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  • TAS from Mach

    Given

    Mach 0.80
    Flight Level FL330
    OAT: ISA+15

    TAS is approximately (compressibility factor of 0.94):

    A 265 kts
    B 480 kts [this is what I get with formulas and CR-3)
    C 420 kts
    D 450 kts (marked correct)

    I am using the CR-3, but even with formulas I keep getting 480 kts.

  • #2
    You are correct. This was a question from a previous question bank where the examiner had erroneously applied compressibility to the TAS found on the CRP-5. This of course is not needed going from Mach No to TAS. I have amended QID 610722 accordingly to reflect the correct answer of 480KTS and it will go live after the next database update.
    Cheers
    JJ

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    • #3
      Hi Tristar,

      I Also had this question on my Gnav exam that I took in The Netherlands.

      Keep in mind that these kind of questions are usually worth 2-3 points! I had 3 of these on my exam. If I remember correctly, one was mach to tas, one from cas to tas.

      Goodluck.

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      • #4
        And did the questions erroneously apply compressibility to TAS?
        I am going to answer what I get based on my calculations and flight computer as well just to double check.

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        • #5
          JJ is spot on with this question - and the error was passed to the CAA several years ago. It should have been amended. You are best advised to go with the correct answer.

          What is Aviation Exam posting?
          Best Regards,

          Tony Pike

          Give Sergei back his dignity......Simples!

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          • #6
            If I remember correctly, Aviation Exam was saying the same. I passed my exams last May and I no longer have access to AE and BGS QB.

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            • #7
              Does it mean on Mach to TAS we do not apply compressibility and on CAS to TAS we Do apply compressibilty ?? As with without compressibility answer is 480kt on CRP5 and with compressibilty on calculator it gives 455kt.Please clarify !

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