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Old 19th Mar 2018, 08:40
  #14 (permalink)  
Pontius
 
Join Date: Jun 1996
Location: Check with Ops
Posts: 734
Some jolly good advice (especially Wiggy's FMA monitoring). Going back to one of the original questions:

in VNAV PTH the FMC will command pitch to mantain pitch and if required it will command the autothrottle to mantain FMC SPEED
I'd have to dig into my old 737/747 books to make sure I'm not giving duff info but I'm 95% certain they're they same as a 767. At the top of descent, in VNAV PTH, the auto throttle mode will change from SPD to IDLE and then THR HOLD. So, in answer to the question, no, the auto throttle will not maintain the FMC speed. The aircraft will pitch to maintain the path but if you get an unexpected headwind and the aircraft pitches up to maintain the path then the speed will reduce as the thrust levers are in HOLD (at idle, unless previously moved). When you reach a restriction it will revert to SPD/VNAV PTH and will kick the auto throttle back into life to maintain the speed.

Treat this, however, with caution as things have moved on from the 767 and the likes of the 737NG may well be more intelligent in working out what needs to be done i.e. wake the auto throttle up if a headwind is encountered in VNAV PTH. That's why those FMAs are so important.
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