What distance should you maintain from a parked or taxiing airplane unless servicing that airplane?

The correct distance to maintain from a parked or taxiing airplane, unless you are servicing it, is indeed 20 feet. This distance is important for safety and operational protocols around aircraft.

Maintaining a distance of 20 feet helps ensure that personnel and equipment are far enough away from the potential hazards associated with aircraft, such as jet blast or rotor wash, as well as any accidental movement of the aircraft. The 20-foot rule is part of standard safety practices in airport operations, aiming to prevent accidents and ensure the safety of both the aircraft and the ground personnel.

Being too close to an aircraft could pose risks not only to those on the ground but could also lead to damage of equipment or injury given the size and weight of airplanes as well as the forces they produce during taxiing or in various operational states. The 20-foot standard appropriately balances operational efficiency with safety considerations.