Planning and Loading
Planning and Loading covers mass and balance: what the aeroplane weighs, where that weight sits, and whether the result stays inside the structural and centre-of-gravity limits for the whole flight.
The mass vocabulary
OEW (or DOW) is the empty aircraft plus unusable fuel and trapped fluids. Adding traffic load gives ZFW, which must never exceed MZFM - the limit set by the wing-root bending strength without fuel. Take-off mass = ZFW + take-off fuel, and must not exceed MTOM. Landing mass must not exceed MLM. Payload is the difference between the allowed mass and the operating mass plus fuel.
Balance
Moments are taken about a datum. Arm is the distance from datum to the item; moment = mass × arm. The CG is total moment divided by total mass. Manufacturers often convert moments into index units to keep numbers manageable. %MAC positions the CG between LEMAC (0%) and TEMAC (100%); a CG behind the aft limit reduces static stability and can make recovery from a stall or spin difficult, while a forward CG raises stall speed and rotation effort and lengthens the take-off run.
Loading discipline
The load sheet is the legal record. Last-minute changes are permitted only within stated limits and must be recalculated, not guessed. Respect floor-loading limits, seat-load limits and cargo-securing rules, and remember dangerous goods need proper documentation, packing and stowage.
Worked example
OEW 5,000 kg at arm 2.50 m gives a moment of 12,500 kg·m. Payload 800 kg at arm 5.00 m gives 4,000 kg·m. Fuel 600 kg at arm 3.00 m gives 1,800 kg·m. Total mass = 6,400 kg; total moment = 18,300 kg·m; CG = 18,300 ÷ 6,400 = 2.859 m. If the aft limit is 2.80 m, the aircraft is out of balance and the payload must be moved forward or reduced.
Traps that cost marks
Leaving fuel out of ZFW (fuel is not part of zero-fuel mass, but it is part of take-off mass); mixing up which units are moments and which are arms; assuming %MAC and arm are interchangeable; and ignoring that fuel burn shifts the CG during the flight.