Every transport-category airliner that rolls down a runway carries with it a carefully engineered set of speed targets that are anything but arbitrary. The rotation speed (VR), takeoff safety speed (V2), and the margins that connect them to other reference speeds are the product of exacting airworthiness certification rules found in 14 CFR Part 25, specifically Section 25.107. These numbers guarantee that even in the worst credible scenario — an engine failing at the worst possible moment — the aircraft can continue the takeoff, clear obstacles, and establish a safe climb. For airline transport pilot applicants and aviation professionals, understanding not just the definitions but the engineering logic and operational implications of these speeds is essential.
Part 25 certification speeds form a family. V1 (takeoff decision speed), VR (rotation speed), and V2 (takeoff safety speed) are the three sequential speed milestones of every regulated takeoff. Each has minimum values set by regulation, and each must be established and verified by the manufacturer through flight testing before an aircraft type receives its type certificate. Operators then use these certified speeds, adjusted for actual weight, configuration, altitude, and temperature, in the performance section of the AFM.
How the Speeds Are Defined Under 14 CFR 25.107
Rotation Speed (VR) is the speed at which the pilot initiates rotation — the deliberate application of back-pressure to begin lifting the nose. Section 25.107(e) establishes the minimum value for VR. It must be no less than V1, because committing to rotate before the takeoff decision speed is made would be unsafe. VR must also be no less than 1.05 times VMCG (minimum control speed on the ground), ensuring that even with the critical engine already failed, the pilot has directional authority before and during the rotation. Additionally, VR must be high enough that V2 can be reached by the time the aircraft is 35 feet above the runway surface (the screen height used in Part 25 takeoff field length calculations). In practice, VR is often only a few knots above V1, and the rotation itself is a deliberate, controlled maneuver — typically requiring 3 to 5 seconds to reach the target pitch attitude.
Takeoff Safety Speed (V2) is the speed that must be attained by the time the aircraft reaches the 35-foot screen height and must be maintained during the initial climb segment. Section 25.107(b) sets V2 minimums: for a two-engine or three-engine turbopropeller aircraft, V2 must be no less than 1.10 times VMC (air minimum control speed) and no less than 1.08 times VS1 (the stall speed in the takeoff configuration). For aircraft with four or more engines, the stall-speed margin is slightly less — V2 must be at least 1.05 times VMC but still at least 1.08 times VS1 for the stall margin. These minimums exist to provide a guaranteed margin above both the stall and the minimum control speed so that the aircraft remains controllable and airborne even if an engine fails at V1.
There is also a practical upper boundary: V2 must not exceed VFTO (final takeoff speed) for the all-engines-operating case, preventing the anomaly of requiring a speed higher than what is used in normal climb-out. Manufacturers also publish a maximum V2 in the AFM, beyond which the structural and performance assumptions of the certification are no longer valid.
The Role of VMC and Why Margins to It Matter
VMC (the air minimum control speed, certified under 14 CFR 25.149) is the lowest speed at which a pilot can maintain directional control following a sudden failure of the critical engine using rudder alone, without banking more than five degrees into the operating engines. The margins built into V2 above VMC are safety cushions: if a pilot is flying exactly at V2 and an engine fails, there is still a meaningful speed buffer before control authority begins to degrade. This is especially critical in the seconds immediately after liftoff when the aircraft is close to the ground, flaps are extended, and a large bank angle to recover control is not available.
VMCG, the ground minimum control speed (14 CFR 25.149(e)), applies during the ground roll and differs from VMC because aerodynamic rudder effectiveness is augmented by nose-wheel steering and asymmetric braking while on the runway. The requirement that VR be at least 1.05 times VMCG ensures that if an engine fails just before rotation, the crew can maintain directional control with aerodynamic rudder alone before they lift the nose gear off the pavement.
How V2 Connects to the Takeoff Flight Path
Under Part 25, the obstacle clearance and climb gradient requirements of the net takeoff flight path are calculated assuming the aircraft is flying at V2 with one engine inoperative. The four segments of the takeoff flight path each have minimum climb gradient requirements (14 CFR 25.121), and V2 is the speed used throughout the first and second segments. The first segment begins at liftoff and ends when the landing gear is fully retracted; the second segment begins there and extends until 400 feet above the runway elevation (the minimum acceleration height for most operators). The entire regulatory edifice of obstacle accountability under Part 91/121/135 rests on the assumption that the crew targets and achieves V2 during this critical phase.
This is why airlines train crews to treat V2 as a minimum in the engine-out case but also as a target: flying below V2 degrades climb gradient and potentially violates obstacle clearance; flying significantly above it wastes performance margin unnecessarily in the early segments. Some modern flight management systems allow the crew to select a V2 + offset (e.g., V2 + 10 knots) to improve climb gradient on all-engine departures while still maintaining a regulatory engine-out floor.
Why It Matters Operationally
The real-world significance of these certification speeds shows up every time weight, altitude, or temperature pushes an aircraft toward its performance limits. On a hot day at a high-altitude airport with a heavy load, VR and V2 will be high — potentially close to the maximum tire speed or structural limit speeds. The performance engineer or dispatcher calculating dispatch weight must verify that every speed constraint is satisfied simultaneously: the aircraft must be able to stop within the accelerate-stop distance, V2 must be achievable by 35 feet, and obstacle clearance must be met with one engine out at V2.
For Part 121 and 135 operations, the AFM-derived speeds are not optional targets — they are regulatory floors. Crews are expected to fly these speeds accurately, especially during engine-out scenarios. Deviation from V2 during an actual engine failure after V1 has caused accidents, typically because crews either rotated slowly and failed to reach V2 at screen height, or accelerated beyond V2 chasing performance that the regulations had already accounted for.
Key Numbers and Rules
- VR minimums: must be ≥ V1; must be ≥ 1.05 × VMCG; must allow V2 to be reached at 35 feet AGL (per 14 CFR 25.107(e)).
- V2 minimums (2- or 3-engine turboprop): ≥ 1.10 × VMC and ≥ 1.08 × VS1 (per 14 CFR 25.107(b)).
- V2 minimums (4-engine): ≥ 1.05 × VMC and ≥ 1.08 × VS1.
- Screen height for takeoff field length: 35 feet above the takeoff surface (Part 25 standard).
- V2 must not exceed VFTO — the final takeoff speed used in all-engine climb-out.
- Minimum acceleration height for typical operators: 400 feet AGL before reducing power or retracting flaps.
- VMC bank limit: not more than 5 degrees toward the operating engines during VMC demonstration (14 CFR 25.149).
Common Test Traps
- Confusing VMC and VMCG: VMC is the air minimum control speed; VMCG is the ground equivalent. VR references VMCG; V2 references VMC. Swapping them on the exam is one of the most common errors.
- Thinking VR can be less than V1: By regulation, VR must be at least equal to V1. A rotation before V1 would mean attempting a low-speed rejected takeoff after the nose is already rising — a dangerous and uncertified condition.
- Misapplying the V2 stall margin: The 1.08 × VS1 requirement applies regardless of engine count. Some students believe the stall margin changes with engine count — only the VMC margin changes (1.10 for 2-3 engines vs. 1.05 for 4 engines).
- Treating V2 as a maximum rather than a minimum: V2 is the minimum safe speed at screen height for engine-out climb. Flying above V2 is generally acceptable (up to the AFM maximum), but flying below it compromises obstacle clearance guarantees.
- Forgetting the 35-foot screen height standard: Part 25 uses 35 feet (not 50 feet) as the screen height for takeoff field length calculations. Part 23 legacy aircraft may use 50 feet for obstacle clearance in certain contexts — do not mix the standards.