Wind Triangle and Enroute Diversion Fuel
You are flying a commercial VFR charter from Alpha to Bravo, 240 NM true track 075°. TAS is 135 kt. Forecast wind is 150°/25. Fuel burn is 42 L/h and usable fuel at departure is 130 L. After 80 NM, you have 105 L remaining. The destination weather updates to 2 SM in mist with cloud at 800 ft AGL. Bravo is in Class D controlled airspace and has no instrument approach and no fuel. The nearest suitable VFR alternate, Charlie, is 55 NM from your present position on true track 160°; its reported weather is 8 SM and scattered cloud at 5,000 ft. You must remain VFR and keep a 30-minute day reserve.
1. Estimate the initial true heading and groundspeed.
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Wind from 150° relative to track 075° is 75° from the right. Crosswind = 25 sin 75° ≈ 24 kt; tailwind = 25 cos 75° ≈ 6 kt. Wind correction angle = arcsin(24/135) ≈ 10° left. True heading ≈ 075° − 10° = 065°. Groundspeed = 135 cos 10° + 6 ≈ 139 kt. No magnetic variation is given, so these are true values.
2. Decide whether to continue to Bravo or divert to Charlie, and support the decision with fuel and groundspeed calculations.
Read the worked answer
Bravo is now 2 SM and 800 ft in Class D airspace, below VFR minima, so a VFR landing is not possible. Divert now rather than continue and hope for improvement.
From present position to Charlie: track 160°, wind 150°/25 is almost a direct headwind (10° off). Headwind ≈ 25 cos 10° ≈ 24.6 kt; groundspeed ≈ 135 − 24.6 ≈ 110 kt. Time = 55/110 ≈ 0.50 h; fuel = 0.50 × 42 ≈ 21 L. Reserve = 21 L. Total needed ≈ 42 L; you have 105 L, so arrival fuel is about 63 L (1.5 h).
Continuing 160 NM to Bravo at 139 kt would take about 1.15 h and burn 48 L, leaving only 57 L at a destination where you cannot land; that is a poor escape margin. Diverting to Charlie is the safer and fuel-feasible choice.