My plane has a similar situation in the aft fuselage, and even with the clevis pin oriented correctly it’s a close clearance as it passes by the last fuselage bulkhead.
Also on my plane the aileron controls for each wing include two bellcranks on top of each other, one on the wing and the other on the fuselage, engaging with each other in a way that allows the wing to come on and off without touching the control circuit. The pivot bolts for each bellcrank are installed co-linear with heads facing each other, which allows the bellcranks to sit closer to each other without the bolt heads touching. The pivot bolt on one bellcrank therefore has to be installed head down, the opposite of normal practice. Since the wing is off when this is done the correct upside down configuration is not intuitive or visually obvious – by design this setup relies on the nut and cotter pin (or safety wire) to prevent that bolt from falling out. If you install the bolt the other way, the head of one bolt touches the end of the other after you install the wing, slowly abrading both bolts. I don’t think it would wear to the point that the head or nut of one pivot bolt would fall off but you can bet that I corrected this situation when I found it misassembled on one wing, where a previous mechanic had worked a few years before. The other side has likely never been apart.
Over a period of years one finds things like this on a plane, learning as you go and hopefully correcting all of them before they cause a problem.
I personally always look at flight control hinges and actuating bits on every one of my pre flights. This is admittedly overkill for an owned aircraft except after relevant maintenance, but should be default practice on rental aircraft.
I always stress installing bolts, nuts and washers with the p/n and in the way depicted in the IPC. I sometimes use pre-disassembly pics for ref, sometimes the IPC figure itself. Most of the times there are few implications, but not always. Admittedly on Cessna+Piper IPC’s there are sometimes errors and you cannot install it in the depicted way, but that is the extremely rare exception vs the norm.
I have made the mistake of not doing it a few times with the result that the assembly could not be completed or installed with sufficient clearance to moving parts etc. Even once our mechanic installed too long interior decor sheet metal screws with the result that the pilots knee was pushing the end into an adjacent wiring loom tripping a CB every now and then. Took ages to figure out what was causing it…
You are the maintenance expert and not me, but the fact remains that the bold was mounted incorrectly which led it to strike metal at every controls free check and also slightly reduced elevator travel. Also the bolt itself did break off.
Airborne Again
This is sounding very much like the clevis pin was over stressed in tension resulting in it failing at the cotter pin hole. With the huge number of clevis pins manufactured and the fact that these almost never fail in the way you describe this is not a suitable subject for AD action.
It is very unusual to see a Clevis pin make the sort of hours that you quote, in 4000 hours flying I would expect to see this item replaced three or more times due to wear on the shank so I don’t think the item was fitted in the factory. Replacement of these items is so common that it is unlikely to warrant a log book entry but would be recorded in the maintenance worksheets ( as would the independent inspection of the replacement ).
A_and_C wrote:
I guess you are saying that once the clevis pin sheared and the cotter pin fell out the nut fell off and the clevis pin migrated out of the fitting and contacted the aircraft structure.
I did not see the elevator in the stuck position myself. The mechanic said that the bold had moved sideways which allowed its head to catch the edge of the opening in the plate.
Airborne Again.
Clevis pins do not just shear across the Cotter pin hole, there has to be a reason for this. My suspicion is the Clevis pin was not the correct part number ( too short ).
I guess you are saying that once the clevis pin sheared and the cotter pin fell out the nut fell off and the clevis pin migrated out of the fitting and contacted the aircraft structure.
A_and_C wrote:
I am astounded that anybody certified the aircraft to fly with the bolt fitted as shown ( are you sure you are not mistaken ?)
Thinking about it, you’re right — this shows the situation before the temporary repair. This happened a few weeks ago so I’m confusing the timeline.
It is unusual for a manufacturer to fit a bolt in a critical system that would jam if fitted the wrong way around
It didn’t jam because it was fitted the wrong way. It jammed because it broke (which was indeed because it was fitted the wrong way).
Airborne again
I am astounded that anybody certified the aircraft to fly with the bolt fitted as shown ( are you sure you are not mistaken ?) if someone in my organisation deliberately let an aircraft fly as shown in the photo it there would be a race between myself and the quality manager to see who could fire the person first.
It is unusual for a manufacturer to fit a bolt in a critical system that would jam if fitted the wrong way around without dire and repeated warnings in the maintenance manual, my conclusion is that there is some other reason why the bolt was jamming so I would be looking for worn or misaligned or incorrectly fitted parts including twisted cables.
The implications of releasing this aircraft to service without being 100% sure that the system is correctly functioning in all respects are so serious that only a very detailed inspection to assure those certifying the aircraft is fit for flight would be the appropriate course of action.
The aircraft was approved by our CAO for a single ferry flight to a maintenance facility with the nut fitted as shown.
That’s amazing.
BTW the IPC illustration shows a castellated nut which is split-pinned.
A_and_C wrote:
I very much hope the aircraft was not flown with the nut fitted as in the photos, as the bolt has not entered the locking part of the nut.
The aircraft was approved by our CAO for a single ferry flight to a maintenance facility with the nut fitted as shown.
If this aircraft was sitting in my hangar we would be looking into why the bolt was able to contact the structure, there is a reason for this and it needs to be fully investigated but checking the correct bolt ( part 15 ) and the condition of the bearing that bolt 18 passes through would be top of my list as would the path the cable takes to the first pulley forward of the bolt. However investigation might well go a lot further than this.
I’m not sure I follow your reasoning. The fact that the opening in the plate was asymmetric shows that the design intended that the bolt should pass through the opening. How does the cables and pulley affect this?
This is no trivial matter as there is something fundamentally wrong with the system and it is only down to good fortune that the aircraft was not lost.
I agree it was not trivial as the elevator got stuck. But you mean there is (could be) something else wrong apart from the direction the bolt was inserted?
