PA-31 lost due to mis-installed trim tabs
 

https://apnews.com/article/myrtle-be...2c6dbdff766a31


Airline pilot lost control and crashed due to improper maintenance in Myrtle Beach.

Yeah, it's a thing. I haven't had flight controls reinstalled backward, though I have had the travel limits backward, which is much more difficult to detect when you're doing the really thorough control check necessary after they've been reinstalled. For what it's worth, and my lesson learned from a very scary circuit in a misrigged Cessna 206, if you have nose up pitching forces you cannot manage, you can equalize them while you work on the problem, by placing the plane in a turn with a bank angle sufficient to lighten the control forces. That said, if it's a bad mis rig, there maybe nothing you can do, but time to think about the problem is always a better idea...

Best idea is to witness the maintainer, with a bubble protractor, showing you the pilot that the control travels are what the type certificate data sheet says that they should be. If anyone can't or won't do it, or understand it, I would not fly the plane. In Canada, it is required that any flight control work have two independent inspection signatures in the logs before flight.

I think that's a fairly widespread requirement - it was certainly the case when I was a hangar rat.

I had the elevator trim tab installed backwards on a T28 Trojan I was to conduct a post restoration maintenance flight test on. Interestingly the up and down travel on the tab is the same which certainly heightens the risk of getting it backwards. Also the takeoff setting is zero degrees. Because this airplane is quite powerful it needs significant nose down trim as it accelerates in the climb after takeoff. When I started trimming the forward stick force required rapidly increased and I knew something was very wrong. Fortunately I remember a piece of advice I was given by a very experienced pilot. He said if the airplane suddenly starts to misbehave right after you have done something start by undoing your action, so I returned the trim to zero which resulted in a diminution of the stick force required and so I was able to return for an uneventful landing. However the bottom line is simple. It was wholly within my power to have avoided this situation by conducting a full control check.

Since that event I have had 2 further instances of control issues after major work. The first was a post repair check flight after a damaged rudder on a C 421 was repaired an reinstalled. When I cycled the rudder trim to the full left position the trim wheel jammed and could not be moved. It turned out an errant lock wire pig tail got caught in the works and jammed the control.

The second was an instructional flight in a C 172. The student was not my own, it was to help out another instructor who had to take a day off due to a family issue. During the control check the student gave a tentative stir of the wheel while watching the flight control surfaces and called the check complete. I interrupted him and said no, he had to check the 4 corners ( i.e. full forward, left and right and then full back left and right). When he got to full back the wheel jammed. Obviously we returned to the ramp and an investigation showed that a fastener for a wire bundle had come loose and the wire bundle sagged into the control path behind the instrument panel. The edge of the sprocket caught the bundle at full aft travel and jammed the control. There was evidence of distress on the wiring bundle so it was likely that this condition had existed for at least a little while.....

I seem to recall an F15 crash (RAF Lakenheath?) on take off killing the pilot was due to the aileron controls being reversed.
Also read an interesting story of a Halifax that crash landed back at base after a raid. On inspection the control runs had been reversed over their pulleys making them hard to operate.
The pilot (who thought all Halifaxes were difficult to control) had a reputation for making heavy landings. With the controls the way they were it was considered the pilot exceptional as the aircraft shouldn't have been flyable.

Very unfortunate for the PA-31 pilot, it seems he kept it in the air for a while before succumbing to the introduced issue.

For whatever reason the possibility of control failure, either by accident or introduction, was something that interested me for a long time. I think this came from reading about Roy Chadwick (https://en.wikipedia.org/wiki/Roy_Chadwick) and what happened to him and his team when the Avro Tudor prototype crashed as a result of crossed-cables (https://www.baaa-acro.com/crash/cras...dford-4-killed). Following that I spent several hours in the air and on simulator practising for various possible issues I could think of. The simulator was particularly good because you could actually introduce a real failure and/or cross-up.

With regard to crossed aileron cables I came to the conclusion that, in a dual-control yoke-style aircraft, it should be possible to reasonably control by grabbing the inside handgrip of each of the two controls, with elevator issues try to use trim if possible, and with rudder problems you might correct a little with aileron (or async engines if in a multi). One important finding was to be very deliberate if you used any crossed or broken control; my view is that it was better to leave that control alone and remove hands or feet from the equipment if possible in order to prevent inadvertant application.

Another thing I did ever since was to specifically check for control-surface sense when doing a 'full and free' check. In all my training this had never been taught, but made absolute sense to do.

As it turned out I was lucky in that the only time I came across such an issue in anger was when doing the inaugural flight of a PA-34 after it had been introduced to the local register from another country. As a result of that it required a reasonably extensive teardown and reassembly, during which time the engineers had managed to mess up the elevator trim. The result was that at take-off the machine pitched up sharply and could have stalled around the end of the runway had I not been able to react quickly enough and maintain sufficient forward pressure on the controls for the subsequent return to fix (this required somewhat more force than one might think!). At this time I was regularly test flying aircraft after they'd had work on them, which probably helped, but of course this turned out to be one event I'd not practised for...

munnst do you have a reference for the Halifax story? It sounds interesting.

