Teach Me About Retractable Landing Gear

NealRomeoGolf

NealRomeoGolf

Final Approach
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NRG
So there I was, capturing the glideslope for the ILS 03 with the needle centered and under the hood. My trusty PA32R-300 (Lance) taking me to the runway sight unseen. At one degree above glideslope my CFII has me drop the gear. Actuate the lever.....nothing. No gear intransit light. No change in feel from the gear now acting as a speed brake. Nothing. I look over at the CFII and say "did you pull my breaker?" I was thinking he was messing with me. "Nope." We start checking breakers. Nothing popped. Gear level back up. Gear lever back down. Nothing. (still on glideslope, mind you :p ) We break off the approach and point towards home. On the approach previous to this one, the nose gear green light hadn't lit until we went missed and then it locked in. Something was not working.

As I pitched up to gain some altitude, and with the gear lever in the down position again, the gear finally dropped. Weird. We were about to go to the manual procedure but it went on its own.

Any ideas on what could be happening? Do gear levers wear out? I mean everything wears out eventually (this is a 1977 model). I could imagine the nose gear thing could be from a spring wearing out, but this last one nothing was moving. That doesn't seem to be related....but what do I know?

Mechanic will be called in the morning but I wouldn't be surprised if he can't look at it until next week.
 
I am not familiar with the Piper gear system but I assume it has the old prestolite gear pump same as my Commander. First thing I would suspect would be the Up/Down switch, on the second try a glance at the ammeter or volt meter would be useful. Best get it on jacks and work it in the shop and try to replicate the situation. A good mech. can check switch for resistance and maybe clean the switch. A new one is not the end of the earth and a fairly easy install. I do an E-Dump every other month just to stay familiar, often the nose will not lock in until the speed and prop wash is reduced .
Life is a barrel of fun.

Ken
 
I would also suspect the switch, or possibly something interacting with the squat switch being engaged when the gear is retracted. When you swing the gear at annual is there a buzzer when you try to pull the gear up with weight on the wheels?
 
airheadpenguin said:
I would also suspect the switch, or possibly something interacting with the squat switch being engaged when the gear is retracted. When you swing the gear at annual is there a buzzer when you try to pull the gear up with weight on the wheels?
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I haven't owned the plane long enough to have had an annual. It happens in April.
 
Could be any number of things. The Lance gear system is powered by an electric hydraulic pump, so could be the gear lever switch not actuating the pump itself. Or could be the pump motor brushes are worn and it's perhaps intermittent when turning in the extension direction (the pump is reversible). If your plane is equipped with the automatic gear extension system it could be the diaphragm in the pressure sensor (common problem with that system). Or it could be one of the hydraulic retraction cylinders (nose gear actuator?) is leaking or bypassing pressure internally.

The Piper hydraulics are generally pretty straight forward systems (at least the one's without the automatic gear extension option), but like everything if they aren't maintained (the motor, the pump itself, the O-rings in the cylinders) they will eventually fail.

Paging @Dan Thomas
 
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GRG55 said:
Could be any number of things. The Lance gear system is powered by an electric hydraulic pump, so could be the gear lever switch not actuating the pump itself. Or could be the pump motor brushes are worn and it's perhaps intermittent when turning in the extension direction (the pump is reversible). If your plane is equipped with the automatic gear extension system it could be the diaphragm in the pressure sensor (common problem with that system). Or it could be one of the hydraulic retraction cylinders (nose gear actuator?) is leaking or bypassing pressure internally.

The Piper hydraulics are generally pretty straight forward systems (at least the one's without the automatic gear extension option), but like everything if they aren't maintained (the motor, the pump itself, the O-rings in the cylinders) they will eventually fail.

Paging @Dan Thomas
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The auto system was removed years ago. Hopefully my mechanic can get it in quickly. Thanks for the thoughts.
 
NealRomeoGolf said:
The auto system was removed years ago. Hopefully my mechanic can get it in quickly. Thanks for the thoughts.
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Good move taking that out. Too much added complexity and failure modes to try to "idiot proof" the airplane. From the symptoms it sounds more like a problem with the gear selector switch starting the pump, the pump motor (almost nobody does PM on those sorts of things any more, unfortunately) or a valve in the hydraulic circuit not working consistently.

Hopefully the problem is apparent, as intermittent problems can be very frustrating to track down sometimes.
 
NRG, fly with a voltmeter attached to the avionics bus (in front of the copilot, and a seat rail ground. Diagnose the electrical system.

I had a recent issue that was resolved by replacing the battery ground strap! (PA34).
 
It could be one of a few switches, a contactor, or the motor on the pump. The worst part is that if everything works right when it is in the shop it will be hard to figure out what happened or what's wrong.

BTDT about a month ago after months of trying to narrow down the search for what was going on.
 
It could be anything. Have you ever put it on Jack’s and performed the emergency gear extension procedure?
 
This happened to me in a flight school Twin Commanche a while ago. It turned out to be the pump motor. A rebuilt motor fixed the problem for a while, but then the breaker started popping when the motor was energized. That was one of many issues in that aircraft, and it ended up being pulled from the flight line and replaced with a Twinstar.
 
Unfortunately A&P can't get it in until next week. And of course this weekend will be the most beautiful flying weather in 3 months.
 
