king air undercarriage problem 2

[imac09]

Any King Air 300 experts out there??
Problem with a b300, undercarriage will not retract. This happens erratically and may go weeks without problem. UC selected up, gear starts to retract and then stops, cb blows after 15 secs. Crew reset cb and retract gear succesfully. No other faults on system. Have changed squat switches and bled system.
Anybody got any other suggestions??

Thanks

 

[MikeHalloran]

No special expertise to claim here.

Logical next step is block it up on the ground, put an ammeter on the circuit, watch what's going on during a retract cycle, try to correlate excessive current draw with portions of the cycle, and start looking for stuff that's binding/ bent/ ungreased/ cracked, whatever.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[FieldTeam]

How many amp CB is it? I've recently completed T/S on similar circumstance (not a king air) and found a weak CB causing intermittent popping. Also, Megging wires has proven successful in finding difficult shorts an auto scaling DMM can not find (be sure to meg only the wires!).

 

[imac09]

Thanks for the replies guys,
The CB popping is a bit misleading as the system is designed to do this.
It uses an electric motor driving the pump through a powerpack assembly. The motor is protected by a 60amp (auto resetting) CB, which also provides power to the motor relay via a 5 amp CB and also the landing gear control circuit which includes switches on the selector handle, solenoids on the powerpack to a shuttle valve and also a timer circuit board. If the pump runs for more the 15 seconds the timer board shuts it down by popping the 2 amp CB. This is what happens at random times - it may go a month without fault and then may fail twice in 2 days. It seems like when the fault happens the system cannot make pressure and the gear does not fully retract - it waits 15 secs and then the timer circuit pops the CB. We have tried bleeding the system and flight tested at max UC speed and steep attitude and the gear retracted within 6-7 seconds, so when its working it works well.
Beech tech support suggested the motor 60 amp cb may be at fault but when that cb pops the whole system is without power so the timer circuit does not work and does not pop the 2 amp cb.
My best guess is a sticking valve - maybe the selector shuttle valve - which bleeds pressure back to the return side, the trouble is figuring out which valve - thermal relief, pressure relief, selector shuttle, emergency hand pump??

 

[thruthefence]

Have you checked the nitrogen pressure in the accumulator? I have seen these over serviced. Does it ever fail in the gear "down" position? One "non-Invasive" way of checking the various valves for bleed off, is to jack the aircraft, with power off, and listen at the various components with a " mechanic's stethescope" If you have one of those ultrasonic leak detectors, thats better. The gear will have try to extend with no hydraulic pressure, and a badly leaking valve will be heard. My money is on the motor/pump assy, tho it's an expensive item to "shotgun"

 

[imac09]

Accumulator pressure is correct (can't remember the number but its marked on the gauge), interesting you said that though as someone else spoke to Beech tech support and they said something about the accumulator too...Hmmm?
It never fails on selecting UC down only on up, it always starts to retract and then stalls intermittently.
Good idea on the stethescope, the tricky part will be getting it to fail on the ground which it has not done yet - probably done 30-40 retractions at different times and its always been ok on the ground, which was why we did flight testing as mentioned before.
You mention expensive shotgun approach and I have found out that the powerpack has been changed 3 or 4 times in the last few years (before we got the aircraft), so I don't think this is a new fault I was really hoping someone else had seen it on a B300. Anyhow thanks for the input.

 

[Sparweb]

Are both mains and the nose are failing to retract simultaneously? But if there's only one leg not coming up, you could look for something jamming that leg. Particularly something that would jam it in flight, but not on the ground.

Steven Fahey, CET

 

[patdaly]

Hate to be the pessimist here, but could it be something structural flexing in flight? Are there any factors such as being close to max weight/max fuel on the reported flights that contribute to the situation? Is there any possibility of cracking elsewhere in the structure that could cause a bind condition when the airframe is loaded?
Once again, god forbid that is the case, but it is worth investigating.

 

[Donethat]

While not an engineer I've worked on several Beech models and they have a lot in common. This problem has cropped up before and many times it turns out to be the emergency extension pump handle not stowed fully. It's just to the right of the pilots seat and easy to accidentally bump with your right foot. Even only slightly out of position can cause the system to bypass fluid and not develop pressure. Make sure the handle is securely in it's clip.

 

[thruthefence]

"Donethat" is correct, I've seen that as well... However, have Y'all 're-racked' the PC board that controls this stuff? Often a little corrosion on the pins will throw these things off a little. I use a product called "tweak" that does wonders for connector pins.

 

[CESSNA1]

IMAC09: Here is my 2 cents. in the air and, presumably climbing, the loads on the structure are different (greater??) than the loads on the ground or on jacks. Could something be loose/worn/deformed/moving, such as a bushing or link?

that is it
Regards
Dave

 

[FranAle]

IMAC09:

I´ve been working in a100 and be200 for a while. I recommend you, make a isolation check where the ground bonds are. Check the AC43-13B Electrical Systems provided by FAA. You will be surprised what you find.Good luck

FranAle

 

[metroman]

I've had a simmular problem on a B100. The pump motor would run a long time, thus poping the motor C.B. This happened intermitently and on the ground. After bench testing the Px and thermal relief valves we found that the thermal relief valve was slowly leaking internaly. also once the valve started leaking by it would take a long time to reseat. We changed the valve and the problem was gone. Because you have the problem at gear up cycle. I would test the Px relief valve. We tested ours with a simple Tron air 5606 servicing cart and guage. Good luck.