Weight and Balance After a Late Load Change
A regional turboprop is being loaded for a 1 h 20 min sector. The load sheet prepared by the dispatcher shows a takeoff weight of 19 800 kg against a maximum of 20 400 kg, with the centre of gravity at 22 % MAC; the forward limit is 18 % and the aft limit is 32 %. Just before departure, ground staff report that a 300 kg pallet of mail has been loaded into the aft hold instead of the forward hold shown on the load sheet, and that two passengers have moved from row 2 to row 12. The aircraft has 46 seats and a full cabin. The commander asks the flight engineer to verify the load sheet before signing.
1. Explain how the two changes affect the centre of gravity and whether the aircraft remains within limits.
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Moving 300 kg from the forward hold to the aft hold shifts the centre of gravity aft. The magnitude depends on the arm difference between the two holds; if the holds are, say, 6 m apart on a 20 m mean aerodynamic chord, the moment change is 300 kg × 6 m = 1 800 kg·m, and dividing by the 19 800 kg weight gives a shift of about 0.09 m, or roughly 0.45 % MAC. Moving two passengers aft has a smaller effect because passenger mass is small and the arm difference between rows 2 and 12 is modest - perhaps 30 kg·m, or less than 0.02 % MAC. The combined shift is therefore well under 1 % MAC aft, taking the centre of gravity from 22 % to perhaps 22.5 % MAC, still inside the 32 % aft limit. The weight is unchanged at 19 800 kg, below the 20 400 kg maximum, so the aircraft remains legal. The flight engineer should still recompute rather than assume, because the hold arms are not symmetric and the actual index must be checked against the loading manual.
2. What should the flight engineer check beyond the centre of gravity before approving the load sheet?
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The flight engineer should confirm the zero-fuel weight and the takeoff weight against their respective limits, and check that the landing weight at destination will be within the landing limit given the planned fuel burn. Structural limits matter too: the aft hold may have a floor-loading limit per unit area, and a 300 kg pallet must be checked against it. The load must be secured against the certified tie-down points, and the cargo compartment must remain within its maximum allowable weight. The flight engineer should also verify that the passenger seating change is reflected in the cabin plan and that the aircraft remains within the seating and emergency-exit configuration assumed in the certification. Finally, the load sheet must be amended and re-signed; a verbal change is not sufficient. The commander signs the final acceptance, but the flight engineer's verification is the technical check that prevents a mis-loaded departure.
3. If the recomputed centre of gravity were 33 % MAC, what would be the consequence and the corrective action?
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At 33 % MAC the aircraft would be beyond the aft limit, which is a controllability problem rather than a paperwork problem. An aft centre of gravity reduces static longitudinal stability and can cause the aircraft to pitch up, reduces the elevator authority available for flare, and can make the aircraft difficult or impossible to recover from a stall or a gust upset. The aircraft must not depart in that condition. Corrective action is to move mass forward: transfer the mail pallet back to the forward hold, or move passengers forward, and recompute. If the aft limit cannot be met by rearrangement, cargo must be offloaded. The flight engineer should document the original error, the correction, and the final index, and the load sheet must be reissued before departure. This is exactly the kind of error that a second independent check of the load sheet is designed to catch.