NG FMC Takeoff Reference page 2
Joined: Oct 1999
Posts: 206
Likes: 6
From: Up there
The FMC has it's own performance computer using runway length and ambient conditions it has access to temp and QNH, it obviously needs wind and runway conditions to be entered.
However it has no knowledge of obstacles or MEL/CDLs so is deemed inappropriate to use by probably all companies.
The figures can however be used as a gross error cross check against company provided figures.
Some FMCs don't compute a V1 so entering wet or dry is meaningless.
And changing the wet / dry on page 2 having entered the company figures on page 1 will lead to a TAKEOFF SPEEDS DELETED.
However it has no knowledge of obstacles or MEL/CDLs so is deemed inappropriate to use by probably all companies.
The figures can however be used as a gross error cross check against company provided figures.
Some FMCs don't compute a V1 so entering wet or dry is meaningless.
And changing the wet / dry on page 2 having entered the company figures on page 1 will lead to a TAKEOFF SPEEDS DELETED.
Last edited by CCA; 18th June 2016 at 09:46.
Joined: Jan 2000
Posts: 860
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From: FL410
NG FMC QRH speeds are generated using basic programmed data from FMC only, it knows the runway direction, elevation and length.
But it can take into account WIND, SLOPE and DRY/WET/SKIDRESISTANT etc...
Entering it prior to entering company speeds will serve as a gross error check only.
IT WILL ALWAYS GIVE YOU BALANCED FIELD SPEEDS, as obstacle data is not available as per post by CCA.
But it can take into account WIND, SLOPE and DRY/WET/SKIDRESISTANT etc...
Entering it prior to entering company speeds will serve as a gross error check only.
IT WILL ALWAYS GIVE YOU BALANCED FIELD SPEEDS, as obstacle data is not available as per post by CCA.
Thread Starter
Joined: Oct 1999
Posts: 1,051
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Sky job
Re gross error check
So if enabled the FMC will give you FMC speeds (small font) assuming Perf page complete. Then you overwrote with company runway analysis speeds.
I've never seen this function fitted on any FMC that I have flown on.
Re gross error check
So if enabled the FMC will give you FMC speeds (small font) assuming Perf page complete. Then you overwrote with company runway analysis speeds.
I've never seen this function fitted on any FMC that I have flown on.
Joined: Jun 2000
Posts: 4,507
Likes: 4
From: last time I looked I was still here.
FMC gives balanced field speeds. There should be little difference, 1kt, between the VR & V2 FMC & Perf tables. If so then there is a problem. 1kt = 1000kgs (+/-). V1 can vary for a multitude of reasons. On long runways it is common for it to equal VR via both calculations. The +/- 1kt is the gross error check. If within that boundary then use FMC speeds and manually enter V1 is outside the boundary. Simple. Switching between DRY/WET will also only change V1in FMC.
