Jammed Ailerons!!!

[Heliplane]

During my primary training, my instructor "informed" me that the yoke had completely failed (ie no direct control of ailerons or elevator). We then proceeded to make a very smooth landing using trim and power for pitch and the doors and rudder for bank. (Cessna 152).

Obviously the type of aircraft will depend on which surfaces you have at your disposal to extend into the slipstream but practicing this sort of emergency is very useful.

Having subsequently taught these emergencies, the best advice I would give is to make all movements very slowly - long, shallow finals are preferable.

On another note, I once taxied over a metal post in a Citabria that was very difficult to see as another aircraft had hit it and bent it over a few days before. It happened during the taxi to the runway and it ripped through the fabric and sheared the bell crank in half (this is the linkage that allows the ailerons to turn). We were taxying back to depart straight after a landing so the normal pre-takeoff checks would have very much been abbreviated but we nonethless checked everything and found that aileron control had been completely lost.

No matter what happens nowadays, I always give the controls a quick check before takeoff. I also teach the "thumbs up" method. If you hold the stick/yoke with a thumb extended upwards, the "up thumb" should always point to the "up aileron" when doing this check (it is not completely unknown for these controls to be rigged backwards - especially following an inspection).

[FlyingForFun]

Regarding trim on jammed ailerons, IO540 said:

If the elevator is jammed whole so it can't move, the trim works the opposite way to normal

And this is true for the majority of aircraft. But the trim on, say, a Piper Cub works by moving the whole of the horizontal stabiliser, rather than moving a trim tab on the back of the elevator - and this type of trim, I believe, will work in the correct sense. (Once upon a time I used to know the name of the various different types of trim, but my memory is fading.....)

It's worth understanding exactly how the controls on your particular aircraft work.

Anyway, congrats to Whirly for spotting the problem, although I'm not sure if congrats are maybe a little unnecessary since all she actually did was display the same good airmanship which is expected from all pilots. Hope you identify the cause of the cause of the failure - and I'll be interested to hear what it is!

FFF
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[Hampshire Hog]

Flying For Fun has possibly answered part of a question I was going to ask. On something like a PA28 with an all flying tailplane, does the trim do anything if the elevator is jammed? I guess it depends on the cause.

I am pretty paranoid about checking control surface movement - I have a fear of a jam, especially the elevator. Anyone know how common such incidents are?

HH

[Whirlybird]

Anyway, congrats to Whirly for spotting the problem

Much as I like to accept congratulations, in this case it was my co-pilot Paul who spotted it. I was sitting there looking at the map, since it was his leg to fly. But we're both pretty careful about pre-flight checks, and after this, I'll be even more careful. It's so easy to think, deep down, that you just parked the aircraft five minutes ago and it was fine, so it'll be fine again. Now I know that's not necessarily so.

[FullyFlapped]

Anyone know how common such incidents are?

Two days ago my preflight checks revealed a complete flap failure. I know I could have managed without them - although not into the strip I was bound for - but it does, as I'm sure Whirly would agree, provide a first-class wake up call, especially if - like me - you've gotten into the habit of doing these checks without really thinking about what you're doing and why !

FF

[2Donkeys]

I had a similar incident a couple of months ago involving a TB10 that was picked up during the "full and free" during a post-annual flight test. In that in case, the control runs were being fouled by avionics wiring.

2D

[Mike Cross]

We had the opposite from a jammed control - one that was far too loose. One of my partners spotted that the lower of the two rudder hinges was soon to come free from its attachment to the aft fuselage frame due to cracking. This would have left it attached by the top hinge only and the control cables. He spotted it because it was already displaced sideways and the elevators were fouling on it. Wouldn't have noticed it from the cockpit but he noticed it when lifting the elvators by hand during the walkround.

[DBChopper]

Hi Whirly - I'm glad you and your co-pilot are ok. Well done both

And remember, no matter how many folk slag off the R22, you will NEVER get jammed ailerons.

Every cloud... eh?

[Whirlybird]

Right, mystery solved...except the answer just poses more questions. Some bearings in the aileron bell crank had corroded and gone completely solid! The engineer had never seen such a thing happen before. The scary thing is that apparently it could have happened at any time, and IN ANY POSITION OF THE AILERON. Can you imagine if it was in a turn? I've no idea what you'd do under those circumstances; I guess full opposite rudder, and try and keep some sort of control until you can find a reasonable place to land.

But anyway, that didn't happen. The engineer has suggested replacing the bearrings in both ailerons, and it seems a good idea...but expensive. So Paul is hoping to pick up KF on Saturday, or next week, and is looking for an aerial lift (free or inexpensive cost sharing) from Sleap to Kemble. Would anyone fancy the trip? Paul doesn't have internet access right now, but says if anyone can help, please give him a call on 07795 965845. Or pm me if you prefer. If nothing else, the restaurant at Kemble is worth the trip.

