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I was practising some mass and balance questions and I found that my answer is a little bit too far from the listed answers. Can anyone help me to see if I did something wrong?

The question was:

Given that the Dry Operating Mass (DOM) is 27 372 kg, there are 12 000 kg of trip fuel and 4 000 kg of fuel are expected on landing, what is the maximum allowable traffic load for the Medium-Range Jet Transport (MRJT) aeroplane?

  1. 23,923
  2. 23,528
  3. 19,005
  4. 19,428

My solution was:

Operating mass = DOM + Usable fuel

$27 372 - (12 000 - 4 000) = 19 372 kg$

That doesn't match any of the options, so what is the correct answer?

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    $\begingroup$ See this document, in particular the graphic on the last page. It seems you miss a parameter: ZFM or TOM. $\endgroup$ – mins May 1 '17 at 17:45
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    $\begingroup$ What is the MSTOM? $\endgroup$ – mongo May 1 '17 at 19:53
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The answer is 19,428, but I could only get there by Googling 'MRJT' to get the missing information:

enter image description here

DOM + all of the fuel is 43,372.

And since MSTOM is 62,800, that leaves you with 19,428 for payload (allowable traffic load).

$$62,800 - (27,372 + 12,000 + 4,000) = 19,428$$


Below you can see the calculations for MTOM, MLM, and MZFM. Since the traffic load for the 'MTOM limited case' is the lowest, the maximum traffic load for the flight is 19,428 kg.

enter image description here
(Table courtesy of DeltaLima.)

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It strikes me that your formula is correct, you just didn't follow it -- Operating Mass = DOM + usable fuel = 27 372 + (12 000 - 4 000) = 35 372

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  • 2
    $\begingroup$ Your answer is not included in the set of options. $\endgroup$ – kevin May 1 '17 at 19:34

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