787-10 EFB - Performance calculator - Wrong inputs considered. Wrong MTOW. The resultant calculations are off by a hardcoded offset

:wave: Thank you for using the Bug section, using templates provided will greatly help the team reproducing the issue and ease the process of fixing it.

2 tags are required: One for platform, and one for aircraft.

Are you using Developer Mode or made changes in it?


Have you disabled/removed all your mods and addons? If the issue still occurs with no mods and add-ons, please continue to report your issue. If not, please move this post to the Community Support section.

Not required

Which aircraft are you reporting an issue about? (Please also add the proper tag for it)


Brief description of the issue:

The performance calculator seems to add extra weight on top of the AUW. This creates an issue with Long haul flights dispatch, the EFB can’t calculate the takeoff because it says the planned weight is outside the limits when the TOW is close to the MTOW. (Why is the EFB considering a planned weight even higher than the Gross weight??)

  • The MTOW that the performance calculator assumes it’s incorrect. (MTOW: 254012kg)
  • There is a 1TN discrepancy between the GW in the MFD vs the CDU (The CDU is correct)
  • The performance calculator shouldn’t copy the GW but the estimated TOW.

Additional findings:

  • For the performance calculator to work, both the Airport and the runway should work. I don’t think this is correct, the airport should be enough (After load in in the POS page).


  • A reference airframe should be provided to standardise the weights on this aircraft.

Provide Screenshot(s)/video(s) of the issue encountered:


Detailed steps to reproduce the issue encountered:

  • Use the performance calculator to get the numbers.

PC specs and/or peripheral set up if relevant:

Not relevant

Build Version # when you first started experiencing this issue:


:loudspeaker: For anyone who wants to contribute on this issue, Click on the button below to use this template:

Do you have the same issue if you follow the OP’s steps to reproduce it?

Provide extra information to complete the original description of the issue:

If relevant, provide additional screenshots/video:

I had a bizarre situation where when adding the weight using Simbrief, the trim was absurdly high, like 2 degrees and the FMC calculated it like this. It didn’t seem right to me. Maybe it’s because of some incomplete update that didn’t properly update the 787, I’m guessing.

Update: I think it may be because the premium deluxe item was not updated with the issue of yesterday’s SU13 failure. If so, I’ll update if it was fixed.

1 Like

Hi there, can you let us know either way?
Cheers :slight_smile:

It looks to me like there’s an error in the invalid weight message. The 78X MTOW is around 254 tons; I believe you’re a hair over MTOW in that shot by a few hundred KG.

Do you have the same issue if you follow the OP’s steps to reproduce it?

Provide extra information to complete the original description of the issue:

If relevant, provide additional screenshots/video:

also unable to import EFB performance to the FMC takeoff ref page, can’t even add it manually, when I try it says take off speeds deleted due to change in take off conditions

1 Like

It happened the same to me.

1 Like

Unfortunately that’s not the case. I gave it a try with 253.9TN and the issue is still there.

However you’re right, and it’s another bug. When you copy data from the FMC it shouldn’t copy the Gross Weight but the estimated Takeoff weight.

Hey Speed, I can’t look to see if this has been fixed. I’m on Xcloud and it hasn’t been updating the content manager since the serious issue with the SU13 release. I sent a Zendesk but I believe it will only be Monday to get a response. Unfortunately for me I have ropes tied to my hand. Lol

1 Like

I saw this EFB gross takeoff weight error today when setting it up for a flight from KMIA ->EGLL.
Set everything up in FMC (from simbrief values) and then went to see what the new EFB said so copied the data in to the EFB and got the “No takeoff Allowed” message. So I just ignored and powered the EFB down again & took off with what I’d entered already in FMC.
It’s ambiguous to me as -

  1. you still set fuel & payload weights in default FS weights/load interface
  2. all additional info flight info (ZFW, MTOW, BLOCK FUEL etc) comes via entering simbrief data into the FMC
    So the EFB functionality seems superfluous (as well as erroneous) to me, so I’m going to continue to ignore it for now.
1 Like

No, that’s not correct. The FMC has no concept of your estimated takeoff weight nor does it attempt to predict it. What it copies now is exactly what it copies in the real 787 EFB.

Since this is a simulation of the actual 787 EFB, and in real life you can’t change the weight and balance of your aircraft via this EFB, this functionality does not appear there. However, in the settings page on the FMC there is a load page for properly loading the aircraft that does not require the sim’s weight and balance panel.

The EFB page is for takeoff computations (and is identical to the real aircraft’s), not specifically for data entry (although you can enter the data there as well). There is no other location where you can get confirmation of safe runway lengths or get a computed and correct derate for the selected runway and length.

If you have no interest in using the correct derates for the field length or validating field length overall, checking if the flaps setting is valid, getting your V speeds, etc, then you may find the EFB takeoff performance page not useful for your particular use case, but that’s what real world 787 pilots use it for.


Oh. Thank you for this. I didn’t know this flightplan loading page was there. I used it this morning and it’s making more sense now. The aircraft loaded fine and the EFB made more sense.

One question - the double LSK soft click on the boxed fields in the FMC pulls values in from the default sim weight section (and not simbrief) though I think? So I entered these values manually to match simbrief, is this correct observation?

ps. Thank you for all the 787 improvements. I really enjoy flying this aircraft now. It has the feel of a premium aircraft. It was more often than not sat in my hanger before, but not now!

Thanks for clarifying that, my bad.

In a side note, do we really need to specify the runway in the CDU for the tablet to work properly? Currently it won’t really work without it. I mean, there won’t be an airport displayed unless airport and runway are specified.

Yes, the runway is required because runway length is required to come up with the correct calculations.

As for the strange weight error, presently our 78X MTOW is set to 252,651 kg max. If you don’t enter a TOW, the computation will be RTOW. We’re not sure why the error message is funny or why sometimes it gets stuck in a state where it’s rejecting valid TOWs, but we’ve logged the issue and are looking through it.

1 Like

I have this problem.
I followed instructions, but still V speeds aren’t accepted…

It was better before, without EFB… Just FMC calculate V speeds.