Stuck Flaps

[BrewMaster]

Today the flaps of one of our 172's got stuck. I was doing a power-off stall with a student and during the recovery, the flaps wouldn't come up. It's an N model with 40 degrees of flaps, but fortunately we only had 30 in. It happened so fast that I didn't get a chance to see if the indicator was up or down. It didn't scare me personally, but the idea of it happening to a student while solo got me a little nervous.

Any ideas where to start the troubleshooting? The mechanics will figure it out, but I'm just curious.

 

[PeterPilot]

I'm more guessing than anything, but I'd suspect either a loose lead from the flap handle or a sheered pin in the flap motor.

Please let us know what they say when the problem is identified.

 

[trafficinsight]

In the 172 the flap motor is attached to a jackscrew, there's a "carriage," of sorts that rides on the jackscrew that actually moves the flaps. At either end of the jackscrew is a microswitch, the "down limit" switch at the far end and the "up limit" switch at the near end. When the carriage touches either switch it breaks the connection to the flap motor.

When the up limit switch sticks due to dirt or age, the flap system thinks the flaps are already all the way up and they wont go up any further, even if they're down. Chances are your mechanic will tap the switch a couple times and they will work.

After that he or she can either clean the switch and hope it was just dirty or replace the switch which is a pain in the ass

Most of the time cleaning the switch is good enough for years of trouble free operation. When it starts to happen more frequently you have no choice but to replace it.

Oddly enough I've never seen the down limit switch malfunction and not let you extend the flaps, only the up limit one.

 

[Douglas]

Today the flaps of one of our 172's got stuck. I was doing a power-off stall with a student and during the recovery, the flaps wouldn't come up. It's an N model with 40 degrees of flaps, but fortunately we only had 30 in. It happened so fast that I didn't get a chance to see if the indicator was up or down. It didn't scare me personally, but the idea of it happening to a student while solo got me a little nervous.

Any ideas where to start the troubleshooting? The mechanics will figure it out, but I'm just curious.

That same thing happened to me and a student in a C-150 with 40 degrees of flaps. Luckily we were on the ground, that airplane can't stay in the air with full flaps.
Ever since they didn't come back up, I will only put them to 40 degrees once or twice, just to show the student what it is like, all other practice is only to 30 degrees.
It really makes you think about putting yourself unnecessarily in an unrecoverable place.
Glad it worked out.

 

[ppragman]

That same thing happened to me and a student in a C-150 with 40 degrees of flaps. Luckily we were on the ground, that airplane can't stay in the air with full flaps.
Ever since they didn't come back up, I will only put them to 40 degrees once or twice, just to show the student what it is like, all other practice is only to 30 degrees.
It really makes you think about putting yourself unnecessarily in an unrecoverable place.
Glad it worked out.

Really? Go out and try. I had them stick down on me once in the 150 with 40*. No problem really, just no way to climb, or turn really. Max power and really gentle is all.

 

[BrewMaster]

Really? Go out and try. I had them stick down on me once in the 150 with 40*. No problem really, just no way to climb, or turn really. Max power and really gentle is all.

I think what Douglas was saying is that you aren't doing much flying beyond that point. It's scary to say it, but I'm pretty sure some student pilots would have a pretty difficult time trying to figure out what's wrong (in a reasonable amount of time) or making the necessary corrections to avoid an accident.

As far as putting 30 or 40 in, I do the exact same thing. I show my students one time what 40 is like and usually they will agree that they are unnecessary. I tell them to only use 30, which is more than enough.

trafficinsight, thanks! That explanation helped me to visualize it. I'm not sure when it's going in the shop, but I'll see if I can talk to the mechanic today and get a better idea.

 

[tgrayson]

Really? Go out and try. I had them stick down on me once in the 150 with 40*. No problem really, just no way to climb, or turn really. Max power and really gentle is all.

Depends on the health of the engine and the density altitude. The one I used to fly could not maintain level flight in slow flight with full flaps.

 

[Matt13C]

Along these lines, is it possible for one of the flaps to retract and not the other?

I was doing a pre-flight and noticed the left flap was very loose feeling while the right one was nice and tight, in the fully retracted position. When I started the plane I ran them full down, 30 degrees, and the left flap was shaking all over the place while the right was steady. I decided to use a new airplane, my instructor agreed.

I never did get an explination as to what was wrong but the owner said it was nothing to worry about.

So is it posible for one to break free and be forced back up while the other is still down? I wouldnt want to be anywhere near the ground in that situation.

 

[OldTownPilot]

Sure not maintaining altitude in slow flight (I assume the power is back a bit) is one thing, but with full power in an emergency the airplane will maintain altitude. As for engine health, its on its last legs before overhaul. It meets specs, but I'm sure it's down a few percent in the hp arena. I don't have an issue using 40, knowing what the airplane can and can't do if needed.

 

[tgrayson]

Sure not maintaining altitude in slow flight (I assume the power is back a bit) is one thing,

Why would you assume that? If I had power available, I would be using it, rather than accept a descent. Cessna eliminated the 40 degree setting for a reason.

 

[-=Deniz=-]

I was bored on a XC flight so I did one, same thing happens and it turned into the longest flight in the world!

