I have just watched Mayday episode 11, season 11, "Nowhere to Land" about TACA Flight 110 incident and I was more than surprised to learn that:
- APU must be turned on,
- APU needs about 5-10 minutes to start powering anything,
- APU can be used to power lights in the passenger cabin (???).
This is the exact flow of events (plus voice description) as it is shown in above cited episode:
- a pilot is shown turning APU's switch,
- narrator explains that a certain amount of time must pass before APU starts working,
- lights in passenger section are turned on after this period of time passes.
Contrary to the above, I was always told (based on Air Transat Flight 236 incident, shown in season 1, episode 6, "Flying on Empty" of Mayday, and based on other sources):
- APU is deployed automatically (gravitational solution) whenever power from engines is lost,
- APU starts powering equipment nearly immediately,
- APU is able to power basic instruments only, even pilots cabin remains dark, not to mentioning passenger sections.
What is the reality?