[Ron Jung]

Ron Jung on December 29, 2020 at 3:46 pm #20439

Ok, thanks Steve I will give that a try and see what I can find. I’ll let you know how it turns out.. Happy new year!
Ron

[STEVE]

STEVE on December 29, 2020 at 2:18 pm #20438

Ron,
As you may know, intermittent problems are the primary cause of grey hair on mechanics.
It’s not that unusual for the hyd pump to cycle when the master is turned on–it means there’s a small leak somewhere in the system that has allowed pressure to bleed off. The pump is reacting to a low pressure sensed by the pressure switch.
You can isolate the internal leak–it’s probably in one of the landing gear actuating cylinders–by isolating them (disconnect and plug the fluid lines to the other two, then pressurize the system.)
If the system pressure drops, that’s the cylinder that has been pressurized is the one that’s leaking between the pressure side and the return side. Do the test on all three cylinders until you find the one that’s leaking. Rebuilding a cylinder is simple.
If it’s leaking with the engine off, it will also leak when the system is pressurized in flight. Are you sure that the pump doesn’t ever cycle in flight?
Since you say you occasionally get a flickering green light on the nose gear that’s where I would start testing for a leaky cylinder.
You can temporarily attach (T into one of the hose connections to one of the cylinders) a pressure gauge to the system to validate my theory. Then note the pressure after you’ve run the engine and compare it to the pressure when you return in a day or two.
Pls let me know what you find.
Steve

[Ron Jung]

Ron Jung on December 29, 2020 at 11:00 am #20437

Hi Steve,

Thanks for the response. I only get the gear pump cycling with the red gear unsafe light flickering on and off (with the pump) occasionally when I apply power to the airplane, and It’s not all the time, sometimes it can go a week or two without it happeneing at powerup. The gear extends and retracts perfectly every time and stays up solidly during flight with no hydraulic pump cycling at all so I don’t think it’s a hydraulic issue. I get the intermittent hydraulic pump cycling (with the gear unsafe light flicker on and off) , only on the ground, during taxi, and on every flight, no common pattern to it just very random, so that sounds like an electrical issue. I have noticed the green nose gear light flickering occasionally as well. Hopefully this info can narrow down the search for the problem.
Thanks again for your help,

Ron

[STEVE]

STEVE on December 24, 2020 at 10:54 am #20431

Hi,
Let’s start at the beginning. When you turn on power on the ground you’re getting a fast cycling gear unsafe indication (red unsafe light on; green gear down lights off).
This only happens on the ground; but never happens in the air.
In order for power to get to the gear up solenoid, the following has to take place when the gear is down.
1) the squat switch (on the left main landing gear) must be closed
2) the pressure switch must be closed; that happens when there’s more than 1500 psi fluid pressure in the gear fluid manifold.

Since you report that nothing is happening, I suggest the following:
A) Power won’t flow to and through the “up” solenoid unless the solenoid control circuit is completed. There are two (and
sometimes three) micro-style switches in the “up” landing gear solenoid control circuit, and they all have to be working
properly to retract the landing gear.
The two switches in every Arrow are the squat switch and the pressure switch. A low pressure (i.e., low airspeed) switch is
part of the backup landing gear extender system. Many owners have removed the backup extender system, so your airplane
may or may not have it in the solenoid control system.
B) The landing gear won’t retract until the squat switch closes. The squat switch is located on the left main gear and it
closes when the landing gear shock strut is fully extended. This switch may need
cleaning or adjusting.
C) The pressure switch is a “normally closed” switch in the gear-up solenoid
circuit. It’s only open when fluid pressure in the gear-up fluid manifold gets to
1,8OO psi. If the switch fails in the “open” position, the motor won’t turn. The pressure switch is located below the reservoir/
motor on the gear up manifold.
If your backup emergency landing gear extender system is stiil installed and operative,
there’s a slow speed switch in it that is in line with the squat switch and the pressure switch. If any one of these switches
malfunction, that will prevent the gear from coming up.
If your emergency landing gear extender has been removed in accordance with
Section I of Piper Service Bulletin 58866A, that “low speed” switch is no longer in the solenoid
control wiring-but the other two are.
Based on these facts, I suggest you look hard at the rigging, bracketry and wiring to the squat switch and the rigging and wiring at the gear extender switch, if it is still installed.
Let me know what you find.
Steve

[Ron Jung]

Ron Jung on December 22, 2020 at 5:24 pm #20424

I have a 1978 PA-28R-201T Piper Arrow III and intermittently on the ground while taxiing or sometimes as soon as I apply power to the airplane with 3 green lights on, I get a gear unsafe light come on and the hydraulic pump cycles on and off, only on the ground, works perfect in flight. The Piper Aircraft Service manual Hydraulic system troubleshooting section, identifies this issue and states that the hydraulic pump up solenoid is shorted and to replace it, which I did, and it did not fix the problem. The cycles come and go very fast, but I also notice at that very short moment when the pump cycles and the gear unsafe light illuminates that there is a flickering of the green nose gear down light. So I have also checked the nose gear down microswitch and traced the wiring for any breaks, chaffing etc. and all looks good. Has anyone else experienced this issue? If so any ideas where to go next?