UdoR wrote:
William, just wanted to thank you to point that out. I haven’t had that potentially critical error mode in mind. In a Comanche that is even more important, because of the stabilator design, there is a huge amount of force on the yoke if you want to play against trim. I’ll investigate on that ASAP to stay “ahead of my aircraft”.
Piper made such a range of aeroplanes, and each of them had slightly different systems. There are some Piper Aircraft that have a trim disconnect under the yoke, and in other aircraft, the same button in the same place is for Autoflite II. You are right to make a note of it, and the associated circuit breakers. For the price of a cup of coffee, you can mark the relevant circuit breakers.
https://skygeek.com/dance-air-10164-5-circuit-breaker-collar-red.html
WilliamF wrote:
In a Piper Electric Trim run away you must either turn off the master or pull the Circuit Breaker.
William, just wanted to thank you to point that out. I haven’t had that potentially critical error mode in mind. In a Comanche that is even more important, because of the stabilator design, there is a huge amount of force on the yoke if you want to play against trim. I’ll investigate on that ASAP to stay “ahead of my aircraft”.
[Thread drift warning: pertinent but drift nonetheless]
WilliamF wrote:
a hugely important safety item
To add some colour, I had two instances of a trim runaway on our Cessna P210. Both due to an intermittent autopilot fault which took some effort to troubleshoot.
On the first occasion the aircraft pitched up wildly over 2G’s before I caught it by pushing on the yoke (see note below) and then the trim disconnect switch. Because of the interconnection between A/P and electric trim on our aircraft, they cannot always be activated/deactivated in the same way depending on autopilot engagement. However, someone at Cessna was thinking clearly when they positioned both A/P disconnect switch and trim disconnect switch next to one another on the yoke itself, in a way that a single flip of your LH hand fingers can disconnect both.
On the second occasion I was half-expecting it after some troubleshooting and turned it off before any harm was done.
Things could have gotten extremely serious had I not been previously aware of these two switches and their functions. Not only had I before flight become deeply familiar with the POH and the intricacies of the variations on our particular airframe, but I also enjoyed a huge luxury worthy of the makings of our Lady of Loreto or perhaps our Lady of Czestochowa who I had been worshiping in situ shortly prior to the incident (or by coincidence if it makes you feel any better):
While I was acquiring the aircraft in Carson City Nevada, I bumped into this wondrous and Christian human soul of a person: the late George Clary, an ex-NASA aerospace engineer , FI, A&P with IA. He offered to do a few hours training with me on the aircraft before I went on my own. Some of the most beautiful pieces of flying I did in my career, around the SW USA. He had this test-pilot mentality of understanding all systems in hand and showing how each one can kill or save you. He later even went on to hangar and look after our airplane for months while I was back home until we could ready it for our epic first transcontinental then transatlantic ferry to our home island….but that is another story. I will never be able to repay George enough.
I was solo with a non-pilot friend at the time of the first trim runaway incident. Had it not being because of George’s generous training, maybe our beloved 210, but perhaps worse, my human body, and even worse still, that of my accompanying friend would now be but yet another mangled heap of metal and flesh on the desert of the Western USA.
BTW I happen to be an aerospace engineer myself and did have a short stint on flight testing in my younger days. I will never again underestimate the importance of putting myself in a position to learn from others…climbing onto and standing on the shoulders of giants…
So kudos to you for engaging in this forum, but I am sure there are also people who you can use for guidance or even just APOE around your place!
Mooney_Driver wrote:
what the Boeing Max folks thought as well
Well it could be read as if Boeing did not build a trim disconnect switch into the Max…not only does it have very prominent trim wheels that are impossible to miss when automatically activated, but also two pedestal trim disconnect switches: in case of doubt you can activate both (the difference between one and the other vs prior 737 variants was source to some discussion during the Max accident investigations). Needless to say in neither of the accident aircraft the trim was disconnected before things got too far out of hand.
APOE= another pair of eyes
(note) Usually when exerting force in pitch on the yoke on an aircraft with autopilot and autotrim engaged, unless in CWS mode, the autopilot will start trimming against you , making things really bad in a matter of seconds. So the "yoke overpowering " option may only work for a very short time until trim overpowers you…the solution is a disengagement of the system, then manual trim until you, first, regain control of the aircraft and then, perhaps figure out what was going on.
Yes, that is the one. If you push that button, electric trim should be disengaged. You might want to try it once on the ground. I thought it’s actually part of the checklist.
Mooney_Driver wrote:
That is what the Boeing Max folks thought as well. Nope, it is very critical indeed.
Ok! Point made! I promise I will take the advice on it seriously.
WillamF wrote:
In a Piper Electric Trim run away you must either turn off the master or pull the Circuit Breaker.
I am not near the aircraft now, but there is in fact a white rectangular button below the yoke and here’s what my POH says:
Antonio wrote:
There should also be a trim disconnect pushbutton switch under the yoke or thereabouts on the panel…is there not? Make sure you test it and it does work. You only have seconds to activate it in case of a runaway before things go out of hand.
Not being pedantic, it’s just such a hugely important safety item. The red disconnect button on a Piper Autopilot disconnects the autopilot, not the trim PET system itself which is constantly energised. The old Piper Autopilots had a yellow annunciator light that lit up when the trim servo ran continuously in any altitude mode. The disconnect button on the yoke only disconnects the autopilot.
In a Piper Electric Trim run away you must either turn off the master or pull the Circuit Breaker.
The information on them is hard to wade through, but in effect, you could end up with 3 systems on board you need to read up on -
1) Piper Electric Trim (PET)
2) Piper AutoFlite (Single button Wing leveller – marketed for emergency/partial panel situations)
3) Piper Autopilot
Mateusz wrote:
I think it is probably not too critical (the electric trim is easily disabled by popping out a circuit breaker).
That is what the Boeing Max folks thought as well. Nope, it is very critical indeed. If your trim goes all the way down or up while you are low altitude, it’s one of the worst things which can happen. Forget about finding the CB, you never will if you are pulling with both hands you can also not reach it. If anything, use the cutout switch under the yoke.
Antonio wrote:
There should also be a trim disconnect pushbutton switch under the yoke or thereabouts on the panel…is there not?
On this pic, I think I can just about spot it.
Mateusz wrote:
the electric trim is easily disabled by popping out a circuit breaker)
There should also be a trim disconnect pushbutton switch under the yoke or thereabouts on the panel…is there not? Make sure you test it and it does work. You only have seconds to activate it in case of a runaway before things go out of hand.
Peter_G wrote:
Has anyone shown you how easy it is to take out either or both of the back seats?
Thank you for your warm words, Peter_G. Yes, a while ago I’ve read that you can remove them without using any tools and figured it out myself. It’s brilliant! This time it made sense to use the seats as a separator between two “luggage compartments”. But I may have use cases for removing them.
The other ‘improvement’, which I can’t be certain does what it says on the tin, was to fit a ‘Black Magic’ Waste Gate.
So yours is Turbo, isn’t it? Just for the record, mine is a normally aspirated example.
WilliamF wrote:
That trim switch on the yoke looks like a regular off-the-shelf switch, and not an OEM one.
That is a very valuable comment! Would never have learned about it. Thank you. I think it is probably not too critical (the electric trim is easily disabled by popping out a circuit breaker). But I am adding it to my ‘pending’ list of issues to be addressed sooner or later.
