I have often wondered that myself, and I looked into it a little bit, finding that there have been ideas for actually weighing airplanes on the ramp going back to the 1930s, but nothing seems to have come of it.
One possible reason might be a usually well-justified concern over adding complexity which could, if it fails, be worse than the problem it solves - but what would it take to measure the load on each undercarriage leg? something to measure its extension? Strain gauges on the structure the legs are attached to? I would really appreciate the input from an aero structures engineer here (paging Walter Bright...)
One other issue this would help is with is ensuring that the center of gravity is within limits (after the crash of Air Midwest Flight 5481, where this was a significant cause, the rule for estimating passenger weights was revised.)
On the other hand, an acceleration test will detect a lot of other problems beyond being overweight. There was a Citation crash near Hartford CT last year where it is suspected that the parking brake did not fully disengage. Why not have both, if they are feasible?
It's difficult because any minute amount of wind will affect the final results, and you don't have the full wind profile over the entire aircraft to compensate for it. Easier and safer to track what's on board and calculate the a/c performance based on that + margins.
I take your point; I have no idea of the magnitude of this effect in proportion to the total weight. I do wonder if a combination of the airspeed instrument readings, their fluctuation, and fluctuations in the measured weight could be used to estimate the influence of the wind (an application for machine learning?) but even so, that would mean that it would no longer be a simple solution.
What I’m talking about is just a way to provide something besides a pilot’s hunch to compare against weight data from flight crews. If it was so windy that it would catastrophically throw off the comparison, I doubt they’d even let the planes take off.
That's not how it works. Airliners can safely take off into strong headwinds. A wind blowing across the wings will produce significant lift. In theory it might be possible to compensate for that effect, but in practice it's just too much hassle.
One possible reason might be a usually well-justified concern over adding complexity which could, if it fails, be worse than the problem it solves - but what would it take to measure the load on each undercarriage leg? something to measure its extension? Strain gauges on the structure the legs are attached to? I would really appreciate the input from an aero structures engineer here (paging Walter Bright...)
One other issue this would help is with is ensuring that the center of gravity is within limits (after the crash of Air Midwest Flight 5481, where this was a significant cause, the rule for estimating passenger weights was revised.)
On the other hand, an acceleration test will detect a lot of other problems beyond being overweight. There was a Citation crash near Hartford CT last year where it is suspected that the parking brake did not fully disengage. Why not have both, if they are feasible?