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BelArgUSA
18th Jan 2008, 17:10
I am a 747-200 pilot.
We have a "ground or flight idle" on our JT9D engines.
Solenoid control...
xxx
Do you have the same feature on your engines...?
Is there a stupid $2.50 solenoid for the idle selector...?
Do you have a "GND IDLE" warning light...?
Are these solenoids prone to failures...?
xxx
Thanks for the info.
:)
Happy contrails

Squealing Pig
18th Jan 2008, 18:37
A further question now the AAIB have stated the Trents failed to respond. Are the power levers PHYSICLY connected to the engines as in a conventional non fly-by-wire aircraft or is it inline with Airbus and just sends a signal to computer that then decides if you really did want a power change or not ?

Check Airman
18th Jan 2008, 19:34
The power levers are not physically connected to the engines, it's electronic. However, the computer does not limit the thrust as you're thinking. If you want full power, slam them all the way forward, and the computer keeps adding fuel until a limit (N1, EGT etc.) is reached.

MaximumPete
18th Jan 2008, 20:25
Could be that alpha floor protection kicked in during gusty conditions.

VERY difficult to spot in the time scan available.

Automation HIDES things!!

MP;)

Clandestino
18th Jan 2008, 21:41
is it inline with Airbus and just sends a signal to computer that then decides if you really did want a power change or not ?

Eeeerm... which Airbus are you talking about? I'm certain that there's nonesuch feature on the CFM powered A319/20 and I sincerelly hope other airbi don't have it too. If you disconnect ATHR, the power you set is the power you get - in accordance with FADEC calculated limitations. On 777 and FBW airbuses thrust levers are not mechanically connected to engines, there are thrust lever angle resolvers beneath the levers and they send thrust demand signals to FADEC. Main difference between 777 and airbus is that thrust levers on 777 have servo motors that set them in accordance with autothrottle command, while on airbus they don't move - it gets a while to get used to.

Could be that alpha floor protection kicked in during gusty conditions.

Don't think so - alpha floor is airbus peculiarity. B777s have something similar though not quite the same. The term I've heard used to describe it was "autothrottle wake-up" though I can not confirm whether this is slang or officialspeak.

Check Airman
18th Jan 2008, 21:44
The "wake up" feature you describe is a toned down version of alfa floor. Basically, if the AT is armed (and it seems that it was) and the system senses a dangerously low airspeed, it adds just enough power to maintain a safe stall margin. If you keep bleeding speed, it adds more power- right up to full thrust if necessary.

Nepotisim
19th Jan 2008, 02:02
To answer the original question........................

First let me qualify that I am not licenced on the 777 or RR Trents.

I am licenced on 747 Cf6 Rb211 D4 and G2 and Jt9 (A while ago)

The FADEC engines RR G2, Cf6 do not have a flight/ground idle solenoid. To increase speed of the engine they just open the fuel valve accordingly until the desired N2 or N3 (according to engine) is achieved.

Hope this helps BelArgUSA.

Clandestino
19th Jan 2008, 22:42
I'm not Trent qualyfied either, just a humble CFM56 powered A320 driver.

CFM56 is a fully FADEC engine and doesn't have idle detents/solenoids, however there are about a dozen of different idle settings (ground, air, eng anti-ice, full anti-ice, OEI, approach...), calculated and set by FADEC. Most of them are not even mentioned in our flightcrew operations manuals.

I guess software error or undetected fadec fault would be the equivalent of faulted solenoid of the classic engine.

Also I assume that other FADEC engines are similar in operation to my CFM, but I could be easily assuming too much.

Clarence Oveur
20th Jan 2008, 04:39
FADEC is a system. EEC is a component.

FCOMs aren't what they used to be. Neither is technical training.

GMDS
20th Jan 2008, 04:51
FADECs are a integral part of all modern engines and are therefore to a high degree engine specific and to a lesser degree programed for the airframe/system fitted to.
The scary part of these little computers is in their first two abreviations: FULL AUTHORITY digital engine control. That says it all .. if it does not want to give thrust, you can shove, hit, bang, slam anything you want in the cockpit, it will not give anything.

pasoundman
20th Jan 2008, 06:27
Squealing Pig
Are the power levers PHYSICLY connected to the engines as in a conventional non fly-by-wire aircraft or is it inline with Airbus and just sends a signal to computer that then decides if you really did want a power change or not ?

