777 VNAV EO Takeoff
 

Hello 777 drivers.

I am looking for a reference of the condition(s) activating VNAV engine out acceleration at takeoff.

Is it only when an engine is sensed failed (N2/N1) ? Or is there an additional condition like Fuel control switch Cutoff ?

If flying through engine out acceleration height with memory items not yet completed, what will happen ?

Pretty much sure I read this already but can’t find it anymore…

Thanks !

Just talking pitch modes…

Assuming you have VNAV armed for takeoff it will engage at 400’ regardless of whether you have an engine failure or not. The engine out acceleration height is entered during pre-flight and may differ from the all engine acceleration entered on the same (TAKEOFF REF PG 2) page. So the aircraft ‘senses’ the engine failure and decides which acceration height to use. The fuel control switch would only come into the equation for e.g. engine fire with no loss of thrust since the engine hasn’t ‘failed’ until the fuel control switch is moved to cutoff. Other failures would be sensed earlier as the engine goes below idle speed. With VNAV engaged the acceleration will start automatically. If you need to delay the acceleration for whatever reason, use speed intervention. e.g. requirement to maintain V2 to V2+15 for a turn.

Anyone know the exact parameter(s) used to sense an engine failed? %N2? Just curious…

For the EO SID to “pop up” the following parameters have to be met…

Difference of >10% in N2
Flaps greater than 0
EO SID in database for departure runway in use.

The EICAS "L/R ENG FAIL" message is primarily based on information from the FADEC (IIRC, it'll fall back to analog N2 if all digital communication with the FADEC is lost).
I don't know if any other systems use the logic from that message.

Condition:

1.After VNAV activation
2.Engine failure is sensed
3.Airplane below engine out acceleration height and thrust reduction thrust reduction point entered in FMC

FCOM chapter 11

Engine Failure Alert System- FCOM chapter 7 might give you an idea on the parameters of ENG FAIL/ ENG THRUST caution messages.

Is it not a 10% difference in THRUST. Hence if the aircraft can not calculate the thrust, due for example to damage to the various probes and sensors then TAC will not kick in initially. It MAY subsequently be available once the engine is secured as the aircraft now knows it is shut down and by definition has 10% less thrust than the other one?

I’ll have to find the reference for you but I’m 99% sure when talking about the EO SID, its >10% difference in N2.