This is an excerpt from a report made to the Aviation Safety Reporting System. The narrative is written by the pilot, rather than FAA or NTSB officials. To maintain anonymity, many details, such as aircraft model or airport, are often scrubbed from the reports.
On a training/currency flight with a private pilot/student, the Cessna 172 started pitching up slightly nose high. Pilot was adjusting trim, and at some point I told pilot that “you are adjusting trim wrong direction.”
Couple seconds later I noticed that pilot had trouble controlling airplane and I took over. Pilot confirmed that “trim is all the way nose down,” and I confirmed same after leveling airplane off, as well as status of autopilot and electric trim.
I asked tower to return to the field and landed on the active runway forcing controls down.
After landing, we found out that trim was actually moving wrong direction (and in fact was all the way “nose up”), due to mechanical issue/error.
Neither of us were aware of recent repairs being performed on the plane, nor need for a test flight.
I’m not sure about a chain of events leading to dispatching airplane as airworthy which must be grounded due to ongoing repairs.
Primary Problem: Procedure
ACN: 1804555
In Canada and other countries a dual logbook signature is required for primary flight control maintenance. This simple and effective rule can be applied without regulations by bringing someone to verify the work before sending an airplane into service that has had this type of work performed. It is actually better than bringing the A&P along for the test flight!
Incidents of reversed control connections keep happening but are infrequent enough to result in inadequate pre-takeoff checks. Don’t let that happen. Verify all controls and trim move in the correct direction 100% of the time.
CHAIN on 172 Elevator Trim Tab Actuator is all too easily installed wrong (flipped) on Cessna 172.
When removing actuator, I use a short length of safety wire on the upper leg of the chain to insure I get it right and re-Install it correctly. A black felt tip marker is a great aid too.
This is one of the very few “traps'” when working on a 172 that can bite you. GREAT AIRPLANE. I highly value its simplicity and durability.
REMEMBER – First flight after maintenance – No family on board and stick close to the airport, just in case…
From the report, it was the electric trim that the auto pilot uses, 2 – axis, which moves the elevator cables.
Part of the runup is to activate the auto-pilot and check the aileron and elevator servos….so, it was a poor/ incomplete systems check.!
With setting nose up, the control yoke should move back against the pilot’s pressure.
That action would have immediately shown a reversed wiring of the elevator servo.
The manual trim, as you noted, moves the trim tab on the elevator, a separate system from the auto-pilot servos.