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View Diary: How Airliners Work - Weight and Balance (160 comments)

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  •  What will the NTSB think? (3+ / 0-)
    Recommended by:
    ER Doc, northsylvania, 207wickedgood
    Below 3,000' MSL you can mostly ignore it. Above 7,000' you're a fool to.
    The good news is the FAA doesn't make up rules like this. The Far/Aim would be twice as thick ;-)

    A better made up rule: What will the NTSB think?

    Under Part 91 (The diarist brought up light singles, so this is fair) 91.103 places the burden on the pilot to be familiar with ALL available information concerning the flight. 91.103(b)(2) relates to aircraft performance. DA must be taken into consideration prior to EVERY flight even at sea-level fields.

    A light single loaded appropriately at sea-level on a winter cold day could be uncomfortable at that same field in the middle of summer.

    •  Well, yes, but IRL? (3+ / 0-)
      Recommended by:
      ER Doc, AdamR510, kurt

      If you actually work out the math regularly, what you care about are weight, altitude, and temperature. Weight and altitude are fairly obvious, tho' there's a double-whammy on altitude -- not only is the air thinner, and the engine less powerful (both ~3%/1000' at low altitudes), but required TAS is higher, with the quadratic effect on energy required (1/2*m*v^2).

      Further, standard temperature drops with altitude -- so at 7,000' MSL, standard temperature is near freezing. Compensate for that, and a shirt-sleeve day puts DA around 9,000'. A hot day puts it over 10,000'.

      Almost-finally, I'm mostly a glider-guider, and they don't make takeoff charts for aircraft towing other aircraft. (At least that I'm aware of.) We can guesstimate, based on weight and relative glide ratios, but experience is mostly what we use. (They certainly don't make takeoff charts for gliders, at least not those without engines.)

      Finally, not even our FAA/NTSB folk always understand DA. There's at least one incident out there citing a glider pilot who landed short of the runway for neglecting DA's effects on flight performance. DA doesn't affect glider performance in the air: it has zero effect on glide ratio (it can affect TASes somewhat, but that's about it). So once you've had an accident, the FAA/NTSB can and probably will cite you for something.

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