PPRuNe Forums - Boeing VNAV Path

Quote:

Originally Posted by JammedStab
What s MD?

FCOM 2: Procedure Fix Waypoint Names: MD – minimum descent

Quote:

Originally Posted by JammedStab
I thought commanded a level off but not sure

Give it a try next time by not recycling FD's
See text from FCOM2 below:

Quote:

VNAV mode is terminated by any one of the following:
• selecting another pitch mode
• glide slope capture
• reaching end of LNAV route
• transition of glide slope intercept waypoint if G/S is armed
• cross track deviation exceeds twice the RNP value during PTH descent for
an active leg with a database vertical angle and LNAV not engaged

The FMC transitions out of “on approach” under the following conditions:
• selecting TO/GA
• the airplane lands
• the waypoint cycles to the first waypoint of the missed approach
• executing a direct-to waypoint in the missed approach.

For an approach without a runway waypoint on the RTE LEGS page, the VNAV path is calculated to the MDA or a calculated altitude at the missed approach point. The calculated altitude may be below the MDA to ensure a flight path angle and normal threshold crossing height.

Quote:

Originally Posted by JammedStab
Not sure if this is true

As per FCOM 2:

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VNAV will remain engaged at all flap settings, allowing approaches to be flown using the vertical angle guidance. Speed for final approach can be set on the APPROACH REF page.

In practice the above means in combination with the auto pilot & throttle logic that VNAV will:
• command with Flaps extended the speed for selected flap setting based on Flap Position Indicator
• command no higher than flap limiting speed to be allowed to be flown (losing the PTH if required to compensate)
• command Vref30/Vref40 + the additive on final approach as entered into FMC
• provide UNDERSPEED protection with Flaps EXTENDED to 0 kts vs flaps up -15 kts

In summary the above is the safest way to fly the VNAV PTH approach, when FMC commands FLAPS UP speed and thus initiates pitch up for flap extension iaw profile, just select Flaps 1 etc on extension schedule, no need for SPD INTV as VNAV PTH uses FMC speeds which are derived from actual flaps selection. Note: the flap position indicator triggers the FMC to command associated speeds, not the Flap lever.