Crosswind runway choice with a short grass alternative
You are inbound to a 2,600 ft dry paved runway 27 (heading 270°) at an airport 1,200 ft above sea level. The ATIS reports wind 320° true at 20 kt gusting 30 kt; magnetic variation is negligible. Your aircraft has a maximum demonstrated crosswind component of 15 kt and a book landing distance over 50 ft of 1,400 ft at MLW, ISA, sea level, still air, dry runway. Apply 10% per 1,000 ft of elevation, 15% for a wet runway, 15% for 4 in grass, and a 10% reduction for each 10 kt of headwind. The only alternative is runway 34 (340°), 1,600 ft, dry but with 4 in grass. You are at 2,300 lb, MLW 2,300 lb. There is no thunderstorm or icing, and you have 45 min of fuel. Decide which runway to use and whether to hold or divert.
1. Calculate the crosswind and headwind components for both runways.
Read the worked answer
Runway 27: the wind is 320°, so the angle is 50°.
- Crosswind, steady = 20 × sin 50° = 20 × 0.766 = 15.3 kt.
- Crosswind, gust = 30 × sin 50° = 30 × 0.766 = 23.0 kt.
- Headwind, steady = 20 × cos 50° = 20 × 0.643 = 12.9 kt.
The steady crosswind already exceeds the 15 kt maximum demonstrated value, and the gust value is far above it. Runway 27 is not a sensible choice.
Runway 34: the angle is 20°.
- Crosswind, steady = 20 × sin 20° = 20 × 0.342 = 6.8 kt.
- Crosswind, gust = 30 × 0.342 = 10.3 kt.
- Headwind, steady = 20 × cos 20° = 18.8 kt; gust ≈ 28.2 kt.
Runway 34 keeps the crosswind within the demonstrated value even in the gust.
2. Estimate the landing distance on runway 34 and decide whether the margin is acceptable.
Read the worked answer
Start with 1,400 ft and apply the corrections:
- Elevation: 1,200 ft × 10% per 1,000 ft = 12%, factor 1.12 → 1,568 ft.
- Grass: 15%, factor 1.15 → 1,803 ft.
- Headwind 18.8 kt: about 19% reduction, factor 0.81 → 1,803 × 0.81 = 1,460 ft.
Against 1,600 ft, that leaves about 140 ft, or 9%. The calculation uses the steady headwind; the gust will reduce ground speed further, but it also increases the risk of a firm touchdown and a ballooned flare. On a short grass strip, 140 ft is not a large margin. I would use runway 34, but only with a stabilised approach, full flaps, and a firm decision to go around if the spot is not made. If the gust spread persists or the grass is soft, holding for the wind to ease or diverting is the better judgement.
3. What if runway 34 were wet as well as grassy? Recalculate and state the decision.
Read the worked answer
Add the wet-runway correction: 1,460 × 1.15 = 1,679 ft.
That exceeds the 1,600 ft runway by about 79 ft before allowing for the gust, standing water, or poor braking. Even with the steady headwind, the landing distance is not adequate. The aircraft should not land on runway 34 in that condition; with runway 27 also unusable because of crosswind, the correct action is to hold if conditions are forecast to improve, or divert to a longer paved runway.
The calculation also illustrates a non-recall point: the maximum demonstrated crosswind is a demonstrated value, not necessarily a legal limit, but a pilot should treat it as a personal limit and should never let a short wet grass runway consume the entire margin.