Very scary moment

[flyboy0681]

Something very strange and extremely scary happened today that I'm hoping someone has already experienced.

 

I was taking off from Venice, Florida,  on a sightseeing flight with friends and about a minute after liftoff the controls started getting very heavy and the plane started to descend. I was struggling to gain altitude and pulling the yoke all the way back to no avail and then the adrenaline flush (not a pleasant feeling) set in. I looked to see if I was making power and everything was normal, I then glanced down at the trim indicator and noticed it was all the way in the full nose down position. I immediately grabbed the trim wheel and was able to level off and then continue to climb. The remainder of the flight was uneventful.

 

An hour later we returned to Venice and I dropped my friends off. For the trip home I did the normal run-up and tested the A/P. As I was taking off was extremely vigilant of the trim and sure enough about a minute after takeoff the wheel started turning by itself. I immediately overrode it by applying nose up trim and it instantly released its grip. The rest of the trip home was uneventful. 

 

As part of my checklist I press the A/P test button in the run-up area and everything looked fine - all lights illuminated and extinguished as the test Beep sounded. I'm assuming that the A/P, which is a KAP 150, was somehow still engaged even though all of the lights were out.

 

Has anyone else experienced this same hair raising situation?

[jetdriven]

I'm glad you detected this trim anomaly. A friend of mine was killed and a 3 million dollar aircraft was destroyed because the trim was wired backwards. This is not your case but I'm glad clear thinking took over and you didn't have more trouble.

[gregwatts]

One of the training items for my Learjet type rating was a runaway pitch trim. I actually had a pitch trim malfunction in a LR 24 leaving MIA once.........scared the hell out of me.

I believe you have a toggle switch on the panel to disengage..........also an independent breaker.

[co2bruce]

Good work diagnosing the problem and maintaining your cool. Your training came through. I would pull the breaker on th AP, until checked out.

[co2bruce]

Good work diagnosing the problem and maintaining your cool. Your training came through. I would pull the breaker on th AP, until checked out.

[rainman]

Had the same thing happen, it was the trim switch on my yoke. Had to replace the trim interrupt switch at the same time. Everyone in the avionics shop was sure it would be the autopilot servo to the trim that malfunctioned but it was not. At the moment it happened, I turned off the autopilot and the electric trim switch on the panel and hand trimmed it as it had gone all the way in one direction . I had an experienced instructor with me at the time and he helped manage the incident. Crystal Avionics in New Braunfels TX fixed it for me.

Ray

[flyboy0681]

Had the same thing happen, it was the trim switch on my yoke.

 

The switch doesn't make sense to me. I had set the takeoff trim manually and the switch was never touched, even after takeoff, and certainly not within the time-frame that this occurred. Then once corrected, it never happened again - until the next takeoff, at precisely the same time. If I had to guess I would say the A/P thinks its exceeded a certain commanded attitude and tries to correct itself by applying the nose down trim.

[flyboy0681]

One of the training items for my Learjet type rating was a runaway pitch trim.

 

To me this wasn't a classic case of runaway trim because by the time I noticed it, the trim was all the way to the stops. I always felt runaway trim was a situation that would be identified immediately and caught when the trim was still in transit.

 

I learned a few things by this, a major one being that I could still keep the aircraft flying with full nose down trim by use of an extraordinary amount of elbow grease, and that's not easy for this 130 pound weakling.

 

But the feeling was extremely unsettling.

[nels]

In a frantic situation such as this, could the auto pilot be disengaged by dropping all the electrical power including the alternator and let the engine run on its magnetos only?

Just a possibility that might work when you don't have time to analyze anything??

[fantom]

I've heard about similar Mooney trim issues with the KAP 150 before, and in both cases it was caused by a faulty split trim switch. If you fly it somewhere for repair be sure to have a finger on the AP disconnect switch and the AP circuit breaker pulled. Those interconnected computers will do very odd things!

[Dale]

Had something similar happen to me when my electric trim button got stuck and put the plane in a nose down attitude. Luckily I caught the problem quickly. Yours does sound more like an autopilot problem. You may want to disengage the breaker on the AP until you have an avionics shop check it.

[takair]

Typically, autopilots have a fairly robust fail safe when off. The failure would need to be at least two deep, autopilot still supplying power to the trim and the trim switch within the elevator servo being out of rig. You can try this, with the autopilot engaged on the ground.....with elevator held neutral, no trim.......push forward, trim runs up......pull back, trim runs down. If the trim always runs down, the switch may be stuck (this is the force switch in the elevator servo). My gut says the problem is not the autopilot, but the trim switch circuit. It may not be the switch itself, it may be chaffed wires in the yoke shorting in such a way that it commands full down. You can try moving the yoke around on the ground to see if you can duplicate the issue. I would suggest removing power from the electric trim until the issue is found. Might be time for the avionics shop to take a look. Glad you sorted it out fast in the air...many people do not.

[jetdriven]

We put colored collars on the A/P and trim circuit breakers.  You can find them fast with those.

[Dale]

We put colored collars on the A/P and trim circuit breakers.  You can find them fast with those.

I do the same. Invaluable when you need to quickly pull a breaker, especially in an emergency.

[flyboy0681]

I've heard about similar Mooney trim issues with the KAP 150 before, and in both cases it was caused by a faulty split trim switch. If you fly it somewhere for repair be sure to have a finger on the AP disconnect switch and the AP circuit breaker pulled. Those interconnected computers will do very odd things!

