Asked by: Billy Doyle, by email
Many airports do have slightly sloping runways - the small landing strip at Santa Catalina near Los Angeles is one example. But a decline doesn't aid take-off, or an upwards slope help with landing. Given the power needed to get airborne, a slope makes little difference either way. The most important factor is wind: planes take off with the wind to maximise airspeed, and land into it.
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