There was a time I would have been shocked to hear that anyone went through basic flight training without being taught "free and in correct sense". Since then I have flown with lots of pilots who, if they do a control check at all, just wiggle the stick or wheel a bit without even a glance outside. One local pilot was able to get a tandem seat biplane in the air with the rear stick secured hard back by the lap belt.

Anyone who thinks they are going to adapt to reversed controls should try riding a bicycle with hands crossed on the bars. Don't do it in traffic!

Blimey - did he get it down again?

Friend I flew with a lot was taught in Arizona. His control checks were full and free several times and visually checking the surfaces moved in the correct sense. I can't believe any instructor would not teach that...

I think an RAF Hawk was lost twenty or thirty years ago with mis-rigged ailerons.

I think that the RAF Hawk accident was due to the ailerons not being connected at all. Subsequently they introduced a procedure whereby the starter crew indicated control deflections to the pilot during the after start control checks.

One problem related to cockpit control checks is that some control surfaces are not visible from the cockpit, especially elevator and rudder trim tabs. The only way that you can then check these is during the pre-flight walkround having set full trim deflection first. However, this requires careful thought because the tab will deflect in the opposite direction to a control surface and will require you to go back to the cockpit to then set the opposite direction. Also, if an aircraft has a mechanically linked nosewheel steering system then full rudder checks can only be performed whilst taxiing and that is not the time to look over your shoulder at the rudder, which possibly you cannot see anyhow. So, there are a few practicalities which do require robust engineering procedures and pilot observations cannot always be used as a mitigation.

There is one interesting control reversal issue that does occur and that is for a pilot from a three-axis control aircraft flying a weighshift microlight (and vice versa). The pedals will generate a yaw rate in the opposite direction for each of these classes. Whilst low gain tasks such as taxiing can be performed with conscious decisions, correction of an uncommanded yaw disturbance during take-off and landing can result in the pilot making an unconscious skill-based pedal input in the wrong direction.

Accident was in 1989 and I remembered the details incorrectly, It was an N3N-3 being flown from the back seat so it was the front stick that was secured.

"FINAL NARRATIVE:

AT THE BEGINNING OF A PLEASURE FLIGHT, THE PILOT REPORTED THAT HE DEPARTED THE RUNWAY USING A THREE POINT TAKEOFF. WHEN THE AIRPLANE BECAME AIRBORNE, THE ANGLE OF ATTACK WAS EXTREMELY HIGH. THE PILOT WAS UNABLE TO LOWER THE NOSE WHICH RESULTED IN THE AIRPLANE STALLING. THE RIGHT WING DROPPED AND THE AIRPLANE COLLIDED WITH THE TERRAIN. AFTER THE ACCIDENT IT WAS NOTED THAT THE FRONT SEATBELT WAS TIED TO THE CONTROL STICK IN THE AFT POSITION. THE PILOT STATED THAT HE MUST HAVE OVERLOOKED IT DURING THE PREFLIGHT."

This is probably the incident I was thinking of.
https://apnews.com/article/8e0bc96b1...e4e62544629a92

I recall the Hawk prang, early/mid 1996, and yes, disconnected ailerons.

I've a lot of hours in both 3-axis and flexwing microlights, and have had no significant issues, nor have almost anybody I know - it's essentially a non-issue with qualified pilots, because (a) training, and (b) they are SO different, it's essentially like going between a car and a bicycle. Also on a flexwing both the nosewheel steering pedals and lateral control through the bar work in the same push-left-turn-right sense.

I do know of one accident, a flexwing instructional flight out of Barton in 2011 where a student was being instructed in PFLs, and close to the ground pulled instead of pushed on the go-around, causing it to dive into the ground, thankfully survivably. The fundamental issue there was out of sequence training - the instructor introduced a relatively stressed and risky manoeuver incorrectly early in the syllabus, before his student was adequately familiar with basic handling.

However, if you really want an exercise in pilot confusion, you want to fly a JC24b Weedhopper. Stick in the conventional 3-axis sense, nosewheel steering in the flexwing/bicycle sense. I have a few hours in one, and managed (somewhat uniquely for the type) never to bend it, but the fact that your stick (actually rudder control, there are no ailerons but lots of dihedral) is push-right-roll-right, whilst the pedals are push-right-turn-left-on-the-ground is deeply anti-intuitive. I resolved it by locking the lateral stick on the ground and steering on pedals along, then when airborne locking the pedals centrally, and steering with the stick only. NOT the easiest aeroplane ever to land. Using stick and pedals at the same time, I had concluded very early on, was just going to end in tears if I tried.

