Warbird Information Exchange

With no system changes, our TBM Avenger began experiencing a consistent problem with the first gear retraction of each flight. Both gear hangs at about 10 degrees (about 80% retracted) and hydraulic pressure is good at 1400 PSI. Manual pump does not help. If I then select "gear down" I get a full and locked (whew ) extension. Any further gear selection up/down works just fine - until the next flight.

If after the first full retraction I can make full stop landings the gear will work fine. If I land, shut down the engine and restart, it will still work. However if I land, shut down, and bleed the "general" system with cowl flap operation, then restart and fly, we go back to "no full retraction" on initial try.

If I take off with say a 15 degree flap setting, and have set myself up for the initial "hang" retraction, after the gear hangs I find that a "more flaps" setting has no effect (flaps still at 15). But a "retract flaps" setting will result in full flaps retraction after an abnormal delay of about ten seconds, followed by the gear going the rest of the way (gear handle still full "up" throughout.) No other interaction of gear/flap noted in other flight regimes.

We have replaced the gear/flap selector and hydraulic pump. The pump we use has a built-in unloader valve and original TBM plumbing modified accordingly a few years ago. No leaks noted. Gear retract cylinders are just four years old. Accumulator holds 500 PSI consistently. Squat mechanism verified as fully functional. Verified that all in-line hydraulic filters are clean. Much of this trouble shooting was provided remotely by John Lane (THANK YOU). We have the original manuals (but would be grateful for additional copies, especially if they are in the original color - that hydraulic system diagram is hard to read in black and white!)

I have just removed the Thermal Relief Manifold for overhaul, and we have had some discussions about "back pressure" but can't find the source.

Any other TBM or warbird Hydraulic Experts out there?

Call John Lane at Airpower Unlimited 208 324 3650. He is the one we always turn to when we have problems with the one that I have flown.

That would be the same John Lane I mentioned in my original post. I have also talked with Harlan and the Candian guys still operating four TBM's as SEATs. It was time to take the problem to the WIX.

Any possibility you are getting air in the system somehow?

Doh! Sorry I missed that!

How is the retrack affected by cowl flap operation? If the cowl flap bleed down seems to be the trigger for the start of the issue, what would operation of the cowl flaps during flight do to the retract issue?

Are there one way valves in the system that could hang up or stick? Are all the systems operated by dual action cylinders? When the gear retract, the "extend" fluid has to return to the system (resevoir) by the piston travel. Is it being diverted to other hydraulic cylinders cowl flaps or flaps that causes the delay as a result of a faulty check valve?

Is it possible to have a faulty accumulator that has bled hydraulic fluid past a diaphram that once cycled properly, functions properly? It could still show adequate pressure but result in a low total hydraulic system fluid volume by having an unaccounted for place for fluid to collect.

Sorry, probably out to lunch but just ramblings of an old Indy car mechaninc.

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"There are old pilots and bold pilots but few old, bold pilots."

Just because something is overhauled doesn't mean it is good.. I had to replace items 4 times untill I got a good one.. which really complicates trouble shooting

BDK - Air was an original thought. So we would exercise all other hydraulic systems several time while on the ground. Gear still failed first retraction. Other than the suction line from reservoir to pump, it seems any place that would draw air would also visibly leak 5606 fluid.

Savage - NP - I often jump to conclusions before reading a long boring thread (like mine!)

S Dennison - the cylinders are indeed dual action. However I am sure the retraction side requires a LOT more pressure than the extension side. Emergency extension is also accomplished with free-fall and zero pressure. That is why the uplocks - don't want any extra drag when trying to run away from somebody who shot up your hydraulics! Another note, we have left the plane in gear up on jacks for hours with no leak down to where the up-locks are engaged. Hydraulic fluid does not appear to get "lost" and the accumulator has held charge with no servicing. John Lane mentioned that many TBM operators have changed from the original diaphragm style to newer piston style as it is more robust. We still might do that.

Cowl flap operation while flying has no apparent affect. I just used the cowl flaps to bleed off all hydraulic pressure as that is the only way I know of, short of breaking a line.

Broken-Wrench - a valid point indeed!

With the system pressure at Zero, what does your accumalator pressure read? How about system pressure at 1000PSI?

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The more I learn about aircraft, the more I realize I still have to learn.

What about the cowl flap operation in relation to the gear retract in flight? Same effect as the wing flaps? What is the color of the fluid? Solid in color or pastell due to micro-bubbles?

What about a possible loss of prime to the pump? How is the pump fed from the reservoir? Gravity? Possible feed line restriction? Can you run the full gamit of diagnostic actions on stands without flying? (sorry)

My thoughts on accumulators are that I have seen diaphragm issues where the accumulator actually stores fluid behind the diaphragm. It will still hold pressure and appear normal but it is working on a reduced volume. More importantly, it has reduced the hydraulic system volume. Once initially presurized by the pump operation, the fluid could be forced back into the system thus filling it and operation normal.

OK, I'll shut up now.

_________________
"There are old pilots and bold pilots but few old, bold pilots."

Here's a question -

Must pressure be bled off the system at shutdown? Just as a "troubleshoot" item, if possible, could you try not bleeding off the pressure one time and see if the problem duplicates without a bleed-down?

I'll be the token "guy that makes a dumb suggestion."

Any chance this issue could be related to the fluid you're using? What's different between what you're using now and what 'the book' says to use?

_________________
Phil K.
Yankee Air Museum
Systems Admin / Ramp Crew / Professional Photo Ruiner

Colour hydraulics diagram for avenger from a Grumman maintenance manual.









I'm definately no expert in this, but the original system worked to prevent gear retraction whilst the flaps were down.

"If I take off with say a 15 degree flap setting, and have set myself up for the initial "hang" retraction, after the gear hangs I find that a "more flaps" setting has no effect (flaps still at 15). But a "retract flaps" setting will result in full flaps retraction after an abnormal delay of about ten seconds, followed by the gear going the rest of the way (gear handle still full "up" throughout.) No other interaction of gear/flap noted in other flight regimes. "

Another dumb question is if this was the case when built, has the system been modified, and is this an issue?

Phil, most likely they are using MIL 5606 as that is the standard fluid that we all use. The other is MIL 83282 is a fire resistant alternative that is compatible with 5606. The only other fluid that is out there is called Skydrol, a nasty substance only found in some civilian jets.

I'll be the second one. I say start at the beginning by draining the fluid over a long amount of time such as overnite. Refill with new fluid. No reason to back this up. Ill be anxious to here the answer.