Better yet, do it like a truck stop and have a scale in the concrete road. And when planes taxi on and off the runway they can run over the scale and be weighed. One or two scales could do what thousands of measuring devices on planes would do, but would be cheaper.

ibcmbry2, I'm not sure anyone knows how to build scales that can weigh more than 500 metric tons (and that airports can afford), but your idea seems more reasonable than gregeb's.

There is one cheap solution (in theory): most planes are moved around by ground tractors when they leave parking. By measuring the forces necessary to accelerate (or break) the plane by a given speed difference, one can determine the plane's mass. The speed and forces measurements just need to be precise enough, and extra factors minimized or known.

Accelerometers installed on the aircraft, together with thrust information from the engines, could even better tell about an aircraft's mass. More importantly, it could determine weight distribution within the aircraft.

Accelerometers are cheap now, this capability may well exist already.

Great improvement, Beaugrand.

Accelerometers are already present in ALL commercial planes's inertial navigation systems, so there's no extra weight to carry (except support for additional processing power).

However, the thrust would need to be measured very accurately (it is quite low when taxiing).

Even so, the impact of "extra factors", like wind, friction, wheel conditions, etc... would probably overweigh a few tens of passengers!

On second thought, I think this indirect weight computation idea is not practically achieveable after all.

Every flight I have been on, My bag has been weighed at check-in. I always assumed that it served this exact purpose. (not to mention allowing them to charge me more) What are they using these weights for then, if their not using them to balance and load the plane properly???

Everything on a commercial transport is currently measured except the passengers, crew, and carry-ons. The bags are weighed, but I think they only use the final totaled weight for the baggage compartment average. I certainly could be wrong.

Each airport could put one relatively low-cost scale after each metal detector when going through security and measure each passengers weight automatically when they present their ticket and ID for inspection. This information can be archived and shared amongst the TSA and airline industry to better serve weight and balance coordination.

This might also help detect persons with fraudulent ID's for terrorist identification. A 200 pound person presents an ID that six months ago was recorded at 165 pounds. This might be worth checking out. And by the time they get to the gate, maybe a change in seat assignment is in order to better help balance the plane for a person weighing 350 pounds.

In the event an aircraft is structurally modified and a different weight and balance results, that is supposed to already be covered by FAA regulations and procedures.

As a private pilot, I can tell you that its not much of a factor being over gross weight, but where that weight is located. In this case the rearward CG (center of gravity was exceeded.) I think that procedures for weight and balance should be improved where it its critical (I.E fully-loaded commuter jets.) And actual weighing of passengers should take place (the FAA assumes every passenger weights 190 lbs.)

Why not ask for weight range at the time of reservation (both of people and luggage?). I heard that even eliminating magazines from the plane saves millions of dollars every year. Eliminate books/unnecessary seat back trays (nothing is served anyway)and make the seat lean. Get rid of the worthless telephones on the back of the seat. Eliminate metal carts and use plastic trays. In short flights encourage the use of restrooms before getting on board and eliminate toilets and carrying water.

We certainly can build scales that can weigh 500 tonnes. Fully laden mining trucks sometimes reach that. And there already exists a company trying to get into this market; Teknoscale is a company that makes portable truck weighbridges and now has an aircraft scale on offer, although I don't think their current range goes up to 747. It is small and inexpensive compared to an aircraft; it can be moved around and set up by one man. Of course, each landing gear is measured separately to get CoG so maximum scale load is a lot less than 500 t.

Also a private pilot, I don't understand why there's not a system of strain-gauges installed on the landing gear that judge the weight-change by the change in strain and are then calibrated to read-out the approximate weight right in the cockpit.

This system could also do your balance calculation, because you'd have the strain-gauges on each landing strut.

Could even put a little picture of it on the EFIS.