NG FMC Takeoff Reference page 2
 

Hi

How does the FMC use the RW COND option?

Don't we input the appropriate speeds in already?

Thank you

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.

thanks.

so with most putting are on figures in it is pointless?

What is your companies SOP on the topic?

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.

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.

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.