Which method is one way to level an aircraft?

Using a spirit level at specified points is a widely accepted method for leveling an aircraft. This technique involves placing a spirit level on different parts of the airframe, typically on the wings or fuselage, to ensure that the aircraft is in a true level position. The spirit level works by indicating whether the surface it is placed on is perfectly horizontal, which is crucial for various maintenance tasks, weight and balance checks, and during pre-flight inspections.

Leveling the aircraft is essential for accurate calculations, ensuring the aircraft's weight and balance are within limits, and facilitating proper control during flight, as well as ensuring the effectiveness of systems that require level positioning. This method is straightforward, requires little equipment, and can provide immediate feedback, making it practical for aviation technicians.

While other methods like using GPS devices, weight measurements, and compasses offer valuable information for various operational and navigational tasks, they do not provide the direct measurement of an aircraft's level state in the same way a spirit level does. Each of those alternatives serves different purposes, such as aiming for navigational precision or assessing the overall weight but does not replace the simple utility of a spirit level in leveling the aircraft on the ground.