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Topic-icon Arrow: Automatic Landing Gear Extension is Breaking My Plane

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07 Dec 2017 23:18 #1215

Pete, I had the exact same issue with R main gear on my Lance - turns out the restrictor was put in the wrong place at some point in time. Had it moved and no more whoomp!

Wrt adjustments on the emergency gear system, if it's anything like the Lance (which I'm pretty sure it is), it can definitely be adjusted. I believe it has to be done in flight so you adjust for the correct airspeeds so you need to go fly with a mechanic who is knowledgeable on this system. There should be a procedure in the maintenance manual. On the Lance, the mechanism is located under center row seats alongside the main spar.

As Steve says, there is a separate air pressure mast for the emergency gear system, and that drives ram air into one side of a "bellows" mechanism, and static air into the other side. When the difference in air pressure is high, the mechanical linkage attached to the bellows keeps the hydraulic shunt valve closed and maintains hydraulic pressure in the high pressure lines (keeping the gear up). When the pressure difference drops below a certain threshold, the spring force over-powers the bellows and the shunt valve opens, shorting the high pressure hydraulic line to the low pressure return line, allowing the gear to drop by gravity.

There is a tension screw on the spring mechanism that can be adjusted with a screwdriver, which changes the airspeed at which the shunt valve opens. There is another adjustment for when it closes. Both airspeed values should be indicated in the maintenance manual.

Hope this is helpful.

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  • Pete Castine
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04 Dec 2017 20:51 #1213

Steve - you were correct. The restrictor was missing from the nose gear line on my plane, which allowed the nose gear to slam down when the emergency extend or auto-land system kicked in. Putting one in results in a much softer "landing" for the nose gear in the down position. Thanks for your help on this issue.

Pete

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23 Nov 2017 15:01 #1209

The service manual has a test to determine if the auto land system is operable.
The auto land system has it's own "airspeed" mast so that system has to be checked too.
I'm not super familiar with the system so I can't really advise on the adjustments; it appears that all adjustments are external and that if the external adjustments are correct the unit itself has to be refurbed.
Since its Thanksgiving Day and I'm going to take off to my sister's in an hour, I don't have time to further research this until I return next week.
I suspect that if the auto land unit needs repair, your only option is to remove it, but again I'm not positive on this suspicion.
Happy Holidays

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  • Pete Castine
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22 Nov 2017 17:10 #1208

Steve,

Thanks again for your help. No, I haven't noticed anything unusual about the speed of the gear going up.

Trying to research why the gear would auto extend if (a) I'm not pushing the emergency down switch (which I understand is a different emergency system from the auto-land or auto-extend system) or (b) the criteria for the auto-land system aren't being met.

Each time the gear has dropped uncommanded, the airspeed *could* have been below 105mph (auto extension speed per my POH). I say *could*, because I wasn't monitoring airspeed at the exact moment the gear fell. However, each time the gear has dropped uncommanded, I'm all but certain the power setting has been above the 14" that you mention above. I have never had an uncommanded drop during take off or climb out, which I normally do at max power and 95mph (Vy per my POH).

Do you know where I could find information about the circuit (or whatever it is) that tells the auto-land system that the power is above the criteria for auto-extension? I'm guessing this is the culprit for my uncommanded gear extension, as opposed to an airspeed issue (although Charlie is checking the pitot system as well).

Again, thanks for your valuable help.
Pete

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22 Nov 2017 04:04 #1207

Pete;
It occurred to me that since the up manifold and the down manifold are right next to each other, it may be that the two fittings (No. 33 and No. 11 in the illustration) may have gotten swapped and mistakenly installed in the wrong manifold. Of course that would most likely slow the speed of retraction.
Has anyone ever told you that your landing gear is slow to go up??

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22 Nov 2017 00:04 #1206

Hi Pete;
I haven't looked very hard for lessened fuel consumption. I expect it's better but haven't done any comprehensive testing.
Good news on the gear. If your mechanic has a service and parts manual he will find the LG hyd schematic (fig 6-1 in the book I have) and there is a detail calling out a "gear down snubber orifice" in the gear down line out of what the schematic calls the "automatic gear down & emergency free fall gear valve." So there is a gear down snubber but it ain't where the schematic says it is.
If your mechanic has a parts book for the PA-28R-201 (it's the one I have) figure 59 shows Hydraulic System Installation. On it there are two manifolds; part 6 called the "manifold, left" and part 7 called the "manifold, right." No. 6 should be called the gear up manifold, and No. 7 should be called the gear down manifold.
If you look at the fittings on the aft end of these manifolds, the gear up one (part No 33) is a "nipple-AN416-4D, which threaded to screw into the manifold on one end and flared to connect to the rigid hydraulic line on the other end. It's a standard aircraft quality part.
If you look at the aft end of the gear down manifold (No. 7) you'll see part No.11. It's called a "Nipple--restricted." There's your snubber. I recommend that you pull No 11 and check to see if someone didn't accidentally replaced the restricted nipple with a standard AN 416 nipple. The part number of the restricted nipple is 67600-00. It's used in many Piper hydraulic LG systems. New price is around $180.
I would next check your logbooks to determine if Piper Service Bulletin 724A has been completed. The title of this bulletin is "Nose gear landing gear inspection and rigging." The applicability section refers to PA-28R-201TIIl and IV so it doesn't appear to apply but the description sounds very familiar. It says, "Reports have been received of cracked or broken landing gear link and brace assemblies, nose gear actuator housings and hat section fairings."
If you can't find that bulletin, I can send you a copy.
Good luck.
Steve

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