Is Mooney pitch trim mechanism similar De Havilland Otter

[M20 Ogler]

I was reading about an AD for De Havilland Otter due to a loss of control incident recently near Friday Harbour. The Otter pitch trim works by changing the incidence of the stabilizer like a Mooney. A mechanical failure of the Otters stabilizer actuating hardware led to a tragic accident. 
 

My paranoid mind now wants to better understand how the pitch trim on my Mooney works. What gets inspection here at annual?

[PT20J]

Many airplanes use a trim jackscrew to adjust the incidence of the horizontal stabilizer. The Mooney design is uncommon (but not unique) in that the jackscrew moves the entire empennage rather than just the stabilizer, but it still uses a jackscrew. In any of these designs, if the jackscrew (or the nut it screws into) breaks, then the horizontal stabilizer will be free to float, and pitch control will be lost.

The Otter failure may have been a maintenance induced failure as a locking ring was found missing. It hasn't been disclosed yet if it was left off or installed incorrectly during recent maintenance, or if it broke. https://www.ntsb.gov/investigations/Documents/DCA22MA193 Investigative Update.pdf

There was another famous accident of an Alaska Airlines MD-83 (AS261) where the jackscrew failed due to lack of lubrication.

The Mooney tail should be inspected during preflight by grabbing the underside of the empennage just ahead of the rudder and lifting to check for excessive play.

During annual inspection, the jackscrew should be cleaned and inspected and lubricated.

Skip

Edited January 6, 2023 by PT20J
Added excerpt from the service and maintenance manual

[Will.iam]

Also one of the reasons i trim manually with the trim wheel, besides saving wear and tear on the trim motor and unobtainium trim switch, manually trimming allows me to feel how smooth the trim is going and if there is any binding. Also it’s amazing how much harder it is to trim when the elevator is loaded up like if you put in full flaps and then while keeping the nose from dropping try to trim is way harder to do than trim the airplane nose up first then add the flaps in to bring it back into trim. 

[N201MKTurbo]

I have tried it. The Mooney is flyable by a normal human in every phase of flight in every trim setting.

Not fun or comfortable, but doable.

This cannot be said for heaver airplanes.

[PT20J]

4 minutes ago, N201MKTurbo said:

I have tried it. The Mooney is flyable by a normal human in every phase of flight in every trim setting.

Not fun or comfortable, but doable.

This cannot be said for heaver airplanes.

I measured the force in cruise in my M20J with a spring scale. With full nose down trim it took 40 lbs to hold the airplane level. It's harder to rig a scale for measuring pitch up force so I haven't measured it but I was not able to get the trim full up before I couldn't apply enough force to keep the nose from pitching up in cruise. But you may be stronger that me.

[N201MKTurbo]

25 minutes ago, PT20J said:

I measured the force in cruise in my M20J with a spring scale. With full nose down trim it took 40 lbs to hold the airplane level. It's harder to rig a scale for measuring pitch up force so I haven't measured it but I was not able to get the trim full up before I couldn't apply enough force to keep the nose from pitching up in cruise. But you may be stronger that me.

Not easy.

[A64Pilot]

Slow down, it will get easier, trim pressure is often a function of airspeed so if lord forbid you had a trim runaway, slow down first, then pull the CB and trim manually

I don’t know squat about an Otter, but doubt the entire empennage moves like in a Mooney. I think that’s a Mooney thing, at least I’ve never seen it, but there are a whole lot of airplanes I’ve not dug into, Otter for instance.

I bet it’s more like a Piper Cub or airliner in that the elevator leading edge is moved up and down via a jack screw

[A64Pilot]

20 hours ago, PT20J said:

I measured the force in cruise in my M20J with a spring scale. With full nose down trim it took 40 lbs to hold the airplane level. It's harder to rig a scale for measuring pitch up force so I haven't measured it but I was not able to get the trim full up before I couldn't apply enough force to keep the nose from pitching up in cruise. But you may be stronger that me.

I know that was a Cert requirement in the Thrush and I had to measure it with a force gauge at both extremes of CG. FAA has a number that an average pilot can exert, I wonder if it’s any more accurate than the 170 lb pilot is though.

I used this thing

http://www.coolcityavionics.com/products/sfi/