Cervieres said:
This happened to me in a flight school Twin Commanche a while ago. It turned out to be the pump motor. A rebuilt motor fixed the problem for a while, but then the breaker started popping when the motor was energized. That was one of many issues in that aircraft, and it ended up being pulled from the flight line and replaced with a Twinstar.
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Twinkies have a fully mechanical landing gear system like the PA-24 singles. They use an automotive seat motor to drive the gear up/down
 
NealRomeoGolf said:
...this weekend will be the most beautiful flying weather in 3 months.
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Of course. Why would you expect to be exempted from any of the immutable laws of GA flying (including headwinds in both directions) that apply to the rest of us? :D

A couple of years ago I put the Aztec gear/flap system on a 3 year preventative maintenance program to gradually bring everything up to reliable standard. First year of that, at annual, we replaced all the hydraulic hoses (most were 17 to 20 years old, but we found one that was original Piper from 1979 :eek:) and repaired a few small leaks. Years 2 & 3 are devoted to rebuilding, in 2 groups, the 7 different hydraulic actuators - gear retraction, gear doors and flap actuator. When this year's annual is done we will have it complete. I like to minimize the probability of getting stranded on a cross country.

The Aztec system is a bit different than the other Pipers as the main hydraulic pumps are engine driven instead of an electric motor.
 
airheadpenguin said:
Twinkies have a fully mechanical landing gear system like the PA-24 singles. They use an automotive seat motor to drive the gear up/down
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That's interesting. Is it really interchangeable with a seat motor?
 
GRG55 said:
Of course. Why would you expect to be exempted from any of the immutable laws of GA flying (including headwinds in both directions) that apply to the rest of us? :D

A couple of years ago I put the Aztec gear/flap system on a 3 year preventative maintenance program to gradually bring everything up to reliable standard. First year of that, at annual, we replaced all the hydraulic hoses (most were 17 to 20 years old, but we found one that was original Piper from 1979 :eek:) and repaired a few small leaks. Years 2 & 3 are devoted to rebuilding, in 2 groups, the 7 different hydraulic actuators - gear retraction, gear doors and flap actuator. When this year's annual is done we will have it complete. I like to minimize the probability of getting stranded on a cross country.

The Aztec system is a bit different than the other Pipers as the main hydraulic pumps are engine driven instead of an electric motor.
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No “power pack” rebuild?
 
mondtster said:
No “power pack” rebuild?
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No need yet. I'm sure it will come in due course. And I know that you know what a b**** that is to extract in order to work on it. :D
 
GRG55 said:
No need yet. I'm sure it will come in due course. And I know that you know what a b**** that is to extract in order to work on it. :D
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I hear ya. I’ve been avoiding pulling out the one I have here that really needs to be sealed up but isn’t “that bad” yet.
 
mondtster said:
I hear ya. I’ve been avoiding pulling out the one I have here that really needs to be sealed up but isn’t “that bad” yet.
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Mine isn't dripping anything. Yet.
There's a small catch tray under it in my plane, which I thought was a nice touch and thinking ahead by Piper to keep the red fluid out of the carpets.
I have a wreck of the same model that I salvage parts from to keep mine flying and I was thinking about pulling that power pack out and have it ready for rebuild if mine starts to show signs of "fatigue".

To me the effort required to extract, service and reinstall that powerpack is proof positive that these mass produced airplanes were never meant to be around and still flying all these years later. My '79 pickup (Az)truck was supposed to be replaced with a newer SUV or something by now...
 
ksandrew said:
I am not familiar with the Piper gear system but I assume it has the old prestolite gear pump same as my Commander. First thing I would suspect would be the Up/Down switch, on the second try a glance at the ammeter or volt meter would be useful. Best get it on jacks and work it in the shop and try to replicate the situation. A good mech. can check switch for resistance and maybe clean the switch. A new one is not the end of the earth and a fairly easy install. I do an E-Dump every other month just to stay familiar, often the nose will not lock in until the speed and prop wash is reduced .
Life is a barrel of fun.

Ken
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I own a PA28R-180. I concur with KSAndrew on this one. Sounds like a switch issue.
 
guzziguy said:
I own a PA28R-180. I concur with KSAndrew on this one. Sounds like a switch issue.
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When you guys say switch, do you mean the switch that the gear handle itself is attached to? In this case it appears to be Piper part 487-936.
 
NealRomeoGolf said:
When you guys say switch, do you mean the switch that the gear handle itself is attached to? In this case it appears to be Piper part 487-936.
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Maybe or maybe not. As I posted up the thread a bit, there are several switches in the system that need to be functional to make things work.

Edit: the selector switch on the panel is a common point with all the switches needed to make the gear go down. So it is possible that it is bad or going bad, but I wouldn't jump to a conclusion without troubleshooting first.
 
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Next question. I was studying the gear design and want to make sure I understand. The Lance gear is held up by hydraulic pressure. So if there were to be a hydraulic leak, would that reduce the pressure in the system and then cause the gear to either hang down a bit or fall altogether? Is that how the physics would work? Just trying to work on my mechanical logic troubleshooting skills.
 
NealRomeoGolf said:
Next question. I was studying the gear design and want to make sure I understand. The Lance gear is held up by hydraulic pressure. So if there were to be a hydraulic leak, would that reduce the pressure in the system and then cause the gear to either hang down a bit or fall altogether? Is that how the physics would work? Just trying to work on my mechanical logic troubleshooting skills.
Click to expand...

You are correct, hydraulic pressure holds the gear up. If the system leaks (either internally or externally) the pressure will fall and cause the pump to run. If it is bad enough the gear may sag or fall out completely.

If you’re ever flying around and you see the current draw rise for a few seconds then fall again it may be the pump turning on to bump the pressure back up. If this is happening regularly while flying it should be looked at and possibly repaired.

I’m curious. Was this not covered when you transitioned into the plane?
 
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