Auto/Continuous Ignition

[uwochris]

Hey guys,

Just reviewing the systems for the Metro, and I've run into a little bit of confusion.

I really don't understand the difference or significance of an "auto" ignition system. I was under the impression that the igniters were always on continously; however, according to the AFM, the igniters can be set to be on continuously, or, to come on automatically once the RPM reaches a certain level (90-92% in this case).

Can someone please clarify the purpose of auto-ignition and continous ignition??

Thanks!

 

[fxbat]

I don’t know about the metro but most A/C have an auto re-light if n2's drop below a give rpm regardless of the start switch position. Continuos ignition means one of the two igniters in the burner can are continually on.

 

[Toobdrvr]

The ignition system has 3 switch positions: Auto, Off, and Cont. Each switch position gives you ignition at specific times:

Auto: Start (10% N1), and when the engine detects negative torque (suspected flameout).

Off: Start Only

Cont: Fires the igniters Continuously.

At AMF, we only used off and cont. mainly to keep us in the loop and actively selecting ingition.

Make sure you have this down because it is about the biggest "Killer" items with the Garret. Lots of pilots have died because they selected the wrong position (thinking ignition was on when it wasn't and having a dual flameout during a circling maneuver in icing conditions).

Good luck!
Toob

 

[rickair7777]

Normally the ignition (ie "spark plugs") on a turbine engine is only used during the engine start seqeunce. Once stable idle speed is reached, it is not required.

Continous ignition is a manual selection to turn the igniters on until manually de-selected. This is called for per the AFM when certain conditions exist, such as during precip, icing, wind shear, turbulence, cross-wind, or contaminated runway.

Auto-ignition is just continous ignition that activates by itself under certain conditions such as normal engine start, wind-shear detection, or low RPM. It usually turns itself off when no longer neeeded.