F100 EFB landing performance calculator: VFTO appears to be incorrect
-
Hi,
I believe there may be an issue with the VFTO value calculated by the EFB landing performance calculator on the F100 Professional.
In the attached screenshot, the landing calculation was made with the following conditions:
- F100 landing weight: 38,952 kg
- Landing configuration: Flaps 42
- EFB-calculated VFTO: 140 kt
- EFB-calculated VREF: 128 kt
- EFB-calculated VAPP: 133 kt
The VREF and VAPP values appear reasonable, and the FMS independently calculates a very similar VAPP of 134 kt. However, the VFTO value does not appear to be correct.
According to the Operations Manual and the AOM procedures, VFTO is the final take-off climb speed, also represented by the green dot on the PFD. It is therefore a clean-aircraft reference speed and is not another landing speed derived from VREF or VAPP.
The AOM also defines the normal manoeuvring speeds during the approach as:
- Flaps 0: green dot + 20 kt
- Flaps 8 or 15: green dot - 10 kt
- Flaps 25 or 42: VMA + 5 kt / final approach speed
This makes the EFB result particularly difficult to reconcile with the aircraft procedures. If the calculated VFTO/green-dot speed were really 140 kt, the normal manoeuvring speed with Flaps 8 or 15 would be approximately 130 kt. That would be lower than the calculated VAPP of 133–134 kt and almost identical to the Flaps 42 VREF of 128 kt, despite the aircraft having considerably less flap extended. This does not appear aerodynamically or procedurally consistent.
For the same aircraft state and approximately the same landing weight, the FMS APPROACH page calculates:
- VFTO 0 = 174 kt
- VAPP = 134 kt
The green-dot symbol on the PFD is also displayed at approximately 174 kt, agreeing with the FMS rather than the EFB. A VFTO of around 174 kt would also produce sensible AOM manoeuvring speeds: approximately 194 kt clean and 164 kt with Flaps 8 or 15.
Therefore, it appears that the EFB is either:
- Using the wrong performance table or speed column for VFTO,
- Calculating a flap-dependent speed instead of the clean green-dot speed, or
- Displaying another speed under the VFTO label.
Could you please confirm whether the VFTO field in the landing calculator is intended to represent the actual final take-off/green-dot speed? If so, I believe the value shown in this example should be approximately 174 kt rather than 140 kt.
The annotated screenshot is attached for comparison between the EFB, FMS and PFD indications.
Thank you.
