How Cathay Pacific balances the weight of its aircraft
Weight is crucial for aircraft. Every last kilogram on board is factored in before take-off. This isn’t just to keep planes below their maximum take-off weight, but also to ensure that weight is distributed evenly, maintaining the aircraft’s centre of gravity which is essential for level and efficient flying.
Airlines regularly weigh aircraft so that they have a base figure for each. Then, before every flight, the crew and operations team review a series of load plans showing the number of passengers and amount of cargo booked to fly.
“Everything that goes on the aircraft, minus the passengers and their carry-on bags, is weighed,” says Head of Line Operations, Captain James Toye. “Every meal, cup, plate, spoon, headset, pillow, safety card and even Cathay magazine is taken into account.”
While our suitcases are weighed, we as passengers are given assumed weights, with additional hand baggage upping our totals by 10kg. The overall sum is the aircraft’s “zero-fuel weight”. This is used to determine how much fuel – the single heaviest component on a loaded plane – is needed for the journey, as well as the thrust required for take-off.
Load plans also determine where in the hold goods should be stored to maintain the aircraft’s centre of gravity – both passenger baggage and cargo can be loaded either in front of or behind the wings. Meanwhile, fuel is principally carried in an aircraft’s wings and in the centre fuel tank between them. “This is ideal because, as that fuel burns, it doesn’t change the centre of gravity on the aircraft much,” says Captain Toye.
The final amount of fuel required is determined once check-in has closed. If there are changes, these are reflected in the final load plan. The flight crew accordingly adjust the aircraft’s horizontal stabiliser – the whole tailplane – which supports it in flight to counteract any variance from the geometric centre of gravity. “We set that to a position that gives us the same feel when we take off, no matter if we are a little nose- or tail-heavy,” he explains.
Crew maintain this sweet spot throughout the flight, even as up to 100 tonnes of fuel are consumed. It’s an impressive balancing act.