What is the emergency action if the APU emergency shutdown switch has no effect after 11 seconds?

The appropriate emergency action when the APU emergency shutdown switch has no effect after 11 seconds is to open door 10L or 14L and pull the APU breaker. This procedure is crucial because it allows for direct intervention to isolate the APU and prevent potential hazards that could arise if the unit continues to operate unsuccessfully after an attempted shutdown.

Opening the designated doors provides access to the APU control systems, and pulling the breaker effectively disconnects power to the APU, halting its operations in a controlled manner. This action minimizes the risk of a fire or other emergencies that could result from a malfunctioning APU, ensuring the safety of personnel and equipment.

The other options represent different measures that may not directly address the issue at hand or could escalate the danger. Evacuating the area may not be necessary if proper procedures are followed, and while notifying the maintenance officer is important, immediate action to shut down the APU is the priority. Starting a fire extinguisher system may prematurely escalate the response when a controlled shutdown is viable.