Our flight was delayed by at least an hour, the United Airlines agent announced, ‘they are working on the APU, the air .. ‘ Auxiliary Power Unit! chimed some mechanically- minded passengers to help her out. But right after the announcement, she said ‘Don’t go anywhere! The APU has been fixed!’.
Honeywell invented the APU in the early 1950s. It is really a gas turbine engine, typically in the tail of the airplane, providing electricity for starting the main engines, enabling the air conditioning, running lighting and flight equipment, and more.
Here are some answers a pilot provided on a message board I found on-line (the questions can be inferred from the answers!).
1. Yes, an aircraft can be operated without an operating APU – it can be a maintenance-deferred item for a certain period of time.
2. Yes, the airport needs to have the following in the event on an inoperable APU :
a. Ground Power Unit (GPU) or land-side power connection – to power the aircraft while the engines are off
b. Air Start Cart to provide pressurized air to start the engine without the APU
3. Yes, engines can be restarted in flight without an APU
4. Yes, the APU is usually turned off on the ground when the aircraft is connected to ground power and it is also turned off in flight
5. Yes, regional jets are somewhat more prone to APU issues
P.S. Alright, so the USA lost the game against Germany 0-1. I watched the last 10 minutes or so in the building lobby (and reportedly President Obama took time out to watch the game on Air Force One). The US team still goes through to the knock-out rounds though, where it will face Belgium on Tuesday.