[pulse1]

Whirlybird

It sounds like you might have the same sort of luck as Brian Lecomber. He wrote an article in Pilot many moons ago in which he describes how his throttle jammed closed........... while he was at the pumps! This was just after an aerobatic sortie in which the throttle was closed several times. He then goes on to describe other similar events and claims that, if you look after your aeroplane, it will look after you.

[Windy Militant]

Has the aircraft been washed with a pressure washer at any time that's always good for taking all the lubricant out of any bearing.
A friend of my brothers bought an aircraft that had been used by the Dutch police as a traffic spotter. He was told that the aircraft was maintained at one of the best facilities in Holland, money no object all that sort of thing.
The gentleman concerned was a bit of a perfectionist and he decided that the control action was not all it could be. Fortunately he had a friend who was a LAE so they set too putting things to rights. While they were at it they found a pair of pliers and two spanners in the control runs and two of the tufnol aileron cable pulleys were seized solid. In fact they'd been seized long enough for the cable to saw it's way down through the pulley to the steel sleeve that the fixing bolt went through.

[Genghis the Engineer]

Originally Posted by Whirlybird

But anyway, that didn't happen. The engineer has suggested replacing the bearrings in both ailerons, and it seems a good idea...but expensive. So Paul is hoping to pick up KF on Saturday, or next week, and is looking for an aerial lift (free or inexpensive cost sharing) from Sleap to Kemble. Would anyone fancy the trip? Paul doesn't have internet access right now, but says if anyone can help, please give him a call on 07795 965845. Or pm me if you prefer. If nothing else, the restaurant at Kemble is worth the trip.

Whirly,

Dependent upon the weather letting me get a currency check done in the next week, I could do with putting a few hours in in my new bird and that would be a nice round trip, give me a call.

G

[Final 3 Greens]

Thanks for sharing Whirly.

Just goes to show what a cheap and wise investment of time a final "full and free" check is, preferably when lined up and ready to go.

[Hampshire Hog]

I'm pleased they found the cause of Whirly's jam.

Thanks to those who added their experiences. It's good motivation for this student to continue to be paranoid about the pre-flight check.

I stopped at EGLK the other day in my car - to let my 3 year old get a fix of anoraking - when I saw an AA5 land, taxi to the stand and a student and instructor get out. Several minutes later, another pilot got in, started and went straight to the power check area - followed by take-off, without ever having checked the outside of the aircraft. Now, if the CFI or his deputy (my instructor!) at my club saw me do that, I would not want to be on the receiving end of the one way conversation that would follow! (Which is, of course, why I fly from that club). Who knows what the previous flight/landing might have shaken loose?

Can anyone answer my question about using the trim tab on a PA28 following an elevator jam? Would it be necessary to maintain a higher approach speed to ensure trim tab authority?

Thanks

HH

[Confabulous]

Can anyone answer my question about using the trim tab on a PA28 following an elevator jam? Would it be necessary to maintain a higher approach speed to ensure trim tab authority?

As IO540 says, in the event of an elevator jam, trim works in the opposite sense - trim down to go up, up to go down. I can explain it to myself, but not to anyone else! The trim tab will work as a mini-elevator, but the sense will be reversed.

Based on fooling about in a sim (i.e, taken with a grain of salt, but useful nonetheless), rudder and elevator control authority will depend on speed to a certain extent, but mainly on propwash - carrying a bit extra power will help. As G says though, a control failure should be easily survivable, depending on the position of the control at the time of the jam - but even with jammed ailerons at half deflection (full deflection is almost never reached except on an aerobatic aircraft or in a serious sideslip), rudder should be able to overcome the problem. Even with a total jam (elevator & trim) the aircraft will probably be controllable with power and flap, unless it's trimmed for some very high or low speed.

Does anyone know if POHs usually give rudder crossover speeds?

Edit: I've seen that turboprop accident - horrifying, I thought it was a fake until looking more closely. It was just out of heavy maint I think - you can't see the controls move at any point during the "wingover", and can only imagine what the pilots were thinking before impact

[wrecker]

It happened a long time ago but perhaps its worth relating.
I was flying a HS121 on a flight from UK to Helsinki one New Years Day There was little traffic about and we had been able to route from Heligoland Direct to the Outer Marker for Runway 22. This was quite a challenge in the days before GPS or INS just using NDBs. The temperature on the ground at Helsinki was -20C and cruise OAT -50C. We had left UK in rain. On disconecting the A/P on descent I found the ailerons totally imoveable. The first approach resulted in a go-around but the second was better and a normal landing made. You refresh your self on the secondary effects of rudder in a swept wing A/C

[FlyingForFun]

Can anyone answer my question about using the trim tab on a PA28 following an elevator jam? Would it be necessary to maintain a higher approach speed to ensure trim tab authority?

