SR20 G3 POH trim runaway + prop control questions

[Bodi_Debnath]

Hi ,

I have the following questions after reading the SR20 G3 Perspective POH. Will be very grateful if someone has some answers for these

1. The prop control linkage from the power lever - if that breaks for some reason - what is the behavior of the prop governor?

2. If there is a runaway trim in the pitch or roll axis, is the only remedy to cut power, pull breakers, restore power? What happens if the trim switch is held opposite to the direction of the runaway. In some aircraft that ends up tripping the breaker.

3. If there is a runaway trim condition and the AP is engaged, will the AP envelope protection kick in and control the axis independently of the trim? Or will it not be able to fight the out of trim condition and cut out again.

4. If power is cut during a trim runaway event, does the trim servo maintain its last “position” or does it fail into a neutral position if power is cut?

Thanks a lot!

Bodi

[thomasan (Thomas Antony)]

@Bodi_Debnath

• If there is a runaway trim in the pitch or roll axis, is the only remedy to cut power, pull breakers, restore power? What happens if the trim switch is held opposite to the direction of the runaway. In some aircraft that ends up tripping the breaker.

I am not sure if this applies to the G3, but on the G6, the electric trim is disabled if you hold down the AP disconnect button. We actually check this during the before-takeoff by holding down the AP disconnect button and moving the trim switch.

[Bodi_Debnath]

Ignore the power lever propeller control system question. Looks like it can fail at any position. Luck of the draw!

[Jim_Barker]

No. Don’t ignore it.

The prop governor is spring loaded to high rpm position.

[turrisi (Brian Turrisi)]

@Bodi_Debnath

1. The prop control linkage from the power lever - if that breaks for some reason - what is the behavior of the prop governor?
2. If there is a runaway trim in the pitch or roll axis, is the only remedy to cut power, pull breakers, restore power? What happens if the trim switch is held opposite to the direction of the runaway. In some aircraft that ends up tripping the breaker.
3. If there is a runaway trim condition and the AP is engaged, will the AP envelope protection kick in and control the axis independently of the trim? Or will it not be able to fight the out of trim condition and cut out again.
4. If power is cut during a trim runaway event, does the trim servo maintain its last “position” or does it fail into a neutral position if power is cut?

Thanks a lot!

1. Jim Barker answered that. It is the same as all constant speed singles (or at least the majority).
2. Depends on the cause of the runaway. There are 4 ways to tuen off the AP. Electric trim has its own breaker to kill it if that happens.
3. The manual control of pitch trim is locked out with the AP on. The scenario you are describing has never happened in a Cirrus.
4. The trim will maintain its last position when the power is cut. A total mis-trim to the stops is still able to be controlled by the pilot albeit with a fair degree of control pressure.

Join COPA to learn a lot more.

[Bodi_Debnath]

My mistake - I saw the broken power lever checklist and it says power could be stuck at any point. I think it meant throttle possibly but not the prop governor. So I would like to ask the same question for the throttle - if the power lever linkage breaks - I think the throttle stays where it was but the prop goes max rpm.

At least according to the checklist that should be correct.

Thanks Jim, Brian and Thomas for your responses !