Yesterday we made three training flights. A broken to overcast cloud coverage in about 4k and about 2k feet thick contained a lot of snow, including some snow showers. Temperatures were below zero, around -2°C, at ground and down to -18°C at FL80. While we didn’t load any ice on the airplane I got quite surprised that my governor was stuck inoperative after passing the clouds. I could lower RPM fromm 2700 in climb to 2500, but not lower. The lever could not be moved any further.
During approach on glideslope the governor became operative again and all was fine.
On second flight we moved the governor every now and then during climb and it had an effect in that we had more of an operating range when we arrived at cruise level FL80. I could lower RPM after climb to around 2300, but – again – not lower. So it was normally operable in between 2700 and 2300.
On third flight albeit again we climbed through clouds to FL80 we had no trouble in setting cruise RPM.
Has anyone had this?
I typically cruise at 2200 or lower. Maybe nobody got aware of that because nobody lowers RPM after climb enough to encounter anything?
And: may that have a technical reason? Maybe wrong lubrication of the linking rod or the like? I want to know whether I can do anything to prevent this from happening. My governor is sitting right behind the nose opening. So the rod is in fact very exposed and it could be that ice is melted in the opening and freezes again on the rod.
Any thoughts?
I would have expected RPM to drop with iced up propeller or governor?
Did you recycle hot oil on the ground from, say, 2500rpm? how low it went?
Also, one can get iced spinner or governor on the ground if you were parked outisde, make sure you visually check it (or frozen milkshake on engine start)
Ibra wrote:
I would have expected RPM to drop with iced up propeller or governor?
I didn’t have visible ice, not on the wing and persumably also not on the prop. It was just stuck. I didn’t think about the oily part of the governor.
I was more of sort thinking about that part of the governor underneath the cowling. But on a third thought the idea about recycling hot oil is interesting. Of course I cycle the governor prior departure, but never considered this for warming up the governor, but for checking its operation.
Edit: Re the question how low went the RPM on ground: per AFM RPM drop should not exceed 400 RPM. So I don’t check the “how low”. I check that RPM drops and that it raises again to the initially set value. Adjustment of the governor on ground was as usual.
Another edit: to make that clear: we had no visual ice. The aircraft was parked in a warm hangar and after landing no ice was on the spinner. So nothing got iced up. Just frozen.
What engine is this?
If hydraulically operated, this is serious.
UdoR wrote:
we didn’t load any ice on the airplane
Points to water freezing up in the control cable… if that is the case, solutions are to service the push-pull control, or replace it.
Or not to fly in that cold an atmosphere 
Dan wrote:
Points to water freezing up in the control cable
Interesting thought, thanks for sharing. At the moment I can’t imagine how that could be in the cable, because that is a steel wire. But I’ll have a look.
Peter wrote:
What engine is this? If hydraulically operated
An IO-540. The control is moved by a steel wire that connects to a linking rod. The governor part in the nose is fed by engine oil. Do you mean this by hydraulically operated?
Well I had the feeling that it had to do with the control rather than the oily part. But the only indication was the stuck lever. This is why I thought that the linking rod could have been iced up.
It was really cold yesterday. I flew in such cold air before, but this was high up, where due to prop efficiency I don’t reduce RPM that much and did not notice anything. So I cannot tell whether this is something new.
This is somewhat similar but he doesn’t report a sticky cable. The OP never reported on the outcome but I heard years later from someone that he found the crankshaft cavity bunged up with debris!
If your governor lever cannot be physically moved then it sounds like debris. I would have it immediately overhauled by a competent company. If they find debris, then you should remove the propeller and take a look down the crankshaft.
I reckon that if you have debris in the governor, you should be able to feel something if you disconnect the control cable from it and turn it by hand.
The control cable could have water in it which froze up. Very possible. It is a flexible steel cable running inside a sleeve which is nylon or PTFE. On most types the front of the cable is exposed and can get water in there.
@Peter I don’t think it’s something physically broken. The governer per se is fine. It’s working flawlessly in normal temperature regimes. Always on the spot, it holds the RPM very accurately, and the lever operates easy and smooth. On the third flight and now it’s working fine.
The issue only was with the very low temperature or maybe included ice.
I’ll check the control cable or let it have checked.
There could be water in the governor too.
I would just get it overhauled. It is easy and not expensive.
The control cable could have water in it. The details will depend on the design; I don’t know yours. I do know it is difficult (but not impossible) to get water into the Socata pitch control cable.
Sounds indeed like moisture somewhere that is freezing. It’s a common thing and a good reason to change/service cables in particular. Moisture in the governor itself? It’s probably possible, it uses engine oil, and water/ice in the engine oil and oil lines is much more common than one night think, and the result could be disastrous. A Cap 10 (if I remember correctly) had moisture turn into a solid block which destroyed the engine in flight due to blockage, some years ago.
If you keep it in a warm hangar, this shouldn’t happen, so it’s probably something else. Water in the cable/wires, if that is possible on your plane, could be it.
