Weight and Airplane Calculations

Q: You previously wrote that the weight of an aircraft affects its performance, and must be calculated prior to takeoff. How is this accomplished with any degree of accuracy?

Passengers are not required to divulge the quantitative specs of their waistlines, obviously, and instead the airlines use standard weights both for people and luggage — 190 pounds per person (including carry-ons) and 30 pounds per checked bag. This is adjusted slightly higher during winter to account for heavier clothing (please don’t ask me about trans-climate routes). Thus, passenger and luggage tallies are approximations. The numbers are derived empirically and are surprisingly accurate.

They are added to something called the BOW or Basic Operating Weight of the aircraft, which includes the ship itself, replete with all furnishings, supplies, and crew. Compounded with fuel and cargo, the result is the total gross “ramp” weight. Fuel used for taxiing, which can be several thousand pounds, is subtracted to reveal the takeoff weight.

Both weight and its distribution are very important. Every flight’s center of gravity, which changes as fuel is consumed, is calculated and kept track of. The smaller the plane, the more important this becomes, and after the crash of a commuter flight in Raleigh in January, 2003, the FAA began surveying verbatim weights to ensure accuracy of the data. Pilots are trained in the particulars of weight and balance, but in practice the grunt work is usually taken care of electronically, presented to the crew in dot-matrix splendor with the rest of the preflight paperwork.

It might surprise you to hear that in the case of a Boeing 747, three hundred passengers and their suitcases, about 65,000 pounds en masse, would make up less than ten percent of the airplane’s total bulk.

This article is part of a collection that originally appeared on Salon.com. Patrick Smith, 38, is an erstwhile airline pilot, retired punk rocker and air travel columnist. His book, Ask the Pilot (Riverhead) was voted “Best Travel Book of 2004” by Amazon.com. Patrick has traveled to more than 55 countries and always asks for a window seat. He lives near Boston.