I did after once flying out of Denver, and the luggage had to be removed because the airplane was overweight for the altitude and air temperature.
Next time you're flying out of Denver, notice how long the takeoff roll is. When my father flew jets out of Denver, he'd hang the tailpipe over the back edge of the runway so he'd have every last foot of runway to get airborne.
The difference in Denver is so significant that United actually swapped all the Houston-based 737s that came over from Continental in the merger with the Denver-based A320s from United. The 737 base moved to Denver and the A320 base moved to Houston.
The 737 has better performance with high-altitude takeoffs.
Checked luggage is weighed when you drop it off, so presumably the exact weights are available to the pilots. For passengers themselves and their carry-on baggage, accurate weights aren't available so statistical averages are used, based on the number of passengers and their baggage allowances.
Airliners do have "squat sensors" in the landing gear, but they're not capable of accurately measuring the aircraft's weight. They're just binary-valued sensors that check whether the gear struts are under stress, to prevent the gear from accidentally being raised while the plane is on the ground.
I wonder if gluing strain gauges to the landing gear struts would be accurate enough once calibrated.
There has been at least one crash due to mis-estimating the weight of the passengers + luggage + cargo. A strain gauge on the struts, even if inaccurate, could provide a backup sanity check for the weights.
As I joined FedEx, I was told that
they had already worked out sensors,
of some kind (I never saw details),
on the landing gear that would give
the data needed for knowing and
controlling
weight and balance.
For balance, right, e.g., don't want all the
weight near the tail and, instead, want
the weight more evenly distributed
in the cargo area along the length of
the plane, that is, want the
load in balance.
So, yes, FedEx did think of having
sensors, of some kind, in the
landing gear.
But I never heard more about
such sensors, and, for the times I
rode the jump seat in the planes,
I never saw pilots working
with weight and balance from
data from the landing gear.
Maybe later, after I went to
grad school, FedEx did do something
with such sensors.
So, right, the sensors are a good idea
and were considered and, maybe, eventually
implemented.
They could put something in the ground - a weigh station - that the plane travels over before getting to the runway. That avoids the need for modifying airside equipment which is a bureaucratic nightmare.
I don't know what happens in the USA, but in Australia each piece of luggage is weighed before it can be checked in. For various reasons: heavy bags (over ~20kg) must have warning labels attached, very heavy bags (over 32kg) are disallowed with no exceptions, and it means a total can be provided to the pilot.
Next time you're flying out of Denver, notice how long the takeoff roll is. When my father flew jets out of Denver, he'd hang the tailpipe over the back edge of the runway so he'd have every last foot of runway to get airborne.