Weight and Balance at Baguio
You are planning a VFR flight from Manila (RPLL, elevation 75 ft) to Baguio (RPUB, elevation 4,252 ft) in a Cessna 172S. The aircraft has a maximum gross weight of 2,550 lb, an empty weight of 1,680 lb, a useful load of 870 lb, and a maximum baggage allowance of 120 lb. Four adults will board: 190 lb, 210 lb, 180 lb, and 170 lb. Baggage is 60 lb. You plan to depart with full usable fuel: 56 gal at 6 lb/gal, or 336 lb. The Baguio runway is 4,200 ft long, the temperature is 28°C, the wind is calm, and there is no close obstacle. The pilot's operating handbook gives a takeoff distance to 50 ft of 3,900 ft at maximum gross weight, 4,252 ft pressure altitude, and 28°C. The flight is about 1.2 hours. You hold a valid PPL and medical. The aircraft has current maintenance. You must decide whether the flight can be conducted safely and legally, and if not, what to change.
1. Calculate the total weight and determine whether the flight is within the maximum gross weight. Show your working.
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Adults: 190 + 210 + 180 + 170 = 750 lb. Baggage: 60 lb. Fuel: 56 gal × 6 lb/gal = 336 lb. Empty weight: 1,680 lb. Total = 1,680 + 750 + 60 + 336 = 2,826 lb. Maximum gross weight is 2,550 lb. The aircraft is 276 lb over maximum gross weight (2,826 − 2,550 = 276). Therefore the flight as loaded is neither legal nor safe. Maximum gross weight is a structural and performance limit, not a target; exceeding it reduces climb performance, increases takeoff and landing distances, and may overstress the aircraft, especially at Baguio's high elevation.
2. If you must keep all four adults and baggage, how much fuel can you carry at maximum gross weight? Is that enough for the flight, and what other loading changes could you make?
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With all four adults and 60 lb baggage, the weight without fuel is 1,680 + 750 + 60 = 2,490 lb. The allowable fuel weight is 2,550 − 2,490 = 60 lb, or 60 ÷ 6 = 10 gal. That is not enough. A 1.2-hour flight at roughly 8.5 gal/hour would use about 10.2 gal, leaving no VFR reserve; a safe planning figure would be about 10.2 gal plus 30 minutes reserve (about 4.25 gal), or roughly 14.5 gal. With only 10 gal, you cannot legally or safely make the flight. Options are to offload at least 276 lb of payload or fuel, for example remove one adult and some baggage, reduce fuel to a safe but still insufficient amount only if the flight were shorter, split the group into two flights, or use a larger aircraft. Reducing fuel alone to 10 gal still does not solve the range problem.
3. Even if the aircraft were under maximum gross weight, what performance and operational concerns apply at Baguio, and how would you mitigate them?
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Baguio's elevation of 4,252 ft and temperature of 28°C produce a high density altitude. Using ISA temperature at 4,252 ft of about 6.6°C, the temperature is about 21.4°C above ISA, so density altitude is roughly 4,252 + (120 × 21.4) ≈ 6,800 ft. At that density altitude, true airspeed for a given indicated airspeed is higher, takeoff distance increases, and climb performance is reduced. The POH figure of 3,900 ft to 50 ft at maximum gross weight already reflects the 28°C and 4,252 ft pressure altitude, but on a 4,200 ft runway that leaves only about 300 ft of margin before any obstacle; at high density altitude, that margin is unacceptable. Mitigate by reducing weight, departing early in the morning when cooler, leaning the mixture correctly for takeoff, using the full runway, rotating at the recommended speed, and planning for reduced climb and rising terrain. If performance margins are unsatisfactory, do not depart.