[hipaulshi]

Pilot here.

Every airplane has a maximum weight it can fly. Different than cars, every airplanes also have an envelope where the center of gravity has to fall enter. If the center of gravity is behind the design envelope, airplane has a tendency to flip backward, stall on take off then crash, it has happened before. It could also means if the airplane enters a spin, the recover may not be possible. If the center of gravity is too forward, it will slow the cruising speed due to increased drag, much easier to stall during cruise and burning more fuel.

So for every single flight, pilot or dispatch has to calculate those 2 numbers, for every passenger and baggage, and decide how many fuel to take on each flight.

Of course, asking each passengers weight would be awkward at best, so airlines and FAA used an average body weight number to avoid this, it worked until 2003. An accident happened which killed 21 people on board a small transportation aircraft. It is found that the average body weight number FAA and airline used were outdated http://www.ntsb.gov/Investigations/AccidentReports/Pages/AAR... FAA has since advised airlines that what FAA presumed average weight of its population has increased, and advised airlines to do the same.

Of course, this will only work on average cases, and will fail if the sample group is out of average. Resampling has to be done to remain operating in the envelope, and if standard deviation is still out of normal, each individual weight has to be taken.

[shimon_e]

Why not add a weight sensor to every seat?

[falcolas]

Easier - add weight sensors to the landing gears. A set of piezo sensors between the mounts and the frames should suffice. Only three sensors to calibrate and maintain, they can give a real-time indication of the actual balance of the aircraft (including fuel), and don't impose on the airline's customers (or staff, other than to move a few people around to correct for a bad CG, something they do today).

[pentae]

It would be more economical to have scales in the floor at the check-in counter, no?

[OrwellianChild]

Thanks for this context... I'm assuming based on the framing of the article that this particular case was based more on a concern for fuel cost than for safety. (Surely a commercial airliner can't be dangerously upset by shifting a few thousand pounds...)

Since the airlines and FAA have to operate averages most of the time and update them as the demographic of their flights changes, would it not be a simpler, more socially opaque solution to just charge slightly more for the flights that tend to carry heavier passengers? More fuel, yes, but now paid for. No one has to endure the indignity of weigh-ins, and the airline is made whole. Why is this not the solution that was presented?

[giovannibajo1]

In many half-empty flights, the crew allows passengers to freely change seats, after take off. Obviously only a few do, but wouldn't that be dangerous anyway, given your comment on balancing weigh?

[ghkbrew]

It would seem that you would only have problems when the weight is unevenly distributed. I've only ever seen people spread out when allowed to take any seat, which would tend to make things more even if anything.

[jessaustin]

TFA references "an American airline". Since we Americans are misanthropes, when we freely choose our seats we have a balancing tendency. Your concern would be more valid for populations who would naturally choose to sit together.

[waqf]

Notice, after takeoff. Takeoff and landing are when centre of gravity is critical. You're supposed to return to your originally assigned seats for landing too.

[wodencafe]

Why is this a manual process? Is our technology not sufficient to build a plane that can detect when it has too much weight on board for a safe flight?

[icegreentea]

No, its just too expensive, and probably too heavy.

If OP is right (pretty sure he is), he said that by using something completely free (average weight), we were able to achieve like 50+ years of safe operation of largish commercial airliners. That's amazing.

Also, the problem isn't too much weight per se, it's weight distribution.

[5706906c06c]

Wasn't this the reason behind Aaliyah's plan crash?