Here is an interesting couple of events with nothing relevant found in the archives.   Aircraft has an estimated 300 take off and landing cycles since new.

About three flights a go I took off and raised the gear.   One main came up, showed yellow, one stayed down and showed green, and the nose stayed down and showed green.  Makes for a funny looking light display on the panel. Recycled gear, no problem, and none in subsequent flights. 

Last flight, after flying an hour to a fly in, staying five hours (cool day), I took off, nose gear retracted and showed yellow, but mains stayed down and showed green.  Recycled gear, no problem.

When I got home, I jacked up the gear and did various retraction tests.  In each case, the nose came up first and mains followed.  A buddy applied about 20-30 pounds of "air load" to the left main before retraction but to no effect.  Again,  nose came up first and mains followed immediately after the nose wheel banged against the stop.  Hmmmm....

Our initial theory was electrical contactor fault, but nothing was found in ground tests. Initial theories about pressure switch dead band (checked OK, about 1100 on, 1200-1220 off) went out the window with the results of the ground retraction tests.

Thoughts among the landing gear cognoscenti?

Fred,

My two cents: Either low system pressure (do you have/can you plumb in a gauge?)—a stuck bypass in the pump that “resets,” a bad pressure switch, or intermittent power to the pump (+ lots of other things L ) OR a blockage in the hydraulic system plumbing (bent/kinked line or hose) or debris in the system. This latter is less likely, but of course, more serious. The nose gear coming up first is my clue that a blockage might be the problem; especially if the pressure remains high. You may recall that there is a restrictor fitting (90 degree elbow, painted red) in each of the actuators, plus a spring loaded one-way valve on the aircraft centerline at the back of the gear box. PITA to do so, but I’d check the all for debris.

Good Luck,

Bob