How long does the PT brake disengage for when doing a Crashback?

The correct answer is based on the operational procedure associated with performing a Crashback maneuver in gas turbine systems. The PT brake, which stands for Power Turbine brake, is designed to disengage for a specific duration to allow for safe and effective execution of this particular operational maneuver.

When executing a Crashback, the PT brake typically disengages for 6 seconds. This duration ensures that the system can transition effectively without damaging components or causing undue stress to the gas turbine. The timing is critical; it allows just enough time for the reverse throttle to engage while maintaining the necessary control over turbine speed and ensuring that the system operates within safe parameters.

Understanding the duration of the PT brake disengagement is essential for technicians as it helps in executing safe operational practices and maintaining system integrity during such maneuvers. The other durations provided would either not give sufficient time for the operation or could lead to extended disengagement, risking system control and safety.