Metro auto ignition

[MerlinMetro]

In relation to the Metro 3. Is the auto ignition that is activated on pwr loss, activated by a speed signal (less than 70%max rpm), or by a pressure transducer switch when a negative torque set up occurs?

[MerlinMetro]

There must be some metro drivers out there who know the answer???

[VH-ABC]

My guess...

The metros that I have flown all had the later version of the two ignition systems available, where you had OFF, which you could start in, but have no 'NTSing' feature (not normally used), normal flight was in AUTO ignition mode, and CONTinuous ignition was available for icing or turbulent conditions at pilot discretion - and also comes on when an 'NTSing' condition was present.

The system would not come on when there was only Negative Torque sensed, but there had to be less than FLT IDLE rpm on the prop, so depending how well its rigged, less than 70%.

If anyone else has other ideas, would love to hear them too.

ABC

[zerozero]

I used to be a Metro III system's instructor (it's been a few years!) but I still have a copy of my Metro Systems book.

<< Selecting the "AUTO" position provides electrical power to the NTS pressure switch through both poles of the ignition selector switch and the relaxed ignition mode relay. The engine mounted NTS pressure switch closes when negative torque (high oil pressure) is sensed, providing power to the ignition exciter. Once the pressure switch has closed, it will remain closed for approximately 30 seconds after the negative torque condition ceases.>>

So RPM has nothing to do with it.

But there is an NTS lock-out when the power levers are brought back for landing. Nobody needs two NTSing propellers when you're trying to flare.

I hope that answered your question.

[MerlinMetro]

Thanks that answers it zerozero
:ok: