A dispatcher calculates that for a planned V1 of 138 knots, the accelerate-stop distance is 6,200 feet and the accelerate-go distance is 5,800 feet on a 6,000-foot runway. To achieve a balanced field length within the available runway, what adjustment should be made to V1?
- ADecrease V1, which shortens accelerate-stop distance and lengthens accelerate-go distance
- BIncrease V1, which shortens accelerate-stop distance and lengthens accelerate-go distance
- CDecrease V1, which shortens both accelerate-stop and accelerate-go distances equally
- DIncrease V1, which lengthens both accelerate-stop and accelerate-go distances equally
Show answer & explanationAnswer & explanation
Correct answer: A. Decrease V1, which shortens accelerate-stop distance and lengthens accelerate-go distance
Balanced field length occurs where accelerate-stop distance equals accelerate-go distance. Lowering V1 means the crew decides to stop sooner (shorter stopping distance) but must continue the takeoff from a lower speed if continuing, which lengthens the accelerate-go distance. Since ASD (6,200 ft) exceeds AGD (5,800 ft), decreasing V1 moves both toward the same balanced value that fits within the 6,000-foot runway.
Why the other options are wrong
- B. Increasing V1 would make the already-longer ASD even longer, worsening the runway overrun risk.
- C. V1 changes trade one distance for the other; they cannot both decrease simultaneously.
- D. V1 changes trade one distance for the other; they do not both increase together.
Balanced Field Length
The runway length at which accelerate-stop distance equals accelerate-go distance for a given V1, optimizing the takeoff decision speed for the available runway.
- ASD increases and AGD decreases as V1 increases
- ASD decreases and AGD increases as V1 decreases
- Balanced field length is the V1 where the two distances are equal
- Not all runways require a fully balanced V1; some allow a range of V1 values
Memory trick: V1 is a seesaw: push it one way, one distance goes up, the other goes down