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Aircraft Performance

Runway Surface Condition

Most aircraft accidents occur during the take-off and landing phase of the flight. Collisions with obstacles during climb out, runway overruns on landing occur every now and then. In this section of the site we will take a look at the various factors contributing to the performance of the aircraft in this part of the flight. Hopefully we help the pilot ensuring safe operation during these phases of the flight as the rules require that of the pilot in command.

The effects of increased weight of the aircraft on stall speed or take-off run might be more than some pilots bargain for. More so when the runway is not perfectly flat or level or the grass is long and wet.

Below we describe what the effects are of each factor on landing and take-off performance of the aircraft.

Effects on performance

An uphill runway increases the take-off run and a downhill runway increases the landing roll. A upslope of 2% adds 10% to your take-off distance and a downslope of 2% decreases it by some 10%. So everything else being equal: take-off downhill and land uphill. It is as simple as that. Be prepared that local rules might require otherwise.

Grass runways

Grass, snow or soft grounds increase the rolling friction and ground runs will take longer than on paved runways. Dry grass can increase take-off runs by some 20%. Long wet grass can increase this number again depending on the length of the grass and how wet it is. Aircraft wheel size and the type of aircraft can play a role too.

Long grass

Taking off in long wet grass on a short runway could not be advisable. Even more so when puddles of standing water are present shortly after a rain shower, acceleration through standing water is very sluggish.

Landing on such a runway can increase the ground roll due to the fact that the brakes are not as effective as on a dry runway. Grip of the tires on wet grass is much less, on long wet grass it could mean a very large increase of ground roll.

Rough runway surface

Runways with uneven surfaces also increase take-off distances, plus that the nose gear takes a beating from all those bumps. The soft field technique helps to prevent against any damage to the nose gear.

Runway contamination

At some point in time runways will be contaminated with rain, snow or slush. You will have to allow for these circumstances as the result can be directional control problems, reduced braking action (or hydroplaning) and more drag on take-off.

When show depth is more than 2" or if water, slush or wet snow covers the runway to more than 1/2", take-off is not recommended. And operating from a slippery runway with a crosswind more than 10 kts, or with a tailwind, take-off should also not be attempted.

Accelerated Stop Distance Available (ASDA)

When calculating the take-off distance with all known factors one should also account for the accelerated stop distance available, this should be at least twice the take-off distance on a paved runway and 2.6 times the take-off distance on a grass runway.

Aircraft weight at the beginning of the take-off run will have a great influence on the ASDA and therefore you need to know the TORA of the runway.

Landing performance

Any water (heavy rain showers), snow or slush can and will have an adverse effect on the landing distance and the danger of hydroplaning (with no wheel braking and loss of directional control) is very real and has led to loss of life in the past already.

Written by EAI.

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