A jet take-off is a sequence of speed events, not one continuous push. Each numbered V-speed marks a decision, an action, or a minimum. Knowing the order and the meaning of each one is what separates a candidate who has memorised the calls from one who actually understands the take-off.
The take-off speeds in order
V1 is the maximum speed in the take-off at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the aeroplane within the accelerate-stop distance. V1 also means the minimum speed in the take-off, following a failure of the critical engine at VEF, at which the pilot can continue the take-off and achieve the required height above the take-off surface within the take-off distance. — EASA CS-25.107, definition of V1
In plain terms: V1 is the decision speed. Below V1 you stop; above V1 you go. It is calculated so the runway available is enough either way.
VR is the speed at which rotation is initiated. — EASA CS-25.107(e)
In plain terms: at VR the pilot pulls back to lift the nose. VR must be greater than V1 and at least 1.05 × VMCA.
V2 is the take-off safety speed — the minimum speed at which the aeroplane can climb after take-off with one engine inoperative. — EASA CS-25.107(b), paraphrased
In plain terms: V2 is the speed flown out to 1500 ft if an engine fails after V1. It is at least 1.10 × VMCA and 1.13 × VSR.
VEF is the speed at which the critical engine is assumed to fail during take-off. VEF cannot be less than VMCG. — EASA CS-25.107(a)(2)
In plain terms: VEF is the certification engine-failure point. The whole balanced-field analysis assumes the engine quits at VEF, the pilot takes one second to react, and reaches V1 by then.
The take-off speeds in sequence:
- VMCG — Min control speed on ground. Lower bound on V1.
- VEF — Assumed engine failure speed. About 1 second below V1.
- V1 — Take-off decision speed. Continue or reject.
- VR — Rotate speed. Pull back.
- VLOF — Lift-off speed. Wheels leave the ground.
- V2 — Take-off safety speed. Engine-out climb-out target.
Balanced field length — the runway calculation
For every flight, a performance computer asks two questions about V1:
- If the engine quits at VEF and we GO, how much runway do we burn before we cross the screen height (35 ft)? That is the take-off distance (TOD).
- If the engine quits at VEF and we STOP, how much runway do we burn coming to a halt? That is the accelerate-stop distance (ASD).
The two distances move in opposite directions as you change V1:
- Higher V1 → the aeroplane is going faster when the engine fails, so less acceleration is needed to reach V2 → TOD shrinks.
- Higher V1 → more energy to dissipate in the reject → ASD grows.
Drag the slider below to see the effect. The point where TOD = ASD is the balanced field length.
The balanced field length is the runway distance at which the take-off distance required (one engine inoperative) equals the accelerate-stop distance required, for the V1 chosen. — Oxford ATPL Performance (2020), Ch.4
If both numbers cross at, say, 1900 m, then a 1900 m runway is enough — you can either continue or stop within the runway available. Anything shorter would force a lower V1 (smaller go zone) or a lower take-off weight.
What changes V1 in the real world
A flight management computer trims V1 inside its allowed band based on:
- Runway length available. Short runway ⇒ lower V1 (forces an earlier stop decision).
- Runway slope and surface. Wet/contaminated ⇒ ASD grows fast ⇒ lower V1.
- Wind. Tailwind grows ASD; headwind shrinks TOD.
- Mass. Higher mass needs higher V1 (V1 must remain above VMCG and below VR).
- Pressure altitude and temperature. Both reduce engine thrust and aerodynamic performance, raising both distances.
- Reverser availability. No reverse credit on a wet runway lengthens ASD.
Quick check
- Engine fail at or below V1 → REJECT. Idle, max brakes, speedbrakes, reverse.
- Engine fail above V1 → CONTINUE. Rotate at VR, climb at V2 to 1500 ft.
- VR must be greater than V1.
- V2 must be at least 1.10 VMCA and 1.13 VSR.
- "Balanced field" means TOD = ASD at the chosen V1.
Common mistakes
- Thinking V1 is the engine-failure speed. It's the decision speed. The engine is assumed to fail one second earlier at VEF.
- Calling V1 a single fixed number. V1 is a band — any speed between VMCG and VR can be chosen depending on field length, weight, and contamination.
- Confusing V2 with VR. VR is rotation; V2 is the climb-out speed reached at 35 ft. V2 > VR.
- Forgetting the unbalanced case. Many real runways aren't balanced — if there's a clearway or stopway, TOD and ASD limits use different distances and V1 can sit off the balanced point.
Why it matters for exams and interviews
- Every airline tech interview asks "what is V1?" Answer with the decision definition, not the engine-failure definition.
- DGCA Performance asks balanced-field calculations using AFM tables — the slider above is the conceptual picture behind those tables.
- "Above V1, you GO" is the most-tested rule in CRM and SOP examinations.