 

[ppragman]

Depends on the health of the engine and the density altitude. The one I used to fly could not maintain level flight in slow flight with full flaps.

Oh sure, technicalities, but seriously, I've flown the hell out of 150s as has everyone else, and the things fly just fine with 40* of flaps, you just have to be careful. Yeah if you're in denver and its 95 out, you might have problems, but then the question arises, "why are you flying a grossly underpowered airplane in colorado in the summer?"

Not fun, but I had a stuck flap situation in the thing on a go around. I made a real gradual turn at about 300 feet or so (luckily that was when I got sent around for an airplane lingering on the runway) and managed to make it back. What I'm trying to say is you're not going to die if you get flaps stuck at 40degrees. Even the 207, as underpowered as it is will hold altitude with full flaps and a full load.

 

[ppragman]

Along these lines, is it possible for one of the flaps to retract and not the other?

I was doing a pre-flight and noticed the left flap was very loose feeling while the right one was nice and tight, in the fully retracted position. When I started the plane I ran them full down, 30 degrees, and the left flap was shaking all over the place while the right was steady. I decided to use a new airplane, my instructor agreed.

I never did get an explination as to what was wrong but the owner said it was nothing to worry about.

So is it posible for one to break free and be forced back up while the other is still down? I wouldnt want to be anywhere near the ground in that situation.

Yes, it's called flap asymmetry. It's scary. But remember, when something really bad happens, just undo the last thing you did. E.g., you are turning base and you drop some flaps and the airplane rolls violently to the left. First thing undo what you just did (e.g. flaps) and then try to hold the wings level.

The flap motor in many cessnas (I don't know the specs on all of them but I'd assume that for the highwing none turbine cessnas its the same) is in the right wing and is connected to the left wing via a set of pullies. Naturally, these pullies can break, or where out, etc. I've had assymmetry in the sled, not really a big deal, but remember, there's a reason not to just slow to the white arc and dump full flaps.

As for shaking flaps, some of them do that, good call if you didn't feel comfortable.

 

[tgrayson]

the things fly just fine with 40* of flaps,.

You simply cannot make these categorical statements about these airplanes. Sometimes in the summer, in Memphis, high time engine, even a C152 will not maintain level flight with only 30 degree flaps and 10 more theoretical horsepower.

 

[trafficinsight]

Along these lines, is it possible for one of the flaps to retract and not the other?

I was doing a pre-flight and noticed the left flap was very loose feeling while the right one was nice and tight, in the fully retracted position. When I started the plane I ran them full down, 30 degrees, and the left flap was shaking all over the place while the right was steady. I decided to use a new airplane, my instructor agreed.

I never did get an explination as to what was wrong but the owner said it was nothing to worry about.

So is it posible for one to break free and be forced back up while the other is still down? I wouldnt want to be anywhere near the ground in that situation.

It is possible for one to extend and not the other. The motor is in the right wing, that flap is connected directly through a pushrod. The left flap is connected to the right flap with cables. If the cables were to break then the left flap would do whatever it wants.

It's normal for the left flap to be a little bit more loose than the right flap, but it shouldn't be excessive. If it is it's a sign that the cables are either worn, or just need to have their tensions set.

 

[Douglas]

Really? Go out and try. /QUOTE]

Sure not maintaining altitude in slow flight (I assume the power is back a bit) is one thing, but with full power in an emergency the airplane will maintain altitude.

Guys I meant what I said, I've flown three different C-150s. All three of them did not hold altitude with full power, full flaps in slow flight.

I have already tried, many times.

In fact, we only do 30 degrees in slow flight and I have them notify my when they are full power and still going down. That way I don't get on their case for not holding altitude and I can tell them to take out flaps to 20 degrees until we get more lift, if needed.
It is not a summer/winter time deal for us, we just came out of winter and we dealt with this all season.

 

[JrsyGuy]

Ive never flown in a 150 and dont know the v speeds but id have to say that the airspeed being maintained for slowflight is below Vy and Vx. In a real life senario im certainly not going to be shooting for slowflight airspeeds.

 

[trafficinsight]

There really is something to that. There's a reason all the 152's are restricted to 30 degrees, even with more power. That said I've been able to maintain altitude in a 150 with full flaps, but it did take full power and I sure wasn't going anywhere. I would imagine with a high density altitude and a little humidity you'd be in real, honest-to-god trouble.

 

[ppragman]

Ive never flown in a 150 and dont know the v speeds but id have to say that the airspeed being maintained for slowflight is below Vy and Vx. In a real life senario im certainly not going to be shooting for slowflight airspeeds.

Depends on where you're going. There are times when touching down right at stall is the only option.

 

[ppragman]

You simply cannot make these categorical statements about these airplanes. Sometimes in the summer, in Memphis, high time engine, even a C152 will not maintain level flight with only 30 degree flaps and 10 more theoretical horsepower.

That's legit, so let me rephrase that. Every single 150/152 I've flown will hold altitude with full flaps. Including ones with 40 degrees of flaps (2 or 3 maybe that I've flown). This includes in about 80degree weather. Is that better?