 

Pressing the disconnect would only work if caught when the trim was in motion, but by the time I noticed something odd it was full nose down. The question still remains, if it is the switch, why only during takeoff?

 

By the way, nice byline.  

[Bennett]

About 15 years ago I while at FL 230 I took a clear air lightning strike that among other things caused the KFC 200 trim servo to command full down elevator. Quite exciting! I did everything I could to turn off the autopilot: AP yoke disconnect button, tried CW steering to decouple, pushed the electric trim switch, turned off the autopilot on/off switch, and finally pulled the AP breaker, which I had previously marked with red nail polish. The manual trim wheel was free now. This process caused a 400' loss of altitude before I could climb back up to my assigned altitude. Murphy's Law in action. The ATC controller's "snitch" went off for an altitude deviation. Later I had "interesting" conversations with a Florida FISDO who would not transfer the "case" to the Bay Area, where I am home based. 13 months later (and over $10,000 in legal costs) at a hearing in Miami, a FAA appointed engineer concluded that 400' was within the certification of that autopilot for a runaway trim servo. I actually received an apology and a withdrawal of proposed action. The repairs for all the avionics damaged ran many thousands of dollars. I think that marking the AP breaker is a really good idea. I bought some plastic snap on covers for my current Mooney, but they don't fit, so it was back to red nail polish.

[bd32322]

In a frantic situation such as this, could the auto pilot be disengaged by dropping all the electrical power including the alternator and let the engine run on its magnetos only?

Just a possibility that might work when you don't have time to analyze anything??

Certainly possible in an emergency. Go back to pure hands on flying and then start pulling breakers. For IFR situations, this is where a handheld radio is critical.

Or just turn the avionics master off .. That way you can have electrical gyros running.

Anyway this is a good reminder for me to practise flying such scenarios. I normally turn OFF all autopilots on takeoff and landing however

[benpilot]

 

Wow glad you made it back ok that is scary! I don't use auto pilot as a student pilot but good to know what sorts of things to watch out for. 

[bd32322]

About 15 years ago I while at FL 230 I took a clear air lightning strike that among other things caused the KFC 200 trim servo to command full down elevator. Quite exciting! I did everything I could to turn off the autopilot: AP yoke disconnect button, tried CW steering to decouple, pushed the electric trim switch, turned off the autopilot on/off switch, and finally pulled the AP breaker, which I had previously marked with red nail polish. The manual trim wheel was free now. This process caused a 400' loss of altitude before I could climb back up to my assigned altitude. Murphy's Law in action. The ATC controller's "snitch" went off for an altitude deviation. Later I had "interesting" conversations with a Florida FISDO who would not transfer the "case" to the Bay Area, where I am home based. 13 months later (and over $10,000 in legal costs) at a hearing in Miami, a FAA appointed engineer concluded that 400' was within the certification of that autopilot for a runaway trim servo. I actually received an apology and a withdrawal of proposed action. The repairs for all the avionics damaged ran many thousands of dollars. I think that marking the AP breaker is a really good idea. I bought some plastic snap on covers for my current Mooney, but they don't fit, so it was back to red nail polish.

Wow! Curious to know how a 400 foot altitude deviation turned into a court battle. I am sure there are a few accidental deviations happening among the many aircraft flying.

[Bennett]

It turned into a fight with the FAA because there was another aircraft in the area that was below me by a thousand feet, and my altitude deviation broke the controller's required separation. At FL 230, i was IFR, as was the other aircraft. This was, of course, an emergency for me, and I told the controller at that time that I had an autopilot failure, but I didn't use the magic words: "I am declaring an emergency". Learned that lesson. A few years later I had an inflight emergency, squawked 7700, called LA center on 121.5, declared an emergency, and ultimately landed successfully. When I called the controller at LA center to ask her what paper work I needed to complete, she said: "You did your job well, I did mine. It all worked out the way it's supposed to. Have a great day". And that was it.

[carusoam]

Thanks for sharing that experience Bennett.

Best regards,

-a-

[flyboy0681]

An update.I went up with my partner today and we didn't experience the trim problem. However, about 5 minutes into the first of three takeoffs, we were level at 2500 ft with the autopilot off when all of a sudden it started beeping and the TRIM light started blinking. The only way to silence it was to pull the breaker. After a few minutes we reset the breaker, put the unit through its test and engaged. It flew perfectly for the rest of the day, including an approach.

[Super Dave]

Maybe I'm misunderstanding your description, but to me this sounds exactly like a runaway trim. A runaway trim is a runaway trim whether the pilot notices it in transit, or after it has reached full deflection. In any case, this sounds dangerous, and I would not fly the airplane until it is understood and corrected. You may have been able to overpower the trim in climb out at a relatively low speed; but what if it happens again at cruising or descent speed, or on short final.

[flyboy0681]

Maybe I'm misunderstanding your description, but to me this sounds exactly like a runaway trim. A runaway trim is a runaway trim whether the pilot notices it in transit, or after it has reached full deflection. In any case, this sounds dangerous, and I would not fly the airplane until it is understood and corrected. You may have been able to overpower the trim in climb out at a relatively low speed; but what if it happens again at cruising or descent speed, or on short final.

 

I fully understand what you are saying, and the gravity of the situation. We plan on taking immediate action on it.

[rbridges]

I'm just glad you're still around to tell us about it.  That had the potential to be ugly.