Figuring An Airplane's Weight

Question:  How do you calculate the aircraft's weight?  Is it simply a guess of the number of passengers and the average weight per passenger in addition to average luggage per passenger plus cargo?  This seems to beoverly simplistic, however!

Joel Gratz, Boulder, CO

Answer:  Aircraft have an established structural weight right from the manufacturer where the aircraft is physically weighed.  There is an average weight per passenger (last time I checked it was 165 summer and 170 winter, or something like that, to allow for the seasonal change of dress), and cargo and bags are all weighed.  This is added to the structural weight to come up with the “zero fuel weight" (ZFW).  Then, it’s simply a matter of adding the weight of the fuel to that for the gross weight of the airplane.

Airplanes with computers have a page where the known figures are entered, including the ZFW, and we can actually watch the weight figure increase as fuel is being added, at least on sophisticated aircraft like the B-777.

Interestingly enough, average weights are adjusted upward when football charters are flown.  Also, when we're at a maximum weight and it looks like either people, cargo or both may get bumped, we sometimes resort to a "kiddie count."  We'll ask the flight attendants to walk through the cabin and count the number of small children.  That information is passed to our load planners and the average weight adjusted for them.  Sometimes it makes the difference whether we have to bump or not.

By the way, I flew on a charter or two years ago when each passenger was physically weighed, and I believe that may still be the norm for some flights depending upon what part of the world the flight originates, whether it's a charter, etc.  It was mortifying, as a teenager, to have to step on a scale and have my weight recorded when I flew on a charter from San Diego to Frankfurt.  Believe me, there was an inordinate amount of grumbling among the passengers, especially the pudgy ones.

On a different charter, we were simply asked to state our weight.  The woman ahead of me must have weighed at least 220 or so, but the agent didn't bat an eye when she said she weighed 150.  When I got up close to the podium I saw he had written 210. 

I lied about my weight about 15 pounds, as I recalled.  There were a lot of overweight people in that line, many of them, especially the women, not able to bring themselves to be truthful about their weight.

It's a wonder we even got off the ground.

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