Original question
Originally Posted by
newifr
Hi everyone
I am just about to start as a Crz FO on the B777 and have a few questions on VNAV.
I have the CD but it does not cover these specific questions.
2. If in VNAVSPEED would it comply with a speed/alt constraint at a waypoint?
Thanks
First answer
Originally Posted by
esreverlluf
1 - no
2 - no
3 - yes (as long as it remains in VNAVPATH)
In VNAVSPEED, the aircraft is pitching for speed, in VNAVPATH it is pitching to maintain the descent profile.
Hope that helps.
Second answer
Originally Posted by
SMOC
2. No as its not on path to comply with the restriction, however the speed window is probably open for you to be in VNAV SPD or you would have recieved a drag required message or been in THR VNAV SPD below profile with the window closed.
Final answer
Originally Posted by
CaptainJim
"during departures or arrivals, the selection of a pitch mode other than VNAV PTH or VNAV SPD will result in a risk of violating procedure altitude constraints."
B777 FCTM 1.38
So yes even in VNAV SPD it will still comply with Alt constraints in the FMC if the MCP is set to a lower altitude as in the case for a descent.
After reading the above as published by Boeing, one can see how this thread is an excellent example of what I frequently come across in aviation. Bad information being passed along by people who sound like they know what they are talking about.
So VNAV SPD will respect at least the altitude portion of speed/altitude constraints.
Perhaps a few could try out their theories in flight or a sim and get back to us on the results.