In a PA28, the trim tab will work in the oposite sense, as Confab says. The reason is because, when you wind the trim wheel forward (nose down) this results in the trim tab moving up. If the stabilator is jammed, the upwards movement of the trim tab would work just like the upward movement of a traditional elevator - causing a nose-up attitude change.

To answer your question about the higher approach speed, I think the correct answer is "it depends". I would guess that the small size of the trim tab would mean that you only have a small range of attitudes, and therefore speeds, available to you. But exactly which speeds would fall into that range would depend on the position of the stabilator at the point when it becomes jammed. If it became jammed in a rear-up position, this would result in a nose-high attitude and a low speed, in which case a little forward trim might well bring you down to somewhere close to normal approach speeds.

On the other hand, if the jam occurs in a rear-down position, this would result in a nose-low attitude, and moving the trim wheel fully forward might well result in a speed which is still considerably above the normal approach speed. In which case I think you are pretty much stuck with that speed, and will need a nice long runway for braking after landing.


Now here's another question, though: use of flaps. Assuming that any real kind of flare would be impossible, I would probably favour using a little flap as possible, since this will give me a higher nose attitude than an approach with flaps. So, if I could achieve a sensible speed, I think I would make the approach flapless.

But what about if the speed remains very high, even with full forward trim? Now, I'm thinking that a little flap might well help slow me down and achieve a more normal approach speed.

I would guess that what you are aiming for here is to land on the main wheels first, at whatever speed that happens to be - or at least a 3-point landing. Because if you land on the nose wheel first, regardless of your speed, you're going to be bouncing rather badly, with no way of controlling the bounce. And if you assume you won't be able to flare, then a landing on main wheels first must require an approach with a nose high attitude if at all possible.

Does anyone else have any thoughts on use of flap in this scenario though???

FFF
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[Hampshire Hog]

Mmmm! Thanks for your answers folks. I think I'd look for a big runway and, as FFF says, go for a flapless approach - not least because this would keep the aircraft more responsive to throttle inputs.

HH

[jabberwok]

Does anyone else have any thoughts on use of flap in this scenario though???

Considering that some aircraft have a marked trim change when flaps are lowered I would have a lot of reservations about touching them. As you rightly say, a trim only pitch control is very limited and flap deployment could easily put you outside your effective control range.

Again the answer is going to be variable because of the aircraft being flown and the exact conditions of the failure. Cessna's have inifinitely variable flap and so you could possibly experiment very carefully. Aircraft with fixed flap selections are going to be much trickier.

[FlyingForFun]

In fact, I have had time to think further about flaps since I first posted.

Based on a C152, which is the type I know most intimately, but my argument would probably work on most (but almost certainly not all) other types:

In a fully serviceable aircraft, when flaps are lowered, if no trim or power change is made, the aircraft will tend to pitch up, with a large reduction in speed. If the aircraft is then pitched back to its original attitude (and trimmed), a lower speed will be observed than before the flaps were lowered. In order to re-gain the original speed, it's necessary to pitch down even further. It is the last pitch down which gives the better forward visibility (and larger flare) which we are used to seeing on a "normal" approach with flaps. However, the initial tendency of the aircraft when flaps are lowered is to pitch up, so therefore a small amount of flap may be beneficial in preventing the nose-wheel from touching the ground first.

Again, in a fully serviceable C152, imagine you set a cruise power of 2200rpm and trim. Now, reduce power to around 1500rpm, lower 20 degrees of flap, and do not touch the trim. The aircraft will tend to settle in an attitude slightly lower than cruise, with a steady rate of descent, and a speed of around 70kt - pretty much an ideal configuration for the initial stages of an approach. Why the pitch down in this scenario, but the pitch up when using flap alone? Because of the power reduction. And this power reduction is, in fact, necessary because otherwise the aircraft won't descend. So this tends to contradict my previous paragraph, because the previous paragraph would only apply if no power changes were made.

When my though process got to this point, I figured that the best thing to do was go and try it and see what happens, adjusting power and flap whilst keeping my hands off the controls and noting the results. But of course trying this in a serviceable aircraft is not a valid test, because in a serviceable aircraft there is nothing to stop the change of flap settings and speed resulting in a small deflection of the elevators when the aircraft is flown hands-off.

So, final conclusions - if this happens, climb up to a safe height, and experiment with various flap, trim and power settings until you find one which gives you a nose-up attitude with a low speed and a rate of descent. This is not something which can be done in advance of the failure; nor, I think, can it be done theoretically by sitting around talking about it, because there are so many factors that work both ways and it is not possible to tell which factors are going to override the others in practice.

Now my brain hurts, and I'm going to go and lie down somewhere.....

FFF
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