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IFR Departure Mins.

Asked by: 1894 views FAA Regulations, Instrument Rating

Why are the standard takeoff visibility mins. different between aircraft with 1 and 2 engines (1 mile) vs. 3 or more engines (1/2 mile)? I am curious as to the FAA logic. Perhaps something to do with climb performance?

 

Thanks for the feedback.

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1 Answers



  1. Tailwheel on Feb 22, 2017

    Hi Dan,

    Honestly, what you’re about to read is what I believe to be an “informed guess”. In a nutshell, I believe you’re right. Anyhow, here goes:

    If we accept that the way TERPS provides adequate obstacle separation is either by
    a: ensuring you’re climbing above said obstacle, or
    b: have the necessary visibility to avoid it visually…

    — and if we accept that the loss of one engine on single and twin engine aircraft has a far greater impact on clilmb performance than the loss of a single engine on an aircraft with three or more engines.
    — and that said loss of climb performance will reduce VERTICAL separation from obstacles,

    — Then it follows that the only other way to maintain a reasonable margin of safety in the event of a single engine failure on a single or twin engined aircraft is to make the takeoff visibility minima greater than they are for a three or more engined aircraft, thus giving the pilot of said aircraf the opportunithy of visually avoiding the obstacles that he/she was supposed to have been above, but – due to the engine failure – is now having to avoid laterally.

    Best

    Matt Crane, MSc
    ATP MEL (E145, BE350)
    COMM SEL/SES
    PVT (Glider)
    CFI/CFII/MEI/AGI (Gold Seal)

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