Why Do Airlines Sometimes Weigh Passengers?

By Spyros Georgilidakis | June 1, 2023

A request from authorities for Air New Zealand to weigh passengers on international flights caused a bit of a stir. But it’s not a new idea.

The tightening of airport security, including newer passenger scanning methods, has caused complaints from the flying public over the years. Separately, some airlines have encouraged passengers to help them fly greener, by reducing flying weight. Years ago, ANA in Japan went a bit further, by suggesting that passengers could help it reduce emissions by visiting the restroom before boarding!

An All-Nippon Airways A321neo. Photo: Airbus

Stories like this might make passengers wary of an airline that wants to weigh them. But there is a perfectly good reason for airlines to weigh everyone – from time to time. In this case, Air New Zealand calls the initiative a passenger weight survey. Which is exactly what it is.

In order to fly safely, an airliner must operate within specific weight limits. And even within these limits, the pilots need to adjust power and trim settings, depending on the aircraft’s overall weight. The plane’s weight distribution is an important factor, for the same reason.

Why Do Airlines Sometimes Weigh Passengers?
Photo: Masakatsu Ukon, CC BY-SA 2.0


Why Weigh Passengers?

Normally the airlines don’t weigh passengers, but they weigh practically everything else. This includes fuel, hold luggage and cargo, meals, and often carry-on luggage. But for the passengers themselves, airlines rely on “average weights”. Aviation authorities arrive at these weights and update them over time, by making studies on large groups of passengers.

Obviously, this initiative in New Zealand is one of these studies. Air New Zealand has already begun to weigh passengers on certain flights, starting from Wednesday the 31st of May. They will continue to do so until the 2nd of July this year. This data gathering will involve several international flights. Before the pandemic, the airline already completed a similar study for domestic flights.

Photo: Cammynz, CC BY-SA 4.0

Naturally, some members of the traveling public are suspicious of such moves. For that reason, Air New Zealand assures its passengers that its process to weigh them is anonymous. The airline employee operating the scale doesn’t actually have a weight readout.

Even with these studies, flight crews may still decide to weigh passengers under some unusual conditions. Flights carrying large groups of young soldiers, or flights with certain kinds of sports teams, may fall well beyond average weight calculations based on the general public. Such conditions are rare, but airline captains have the final say on what to do in these cases.

Why Do Airlines Sometimes Weigh Passengers?
Photo (cropped): Mark Harkin, CC BY 2.0


Calculations Gone Wrong

Also, we sometimes hear of mistakes in weight calculations, for unusual reasons. Back in 2020, TUI Airways later discovered that a flight took off 1,244 kg (2,743 lbs) heavier than what its crew had calculated. The company had just upgraded some of its computer software.

But because of a program setup error, the new software identified everyone who had the title “Miss” as a child. At the time, the airline used 35 kg (77 lbs) as the average weight of a child, and 69 kg (152 lbs) as the average for female passengers.

Why Do Airlines Sometimes Weigh Passengers?

One of the pilots did notice an unusually high number of children in the flight’s paperwork. Still, the flight progressed normally, without either pilot noticing any handling issues. Their 737-800, which was NOT overweight despite the error, flew as expected. As a testament to the safety margins airliners incorporate in their design, this weight difference would have required only 1 knot higher rotation speed, with only an extra 0.1% of power (N1) from the engines.

Still, studies like this one in New Zealand are vital. These large safety margins could mean that the airline industry may be slow in noticing rising weight trends in the population. Hence why the need to weigh passengers occasionally, as awkward as it may be, is really important.


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