B744 Thrust Mode At Altitude Capture
 

Scenario: 744 takes off without VNAV armed. At 1000', the A/P is engaged (in current TO mode). The aircraft reaches, say 5000' (MCP altitude).

Is there an automatic A/T mode change? e.g. SPD... or...
Does the A/T remain in HOLD or THR REF at ALT capture/hold (until, say, a flap limit is reached or does it overspeed?)

Thanks.
Rgds.
NSEU

if it anything like the 733 it should go into MCP SPD mode at ALT CAPTURE

My understanding is that when the TOGA is pushed for T/O (prior to 50 kts) without VNAV armed the following events occur:

1. The thrust levers advance to the selected T/O thrust (THR REF) and the vertical mode will be TO/GA.
2. At 65 kts the autothrottle annunciates HOLD
3. At 400' the autothrottle again indicates THR REF
4. At the selected altitude, the vertical mode changes to ALT but the A/T remains in THR REF and the aircraft accelerates up to the flap placard speed or VMO as applicable.

Therefore SPD mode needs to be selected or alternatively, select FLCH SPD while still climbing.

Regards

csd

Agree with CSD........

The pitch mode for takeoff is initially TOGA. If VNAV is not armed then TOGA will remain the pitch mode until altitude capture indicated by ALT.

The A/T mode for takeoff is THR REF followed by HOLD. I think that without VNAV armed it will remain in HOLD even through 400'.

At altitude capture, the autothrottle will remain in HOLD and the aircraft will accelerate until a placard speed limit is reached.

To prevent this another A/T mode needs to be selected i.e. SPD if the altitude has already been captured of FLCH (which is a combined pitch/power mode) if still climbing.

We had a look at this in the sim some years ago and (allowing for 'wrinkly' memory lapses) I think the CSD version is correct.
Just one 'picky' point, the acceleration will be to 5 knots below configuration limiting..... it most certainly will not overspeed.
Irrelevant, maybe, but without VNAV being armed one supposes that FLCH will be engaged at the assigned thrust reduction point.

Many thanks, guys.

Any ideas what thrust mode will be displayed when the flap speed limit comes into play (SPD?). Some weird submode of THR REF, SPD,....?

Cheers.
NSEU

Reasonably certain that the A/T FMA will remain at THR REF.
It's worth bearing in mind that the THR REF annunciation indicates the POTENTIAL thrust setting as distinct from a set value. Thrust can be set to any value up to, and including, the specific Reference Thrust, which could be, for example, TO1, CLB, CLB1 etc. What will be set, or adjusted to, will be dictated by the safe operating envelope. That reference value will alter with the various stages of flight and dependent on initial set-up inputs. What is active at any time is what appears at the top of the lower EICAS display.
In parallel with the above, it is worth noting that at least one, very expensive, computer-based training programme DOES NOT reflect real-life FMA's for non-procedural, ad hoc scenarios.

Cornish Jack

I would have thought that it would have gone to THR. I've always thought that THR REF indicated that the thrust rating, as indicated on the upper EICAS, has been commanded.

This is just an educated guess and I may well be wrong though!

Regards

csd

AFAIK, the THR annunciation is only a product of the THRUST button first press during Go-Around. This changes the thrust mode from THR REF to THR and commands a RoC of 2000'/min. The differentiation is this specifying a rate of climb. THR REF isn't interested in RoC - just configuration limits and FMC programming.
In the scenario mooted, the non-standard configuration (no VNAV, no pilot input etc.) doesn't have a practical application.