Think moving seats after your plane takes off is harmless? Here's why you're wrong

Telegraph

01-06-2025

We've all done it. Having dodged the costly charge to choose your own plane seat, and been assigned a spot squeezed between two strangers, you spy an empty row. Surely trading your cramped quarters for somewhere more spacious won't cause any harm? Don't be so certain.
Airlines are reluctant to condone the practice, in part because of their emergency protocols. If, for example, a passenger was to collapse or become otherwise unwell, airline staff need to be able to access as much information as possible about them – and quickly. If the person in 15A is now in 27D, those vital, life-saving details could be hard to ascertain. It's especially important if that person is travelling alone.
Swapping seats might also throw a spanner into the works when it comes to the balance of the plane. It might seem unlikely, but the centre of gravity on every flight is a carefully calibrated thing – even on those quick, short-haul trips to Europe. It's especially important on smaller aircraft, where the weight of each section is a finely measured thing. Disrupt the balance, and the safety of the flight could be compromised.
While weighing passengers ahead of boarding has been mooted, the approximate distribution of mass does have to be calculated before each flight. Airlines are keen to emphasise that if one side, or section, of the plane is heavier than another part, flying the aircraft can become difficult. Any extra 'drag' – when air resistance becomes noticeable – is something the pilot must consider. And it can increase fuel costs, too, which can in turn affect ticket prices – something none of us want.
Vital calculations
In fact, the impact on fuel is particularly significant. That all-important centre of gravity is calculated before a plane takes off, and is used – most crucially – at landing. As planes are considerably lighter at landing due to fuel depletion, these calculations are a vital part of getting onto the runway safely. It's based on the allocation of human weight, so if a party has shifted to another side of the cabin, that information is no longer accurate (and makes getting onto the runway that bit more difficult).
A guidebook released by the Federal Aviation Administration, the American government agency that operates civil aviation, emphasises the importance of these calculations. Its introduction states that 'the weight and balance system commonly employed among aircraft consists of three equally important elements: the weighing of the aircraft, the maintaining of the weight and balance records, and the proper loading of the aircraft.'
The information goes on: 'An inaccuracy in any of these elements defeats the purpose of the system… Improper loading decreases the efficiency and performance of an aircraft from the standpoint of altitude, manoeuvrability, rate of climb and speed. It may even be the cause of failure to complete the flight or, for that matter, failure to start the flight.' It's not a great idea, then, to take that empty seat a few rows ahead (unless you're expressly asked to by airline staff, who might want to balance the cabin).
Financial reasons
Of course, airlines are also keen to discourage seat-swapping because ancillary payments (for snacks, luggage and a preferable location) are a valuable part of their business model. Ryanair reportedly netted some £3.5 billion from additional fees in 2023, for example, and a recent survey by financial site TradingPedia found that customers who tried to book 'rock bottom' tickets at budget airlines often ended paying up to £200 more than the advertised initial price, with providers like Wizz Air, Ryanair and EasyJet among the worst offenders.
The best way to ensure good seats is, unfortunately, to pay for them. But there are a few tricks that may help to bag your ideal spot in the cabin. Some airline staff suggest that parties of two should book the aisle and the window seat in the hope that no one nabs the one in the middle. While being able to see in advance where children are sitting in the cabin has proven controversial, taking a look at the seat map is a good way to work out where larger groups might be situated (and decide whether or not you would prefer to steer clear).