gear doors wont stay closed

[nick]

guys i have a problem with my gear doors and need help! it happens only in flight, when i retract the gears to up position gears go up and the doors close too but i see in the mirror that leaf doors and aft doors drop open and the gear handle stay in the UP position and i have to manually return it to neutural. we put the aircraft on jacks and swing the gear a lot times and not even once did it fail. we also check the wiring and switches and they seem to be fine and also checked the nose strut for proper inflation and that is fine too. I also slow charged the battery fully and made sure it is OK and took it on a test flight and NO change. anybody with any suggestions please letme know. my e-mail nicknazari@gmail.com 1969 T337D

[Pete Somers]

Nick
This looks like one of the uplock micro switches is not working or the aligmnent of the switches is out, it only needs a touch. If the doors close on putting the gear down and on the gear down and locked the handle returns to neutural the power pack must be ok and the pressure must be ok.
Check each switch and pull dpwn on the gear and see if one of them is intermittant, the rollers and leaves get worn after a while and if you are using a mule for running the gear up/down this provides more positive pressure.
Does the gear work ok on the down cycle?

Regards
Pete

[nick]

thanks pete,
gear works fine on the down cycle and the gear doors close ok, only in flight in the gear up cycle the gear doors close and then they drop open. we use a mule with the plane on the jacks and everything works fine. I am not sure but I think the nose gear door stays closed
and work normal all the time!!!
gear handle does not come back to neutural only in flight and in the gear up mode, the rest of the time it works normal. keep in mind that i have dual hyd pump and the system works fast and does not drag at all.

[Pete Somers]

Nick
When the gear is locked up and the handle returns to neutral the hyd system is unloaded and the gear sits on the uplocks, any amount of play or misalignment of the uplock microswitches will cause the doors to open. Does the orange gear light stay on or does it go out as the doors open in flight, this would be a good clue. Check the microswitch on the gear handle and make sure it does make positive contact. It is just a matter of saying to yourself, what is different when I am operating the gear in the air, well airflow and vibration all affect the system.
Check the wiring to all the micro switches, on the nose gear where the wiring is run from the gear to the terminal block in the port side of the nose gear bay.

Then I am afraid you will have to go to the power pack, which I assume is original. You will have to start checking pressures from the pumps and the output of the power pack.
Have you replaced the HYD fluid recently? and serviced the filters.

Let me know how you get on

Regards
Pete

[nick]

pete

the orange light stays off when the doors fall open. I am hesitant to think that i have a problem with my powerpak because it works fantastic on the jacks with the airplane battery as the power source. airplane is a 1969 T337D with only 1500 total time. It sat in a heated hanger for 15 years before I bought it, five years ago. we completely restored it to almost new condition(paint, interior,garmin stack,stec 50,full de-ice and lots more). I am pretty sure the powerpak is original because I did nt find anything in logs and I also have all the repair invoices since day1. I suppose we could have moved or shifted one of micro/uplock switches in the paint stripping process! I am not sure how to go about checking them and I think my mechanic is kind of giving up on it too. I can use all the help I can get.

thanks again

[Pete Somers]

Nick
If the orange light goes out, this proves that the problem is with one of the uplock microswitches as you should have a orange light on completion of the retraction.

1 Check that all the uplock switches are free from dirt,grease etc.

2 Check the uplock rigging as per the Skymaster Service Manual.

3 Check all wiring and connections to the switches.

This is a process of elimination and will take some time to find.

I will email you the wiring numbers to check when I have found the diagram.

Regards
Pete

[stackj]

Nick,

Pete is right. Look at figure 5-40 on page 5-92 in your service manual for a simplified landing gear wiring circuit. The three gear up switches are in the center of the drawing. The amber light will be on if all three of the switches are closed. This indicates that power is being applied to the Landing Gear Door solenoid, allowing hydraulic pressure to close the doors.

The handle Up-Down switch could also cause your problem, however, if that was the fault, your amber light would be on.

See attachment.

[Pete Somers]

Nick
Did you get the gear doors fixed? Just interested in what the fault was.

Cheers
Pete

[nick]

pete,

not yet. I have been very busy, also I am trying to find somebody with enough knowledge
about this system to help me. I will let know you know.

thanks