B 777 APU tail pipe fire on APU start up

[peacock1]

Hi, 'specially triple 7 drivers.
Recently observed a nasty looking, but thankfully momentary, APU fire on a 777 that was taxying in front of my aircraft.
I reported on ATC and spoke directly to the crew of the affected aircraft, with the welcome news that the flames were short lived and that there was no further sign of fire.
They didn't appear too fazed.
My question is - is a momentary APU "flame" on APU startup, a known phenomenon on the 777?
The aircraft in question was 2-3 years old, 777-300LR.
Ta.

[peekay4]

Sounds like "APU torching" which is not uncommon on all types during start.

Torching is usually due to excess fuel, especially if the APU failed to start on the first attempt. The leftover fuel pools, then gets ignited on the 2nd start attempt, causing flames to momentarily push out from the exhaust. (Could also happen on 1st start if there's excess fuel due to a minor leak, etc.)

On 727s, the APU exhaust is located on the right wing root, next to the passenger windows. You can imagine the surprise when passengers see flames shooting out the wing-- in a couple incidents, pax have actually opened the emergency doors and jumped out the plane in panic.

Usually there is enough exhaust pressure so the flames simply clears the exhaust and do not cause any issues. The ERJs had a problem where torching flame could re-enter the APU compartment via the "eductor" (cool air) inlet, if the APU is started at high altitude.

[777boeings]

peacock1
Just a slight correction. That would be a B777-300ER.

Been flying the triple for 18 years. Never known an APU TP fire (yet). I guess it must've been a fuel metering issue with a fault in the system. :)