What is the function of the second detent of the parking brake handle?

The second detent of the parking brake handle serves a specific function related to aircraft safety and operation. When the second detent is engaged, it keeps the parking brake in a position that maintains engine operations, particularly during certain scenarios like engine starts or during ground operations when the aircraft needs to remain stationary.

This functionality is essential because it prevents the brakes from inadvertently releasing while the engines are running or before a full pre-flight check is completed. It's not about applying thrust reversers, activating engine starts, or simply releasing the parking brakes, as those are distinct and do not relate to maintaining engine operations securely with the parking brakes engaged. Thus, the presence of a second detent in the parking brake handle plays a crucial role in the proper handling of the aircraft on the ground.