The engines are FADEC controlled.
http://en.wikipedia.org/wiki/FADEC

That means no physical connection, just an electronic data signal.

FADEC system itself is not FBW although FBW aircraft use it. You can have a 'conventional' aircraft and fit FADEC engines. It's the norm these days. It's simply another, better - usually ! :-( way to control an engine.

Feathers McGraw
20th Jan 2008, 08:57
I asked this in the R&N mega-thread, but received no response, so here goes again.

There is at least one report that the EPR "gauges" failed in this case, what I'd like to know is, how is the EPR signalled to the cockpit and, in the event that the EPR measurement on each engine failed, how would this affect the FADEC/EEC? How many redundant EPR measuring "channels" are there on each engine?

I suppose what I'm really asking is, in the absence of EPR inputs into the whole engine control system, what would the FADEC do?

gas path
20th Jan 2008, 09:15
I suppose what I'm really asking is, in the absence of EPR inputs into the whole engine control system, what would the FADEC do?
Reverts to N1 control!
This would bring on the EEC ALTN light. The pilot would then select BOTH EEC's to alternate control. (selecting both takes out the resulting throttle stagger.)

Joetom
20th Jan 2008, 11:10
Am I right in saying the system operation would be.
. When FADEC wants EPR mode to stop being used, Engine is held at present values and crew action is reqd ( press a button to select N1 mode ) and only then will Engine respone to Thrust Lever commands?

NSEU
20th Jan 2008, 12:33
"When FADEC wants EPR mode to stop being used, Engine is held at present values and crew action is reqd ( press a button to select N1 mode ) and only then will Engine respone to Thrust Lever commands? "

It's not (absolutely) necessary for the crew to select the alternate N1 mode if the EEC's have already done it automatically in response to specific failures (however, if one has gone to N1 mode and the other hasn't, then for reasons stated above, you would manually select both to ALTN).

One of the reports said the pilots lost their EPR's. This is an indication that perhaps both the EEC's had switched modes (automatically).

The Flap Slat Electronics Unit tells the EEC's that the flaps have been extended and the EEC's select approach idle (as opposed to minimum idle). Gear extension produces "intermediate idle".

Yes, many aircraft systems still have old-fashioned relays, all prone to failure over time (as anything is). However, depending on the circumstances, the crew are informed that the engines are not in the appropriate idle state.

Rgds.
NSEU

kimoki
20th Jan 2008, 13:12
Is anyone "in the know" prepared to state whether BA had any updates to the FADEC software on the 777 recently?

monkey_wrench
20th Jan 2008, 18:43
Kimoki its a good question.

It is an oddity that on ETOPS aircraft, specifically, and multi engined aircraft in general, it is good maintenance practice not to work on more than one powerplant at any one time (safty critical task in the MPD).

Software upgrades to the FADEC is an exception to this as you normally cannot operate the aircraft with a different software configuration installed on each engine i.e. update one engine, fly and then update the other. Most times you don't even need to perform an engine run after the update. The FADEC software is categorised as "critical" but on other systems errors do creep into the lines of code which is why we end up with FMS version 10.6, 10.7, etc, which is not always to add functionality but more often to correct mistakes...

chemical alli
20th Jan 2008, 23:53
FADECs are a integral part of all modern engines and are therefore to a high degree engine specific and to a lesser degree programed for the airframe/system fitted to.
The scary part of these little computers is in their first two abreviations: FULL AUTHORITY digital engine control. That says it all .. if it does not want to give thrust, you can shove, hit, bang, slam anything you want in the cockpit, it will not give anything.


how about if you just select to alt on the eec then no need to shove ,hit or bang anything,also if the eec fails a resolver in the fmu schedules max cruise pwr .

Cubbie
21st Jan 2008, 01:35
From the 777Mel regarding an inop autothrottle-
1.) Autothrottle commands are provided by the Thrust Management Computing Function (TMCF). TMCF also provides EICAS indications of EPR reference values, thrust mode, and selected temperature.
In some failure modes of the autothrottle system, these EICAS indications will also be inoperative.
2.) The flight must remain within 180 minutes of landing at a suitable airport.