I have over the years been involved in investigating a number of accidents where pilots of larger (say 172 sized) aeroplanes broke 3-axis microlights, despite identical control senses, because the speeds, attitudes and key heights were different. At one point I was flying regularly (purely for my pleasure and enjoyment) a Thruster TST 3-axis microlight, a Raven flexwing microlight, and a PA28-161. The switch that gave me concern was between the PA28 and Thruster, for just this reason: particularly in the landing, the controls worked the same way, but all of the heights, speeds and visual attitudes were totally different.

G

G,
The Weedhopper sounds like a HF nightmare and I am amazed that it was ever certificated. I had about 3000 hours on 3 axis aircraft before I flew a flex wing (Hornet Raven) so had very ingrained skill based reactions for yaw control. The biggest problem area was on landing if a quick directional correction was needed because there was no time for a conscious decision to be made. I suspect that it was my background which actually generated this problem compared to yourself and the others to whom you refer.

The Hawk Aileron problem referred to was that during a routine servicing requirement,an Aileron control system bolt up in the 'Hell Hole' (under fuselage between the mainwheels) had to be disconnected for access.For the pilot - the disconnection would have been masked by the aileron system centering springs - ie the stick would remain centred in the cockpit and 'feel' fairly normal if it was moved (although without hydraulic pressure the control column would have been capable of deflecting further than normal due to the disconnection).

The Weedhopper was very very "Mk.1" and to describe it as certificated is probably doing it more justice than it deserves. It existed before any kind of modern safety regulations did, and hadn't killed anybody, so didn't get banned when regulations came in. It actually did evolve into a number of quite excellent little aeroplanes, the best of which is probably the Raj Hamsa X'Air - which has ailerons and conventional rudder pedals, and is one of the easiest most relaxed pleasant aeroplanes I've ever flown.

I had hundreds, rather than thousands, of 3-axis hours when I first flew a flexwing, and won't deny a few issues myself - but the reality was that that was in dual controlled aeroplanes with a grown up sat behind me (the Hornet R-ZA you flew was an evolutionary dead end, probably the last ever side-by-side flexwing). Nowadays at least, there's a clear training requirement (in Britain anyhow) so the first few hours should never be done such that those 3-axis ingrained habits are problematic. Of course, this is a pretty generic point: anybody switching to a totally new form of flying machine to them, needs some robust training and safety planning. The same would apply going between nosewheel and tailwheel.

Very best,

G

It's shocking that a regulatory system allows this sort of thing to happen. It's mandatory under the British CAA system that any component/s that affect/s flying and engine controls must have a duplicate inspection carried by appropriately-qualified engineers if they have been disturbed in any way. The inspections include correct senses, ranges of movement, cable tensions and split pinning & wire-locking, The engineering licence examinations include a thorough knowledge of aerofoils, associated controls and their effects upon flight. It's rare that any discrepancies get past the hangar doors.
A long time ago I re-rigged a PA28 stabilator control system on an annual inspection because the ranges of movement and neutral position didn't conform to the maintenance manual. Duplicate inspections were carried out satisfactorily. The aircraft was test-flown by a very experienced ex-Queens Flight pilot with no problems reported. The GA pilot arrived to collect it and aborted the take-off because the yoke position felt abnormal. He was shown the maintenance worksheets detailing the tasks carried out and the range of movement conflictions and rectification. He was so used to flying a mis-rigged aircraft that he thought something was wrong.
Slightly off subject but still relating to control issues, the late Jack Curry in his excellent book Lancaster Target, relates how his Lancaster got into a spin when he was caught in a thunderstorm when returning from a bombing mission over Germany at night time and managed to regain control of sorts. Both ailerons had been torn off and he flew the aircraft back to Wickenby by using differential engine power for turns and landed it!

NASA/DAC/Honeywell demonstrated multiple successful MD-11 autolands using only thrust control and no primary flight controls. The research program increased the FADEC trim authority to allow the flight control computers to control each engine independently.

I picked up a friend's C150 once, which had been sitting for months tied down, and lonely. After checking it over really well, jumping the battery, getting it running adequately, I took off to fly it home - entirely normal flight. When I was on short final, I pulled to raise the nose, and the elevator seemed jammed. With only a moment to spare as the ground rushed up, I pulled like hell, something released, and I could pull to flare, and landed okay. Very startled, I examined.

What had happened was that it sat all that time with the control lock through the control wheel tube. The constant motion (as it was parked down prevailing wind) had caused a burr on the control wheel tube around the control lock hole, which was just enough to catch in the plasitc bearing block on the instrument panel. It was enough to cause a jam. In takeoff and cruise, it was not a problem, as the control wheel was always well back. However the change in trim when the flaps are extended to 40, places the control lock hole just into the plastic bearing, and the jam is possible.

If on my preflight, I'd checked the "free" more cautiously with the "full", I might have noticed. But at the time, it had gone un noticed - and I learned....

if you hadn’t managed to save the aircraft that fault is so subtle it might be hard to pinpoint in a post crash inspection.

EXDAC

"
Anyone who thinks they are going to adapt to reversed controls should try riding a bicycle with hands crossed on the bars. Don't do it in traffic!"

I going to say that. Don't ask me how I know.