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Topic-icon Arrow, In Transit gear light PA28R-180

6 months 3 weeks ago #2150


Wow, thanks for that! I just had that discussion with my mechanic last month. I will check like you said when I get our plane back from the panel upgrade.


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6 months 3 weeks ago #2148

Hi Robert;
Your turbo Arrow landing gear system is very similar the one in Newell's PA 28R-180
As I read the manual for the turbo arrow, it shows that there aren't gear up microswitches. So having one or more gear legs sag out of the switch momentarily during turbulence-thereby causing a gear up switch to open-can't be the reason your gear unsafe light blinks on.
One check you can do to verify that it's the gear pump coming on-and lighting the light-is to see if the instrument lights dim if flying at night, or if the needle of the loadmeter twitches toward the discharge side when the light comes on. This dimming is of course caused by the large current draw of the electric motor driving the hydraulic landing gear pump.
As you say, it's not really a safety of flight issue, but I expect it to happen more and more often as the seals in one of your actuating cylinders continues to wear.
Happy Flying

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6 months 3 weeks ago #2144

Hi, Your gear in transit light is turned on when the electric motor that spins the hydraulic pump in the landing gear power pack system is energized which causes the pump to put out pressure.
The pump is automatically turned on when the hydraulic pressure at the pressure switch goes below a set point. I believe the set point to turn on the pump is 1500 +/-100 psi.
The hydraulic pressure should not drop below 1500 psi during flight with the gear up. If it does, like in your case, it means there's a leak in the landing gear hydraulic system.
The most likely place for a leak to occur is in one of the landing gear hydraulic cylinders. Each cylinder is a tube. Hydraulic pressure to move the that specific landing gear (left main, right main or nose) either up or down. Pressure on one side of a piston moves the gear leg up; pressure on the other side of the piston moves the gear leg down. The part that separates the two sides hydraulically is a single O-ring in a groove in the piston.
When the O-ring is tired, or the cylinder bore is worn, hydraulic pressure can leak from the "up" or "down" side of the piston to the other side. When this happens the pressure in the system drops below the trigger pressure at the pressure switch and it closes, turning on the motor, which spins the pump and pressure increases until it reaches the pressure switch opening pressure.
To determine which gear actuating cylinder is leaking you can disconnect the "up" and "down" fluid lines from the cylinder to see if there's a pressure loss when that particular cylinder is "out" of the system. You should find that the system pressure is solid when the leaking cylinder is disconnected from the system.
Remove the cylinder, disassemble it, clean it up, measure in inner bore of the cylinder to determine if there's wear (compare the measurement at the middle to the measurement at the ends of the cylinder). If there's no or negligible wear, then replace the O-ring, and re install the cylinder. Re-connect. Run the gear up and down a dozen times on jacks. This should solve the cycling problem.

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6 months 3 weeks ago #2143

Hi Newell,

My Turbo Arrow does the same thing, usually in turbulence. I'm assuming you're not venting fluid overboard with the gear motor is continuously running.

It's hard to reproduce on the ground, and I just got used to it. Mine only illuminates when the gear is up, it doesn't go on gear down (and locked).

The rigging may be a bit loose, or a microswitch may need to be tweaked. You can have your mechanic swing the gear, and adjust those, but it was a waste of time/money for me. I just use the light as turbulence notification in cruise, but that's after I did get it checked out.


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  • NEWELL STAMM's Avatar Topic Author
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6 months 3 weeks ago #2142

The gear in transit light comes on comes on during cruise flight and I have to recycle the gear switch to make it go off. This is an occasional issue, sometimes five flight hours without happening sometimes twice on a lunch run.
Is there an order of system components to check to trouble shoot?

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