Primarily for general aviation discussion, but other aviation topics are also welcome.
By Lefty
FLYER Club Member  FLYER Club Member
#1709826
Flying a number of different aircraft, I have noticed that there appears to be no standardisation in a/c checklists - as to whether the electric trim (and / or autopilot) should be selected off - or on for takeoff and landing. (but particularly takeoff)?

This all started when I queried a student for trying to take off with the electric trim on - until he showed me the club checklist - that said "Elect Trim - A/R"

Since then I've been looking more carefully at the different checklists - and I've found different checklists that say "electric trim off", "electric trim on" and "electric trim A/R" prior to takeoff.

Maybe its an old fashioned thing (emphasis on "Old") - but I was always taught that in light GA aircraft, - and in all single pilot operations, that both electric trim (and autopilot) should be off for takeoff - and when below 300ft on landing. The rationale being that you would probably not be able to retain control of the aircraft in the event of a "pitch runaway" problem.

Are newer systems that fail safe that they can safely be left on? I think not.
(please - no one mention the 737Maxx - that's a whole different discussion).
#1709828
I can't think of a reason why I'd want it on. Just seems like something else to go wrong and that I'd have to turn off if there was a problem with it.

Querying the 'as required' justification for switching it on, why would anyone require it on? Or do we read 'required' as 'desired'?
By Lefty
FLYER Club Member  FLYER Club Member
#1709837
Flyin'Dutch' wrote:Off, unless POH says different or there is no off switch (Cirrus)


To be fair, the Cirrus doesn’t have a manual trim, so you have have the electric trim on. However their POH does say Yaw Damper and A/pilot off below 300ft.
By Lefty
FLYER Club Member  FLYER Club Member
#1709840
Staggering wrote:On if it is a G1000 equipped Cessna with a KAP140 or GFC700 autopilot as there is no power off switch.
Being able to keep one hand on the yoke and one on the throttle and still be able to operate the trim seems quite useful.

I’ve never seen a Cessna single without a manual elevator trim. They might exist, but I’ve never seen one.

I assume you can still select a/pilot on or off (eg you can still fly the a/c manually without the a/pilot). If the a/pilot is off, then surely the a/pilot driven pitch trim is also off? Certainly that is the case in my mates’ G1000 equipped C172 and 182. Or am I wrong?
#1709846
Yes they still have a manual trim but you have to take your hand off the throttle to operate it. A minor point I guess but my thinking is that you can ensure you have full throttle, control the aircraft and operate the trim at the same time.

You can select the autopilot off, and it should be off for take off, but the electric trim is still powered and uses the autopilot servo's.
By Lefty
FLYER Club Member  FLYER Club Member
#1709850
Staggering wrote:Yes they still have a manual trim but you have to take your hand off the throttle to operate it. A minor point I guess but my thinking is that you can ensure you have full throttle, control the aircraft and operate the trim at the same time.

You can select the autopilot off, and it should be off for take off, but the electric trim is still powered and uses the autopilot servo's.


If an electric trim system is “On” (powered up) - then it could suffer an electrical or electronic failure that cause the trim to run to maximum deflection - either up or down. (Known as a “trim runaway”). If this occurs at low level - eg below 300ft, then it will almost certainly result in a very serious accident.

The only way to mitigate this risk is to not have it powered up (when at low level).
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By PeteSpencer
FLYER Club Member  FLYER Club Member
#1709852
Electric trim off for takeoff every time in our arrer.

Interestingly the checklist says 'Check trims (both)' long before the master goes on: I've never felt inclined to flick the master on then off just for this item so I check electric trim once master is on and everything cooking nicely.

Peter :wink:
#1709853
In my Cessna, the electric trim as operated by the pilot, is independent from the autopilot, so can be used at any time.
The electrical cut-off is on the Yoke, next to the A/P disconnect, so I've never considered turning it off before.
I have actually considered it, I just ended up being happy to leave it on and rely on the disconnect close to hand.

It is of course possible that in the heat of the moment (more critically take-off)
I could be distracted enough to not recognise the cause of the issue and be in trouble, but there are so many variables to flying that each person has to choose a point where their personal risk level meets the practicalities of flying at all.
Staggering, 2Donkeys liked this
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By Dodo
FLYER Club Member  FLYER Club Member
#1709867
I check the electric trim is off for take off and landing in our group operated PA-28-181 (though it is not unusual to find it has been left on by a previous user so presumably we don't all do the same thing.)
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By Murgatroyd
FLYER Club Member  FLYER Club Member
#1709877
Looks like there’s a good consensus and reasoning for not having the electric trim on at these times. I switched mine on a year and a half ago... and haven’t switched it off since. There’s no mention in the checklist, but it does refer to the auto pilot off.
I’ll make a note in my checklist. !