One of the basic principles of learning to fly is learning the importance of proper weight and balance and how to compute it for a given airplane. This basic skill is covered on every written test and most practical exams, and in the training world, we learn the need to ask people for their weight or to guess on the heavy side to make sure we get it right.

Airlines, however, are not about to ask everyone what they weigh. Instead, everything is based on standardized weights. Passengers are assigned a standard weight that is intended to be a realistic average across gender, height, and age. Kids below a certain age are assigned a weight, as are service animals in the cabin. Luggage is also standardized, usually into three broad groups of below fifty pounds, fifty to a hundred pounds, and over a hundred pounds. Carry-on bags are assigned a weight as well. In fact, a suitcase may ‘weigh’ one thing in the cabin, and be completely different in the cargo bin. You can’t make this stuff up.

Not every carrier uses the same formulas, however, and even within one airline things can vary. My company, like most, uses certain weights based on the season, with winter weights being higher. But we also have weights that are destination-specific or geographically specific. Island destinations usually have slightly different weights to account for the number of people who bring scuba gear, and ski destinations are different as well for obvious reasons.

Charter flights also pose issues, because luggage and even passenger weights can be out of the norm. An NFL charter may need to take into account that the players are bigger than the norm, and all of the equipment has to be accounted for. If you’ve never seen a football team travel, it’s a treat. There are dozens of trunks, duffel bags, and individual luggage to account for. Everything you see on a sideline or in a locker room on TV gets packed for the round trip, and it’s heavy. Military charters are also a challenge.

All of this is done based on the airline’s approved weight and balance program, which is coordinated with the flight standards district office that oversees the certificate. Sometimes changes are required. In 2003, when Air Midwest (Mesa) Flight 5481 crashed in Charlotte, one of the culprits was that passenger and baggage weights were no longer accurate as Americans had gotten heavier. Over the next year or so, passengers were randomly weighed in order to reset the weights. It’s probably time to do that again.