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A crew is planning their departure from Mykonos (Greece), expecting a take-off towards the sea, from a short field runway. Which of these is most likely to be the limiting take-off mass?
  • A
    Climb limited take-off mass.
  • B
    Field-length limited take-off mass.
  • C
    Tyre limited take-off mass.
  • D
    Obstacle limited take-off mass.

When we do our take-off performance calculations for a specific runway in specific conditions, the biggest factor (and often the figure we are trying to find) is our maximum take-off mass (MTOM). In actual fact, there are many different MTOMs, and we have to find the most limiting, which will be the lowest of the set.

This is called our MATOM (maximum allowed take-off mass), and is the most limiting of our climb limited take-off mass (CLTOM), obstacle limited take-off mass (OLTOM), field length limiting take-off mass (FLLTOM) and maximum structural take-off mass (MSTOM). The most limiting (smallest value) of these will be the one where our aircraft will struggle most for performance, so if we have a long runway surrounded by mountains, then we will likely be limited by the obstacle limited take-off mass, as its value will be lower than all the others.

In this question, we have a short-field runway, with a take-off profile over the sea. This means that we will be very much field-length limited, but not at all obstacle limited, as there are rarely obstacles to avoid in the sea. Therefore, our FLLTOM will be the lowest (and most limiting), as a heavy aircraft would not be able to lift off the short runway in time, but would not have a problem with obstacle clearance.

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