B777 EEC
 

Can the B777 EEC be reverted from hard Alternate mode to Normal mode when airborne? That is, if I push the ENG EEC button back in, will the engine revert back to normal mode assuming no defects?

Yes, you should be able to. Why would you be in that situation though? :}

Got to agree with STBYRUD.. why would you?? The ADIRU switch can also be turned off in flight without removing power (according to the FCOM) but why would you want to test the theory??

If it aint broke.....

Consider this scenario:

1) ENG EEC L fails.

2) Checklist calls for BOTH EECs to be switched off.

3) Later on, ENG L fails and is shutdown.

4) The good engine, R engine, also has a good EEC. So should I choose to turn the EEC R back on, can it be done in flight?

It depends on the engine type and reason for reversion to Alternate mode.
IF the EEC was happy and healthy and is only in Hard Alternate due to manual selection of the EEC mode switch, it can be returned to Normal mode at any time by selecting the EEC mode switch back to Normal.
On the EPR engines (Rolls/Pratt), if the reversion was due to loss of inlet probe heat, Normal mode cannot be re-selected without shutting down and restarting the engine even if probe heat has been restored.
On GE, if the EEC went to alternate mode due to a temporary loss of Air Data (ADIRU and/or SAARU) or air data disagree, once normal air data has been restored Normal mode can be reselected.
Clear?

surely the electronic checklist would dictate the correct course of action.

Combined failures
 

Not flying the 777, so may be completely wrong, but AFAIK, QRH procedures do not usually cover combined or multiple failures ,with exceptions for some types of aircraft.

Our colleague says, EEC on Hard mode on both engines, then, one engine fails......

That is 2 failures, there would not be a QRH for that situation.......

So finding a procedure for it on the manufacturer books may be not possible.

Would it not be only a minor failure condition and the aircraft will still fly allowing lots of time to contact engineering for a discussion.

As I noted in my previous post, if the EEC is healthy and the only reason it's in Alternate mode is due to manual selection of the mode switch (e.g. because the other engine EEC did have a fault and auto-reverted to Alternate), Normal mode can be selected at any time by simply re-cycling the mode switch.
That being said, if you want to get back to Normal mode, there is little down side to simply cycling the mode switch to see what happens. You're not going to hurt anything, the only real draw back is having to retard the throttle to a mid position before you cycle the switch (the short time loss of thrust might be undesirable if you're operating single engine).
BTW, I was involved in the original development of the 777 engine control/EEC - I do know what I'm talking about...

Not true. Turning off the ADIRU is inhibited above 30Kts.

Do you have an ice crystal icing checklist and does it mention anything about the EEC'S?

I don't understand the sense of the question.

The EEC is a computer based device which is designed and programmed to automatically accommodate engine operation in known regimes including ice crystals.

Does your question ask more than that?

Lomapaseo, EPR engines have a bad habit of icing up the temperature portion of the inlet P2/T2 probe in ice crystal icing (the pressure is usually OK because there is a lot of heat applied - ~500 watts - but for obvious reason the T2 sensor needs to be separated from all that heat and ice crystals can foul it up). This can really foul up thrust setting with the EEC in "normal" mode because the inlet T2 will read right at freezing (0 deg. C) - well above the rating corner point at high altitude. As a result the EEC may calculate a max EPR below what's necessary for maintaining altitude/airspeed. So if inlet probe icing is suspected in ice crystal icing, the checklist says to select EPR engines to Alternate mode to restore proper thrust setting.

I accept that as a selectable precaution (pilot action) if indeed they suspect they will enter icing.

However, when you are caught off unawares, it's the engine certificated job to accommodate the threat on its own (by virtue of sense and response via the EEC etc.).

I realize that the EEC may be caught by newly encountered problems from time to time and that temporary work- arounds may find their way into FCOMs but in the end the problem needs to be addressed either under limitations of where you fly or by the engine itself before it becomes a glider.

I brought the Ice Crystal Icing point up as on my type (plastic) said checklist asks for the EEC's to be put to alternate in that situation.

Then when you exit the condition, it asks you to return the EEC's to normal, which kinda answers the OP's original question. However, I don't fly the 777 (although my type is very similar!) hence my question to see if a similar situation arose in the 777 QRH/ECL...