What method uses air pressure from another aircraft to drive the pneumatic starter?

The method that uses air pressure from another aircraft to drive the pneumatic starter is known as a buddy start. In this procedure, one aircraft assists another by providing pneumatic pressure through its engine bleed air system, enabling the second aircraft to start its engines. This technique is particularly useful in situations where the aircraft in need of a start may not have enough power or battery capacity to initiate its own engine start. The versatility of a buddy start allows it to be performed in various operational environments, enhancing the overall effectiveness of the aircraft fleet.

In contrast, other options involve different methods of starting engines or providing pneumatic power. APU pneumatics refers to the use of the Auxiliary Power Unit to provide pressure for starting the aircraft’s engines. External pneumatics typically involves ground support equipment connected to the aircraft for starting, while engine bleed air indicates a process that utilizes the aircraft's own engine system rather than support from another aircraft.