Piper Arrow gear problems

[MtrHedAP]

1971 Piper Arrow PA-28R-200

Ok here is the deal. Pilots reported gear would not extend during flight. After going through checklists they manually (emergency) extended gear and landed. They reported In-transit light being lit with gear down selected but no extension.

Upon intial inspection on jacks the gear retracted normally. While extending the In-transit light was on, the hyd. pump was running but did not extend gear. No outside visual leaks found, pump fluid full. The gear will retract and extend normally most of the time. Other times while selecting gear down the pump will run, In-transit light will be on but gear does not extend. While retracting gear it will operate normally until almost all the way up and then the hyd. pump will kick on and off until gear is all the way up. Emergency extension always works fine.

It works on a reversible motor driven pump. It has a pressure switch that opens circuit to pump at 1400 psi and closes at 1100 psi. Automatic gear extension system has been disabled.

So basically I know the gear control circuit is operating correctly because I can hear the solenoids closing and the pump will operate either direction. That leaves me to believe that it has to be a hydraulic issue. It must be the pump motor, pump, pressure switches or something.

Anyone with any information to share about this issue please do. I would really like the help as I am not too familiar with this system. Thanks

 

[skid]

Not a mechanic but have instructed in and have about 300 hours in Arrows of multiple models. Its been 3 1/2 years since I have thought of this stuff but here goes. What you may have can be any number of problems...

- Check the manual extention valve. This may be leaking hyd fluid past it. AKA not in full open or closed position/bad seals. This may be causing some situations where the pump will not allow the gear to fully retract. I had this happen once when we bumped it when getting in.

- Suggest testing all electrical wires in the system. The pump activates via electrical signals to activate the hydraulic pump. AKA elect starts it/hyd moves the gear. You may be having a bad signal from pressure sensors/chafing wire. May be cause of surging.

- Test hyd pump pressure sensors. I know they are supposed to be at those specific values but most mechanics dont get them to that point. Also check the over pressure relief valve. This may be a reason that the pump would continue to operate after the gear is in an up position. EX. Hyd pressure is what holds this gear up. When pressure reaches a specified amount it assumes gear is up and turns off. If the high pressure relief valve is mis set to a lower value than the sensor to shut off the pump is, then it will just allow fluid to flow back to reservoir and never reach shut off pressure. Note: If I remeber right I have heard this value for the high pressure relief valve is about 4000 PSI (mostly for thermal relief)

- The '71 Arrow has that nifty insurance saving auto extend feature (that pitot on the side of the Fuse) THis has caused a number of gear problems in a '72 model I have flown. The system is supposed to auto drop the gear if you get below a certain speed and power setting and also not allow retraction at below a specified speed. This system never worked right on our Aircraft. This is why most of the time you have the emergency lever in the locked out up position (with the flashing light by the gear indicators) overriding this system. In our aircraft it would try to drop the gear at 130 knots and would never allow retraction. (This system has been removed from newer models and we also removed it)

- The last thing to check is the pump itself. obviously proper fluid level and such but you may have to have someone get messy and totaly check it out. Verify fluid movement out of the system and through all the lines. I have heard of pumps getting weak and really messing with peoples heads. All it really needed was to be rebuilt.

I know this is a long message but I hope it helps a bit good luck and let me know what you find out.

Somewhere in my library of stuff I have a piper maint manual/CD with a good description and diagram of the system I used for teaching. If you are interested PM me and I will see if I can dig it up.

 

[Jrparne]

Def. check the emergency gear extension like skid said. i had a problem once where the switch was down just a hair and it just bleeds the pressure in the lines and the gear wont do anything, then you get all goofy lights while flying. eventually the pump triped the circuit breaker because it was trying to catch up. im not a mechanic just my two cents.