Payload discrepancies? Truncations due to unit conversions? Am I misunderstanding the numbers?


Since a couple of days ProSim may import SimBrief PERF into our CDU’s. That’s nice except that I don’t understand some discrepancies (2).

1/ Using KG as units
My B738 is defined this way:
SWR HB-100

I have 103 PAX (10 B + 93 Y as “systems” can’t make a difference between B and Y all PAX are 70 kg with 25 kg baggage). I have 400 kg cargo on board.
That is a total payload of 103 * (70 + 25) + 400 = 10 185 kg.
My ZFW should be 41863 kg + 10179 kg = 52 048 kg (?)

SimBrief says 51 846 kg that is 202 kg lighter (not so big… but I imagine you’re using a computer :wink: ). Where am I wrong? The difference could result of a computation conducted in LBS with “bad” rounding?

So let’s try with LBS.

2/ Using LBS as units
My B738 is defined this way:

I have 103 PAX (10 B + 93 Y as “systems” can’t make a difference between B and Y all PAX are 154 lb with 55 lb baggage). I have 882 lb cargo on board.
That is a total payload of 103 * (154 + 55) + 882 = 22,409 lb.
My ZFW should be 92,292 lb + 22,409 lb = 114,701 lb (?)

SimBrief says 114,821 lb that is 120 lb heavier (That seems “better” even not truly perfect).
As there can’t be conversion or truncation here… I must conclude that I am making some error. Could you tell what it is?

3/ A question
In this case:

In your opinion what quantity should be considered as “Reserve Fuel”?
(7,998 lb?)

Thank you very much,


(1) not a rounding issue (difference would be 1, maybe 2kg maximum if it did happen, but AFAIK any known conversion-related issues were fixed some time ago)

instead, look for PAYLOAD/CARGO LIMITED BY MTOW or PAYLOAD/CARGO LIMITED BY MLW in the briefing remarks

(2) you cannot have 882lb of cargo onboard, SimBrief lets you specify cargo in increments of 100lb (or 100kg) – unless you are maybe generating your briefings programmatically using the API?

otherwise I’m not sure how you’re entering your freight figure, but the discrepancy must come from there (might also be the cause of issue 1)

(3) in what sense (i.e. what/where do you want to use this figure)?




(1) Not the case… See PDF:
LSZHEDDB_PDF_1641918734.pdf (640.7 KB)

(2) My bad! For the “LB run” cargo was 1,400 lb (and is programmatically injected using the API, we use phpVMS). The difference is 75 lb.

Here is the PDF:
LSZHEDDB_PDF_1641979617.pdf (657.5 KB)

(3) I want to use it here:

Best regards,


Hi, a few things I noticed:

  • You aren’t using your custom airframe. When you create your flight, you need to select that specific airframe from the aircraft list. Currently you’re selecting the default “B738 - B737-800”. Your custom airframe will appear near the top of the dropdown selection, and will be labelled by registration.
  • If you’re generating your flights through the API, you’ll need to explicitly set your custom airframe’s ID as the “type” parameter. I don’t know if phpVMS supports this. Using custom airframes - The SimBrief API . If you can’t do that through phpVMS, you’ll need to set all the aircraft options using the acdata parameter. Currently I see phpVMS is only sending {'paxwgt':209}. Using acdata - The SimBrief API .

To reiterate, when using the API, if you want to customize the empty weight, passenger weights, etc, you either need to set your airframe ID as the “type” parameter, or send all the applicable aircraft options through the acdata parameter. The airframe ID is shown at the top when you open your airframe for editing.

If you are generating directly on the website, make sure to select your custom airframe in the aircraft dropdown, and not the default “B738 - B737-800” profile.

For reserves, I think it depends on the airline. But as far as I know, many of them enter the FINRES + ALTN fuel here. That sum is included in the FINRES+ALTN line under FMC INFO for convenience.

Best regards,

1 Like

Thank You so much!

I was selecting the correct “Tail Number” in phpVMS and was (stupidly) thinking the corresponding SimBrief airframe was used (as I do when manually generating the OFP) :innocent:

Made a temporary patch to our phpVMS, now that rocks!

I agree with you about the reserves… Now I’ll ask ProSim why they solely consider FINRES :wink:

Kind regards,


Hey, I hadn’t thought of the wrong airframe being used. If you had shared the complete briefing initially, I might have noticed the OEW discrepancy though.

Regarding (3), interesting that Boeings work this way (Airbus has separate fields for contingency and final reserve). FlightDeck2Sim does indeed enter FINRES+ALTN there so I guess that’s fairly standard on Boeings:



I was convinced SimBrief was using my saved airframes so OFP seemed (to me) useless… But of course SimBrief identifies an airframe by its ID not by its type+registration!

Here is the thread on ProSim forum about FINRES+ALTN :wink: Enjoyable.


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