Boeing FMC V-speeds

[JammedStab]

Do you use the FMC V-speeds calculated by the FMC in your Boeing aircraft?

[D'pirate]

No - for the 744 in our company we use the figures from the EFB, however, the FMC computed figures are used as a gross error check when entering the EFB values.

[Broomstick Flier]

Ours, on the B763, the box does not generate take-off speeds, so we get them from the OPT software. For landing we normally use the FMC speeds (with cross check with the EFB, they are normally the same, give or take 1kt)

[ricfly744]

my understanding is that FMC speeds are ALWAYS for BALANCED rwy calculation. In this case it is safe and could be used.
If using any other performance inputs in the calculation, as improved climb, clearway and stowaway credits, that we normally do, the FMC V speeds cannot be used.

[Denti]

For takeoff we do not use the FMC speeds, on newer aircraft we do not even have that option anymore. EFB takes quite a bit more info into account and those figures are used. For landing we do take the FMC speeds though.

[Skyjob]

ricfly744 my understanding is that FMC speeds are ALWAYS for BALANCED rwy calculation

You are correct.

NEVER fly FMC speeds as they ONLY provide balanced field speeds.

The FMC does not take into account runway details such as but not limited to:

Slope
Stopway
Clearway
Obstacles (Most important!)
Intersection details (unless entered as a shift)


This is why EFB's and RTOW chars exist, to take these factors into account. Next time you use the RTOW/EFB see what the limit is for you calculation [calculation details in EFB]. Only on a runway where the above items are not any factor will balanced field speeds match FMC speeds.

Similarly, due to the same restriction in capability of FMC prediction of speeds, NEVER use DRY/WET/Skid-Resistant selection when calculating FMC speeds used or reference.
A very long wet runway may not at lower weights [using RTOW/EFB] require a reduced V1-wet, but the FMC will always provide a reduced V1 as it provides only Balanced Field data.

[JammedStab]

I asked the question because apparently some "geographically constrained" airports will have an ASDA less than runway length due to part of the end of the runway being used as a safety area because not enough land is available off the end of the runway for the safety area.

At least some Boeing FMC's have slope input.

[ImbracableCrunk]

Our Vspeeds for takeoff are uploaded from ACARS which populates the fields for us.

[Skyjob]

some "geographically constrained" airports will have an ASDA less than runway length due to part of the end of the runway being used as a safety area

My point exactly.
FMC speeds only provide balanced field speeds, they do not know about the geographical restraints and thus must never be followed.

Only ever use them as a reference when obstacles etc are not any factor and use the FMC speeds as a gross error check only.

[underfire]

IC,

That is what I have been led to understand....
ACARS for takeoff,
FMC for landing (at least for Vref).

[ImbracableCrunk]

IC,

That is what I have been led to understand....
ACARS for takeoff,
FMC for landing (at least for Vref). We can do landing speeds, too with all the distances and weights, QTAW, hits for MELs, Vref ice, etc from ACARS, too, but it won't populate the fields like for T/O.

[r747]

I am rated on the 757/767 and 744. I have worked with three different companies, and also as a simulator Instructor (TCI) and examiner (TCE) for Alteon (Boeing).

In every case we used the Runway Analysis Manual to determine the MTOGW or RTOGW, which is the term I prefer.

These weights are the lower of :
1. Corrected Runway Weight
2. Corrected Climb Limit Weight
3. Max Certificated (structural) T/O Weight
4. VMCG limit Weight

We then used the Actual Take Off Weight to obtain the V-Speeds calculated by the FMC and used these speeds.