Warbird Information Exchange

How about a gasket improperly positioned and covering a fluid passage up?

Great stuff - thanks to all who have helped here!

S Dennison - I have not tried cowl flap, or any other hydraulic system to free the "stuck gear" syndrome. That sounds like a good test. The flap was a more obvious choice as the two selectors are in the same assembly and share the same fluid return path. The pump is advertised as "self priming" and installed at the lower portion of the engine accessory section so it is quite lower than the reservoir - in flight. I will check to see if this is true when resting on the ground. I see your point on the accumulator's possibility of causing the issue. I am pretty sure the gear retraction is the largest hydro load, and perhaps the fluid gets extracted from behind the diaphragm after the first full gear cycle???

Chico (et al) - Species 5606 Fluid has good color, no bubbles noted (spilt a bit when checking those hard-to-reach inline filters). Accumulator pressure tracks hydro pressure except with engine off.

CAP flyer - I fuzzily recall that a engine shut-down w/o hydro bleed-off would not have the failure mode, but I will re-check that on our next test hop.

PR May - you da man! Thanks for the color images. I am an expert with Photoshop and will sew them back together. I am "pretty" sure the flap interconnect system you cite is from an older model, our is a TBM3-E. There is no "protruding arm on the flap lever". I can try specifically raising the gear with the flaps down, but from what I know, this is not precluded. There is a cable connected to the left landing gear scissors which holds a pin in the gear control lever. This performs a mechanical interlock to keep from raising the gear when there is weight on them. There is also a double mechanical lock on the gear switch which requires two separate simultaneous finger flicks before one can raise the gear lever. Must be some kind of dexterity test designed to weed out dumb pilots!

Versatile - I will put your suggestion last in line. You did not say "where" to drain the hydro fluid. The provided plug on the accumulator seems obvious, but somehow inappropriate.

"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."

The manual states, "When the landing gear and flaps are down, the flaps may be raised, but the landing gear cannot normally be raised until the flaps are raised. This feature is intended to prevent accidentally raising the gear just before landing."

In the scenario you outlined it appears that you are raising the gear before the flaps are up. What happens if you follow the procedure in the manual of flaps then gear?

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

As I previously mentioned, I think that system was for a different TBM model. Our flap selector does not have the interlock override mechanism which is cited in the manual text. Besides, with flaps 15 on take-off, when I select "gear up" they start to retract immediately and "normally" until they stop at 80%. I also flew quite a bit with flaps at 15 degrees and cycled the gear with no problem after the initial partial retraction problem was cleared by recycling.

Bottom line - there is no normal interaction between flap operation and gear operation. Both can be used regardless of the other's position. What I found was that when the gear is hanging partially retracted - its sole failure mode, and only on the first operation - then retracting the flaps clears the problem and the gear will retract the full amount.

I really aren't qualified to say much,; but since the electrons are free. I would drain the fluid and strain it as it is drained. Might be gasket particles etc causing blockage. Might be moisture has got into the fluid as well. Everything works after you cycle it like you have said. The one component similar to the system is the fluid. I won't mind being wrong at all and will learn as well.

I really aren't qualified to say much,; but since the electrons are free. I would drain the fluid and strain it as it is drained. Might be gasket particles etc causing blockage. Might be moisture has got into the fluid as well. Everything works after you cycle it like you have said. The one component similar to the system is the fluid. I won't mind being wrong at all and will learn as well.

Versatile - Sorry I was not clearer in my original response to you. It seems you think there might be a dedicated "low spot" where one could drain all the fluid from the system - much like you would prepare your lawn sprinkler system for winter. There is not. I suppose I could drain from all the many bends and low spots, perhaps blow air through all the lines, etc., but I am not sure what this would provide me. The fluid looks good, no bubbles or moisture noted, and all the fine mesh wire and CUNO filters are debris free. In case you were suggesting this, one does not ever re-use hydraulic fluid either.

The fact that the problem is so repeatable and only under certain conditions, makes me "pretty" confident that the fluid itself is not the problem. As you can see by the system diagram, there are lots of common items besides the fluid.

Duncan, if not bleeding down the system cures the issue, then maybe somewhere there is a restriction to flow possibly in the form of a slow-operating or stuck valve? My limited knowledge would indicate that if there's not pressure, it's possible that a valve is not properly operating and thus the pressures on that first use are not sufficient to force the valve all the way open past whatever is causing it not to operate properly. I've seen it happen on other hydraulics I've worked on in the past. Usually there was a failed bearing or dirt in the bearing or bushing of the valve.

I'm still tending towards air in the system (I'm far from an expert however and know absolutely nothing about TBMs). Are those filters on the suction side? Maybe you are sucking air through one of the gaskets?

The highest hydraulic pressure requirement on the gear is just as the uplocks snap into place when the gear are horizontal. When the gear are vertical (close to the down position), they swing from side to side easily. As they approach the uplocks they get harder and harder to raise due to gravity.

Filters are on the pressure side. We replaced the o-rings when we checked the filters. As previously stated, pressure is good. Our gear uplocks don't really do anything, unless we lose hydraulic pressure.

We have a closed hydraulic system with a given volume of piston(s) and swept area and a fixed volume of fluid to work both sides of these cylinders. When the gear is raised, the hydraulic fluid and pressure fill the active side of the piston, moving the piston and forcing the fluid out of the non-active side of the cylinder. The oil on the non-active side returns through the "system" to the reservoir.

So, if on first operation, the gear hit a spot where the active side of the gear stop moving, I think you have two possibilities. The first is the active side of the cylinder stops getting fluid due to a lack of pressure or lack of fluid supply and therefore stops moving until either the pressure or fluid supply is restored.

The second possibility is that there becomes a temporary hydraulic lock that restricts the fluid from the non-active side of the piston from leaving the cylinder and you have a pressure stand off between the two sides and the piston stops moving until one side or the other regains a pressure/supply advantage.

Root causes could include my previous theory of the diaphragm rupture in the accumulator. It could be an air pocket that gathers somewhere in the system that reaches the pump at that "stopping" point until the air bleeds out and pressure is restored. (There should be a momentary systemic pressure drop that would accompany this.)

It could also be a hanging check valve that restricts the fluid flow from the inactive side of the cylinder on retract. I'd think this issue would be accompanied by a spike in hydraulic pressure at the moment of lock up.

I am not an aircraft mechanic and I did not even sleep in a Holiday Inn Express last night but can you cycle the gear on jack stands and watch the fluid level in the reservoir as well as line pressure at various locations in the total hydraulic system?

Thanks for allowing my input.

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

S Dennison - this is why we are replacing the Thermal Relief Valves as I suspect we have a "hydraulic lock" on the back-side of the piston which get cleared upon adding fluid/valve action to extend/recycle the gear.

The accumulator will be next in line, if this does not fix it. I am asking for input 'cuz we have already stumped the experts. Pogo: "We have met the enemy and he is us."

Thanks for the reply. I really look forward to hearing the resolution of your "squawk". I'm always looking to learn.

Thanks Dude!

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

Could the hydraulic Quantity be over serviced?
On some airplanes you must have the landing gear, flaps, wing fold, cowl flaps actuators in a specific position when servicing the quantity.

Steve

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"Any excuse is good enough if you're willing to use it!"

Duncan you are spot on - the interlock (mechanical) was removed on later models of the TBM-3. I found my copy of the flight manual and post the relevant pages below - I should have looked at this first!. The -1 manual also has another version of the hydraulics diagram if this helps you out.

regards

Peter