EFB V-Speeds Too Low

[Aryeh123is]

Aircraft Version

Development

Build info

{
    "built": "2024-07-28T13:25:31+00:00",
    "ref": "refs/heads/master",
    "sha": "5d3514841d8c554bd1b7402e0a4295f01dd10f11",
    "actor": "flogross89",
    "event_name": "manual",
    "pretty_release_name": "master:5d351484",
    "version": "a32nx-v0.12.0-dev.5d35148"
}

Describe the bug

The V-Speeds taken from the EFB take-off calculator are all too high compared to the ones from FlySmart (the real one). Also, the Flex Temp from the EFB is lower than the one from FlySmart.

NOTE: Both calculators had the same parameters. Shomas aided in the FlySmart side of things in the Discord server a few weeks ago.

Expected behavior

The take-off figures should be around the same ballpark.

Steps to reproduce

1. Load in the plane and turn on EFB
2. Fill out the take-off calculations from the EFB
3. See if they match up to FlySmart (if you have access to it)

References (optional)

Additional info (optional)

No response

Discord Username (optional)

aryeh123is

[donstim]

Thank you for your input. The differences you observed can be traced almost entirely to a combination of user input error, normal tolerances, and conservative bleed corrections. However, the Flex calc for this condition needs a bit further analysis.

User input error: For some reason, you chose to input the runway parameters individually rather than entering the runway designation and allowing the calculator to automatically fill in the runway inputs. By doing so, you made an error in the runway slope entry. The runway slope is -0.09% rather than your input value of 1%. This has a noticeable effect on both the takeoff speeds and the Flex temp.

A second input error was that you used a runway entry angle of 90 degrees rather than the actual entry angle of 180 degrees. This error, however, did not noticeably change the takeoff speeds and Flex temp.

Here is the takeoff calculator output with these input errors corrected (and using the TOW in the FlySmart calculation):

Conservatisms: The A32NX takeoff performance calculator uses conservative adjustments from the FCOM applied to the Flex temperature for A/C and A/I bleeds. This may result in a larger correction and lower Flex temp for a given takeoff than would be shown by the FlySmart calculation. (I do have to ask, though, why would you be taking off with A/I engine bleed on with an OAT of 20 degrees C?)

Tolerances: The target accuracy tolerance for the A32NX calculator is about 2 degrees in Flex temp and 2-3 knots in airspeed through the majority of the takeoff operating envelope. As you can see from the results above, we've achieved that in this case with VR and V2 speed. V1 is a bit different in that there can be some additional variability based on operator SOPs. That being said, the FlySmart V1 for EGGW is lower than expected based on a different runway of about the same length, slope, and elevation that we used in developing the A32NX takeoff calculator. We are still looking into the potential reasons why.

Notwithstanding the above explanation regarding conservative bleed corrections for Flex temps, the A32NX calculator Flex temp for this condition is still a couple of degrees lower than expected. We will be looking into this further.

[Aryeh123is]

Hi and thank you for the reply.

1. Sorry on my behalf of the user input, in a different screenshot I picked the runway 07 and didn’t enter the details manually but I couldn’t seem to find that one.

2. I just wanted to see how the figures would change with A/I for the engines. Hope that’s ok?

Thank you for looking into the issue.

[donstim]

2. I just wanted to see how the figures would change with A/I for the engines. Hope that’s ok?

Ahh, okay. FYI, the Flex temp is reduced by 2 degrees C for engine A/I, by 6 degrees for engine+wing A/I, and 2 degrees for A/C bleed.

Thanks for the questions.

[Aryeh123is]

Oh I never knew that.

Thank you