Originally Posted by
Outwest
I can understand the logic of having a separate ignitor switch for use in water washes, etc. In a helicopter we have to pull the CB for these or other reasons when we don't want ignitor activation with the starter. What I don't get is the need to turn that switch on at 12%, why not select it to Start/on, hit the starter and go from there just as we do with a RW installation.
So, I looked in the PWC PT6-34AG Maintenance Manual, and this is what is has for engine start:
PWC PT6-34AG MM Jan 18, 2021
PWC PT6-34AG MM Jan 18, 2021
This is from the Air Tractor Maintenance Manual:
Air Tractor AT-502A/502B/504 Maintenance Manual - Mar 14, 2019
So, interestingly, the PWC MM mentions 12% as the minimum Ng for a successful light....and that number is referenced in the AT pilot training course and official checklists as the value for when to turn on the ignitors. My guess is that they figure it's best not to introduce spark until past the bare minimum Ng that won't torch the engine, in the event that some fuel is present? It's also interesting that the AT MM lists 15% as the value to turn the igniters on.
I'd be curious to see the "official" answer from Air Tractor.