Performance-Limited Take-Off Mass With Payload Already Loaded
A twin turboprop has a dry operating mass of 4,600 kg, maximum take-off mass 7,500 kg, maximum landing mass 7,100 kg, and maximum zero-fuel mass 6,500 kg. The planned fuel is: taxi 40 kg, trip 650 kg, contingency 5% of trip fuel, alternate 150 kg, final reserve 200 kg, and additional 100 kg. The payload is 1,400 kg. For the departure runway, the performance-limited take-off mass is 6,900 kg; the climb-limited mass is 7,200 kg; the obstacle-limited mass is 7,000 kg. The landing mass must be checked at the destination, where no fuel is planned to be added. The crew must decide whether the aircraft can depart as loaded and, if not, how to adjust.
1. Calculate the fuel at brakes release, take-off mass, zero-fuel mass and landing mass. Identify the limiting mass.
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Contingency fuel = 5% × 650 = 32.5 kg. Total planned fuel = 40 + 650 + 32.5 + 150 + 200 + 100 = 1,172.5 kg. Taxi fuel is burned before take-off, so fuel at brakes release = 1,172.5 − 40 = 1,132.5 kg. Take-off mass = 4,600 + 1,400 + 1,132.5 = 7,132.5 kg. Zero-fuel mass = 4,600 + 1,400 = 6,000 kg. Landing mass = 7,132.5 − 650 = 6,482.5 kg. Compare the limits: MTOW 7,500 kg is not limiting; climb limit 7,200 kg is not limiting; obstacle limit 7,000 kg is not limiting; the performance-limited take-off mass of 6,900 kg is limiting. The actual take-off mass exceeds it by 232.5 kg. ZFW and landing mass are within their limits.
2. Calculate the maximum payload that can be carried with the present fuel and runway, and state the reduction required.
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Using the limiting performance take-off mass of 6,900 kg: Maximum payload = 6,900 − 4,600 − 1,132.5 = 1,167.5 kg. The loaded payload is 1,400 kg, so the reduction required is 1,400 − 1,167.5 = 232.5 kg. The resulting ZFW would be 4,600 + 1,167.5 = 5,767.5 kg, below the 6,500 kg MZFW, and the landing mass would be 6,900 − 650 = 6,250 kg, below the 7,100 kg MLW. The limiting factor is take-off performance, not structural mass.
3. If the payload cannot be offloaded, what operational options remain, and which fuel items must not be reduced?
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The crew could reduce fuel only within the required reserves: the additional 100 kg may be removable, but taxi, trip, contingency, alternate and final reserve must remain. Removing the additional 100 kg still leaves 132.5 kg to solve, so further payload reduction or a performance improvement is needed. Other options include using a longer or better runway, waiting for a lower temperature or better wind, reducing obstacle accountability by using a different departure procedure, or splitting the load. The crew must not reduce the final reserve or the alternate fuel to make the mass fit. If none of these options works, the aircraft cannot depart as loaded.