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The strength of gravity at the Earth's surface is not constant, but varies from place to place by as much as a few percent:

a diagram showing where to go if you want to weigh less

(Image by NASA.)

As a result, an identically-loaded aircraft weighs less in (for instance) southern India, Uyghurstan, the eastern Caribbean, or the Hudson Bay area than it does in (for instance) Indonesia, Greenland, Liberia, or the Russian Far East, which should (in theory, at least) affect its operations in several different ways:1

  • An aircraft in a lower-gravity region won't need to generate as much lift in order to become, or remain, airborne, allowing it to take off and land at slightly lower speeds, to climb slightly more steeply, and to cruise at slightly higher altitudes.
  • An aircraft in a lower-gravity region can be loaded slightly fuller without exceeding its maximum allowable takeoff weight (potentially giving it a range advantage over an aircraft launched from a higher-gravity region, if the extra capacity is used to carry more fuel), and can land slightly fuller without exceeding its maximum landing weight and risking structural damage.
  • An aircraft landing in a lower-gravity region will have less weight on its wheels, slightly reducing the maximum braking force available from the wheelbrakes (which might well cancel out the landing-weight advantage mentioned in the previous bulletpoint), and, thus, requiring a slightly longer runway.

Do aircraft performance figures and calculations include corrections for local and/or regional variations in the strength of gravity, or are these variations simply considered too small to bother accounting with?


1: This is by no means meant to be an exhaustive list.

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    $\begingroup$ 1 gal is about 1/1000 of 1 g. 1 milligal is 10^-6 g. 100 milligal = 10^-4 g. I do not see several percent of variation. $\endgroup$ – bogl May 18 at 22:04
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    $\begingroup$ The variation of gravity is very small. For an A380 with MTOW of 590t, this makes just 0,6t. More noticeable is the lifting effect of earths rotation, which makes everything about 0.34% lighter at the equator that at the poles. That makes about 2t for the A380. Still not much. $\endgroup$ – sweber May 19 at 9:56
  • $\begingroup$ @sweber: I agree, not much, but, given that airliners frequently operate within a few hundred kilos of their maximum allowable weights (otherwise, they're not making as much money as they could be), that could still be the difference between (say) being able to load one more cargo container into the aircraft, or having to leave it by the side of the runway. $\endgroup$ – Sean May 20 at 0:54
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No they don’t. Any variations in gravity are swamped by variations in temperature, pressure, density, winds, runway surface, runway slope, runway conditions (wet?) etc. that all have a major impact on performance.

But it is an interesting question, and I learned something by following the link. Thanks!

I know it does have an impact on navigation for submarines, which use variations in gravitational fields in their inertial nav algorithms.

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    $\begingroup$ Some fuel performance calculations I know take latitude/longitude into consideration; however that only considers gravitational variations on an ideal ellipsoid (probably WGS-84), not the detailed mapping in original question. $\endgroup$ – Cpt Reynolds May 19 at 0:30

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