Take-off performance covers the distance from start of roll to reaching a defined altitude (typically 50 ft / 15 m above runway).
Factors that increase take-off distance
| Factor | Mechanism |
|---|---|
| Higher mass | More inertia + higher stall speed → longer acceleration + longer airborne segment |
| Higher density altitude (hot/high) | Lower air density → less engine power + less lift per speed |
| Tailwind | Increases ground speed for given TAS |
| Uphill runway | Gravity component slows acceleration |
| Soft / contaminated surface (grass, snow, slush, mud) | Higher rolling resistance slows acceleration |
| Reduced flap setting (for a given speed) | Less lift → higher lift-off speed |
Special case: grass strip with slush
A grass strip covered with slush (snow-water-ice mix) causes a significant increase in required take-off distance — rolling resistance rises both from grass (friction) and from slush (friction + extra weight from spray + possible freezing on tires and flaps). Pilots reckon TODR + 30–50 % vs asphalt and may reduce take-off mass.
Factors that decrease take-off distance
| Factor | Mechanism |
|---|---|
| Headwind | Reduces ground speed for given TAS → shorter ground roll |
| Lower mass | Less inertia |
| Lower density altitude | More engine power + more lift |
| Downhill runway | Gravity component accelerates |
| Paved + dry | Less rolling resistance |
| Suitable flap setting (AFM recommendation) | Optimal lift at lift-off |
Flaps on take-off — trade-off
Take-off flaps are a trade-off between shorter ground roll and reduced climb capability:
- Higher flap setting: lower lift-off speed → shorter ground roll. BUT: higher flap drag → worse climb performance after lift-off (gradient and rate both reduced).
- Low or no flaps: higher lift-off speed → longer ground roll. BUT: optimal climb performance after lift-off.
Consequences:
- On take-off, flaps are NOT fully extended (landing flaps) — landing flaps create too much drag and critically reduce climb capability.
- Typical AFM take-off flap setting: 10°–20° (POH-specific).
- Best climb performance is obtained with flaps fully retracted — after lift-off and reaching a safe altitude (typically 500 ft AGL) flaps are retracted in stages.
Propeller types and take-off acceleration
The propeller choice strongly affects acceleration during the take-off roll:
| Propeller type | Take-off behaviour |
|---|---|
| Constant Speed Propeller (CSU) | Highest acceleration on take-off, because the governor automatically sets the blade to fine pitch — the engine runs at full RPM, and the propeller "bites" optimally into the air at low TAS. |
| Fixed-pitch propeller (fixed blade angle) | Worst efficiency on take-off, because the blade angle cannot be adapted — it is optimised either for cruise or for take-off, not both. |
| Fixed low-pitch propeller ("climb prop", shallow pitch) | Best acceleration among fixed-pitch types on take-off — small blade pitch matches low TAS in roll, high engine RPM yields maximum thrust. BUT: poor cruise performance (propeller "spins free" at higher TAS). |
| Fixed high-pitch propeller ("cruise prop") | Poor take-off acceleration (blade too steep at low TAS, engine cannot reach full RPM), but good cruise performance. |
→ Most CSU aircraft are PA-28R Arrow, Beechcraft Bonanza, etc. Most trainers (C172, PA-28-161) have fixed-pitch — the exact pitch is in the POH (typically a compromise).
Operating limits — only changed by the manufacturer
Operating limits of an aircraft (MTOM, V-speeds, performance, flap limits, etc.) are defined in the AFM/POH and may only be changed by the manufacturer, after the national or European aviation authority (EASA) has approved the change.
Consequence: a pilot, flight school, or operator must never change or exceed operating limits — for STC modifications the manufacturer (or STC holder) documents the change and EASA must approve.
Rules of thumb (rough estimate — use AFM!)
| Condition | Effect on TODR |
|---|---|
| +10 % mass | ≈ +20 % TODR |
| +1 000 ft DA | ≈ +10–15 % TODR |
| Tailwind 10 % of lift-off speed | ≈ +20 % TODR |
| Grass (dry) instead of asphalt | ≈ +20–30 % TODR |
| Grass (wet) instead of asphalt | ≈ +30–50 % TODR |
| Grass + slush | ≈ +40–60 % TODR |
| Upslope 1 % | ≈ +5–10 % TODR |
AFM wind correction
Many AFM charts demand an explicit safety margin:
- Headwind: count only 50 % (conservative)
- Tailwind: count 150 % (risk margin)
Part-NCO obligation
Per NCO.OP.180 the PIC must check performance data so that adequate safety margins exist for the planned operation. In practice: consult AFM charts, add margin where uncertain.