I had a trim failure yesterday when flying from Sabedell back to The Netherlands.
Flight was with a DA40 at FL180 with OAT of around -25 ºC.
The trim wheel was slipping; I could turn the wheel but no difference in trim setting.
The aircraft was still trimmed for the climb, so a lot of pressure was needed for the enroute / descent phase…
I was with a second pilot so we decided to continue hand flying. I would not have done that if I was flying alone…
When we descended in warmer air, the trim magically started to function again :)
My suspicion is that there is water in the trim cable, which is freezing up when flying at a high altitude.
Is this a known issue? How can it be prevented? Aircraft is always parked inside so you don’t expect any water in the aircraft…
Almost certainly a case of dodgy maintenance and the wrong lube squirted in there, like I got on this trip, right after an Annual.
Dodgy maintenance is a widespread issue, and wrong lube even more so because 99% of clients will never discover it.
In my case they used a locally made motorcycle lube, with no known temp range. I phoned up the mfg and they said they have not had any complaints in 25 years.
The problem is that you now have a bit of work to get the old gunge out of the trim jackscrew mechanism
Mine took all day to do, two of us, in a rented hangar.
There are also airframes where a blocked drain hole can cause water to accumulate sufficiently to create a massive block of ice which encloses the trim. I know of a PA46 incident where this happened. I would think the required amount of ice to reach the required height was 10s of kg.
Indeed Peter, this is a known issue in the PA46; John Mariani, who took part in the design, testing and initial instruction on the airframe, was almost killed by it himself and advises widening the drain holes. When I had it done on mine, sludge ran out of the holes for a few minutes.
However I’m surprised that in this case the trim wheel was travelling at all?
I had that too in the Warrior … the trim practically froze! It’s almost always wrong lube, just as you said!
The trim system on a DA40 is completely different that that of the PA46.
The trimwheel has a slip clutch on the DA40, so either the clutch was adjusted wrong (to low) or your trim was actually stuck. Did you get it going after landing? Be sure to have this checked. Have seen incorrect clutch settings.
Cable should not be lubricated
I got response from the maintenance company that no lubricants should be used for the trim cable.
Might be the slip clutch indeed, like Jesse suggested. After landing the trim was working fine. Already in the descent the trim started working again, so it must be temperature related…
Temperature could have an effect on cable tension.
It could be that something froze and blocked the trim cable, as Peter suggested, it would have that effect on the clutch.
The lubrication in the Diamond range of aircraft is clearly stated in the AMM, my guess is the wrong lubricant is was used or was displaced by water.
While away form the manuals I can’t say exactly what is required in the trim system but I know when we got the Diamond maintenance aproval we had to sorce a number of lubricants that we had not used before and one of these was an oil with a very low temp operating range.
The trim cable one the Diamond’s I know should NOT be lubricated, it is “maintenance” free.
The diamond manual specifies a small number of items to be lubricated, and quite some that should NOT be lubricated.
