Trim/ Autopilot Disconnect.
 

Just reading some articles on accidents in a 310 and Aero Commander. Incidents like trim runaways and autopilot malfunctions are not really highlighted in Flight manuals.

• Any advice on how to handle them should they arise ?
• Are there CB’s that can be tripped on these aircraft to sort the problem out?
• If CB’s were not immediately handy, would electrical isolation do the trick?

The big red button on the yoke will do it...... so will the CB.
some even disconnect when a certain amount of resistance is used to overcome the auto pilot. also some will disconnect when you use the pitch control on the autopilot when its still in alt hold, and useing the electric trim on the yoke will disconnect some as well.
I would suggest reading the information contained in the manual that comes with the aircraft. they all have their own little differences and quirks.

Disconnect.
 

The BIG RED BUTTON is the obvious disconnect. Also some resistance can have the effect of the AP trimming the other way, so when it does disconnect you can have a lot of trim in one direction.

If things were going really pear shaped and it was near impossible to disconnect the AP or stop the trim runaway, would disrupting the electrical power by switching off the generators and battery momentarily have the same effect? I am talking about this as a last ditch effort to remedy a bad situation.

I believe a force of 40 pounds should disconnect an AP, however I have not seen it written any where.

Completely dependent on the autopilot fitted to the aircraft you fly, they are all a little different so best be clued up on what you have in front of you.

One good piece of advice for all autopilots and trim systems is to hold on to the stick TIGHT when disconnecting. Have had first hand experience of what can occur if you dont, and it took weeks to clean the mess off the seat!

DO NOT ENGAGE an autopilot until you have identified at least 3 separate ways of disengaging same!

Dr:cool:

Good medicine there from the Dr.

1. Batt & Generator (or master as applicable) switches OFF
2. Avionics master OFF
3. Disconnect on yoke
4. OFF switch on autopilot control panel
5. Autopilot C/B Although might be hard to find in the dark in a hurry.

Very much depends on the type, some will disconect with excessive outside influence from the pilot or turbulence.


200

Just adding to TwoHundred's list:
6. Operation of electric trim with autopilot engaged.
7. Overpowering autopilot with force, some up to 80ish pounds I believe, but varies with make.
8. Failure of any one of many inputs (ie: ASI, VSI, Altimeter, etc..).

Cheers, HH.:ok:

You guys actually fly aeroplanes that have serviceable autopilots.
No wonder you're all so nervous about how to switch it off. :E

Know your aircraft and the operating systems. ALWAYS be able to identify the A/P CB. I noted in my long career as a CFI that there wern't too many pilots who knew this or performed a ground check of the A/P and slipped the clutches (if appropriate) before flight.

PA39

".... there wern't too many pilots who knew this or performed a ground check of the A/P ...."

Yes, PA39 you are correct. I was going to add that to my earlier post.

The Century III in my Bonanza performs very well, with no surprises if I carry out the correct pre-flight, on the ground, before use .... but if I don't (you know - in a hurry, by myself), the excursion when I hit the on-switch sometime on climbout can be interesting to say the least.

Dr:cool:

Yes, live (hopefully) and learn (hopefully)!!

Years ago and before auto disconnect, I had test flown a Chieftain with an altimatic 111 which had just came out of the avionics shop for A/P repair. I took it to 6000 and engaged the A/P. The darn thing rolled nearly inverted so fast that I was left upside down and clambering for, and trying to find the CB....the "push for off" button didn't disengage the thing. I certainly wasn't at 6000, and completely disorientated by the time I recovered. Scared the duds off me!! That was an easy 20 yrs ago, and you know, every aircraft I flew from that day on, i identified the location of the A/P CB and if I had an off sider I would ask him or her to identify and confirm same and ALWAYS added the A/P ground test to the checklist if need be.

Some of the S-Tecs are so good they quickly pick up the yaw of a failed engine, and the pilot (usually under test) doesn't become aware that he has lost one until he realises the decay in airspeed and climb performance !!

Hmmmmmm! This is a valuable thread. I was always taught to test the AP and the disconnect switch but I never quite understood exactly why it was so important.

I know about electric trim runaway and always check the on/off switch operation, but I've never thought about finding the circuit breakers and seeing if using the electric trim disconnects the AP.

Recent incident in a CRJ - a good read :ooh:

Just to add another disengage method -
engage the go-around mode (wrt my type).

Also worth knowing when your system decides to disengage automatically

- interruption / failure of electrical power
- depends on system again in my case the vertical gyro failure
- flight control system power or cb failure.

As an aside lots of suggestions from POH re engine failure and prop rpm during ILS coupled approaches may be lurking in your notes.

Muff

Trim runaway
 

I once simulated an electric trim runaway in a Partenavia. You can only just hold it, using two hands on the yoke. You would not be able to do anything else.

I have vague memories of a fatal Partenavia crash due to a mis-set or runaway elevator trim. Maybe somewhere around the Whitsundays???

Anyone remember?


200

Beware Chieftain trim runaways as I have and many other PA31 pilots have also had the fun of experiencing.

Some are quite friendly and just need the AP disconected (gives the passengers a quick negative feeling sometimes). Others just require the CB pulled.

OR . . .you will be nose up in the vertical about to roll over the top above an international airport before you work out the CB/Master/Disconect does nothing, you then break the trim wheel/cable by hand, push over the top with 9 "white" blackfellas in the back screaming and your pants are a new shade of brown.
You land with some wobbly arms and swear never to get back in one again when you know you will be back up again 2morrow. Story was the trim wires under the left trim switch had fussed/burnt themselves together and caused their own electrical system?....fun days they were?

OR . . .as a few others have learnt, if the trim is in the full forward position and you realise at rotate and dont know why it wont fly and dont have the strength to pull it off, its expensive.?:ugh:

RW

Lockheed 18 trim runaway

45 years ago! When do we learn?

200
 

If that is the accident I remember, it was a takeoff aborted too late due to a mis set trin, or incorrect loading, which resulkted in a heavy nose.
The real problem was indecision..