for normal engine starts. The SEI EGT limit is used as the inflight start EGT limit only when both engines are failed.
A hung or stalled engine start is normally indicated by stagnant RPM and increasing EGT. During start, engines may accelerate to idle slowly. Action should not be taken if RPM is increasing and EGT is not near or rapidly approaching the SEI maximum EGT limit.
Boeing Flight Operations Information Bulletin 2000-1, 21st January 2000