Finding a jumbo jet's mass with no weighing scale

You have no scales available. How could you determine the weight of a large aircraft?

Use buoyancy or tyre pressures. Float the plane onto a barge or ship, mark the waterline, and measure how much extra water is displaced: by Archimedes' principle its mass equals the displaced volume times water density. Alternatively, the weight on each wheel equals tyre pressure times the tyre's contact patch area, so measure the pressures and patch areas and sum. Mentioning more than one method and its error sources is a plus.