The perfect timing for a gear failure

[gkey]

So there we were, my CFI and I, going through the different excersizes for my upcoming twin checkride, when it happened.

The departure went fine, and the gear retracted as usual on climbout. We arrived at the excersize area 8 minutes later, and hung around at 5500'. First we did the "slow flight, clean config". All went well, and we were doing 90 KTS (blue line) and holding altitude and heading. Then my CFI wanted me to extend gear and flaps and keep her in the 90 KTS/same ALT/same HDG. So, I extended the gear, let her stabilize a few seconds, and then lowered 1/3 flaps, and finessed her a bit to keep the flight requirements for this test.

CFI satisfied, and I retracted the gear. By this time (collectively 25 hours on this plane) I became used to the sound the gear motor makes, and this time the sound was higher pitched. There is also usually a little thump noticable through the right rudder pedal when the the gear retraction cycle ends. Usually it takes about 15 seconds to retract the gear, the little thump through the rudder pedal, and then the orange light. But this time the motor was still whirling after 30 seconds, no thump and the orange light (gear up) did not light up. I looked in the mirrors, and the gear was half way retracted with the doors still open.

Right or wrong, I flicked the gear switch to "gear down", but not a peep. No movement, no sound. I checked the breakers, and the most foreward one in the middle row (labelled gear motor) breaker had popped. I put "George" in command to fly the plane and hold ALT and HDG, and checked my POH on this issue. So the manual gear pumping began. We lost count after 64 pumps, but kept on pumping until the gear was extended, the doors were closed and our arms were falling off.

My CFI took over for the landing, and Kudos to him for the softest power-on landing I have ever witnessed.

On the ground we checked the hydraulic reservoir - it was still full. Then we looked at the logbooks just for tickle's sake. We noticed that the "RH upgear switch" had been replaced in Sept 2004, and again in December 2004. The last time an "upgear block" was also replaced. Does this bear any revelance to our incident? Or was the plane maybe unhappy with doing gear swings in mid-air, while hanging off the props in slow flight, angled at 30 degrees or more?

[Dave Underwood]

Well done for making it home in one piece. Based on my limited experience and the gear extend speed range, there should not be any problems there.

A couple of thoughts follow as my aircraft had a similar event, which ended up with a gear up landing. The good new is the gear up is generally rather uneventful. The gear doors take the brunt of the damage when closed and you can feather the front engine.

Did you cycle the master and alternator switches during the event? That resets everything and is suggested in the manual.

In the amplified emergency procedures for my 1977 FT337GP, it suggests by doing so, you recycle the door control value to the gear extension position and that allows extension. That may or may not have helped, but would be worth reviewing in your POH.

Some thoughts and suggestions:

1) The gear system requires a thorough review.
2) The gear set-up and geometry should be checked per the manual.
3) Hose position is also important as otherwise you might find the down locks pressurising and closing before the leg has tripped it. As a note, on our models, as I recall the description, the down locks are not supposed to close and pressurise until the gear leg has gone to the full down position and started to move the down lock.
4) You will want to confirm the operation and correct position of all the micro switches. I have had one switch that was affected by air loads that prevented retraction at one point.
5) You should do a gear swing and my suggestion is to simulate air loads. Operating properly, you will be pushed out of the way on extension.
6) I would also suggest you replace all the seals in the power pack. I don’t believe mine had ever been done and some were at the end of their life. On the power pack, one of the areas to consider is the solenoids can get gummed up and can cause problems. The work on the power pack is not that big a deal.

In my case the actuator seals appeared to have failed internally and leaked fluid so the right leg extended part way but would not over come the air loads for full extension.

My two cents worth.

Regards - Dave

[gkey]

Well, it's time to report back. My AME called me this afternoon, and GKEY is ready for pick-up. They could not find anything wrong with the gear. They put her on jacks and did the gear swing 20 times. Perfect. No hesitation. Like a model. Then they applied some resistance to simulate air loads, and again she did a perfect job. Every time. The hydrolics are perfect, the seals are fine, the switches are nice and tight and performing 100%. ON THE GROUND IN THE SHOP, THAT IS.

Makes me think: the problem is still not really sorted out, is it?

Maybe I'm dumb or stubborn about this, but I still think the exact exesice I was doing (slow flight, literally hanging off the props) could have something to do with her refusing to complete the gear-up action. I think the air loads in such a configuration can be tremendous, especially inside the wheel bays.

I guess from now on I'll just lower the gear much earlier in decent at higher altitudes and further away from my destination, just in case I'll have to pump away untill my arm falls off...

[Pete Somers]

Had this problem and found that the pressure switch on the power pack went intermittant. You can remove those switches and clean them out.
This one has been no problem after cleaning it out.

Pete

[Ernie Martin]

I'm sorry I didn't answer earlier (I was at the annual meeting in Lucaya and didn't focus on your message when I returned).

I have been having essentially the same problem, and in my case it's due to insufficient electrical power.

The key similarity to my case is that you popped the breaker and were likely at low engine power (and thus at low alternator output).

Basically, the powerpack has a huge apetite for power and needs both a healthy battery and lots of alternator output. For me, I'll pop the breaker if any of these two are present: low engine power or a weak battery (this last point is exacerbated in the summer).

I now religiously service the battery every couple of months (remove it, add distilled water, trickle charge), and I have a new entry in my landing checklist, just before gear down: RPM and MP to 25. Of course, you need to plan in your descent for this 15-second burst of power.

Since I've instituted these measures, no more problems.

Ernie

[Ernie Martin]

GMAS, an expert on Skymasters, has reminded me that you should have the solenoids checked and cleaned, as they may be sticking. He says that they are located on the pump pedestal, on each side by the pilots feet. The book says to change them to the ones that the tops can be removed and the plunger cleaned, since hyd fluid coming up through the port makes them sticky. He goes on to say that when you're on the ground, the right side one gets warm from the current flowing, and guess what happens to the paraffin base oil that is not supposed to be in with the plunger? This is often why the gear won't complete its cycle.

Thought I'd pass it along.

Ernie