Factors Affecting Take-off and Landing Distances

Factors affecting take-off and landing distances

The take-off and landing distances published in the AFM/POH apply to standard conditions (ISA, paved/level/dry runway, zero wind, MTOM). Real conditions differ and influence the distances significantly.

1. Mass (weight)

Higher mass → longer take-off and landing distances.

• More mass → higher stall speed → higher liftoff/touchdown speed → more accel/decel distance.
• More mass → lower climb performance.

Rule of thumb C172:

• 10% more mass → about 20% longer take-off distance.

2. Wind

Headwind → shorter distances:

• Reduces the groundspeed required to reach liftoff/touchdown speed.
• Rule of thumb: 10% headwind reduces take-off distance by about 10%.

Tailwind → markedly longer distances:

• Increases the groundspeed required.
• Rule of thumb: 10% tailwind increases take-off distance by 20–30%.
• AFM often gives a maximum allowable tailwind component (typically 10 kt).

Crosswind does not directly affect distance, but:

• Maximum demonstrated crosswind component (e.g. C172: 15 kt) — limit for pilot control.

3. Runway slope

Uphill take-off: longer distance (acceleration impeded).

• AFM: typically +10% per 1% upslope.

Downhill take-off: shorter distance.

Uphill landing: shorter (better braking effect).

Downhill landing: markedly longer distance.

4. Runway surface

Asphalt/concrete (paved, dry): AFM standard, shortest distance.

Grass (unpaved):

• Dry, mown grass: AFM +10–15%.
• Long, wet grass: AFM +25–40% on take-off, −25–40% on landing (worse braking but longer rollout).
• Convention (Part-NCO): +30% to AFM value for unpaved.

Standing water / puddles:

• Hydroplaning risk.
• AFM: +30–50%.

Snow/ice: extremely variable; usually operation prohibited.

5. Density Altitude (DA)

Altitude + temperature determine air density and therefore:

• Engine power (less air → less combustion → less thrust).
• Propeller efficiency (less thrust).
• Aerodynamics (higher TAS required, since the same lift coefficient at lower density needs more TAS).

Rule of thumb:

• +1 000 ft DA → take-off distance +10%.
• +30 °C above ISA → DA increases by about 4 000 ft (summer on a mountain airfield!).

Example: C172 at an aerodrome at 5 000 ft AMSL, 30 °C:

• DA ≈ 5 000 + (30 − 5) × 120 = 8 000 ft DA.
• Take-off distance about +80% versus sea-level standard.

6. Flap setting

More flaps: shorter take-off (liftoff at lower speed), but lower climb performance. Less flaps: longer take-off, but higher climb performance.

Follow AFM — for PPL aircraft usually:

• Normal take-off: 0° or 10° flaps.
• Short-field take-off: 10° flaps (C172) or maximum allowed.

7. Pilot technique

• Hit V-speeds exactly: V_R (rotation), V_x (best angle climb), V_y (best rate climb).
• Rotate too early → longer distance.
• Rotate too late → longer distance.
• Braking technique on landing: maximum braking (aerodynamic + wheels).

8. Engine condition

Dirty engines, weak engine, wrong mixture → less power → longer take-off.

Mixture at altitude: at high DA the mixture must be leaned (see Mixture control).

Correction factors — summary

These rules of thumb are only orientation — always use AFM/POH data!

Practical application (example)

Scenario: PA-28 on 600 m grass runway, MTOM, OAT 25 °C, wind 5 kt headwind.

AFM value at standard: TOD = 380 m.

Corrections:

• Grass dry: +15% → 380 × 1.15 = 437 m.
• Part-NCO safety factor: +33% → 437 × 1.33 = 581 m.
• 5 kt headwind: −5% → 581 × 0.95 = 552 m.

TODR ≤ TODA: 552 ≤ 600 m → OK, but margin is small.