Explain the difference between APU start permissives and the actual start sequence?

Explain the difference between APU start permissives and the actual start sequence?

• A. The start sequence is the set of conditions to enable the start; permissives are the steps to start.
• B. Permissives are the conditions required to enable the start; the sequence is the commanded procedure to execute the start.
• C. There is no difference; both terms refer to the same concept.
• D. Permissives are the steps to start; the sequence is the set of conditions to enable the start.

Answer: (B)

Permissives are the gating conditions that must be satisfied before the APU start can be commanded. They are checks and signals that indicate the system is ready—power available, no faults, appropriate valve positions, and other readiness criteria. They don’t perform any action themselves; they simply permit the start to proceed. The start sequence, once permissives are met, is the actual commanded procedure to bring the APU online. It covers the steps the system will execute in order: energizing the starter, initiating fuel flow, applying ignition, monitoring parameters, and transitioning to normal running. That separation is why the best description is that permissives are the conditions to enable the start, while the sequence is the steps to execute the start. The other options mix up which part is the enabling condition versus the procedural actions.

Permissives are the gating conditions that must be satisfied before the APU start can be commanded. They are checks and signals that indicate the system is ready—power available, no faults, appropriate valve positions, and other readiness criteria. They don’t perform any action themselves; they simply permit the start to proceed.

The start sequence, once permissives are met, is the actual commanded procedure to bring the APU online. It covers the steps the system will execute in order: energizing the starter, initiating fuel flow, applying ignition, monitoring parameters, and transitioning to normal running.

That separation is why the best description is that permissives are the conditions to enable the start, while the sequence is the steps to execute the start. The other options mix up which part is the enabling condition versus the procedural actions.