Weight, Fuel and Crosswind at Ramon
You are planning a Cessna 172S flight from Ben Gurion (LLBG) to Ramon (LLER) with three passengers and 60 lb of baggage. Empty mass is 1,680 lb, MTOW 2,550 lb, usable fuel 53 US gal. Pilot 180 lb, each passenger 170 lb. Forecast: headwind 25 kt, TAS 115 kt, trip distance 150 nm, fuel burn 9.5 US gal/h, taxi 10 min. Reserve 45 min, alternate LLET 15 nm away (10 min), contingency 15% of trip fuel. LLER forecast wind 320/18G28, runway 01/19. You have 1 h 40 min of daylight left. The aircraft has no ferry fuel tank and no removable seats. You must check weight, fuel, and crosswind before departure.
1. Calculate zero-fuel weight, maximum fuel weight available, and required fuel. Is the flight legal and safe as loaded?
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Zero-fuel weight = 1,680 + 180 + (3 × 170) + 60 = 2,430 lb. MTOW margin = 2,550 − 2,430 = 120 lb. At 6 lb/US gal, maximum fuel by weight is 120 ÷ 6 = 20 US gal. Required fuel: ground speed = 115 − 25 = 90 kt, so trip time = 150 ÷ 90 = 1.67 h, trip fuel = 1.67 × 9.5 = 15.8 gal. Reserve = 45 min × 9.5 = 7.1 gal. Alternate = 10 min × 9.5 = 1.6 gal. Contingency = 15% × 15.8 = 2.4 gal. Taxi = 10 min × 9.5 = 1.6 gal. Total required ≈ 28.5 gal. The aircraft can carry only 20 gal at this weight, so the flight is not legal or safe as loaded. You must offload weight or make a fuel stop.
2. The crosswind at LLER is 320/18G28 on runway 01. Compute the crosswind component and decide.
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Runway 01 heading is approximately 010°. The wind is 320°, so the angle between runway heading and wind is 50°. Crosswind = wind speed × sin 50° = 0.766 × wind speed. With the sustained wind: 18 × 0.766 ≈ 13.8 kt. With the gust: 28 × 0.766 ≈ 21.4 kt. The gust crosswind exceeds the typical C172 maximum demonstrated crosswind of about 15 kt, so a landing on runway 01 is not acceptable in the gust. Runway 19 gives the same crosswind magnitude with a possible tailwind component, which is worse. Decide to hold, use another aerodrome, or wait for the gust to decrease; do not plan a landing that requires exceeding the demonstrated crosswind limit.
3. What would you change to make the flight possible?
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Reduce weight first: offload one passenger or the baggage, or make a fuel stop. With one passenger fewer, zero-fuel weight drops by 170 lb to 2,260 lb, leaving 290 lb for fuel, which is about 48 gal, enough for the 28.5 gal required. Alternatively, keep the passengers and plan a technical stop for fuel, but that adds time and complexity. For the crosswind, choose a time when the gust is below the aircraft limit, or use a runway with a lower crosswind component. The final go/no-go decision must satisfy both weight and fuel requirements and the crosswind limit; solving only one problem is not enough.