There are two EEC / ELC fault scenarios. The first is concerned with engine start and subsequent despatch with EEC inoperative, this instruction formed FSI B757 13/2001 and remains unchanged. The second is concerned with potential engine run down while at low altitude and low engine power with the bleed valves in the unpowered position.
Recent communication from Rolls-Royce has described a small number of recent events involving the failure of Electronic Engine Control (EEC) and Engine Limiter Control (ELC) during engine start. In some cases, where the flight has subsequently despatched with the EEC inoperative, the affected engine has failed to deliver the required take-off thrust, resulting in a rejected take-off.
Such events have been extremely rare. However, the manufacturers of the EEC units are investigating the cause and will take corrective action. In the meantime, the following procedure must be observed in the event of EEC and ELC malfunction during engine start:
| Indications | EICAS | L/R ENG EEC and L/R ENG LIMITER |
|---|---|---|
| LIGHTS | EEC and ELC control switches INOP |
If the engine starter cut-out functioned normally, attempt to reset the system by cycling the EEC switch whilst the engine is operating. This can be attempted several times if necessary. If the system resets, then normal operation may continue, but the temporary appearance of the fault should be recorded in the technical log on return to a maintenance base.
If the system cannot be reset then a thrust shortfall on take-off may result, and engineering action is required before despatch.
If the engine starter did not cut out normally, the EEC fault is indicative of a dedicated generator failure. Engineering action is required before despatch.There have been a number of operator reports of both the EEC and Limiter becoming inoperative during flight. During the later stages of a flight (primarily descent), the affected engine may experience an engine rundown (uncommanded inflight shutdown) while at low altitude and idle engine power.
To prevent engine rundowns, use of engine thermal anti-ice (TAI) during descent is recommended. Use of TAI increases engine speed to approach idle, which provides increased surge margin at low power. In addition to completing the relevant QRH drill, the following are guidelines concerning TAI use in this scenario:
Note: Boeing and Rolls-Royce did evaluate use of the TAI system during all possible OAT/TAT conditions. Use of TAI during descent as outlined on 757 airplanes with Rolls-Royce RB211-535E4 engines is acceptable even during the warmer summer months. Rolls-Royce advised that on a 54 degree Celsius day, the inlet lip skin temperature does not exceed 130 degrees Celsius, even when the engine is accelerated. The inlet is capable of withstanding temperatures of this magnitude.
Caution: In the event that pilots need to carry out these actions, it is imperative that you warn maintenance personnel that there is a possibility of injury due to hot inlet cowl lip skins, if the flight crew does inadvertently leave TAI on upon arrival to the gate.
Amplified Normal Procedures & TCX Flight Staff Instruction B757 04/2005, 21st April 2005