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in my aircraft operation manual it is written that climb speed till 5000 feet indicated is 80 knots and above 5000 feet indicated is 75 knots. plz someone guide me regarding the following points:-

1. why climb speed should be kept less than normal above 5000 feet indicated?

2. why climb spleed has been mentioned in relation to indicated altitude rather than density altitude which is applicable for performance and aerodynamics of normally aspirated engine?

3. why this indicted altitude is 5000? why not 4000 or 6000?

2 Answers



  1. Mark Kolber on Jun 11, 2013

    1. why climb speed should be kept less than normal above 5000 feet indicated?

    A lower climb speed at higher altitude =is= normal. Vy increases with altitude.

    I can’t say why your operations manual uses indicated rather than density altitude or why it uses 5000 as a changeover point rather than a proportional reduction as altitude increases. My best guess is that, for the aircraft in question, the difference is such that it’s not that great on a per-1000 ft basis and a decision was made that represents the writer’s balance between workload and precision.

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  2. Brian on Jun 12, 2013

    I suspect they used indicated, but did so on a table that is converted to indicated altitudes based on standard day conditions. Does the table happen to include a temperature column?

    In either case, basing our calculations on this assumption, there would be no difference between indicated and pressure altitudes. In a POH like that I always make the assumption that those are standard day indicated altitudes, and as such are synonymous pressure altitude.

    In other words, pretend they are pressure altitudes and use them as such. In any case you will be off by a mere knot or two, something not worth fretting about.

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