@T28 presumably that also applies to the 180 and 182 through C model?
Had not come across this design failing, which would also lead per forza to a mandatory AD requiring a proper engineering fix, not just an inspection.
LeSving wrote:
Does anyone know of any accidents where the elevator control linkage failed?
I know of a now-certified aerobatic type on which the elevator pushrod design was changed from carbon fiber to aluminum after an in flight failure, after which the pilot landed it successfully! I can’t remember whether the particular plane was in the now-certified configuration, I suspect not, and the subsequently built certified planes do not have this issue.
I know of another one, experimental category, due to a construction error and aerobatics. link
This one, also occurring during aerobatics in an experimental category aircraft, was apparently due to a fatigue related aileron control failure. link
@T28 presumably that also applies to the 180 and 182 through C model?
Presumably. The (trim wheel attachment to chain sprocket) design was changed in 1985 (i think?) moving from roll pins to rivets. There’s also thicker roll pins around to replace the original ones. Thread stripping on the jackscrew has also well known (& recorded) in-flight consequences that were “fixed” not with an AD but with an added friction part.
From a Cessna book:
As the airplanes aged in rough service, we received reports of stabilizer slippage in high-speed letdowns. To our amazement the two “irreversible” jack screws that supported the stabilizer were slipping in an airplane-nose-up direction. In production flight tests at redline speed, this produced an alarming “g” load, pitching the nose up vertically. On one occasion the test pilot blacked out momentarily and the wings received a permanent set of 50 at the strut/wing juncture. We were unsuccessful in reworking the jack screw tolerances, and the decision was made to add a friction device to the longitudinal trim wheel mechanism. This produced a “ratcheting” noise in the cockpit and increased the force required to make trim changes. However, it solved the stabilizer slippage problem, and the device remained on the C-180/185’s throughout the production run.
The combination of the roll pins croaking and the “friction device” not frictioning is not a happy combo.
T28 wrote:
we received reports of stabilizer slippage in high-speed letdowns. To our amazement the two “irreversible” jack screws that supported the stabilizer were slipping in an airplane-nose-up direction. In production flight tests at redline speed, this produced an alarming “g” load, pitching the nose up vertically.
I have had this happen once during a 185 floatplane test flight. The spring loaded detents which run on the trim wheel, and make the click click sound were not adequate, and the trim wheel ran away. I was able to grab and hold it while I slowed down. I reported the maintenance snag for a new spring loaded detent part to be installed. It was the same part as those in the wing root fresh air vents. The airplane did pitch up pretty rapidly!
“I certainly don’t want to second-guess you, but wasn’t that noticeable at the “controls full and correct check” before take-off?”
It should have been. It wasn’t. I checked movement moving the stick from outside, looking at elevator. Then I got in and checked full and free movement, sitting on and squashing cushion. I thought I had full movement. Landings smooth but not 3-pointers. But the two of us who flew her on the tests were out of currency after a long repair job. It took several landings to realise 3-pointers were impossible.
LeSving wrote:
Does anyone know of any accidents where the elevator control linkage failed?
The Piper Comanche suffered from some trouble with the stabilator control. In particular, the stabilator horn seems to have cracked on some planes, where the control is not linked anymore with the stabilator control surface. You need to know in such a moment that you can still have control with the trim. This is not related with the “other” stabilator problem of the Comanche, that it may flutter in (too) high speed (the Comanche once was released for more than 200 knots indicated).
In fact, both problems are well under control nowadays and there have been placed speed limitations to cure flutter and an AD to check the stabilator horn for cracks every now-and-so-often (5 years).
That’s one thing I actually do like in old planes. Most of the things which can go wrong have already been found by someone (else). And most if not all trouble which relates to age of the plane does not or only partly affect safety.
The A-UPRT course devotes some time to practising control restriction in the different axes, and being able to turn and manage climbs and descents. While a contrived scenario, it does demonstrate that with patience, small remaining control inputs and trim inputs, controlled flight can be re established.
Does anyone know of any accidents where the elevator control linkage failed?Quote
Air Moorea Twin Otter many years back:
