View Full Version : B757 RR engine controls

21st Aug 2002, 22:32
Another teaser from the B757.

I was in the sim' and in the middle of a total (aircraft) A.C. failure. No dramas but I noticed the EEC & ELC inop lights were on. Engines burning and turning and I thought these control units had their own dedicated generators. So, why the loss of A.C. causing them to be INOP, or was it a sim' gremlin?

Local bods had no quick answer and I've been out of touch since, so please help if you can.


22nd Aug 2002, 12:47
This is the first time I've heard that the EEC has its own generator, even thought that might well be. It is however not a reqiuerment as the 757 has not FADEC and there is a hydromechanical system that serves as a backup.

22nd Aug 2002, 13:01
Dedicated Generator 1 per engine provides power for the EEC (also Bleed valve control and Transient Pressure Unit) via one of 2 Dedicated Generator Control Units (duplicated for redundancy).

The EEC only performs supervisory role to match commanded and actual EPR values or a limiter role to prevent N1 speed exceedance. both achieved by downtrimming the mechanically scheduled fuel.

If either or both roles fail then the respective INOP lights will illuminate.

The Motor will continue to turn and burn but there will be no automatic control of EPR or N1 max speed.

Couldn't find anything in the System Schematic Manual to cause the INOP lights to illuminate under the conditions mentioned.

Bally Heck
22nd Aug 2002, 20:49
The following from Boeing manual: (535-E4 engines)

"Each engine EEC is powered by dual dedicated generators."


"The inop light is illuminated when the EEC is turned off or a failure is detected in the system."

Ditto for ELC.

It sounds like a sim bug, but I suppose it is possible that the circuitry for the inop lights might be affected by a total AC failure. The chances of eight dedicated generators failing simultaneously must be one of life's remoter possibilities!

I'm not going to try it on the aircraft tomorrow anyway.

23rd Aug 2002, 19:36
If the EEC detects a fault (loss of a signal) from certain interfacing components such as an Air Data Computer, those lights will illuminate with the associated EICAS messages (None in this case since AC pwr was lost).
The Air data Computers are powered by 115VAC, so with the loss of AC pwr went the signal from ADC that the EEC needed.
So, no it wasn't a simulator error.

24th Aug 2002, 00:11
spanner-do & comxtek;

Many thanks. It would seem that this is an OK indication, though with some hanging doubt, but one agian where the AOM leaves the pilots sadly lacking in data.
Since the new A5 books of cornflake packet freebies info have appeared from Seattle, as an instructor I am for ever saying to the sponge headed students, "I'll try and find out" Makes one feel even more inadequate than usual.

Going to work for an ego boost has been severly curtailed.

I'll stay at home and feel inadequate, or try and fix the plumbing. Floods? What floods!

24th Aug 2002, 14:11
What you need is a maintenance manual.

It's like taking the course again only now you get to know how it really works..

Or as our engineer put it, "If the put the truth in the pilots manual, no pilot would dare to fly.."


25th Aug 2002, 20:59
Brenoch and everybody else:

Many thanks for all your researches and replies. The comment about maintenance manuals and the new A5 format was illustrated again today.

B767 accessory panel; in my old A4 books there was mention of this panel and the Field relays for the IDGs. In the A5 version no mention of Field relays at all and no referal to the switches on the accessory panel. However, in the tech questions there was a question about Field Relays and the GEN control switch. I engaged MK.1 memory, stuck my neck out, tried to draw the circuit and it all made sense. Fortunately we had an empty sim' at hand to test the theory. I won the beers. There was not a jot
(n)or tittle about it in the books.
Do I hear a cry at the back for "bring back the FE?"

But that's another topic.

Thanks again. If I have any more starters for 10, I'll know where to come. No commissions!