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

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4 weeks 1 day ago #1203

Second time the emergency gear extension has broken something on me...

Last year, an uncommanded gear extension cost me the drag link on my nose gear. Just a few weeks ago, another uncommanded extension broke the nose gear cylinder mount.

When the emergency system is activated, the gear literally slams out with a loud thud. Very violent. My mechanic thinks this isn't normal. Wondering if the system requires a snubber or something to limit the violent extension.

Does anyone have any insight or experience with this? Yes, I know the system can be disabled. I'd rather just keep it activated, as long as it will stop breaking my plane!

Thanks for any advice or assistance!
Pete

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3 weeks 4 days ago #1204

Hi Pete;
I'm working on getting you a good answer. As I understand it, whenever the automatic system is activated, it opens the return lines in the landing gear hydraulic system, then the gear (s) free fall to the down position aided by springs.

Does your Arrow have the three position manual over ride switch? If so, one option is to pull the handle to the manual over ride "off" position and install the Lockout pin. I know that's not the answer you're looking for so I'll get back to you.
Steve

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3 weeks 4 days ago #1205

Thanks Steve! My Arrow is a 1971, which doesn't have the lockout pin. So you have to hold the override up.

BTW, I read your great article on the EIS install for your Comanche. My A&P just ordered the system and switch for my Arrow today (since it's in the shop getting landing gear fixed anyways...) Have you seen the claimed fuel economy advantage?

Thanks for your help,
Pete

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3 weeks 4 days ago #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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3 weeks 4 days ago #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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3 weeks 4 days ago #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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