A pilot is planning a takeoff on a dry grass runway that slopes downhill 2%. Compared to the takeoff distance computed for a paved, level runway under the same conditions, the pilot should expect:
- AA longer takeoff distance, because grass and downhill slope have fully additive negative effects on performance
- BA shorter takeoff distance, since both the grass surface and the downhill slope reduce required distance
- CNo change in takeoff distance, because slope and surface effects always cancel exactly
- DA longer takeoff distance, since the increased rolling resistance from grass is only partially offset by the downhill slope
Show answer & explanationAnswer & explanation
Correct answer: D. A longer takeoff distance, since the increased rolling resistance from grass is only partially offset by the downhill slope
A soft or grass surface increases rolling friction and lengthens the takeoff roll, while a downhill slope helps accelerate the airplane and shortens the roll. These effects work in opposite directions, so the surface penalty is only partially offset by the favorable slope, typically resulting in a net increase in distance over a paved, level runway.
Why the other options are wrong
- A. They do not add together in the same direction since slope and surface act oppositely.
- B. Grass increases distance; only slope decreases it, so they don't both shorten it.
- C. The corrections rarely cancel exactly; POH tables give different percentages for each.
Runway Surface and Slope Corrections
Soft/grass runways increase takeoff distance due to added rolling resistance; downhill slopes decrease takeoff distance by aiding acceleration. Both corrections must be applied together using POH data.
- Grass, soft, or wet surfaces increase takeoff roll (commonly 7-25% depending on POH)
- Downhill slope decreases takeoff distance; uphill slope increases it
- Corrections must be applied independently and combined, not assumed to cancel
Memory trick: Grass grabs, slope shoves — check which wins