Menu Sign In Contact FAQ
Banner
Welcome to our forums

In case of loss of stabilator control: using trim control?

As I’m just technically into the mounting of the stabilator (having taken it apart) I came across an interesting remark in a maintenance manual part. If stabilator control was lost, it is possible to gain a (however limited) control of the stabilator by the trim mechanism.

I carefully reviewed this possibility on my aircraft and can confirm, that at least on my aircraft the trim is actuating practically independent on the stabilator. The stabilator is held in a neutral position by means of a big spring and counterweight, so control from the yoke may even be disconnected at all and stabilator will be kept in more or less neutral. So with a blocked yoke or broken steel cable stabilator can still be adjusted quite a way by means of the trim mechanism, which acts on the stabilator by means of the trim tabs.

I never really gave it a thought about what options you’d have with a loss of stabilator control and instantly realized that I’m not sure if I would have thought about the trim in such a moment. Flaps and engine power are more obvious options, but far less sensitive. Will evaluate on that a bit on the next flights to get a feeling for the extent of pitch control.

This maybe won’t count for any aircraft, as I’ve flown aircraft where trim control is not involved like this (e.g. in gliders) but as some sort of redundancy will most probably be true for a lot of the “touring aircraft class”.

Also noted, that left and right aileron are separately connected to the yoke, so loss of one aileron control will not result in a near-to-total loss of control about the roll axis.

All that surely raises confident level for me. Didn’t know that before. And wanted to share this, as maybe I’m not alone.

Germany

yep, good to know… if that works on your aircraft… and if it happens, sure could save the day

A seldom occurrence indeed, having read quite a few occurrence reports, most case are more difficult, such as blocked elevator… loose counterweight, tooling forgotten, broken control stick, etc. Alternative control is a good thing.

Life's short... enjoy!
LSZF, Switzerland

When I did my PPL, on C150, my instructor taught me to land using for pitch control only power and trim. You need a long runway so you can flare smoothly, though. That will only work in case the failure is the breakage or disconnect of control cables or something similar that leaves the elevator free to move.
I also remember having seen somewhere that a jammed elevator on conventional aircraft will still allow some pitch control using the trim reversed, but I dont recall that being a POH!
All high-wing cessnas will lose both ailerons with most major mechanical failures or most control disconnects in one system (except the final rod from wing quadrant to aileron). They are however quite reasonable to control laterally feet-only. My instructor also taught use of open cabin doors for lateral control, but that is not really required.

It is amazing the POH in the Comanche mentions such backup!

Antonio
LESB, Spain

Nor surprisingly, these tricks work just as well in a C172. Did it a few times at Son Bonet, and easily stopped her within the thresholds at Son Bonet (1000m). In a C182 or other Cessna’s it would also work or not?

Last Edited by aart at 09 Jun 12:31
Private field, Mallorca, Spain

Antonio wrote:

It is amazing the POH in the Comanche mentions such backup!

No it’s not in the POH. I found it in the maintenance manual. One thing more to note, that the maintenance manual of the Comanche is meant to be read by the enthusiastic owner

Germany

Antonio wrote:

My instructor also taught use of open cabin doors for lateral control, but that is not really required.

Did those things too, in a 172. But pitch control was always about power and flaps only, and praying that stabilator will stick in place.

It’s true that the use-case seems to be quite small. E.g. stuck cables will block the stabilator. So it’s really condensed to a cut or broken wire, or any other sort of disconnection. If anything is blocked in there, you won’t override it with the thin trim cables against the rather thick cables from the stabilator control (yoke).

I was concerned a bit about this very topic due to the requirement to check for cracks in some parts of stabilator connection of a Comanche. But even in the event that the fixation of the stabilator should break then you still can have control with the trim.

You know, I’m flying for practically all of my life, and the only thing I would fear is loss of stabilator control because there seemed to be no option left. But now there is.

Germany

Stabilator equipped aircraft like a Comanche are often particularly good in this regard.

It’s a certification requirement that this be possible for small GA planes:

23.145
…..
“e) It must be possible, by using the normal flight and power controls except the primary longitudinal control, to control the descent of the airplane to a zero rate of descent and to an attitude suitable for a controlled landing, without exceptional piloting skill, alertness, or strength, and without exceeding the operational and structural limitations of the airplane.”

Home runway, in central Ontario, Canada

I’ve tried flying Jodel DR1050, Pa38, and Bolkow Junior on throttle, rudder, and trim. (The Pa38 is probably pointless, as the trim is a spring.)
I didn’t land, going to normal controls at round out. But the landings would be survivable, although not good.
The Jodel needed high airspeed to round out, and would have been a very fast landing, with resulting tailwheel problems.
I’ve flown the Jodel from east to west Scottish coast and back on only these controls.
Following a C of A inspection, before becoming LAA Permit, after flying back to Inverness, I found the controls did not allow this flying, until we had them adjusted.

Maoraigh
EGPE, United Kingdom

There’s a longer version in his book, but here’s the Barry Schiff article Look Ma, no elevator, which also references Look Ma, no rudder

Key points: only one cable out of the pair might be broken, and you need to have the trim quite far forward to then be able to trim back and flare

EGHO-LFQF-KCLW, United Kingdom
12 Posts
Sign in to add your message

Back to Top