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For the EASA PPL(A)-exam I got the following question:

An increased density altitude has the following effect:

  1. Increased take-off speed and decreased acceleration
  2. Decreased take-off speed and decreased acceleration
  3. Increased take-off speed and increased acceleration
  4. None of the above

As this question is ambiguous, I asked the examiner which speed was meant: indicated airspeed IAS or true airspeed TAS. She confirmed that the question was about indicated airspeed IAS.

In that case I would say "4. None of the above". However, during debriefing a fiery discussion amongst the students arose and we didn't reach an agreement about the question. So I'm checking here... [EDIT: btw, I passed the exam :-) ] [EDIT: after the discussion the examiner counted both 1. and 4. as correct! If we're talking about IAS it should definitely be 4. in my opinion; if we're talking about TAS it should be 1. in my opinion. Just checking with you guys.]

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    $\begingroup$ During the debrief, were you not told the correct answer? I agree, as worded, it is ambiguous. If you want to test knowledge, you need to have a clear question. They should have stated TAS. That would have been the best way to test knowledge on high density altitude. Due to the ambiguity, the best answer would be 4) None of the above. If they had stated IAS it still would be 4) because IAS does not really change with density altitude. $\endgroup$ Mar 17, 2023 at 15:15
  • $\begingroup$ What Mike Sowsun said x100. $\endgroup$ Mar 17, 2023 at 16:57

1 Answer 1

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Higher density altitude means less dense air, does it not? If so, then taking off at a density altitude of 10,000 feet compared to zero feet (sea level) will furnish less oxygen to the engine, reducing the horsepower output, and at the same time will require more airspeed to produce the necessary lift for takeoff.

Less horsepower yields less acceleration and at the same time requires greater true airspeed to take-off, so the right answer in that case is #1. If "airspeed" is defined as indicated, or IAS, then the correct answer is #4.

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  • $\begingroup$ More TAS, same IAS. $\endgroup$ Mar 17, 2023 at 18:27
  • $\begingroup$ "…means less dense air" - and there I was reading it as an "increased-density altitude", i.e. a lower altitude :-) $\endgroup$
    – Bergi
    Mar 18, 2023 at 3:21

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