FAA Powerplant Written Practice Test

Under which starting circumstance might the start stop button be necessary in a starter-generator system?

1. Routine maintenance

2. Pneumatic start

3. Hung start

4. Nozzle adjustment

The correct answer is: Hung start

The start stop button is essential in a starter-generator system particularly during a hung start scenario. A hung start occurs when the engine fails to accelerate to normal operating speed after the starting cycle has been initiated. This could potentially lead to excessive fuel being injected into the combustion chamber without achieving a proper engine run. Using the start stop button allows the pilot or operator to halt the starting process manually, preventing damage to the engine from continued attempts to start under these conditions. By stopping the start sequence, it is possible to address any issues that may be causing the hung start, such as fuel flow problems or mechanical issues within the engine. In contrast, routine maintenance typically does not require the immediate use of a start stop button as it involves checks and adjustments done without the engine being in the starting phase. A pneumatic start can refer to a starting method that may rely on air pressure but does not inherently require the function of the start stop button. Similarly, nozzle adjustments fall under maintenance or operational procedures that do not involve pressing the start stop button during engine starting. Thus, in a hung start, the start stop button plays a critical role in engine management for safety and system integrity.