Piper automatic gear extend

[Mjg2011]

Looking at the hydraulic diagram for the piper arrow gear system with the auto extend feature, I was wondering if the emergency gear extend valve being open or partially open would allow fluid to flow back into the gear up side of the actuators as well as the gear down side preventing gear extension through the emergency valve. If the auto extend diaphragm got stuck, maybe the emergency valve would be stuck partially open. Could this lead to a failed gear extension? I don’t have access to an airplane with this system to test it, but has anyone ever tried to put the gear down with the emergency valve open and the hydraulic pump running in the gear down direction? Is this why the checklist says to put the emergency gear valve in override first before emergency gear extension? I guess that would fully close the valve so no back flow will occur.

 

[Gilbert Buettner]

Maybe post this at the Piper Aviation and Pilots Forum.

 

[Bell206]

I was wondering if the emergency gear extend valve being open or partially open

Why the wonder? The only experience I have with the auto function was to disable it per a Piper SB. While I think the system got a bad rep due to other reasons like the GO-300 engine, if the auto system is properly maintained you shouldnt run into any situations as you discribe?

 

[Datadriver]

The emergency procedures are inadequate because they don't tell you what to do if the gear indicator breaker is blown.

48 hours I ago I was in this situation: gear handle down, no green lights, and the pump did not even run. The pump running is visible as a spike in amps. The gear indicator breaker was blown, but the gear pump breaker was in. Reset the indicator breaker but it was blown.
Pushed emergency gear lever all the way down, heard pump running. Reset indicator breaker - it stayed in this time: 3 green, landed.

I'm curious if the normal actuator control and indicator lights are on the same circuit. The pump itself is on a different breaker.

 

[Jim K]

The auto-extend was disabled in my plane before I got it, but the diaphragm is still under the floor, and it connects to the same valve as the emergency gear drop lever. Sometimes it's referred to as the "Hoof Valve", after the manufacturer. On my second flight in my plane we couldn't get a nose gear indication. We ran the checklist several times and tried everything we could think of. Turned out to be a bad microswitch on the nose gear, so it was working, but we didn't know that. We fixed that, but then the gear wouldn't go up.

My mechanic took the Hoof valve apart (after we learned that an overhaul was 4 figures) and found an o-ring that was damaged. He replaced that and problem solved. We believe that at one point we used the emergency gear drop with the gear switch in the up position and the pump breaker in. The pump runs whenever the switch is in the "up" position and the pressure sensor reads low pressure. In flight the gear is held up by pressure. If a hose or seal blows, the gear drops by gravity/spring pressure. The emergency lever just dumps the pressure and allows the gear to fall. By working the lever with the pump running, the flowing oil damaged (cut or dislodged, I don't remember) that o-ring.

I don't know what prevents that from happening when the auto-extender drops the gear. Maybe it does and that's your problem? The override position just prevents the diaphragm from operating the Hoof valve. The important thing in my mind is to make sure the pump breaker is pulled before using the emergency drop lever.

The indicator light system and pump are completely separate systems. The only function of the micro-switches at the gear is to light up the three lights. The pump is controlled by the gear lever, the pressure switch, and the weight-on-wheels switch.

I hope this helps. It sounds like your issue is similar, with the added complication of the auto-extender. I'd yank that thing while I'm in there if I were you.

 

[hindsight2020]

Post above have hit the highlights regarding the Arrow gear system. I had one of those with the rube goldberg auto extender. It was actually more patronizing than that. It would also keep the gear from extending if the pressure switch or connections, or diaphram, was on the fritz. Mine started disallowing me from extending the gear normally until it hit the no kidding pitot pressure low-airspeed trigger point of the auto extender itself, otherwise you had to fly everywhere with the override switch engaged so the system could honor your gear selector commands at the time you actually wanted them! Then it wouldn't even do it with it (straight up electrical issue somewhere, not associated with the auto extender pressure switches) It just became a headache. In retrospect I blame much of that to my sideshow gig AP, the guy previous to him would overcharge like you read about, but at least he devoted full time to you as a customer. The last guy I was just low man on the totem pole, captive audiences abound, and the work quality showed it (different problem about this hobby, not the arrow's fault). Digressing.

Towards the end of my ownership tenure, the retract system was the main source of my woes. I wanted to yank it [auto-extener] out, but in true POA fashion, had a 'philosophical' objection to spending more money to do it than tinker with it, and I was already in take my ball and go home mode with that airplane.

Apropos of nothing, the purpose of the ill-fated flight was to troubleshoot for the 69th time whatever "calibration" my on again off again AP had done to fix the "unable to retract" problem. Then the cosmos released me from my suffering lol. Little known fact about that flight, I had to make the powered[ish] glide profile with the gear stuck down, because when I went to raise it to extend my glide, it wouldn't. That [redacted] system was like the cops...never there when you need them.

2/10 would not recommend [the auto extender]. My next airplane will be a FG. I've grown quite tired of gratuitous complications for little value added (oops, I misspelled fac-built). Now get off my lawn.

 

[Dan Thomas]

The Piper SB to disable the auto-extend system came about after an accident or two with these airplanes. If the pitot iced up, the pressure in the pitot system would bleed off and the gear would extend, right when you're already accumulating the drag and weight of ice, and the gear's drag pulled the airplane down to the crash site.

 

[Jim K]

The Piper SB to disable the auto-extend system came about after an accident or two with these airplanes. If the pitot iced up, the pressure in the pitot system would bleed off and the gear would extend, right when you're already accumulating the drag and weight of ice, and the gear's drag pulled the airplane down to the crash site.

Wasn't there also a couple where the pilot was taking off from a short field, and the gear dropped, putting him into the trees? I swear I read that story somewhere. I can think of a lot of scenarios where that system could kill you, and none where it could save your life.

 

[Warlock]

Trying to extend your glide in an engine out to make the field then hit gear down speed and end up in the trees and die…one of the lawsuits from the grieving family.

 

[Bell206]

The Piper SB to disable the auto-extend system came about after an accident or two with these airplanes.

And I'm sure it was Piper's legal dept that pushed it. I think the Piper summed it up in the "Purpose" section of the bulletin:

Piper SB 866A

 

[morleyz]

Removal was never performed on my Arrow, but I always keep the override activated. The nice "feature" of the override is the gear warning light and scream go off still and would do so around base to final if I actually forgot the put the gear down. I don't know that still works after removal.

That being said, it also has gone off while doing some low speed maneuvers, including practicing power off anything even if you're at 10,000 ft AGL. The POH gives you the impression this won't happen, but from experience it can go off at any altitude with an unpredictable combination of throttle and airspeed. I imagine it could really surprise you if the gear actually came down in the middle of something where you're already going slow or at low altitude. You get a LOT of drag in a couple of seconds. It took me a decent amount of practice to not lose a few hundred feet on downwind just by extending the gear.

The idea is sound, but the implementation was not great.

 

[Datadriver]

The auto-extend was disabled in my plane before I got it, but the diaphragm is still under the floor, and it connects to the same valve as the emergency gear drop lever. Sometimes it's referred to as the "Hoof Valve", after the manufacturer. On my second flight in my plane we couldn't get a nose gear indication. We ran the checklist several times and tried everything we could think of. Turned out to be a bad microswitch on the nose gear, so it was working, but we didn't know that. We fixed that, but then the gear wouldn't go up.

My mechanic took the Hoof valve apart (after we learned that an overhaul was 4 figures) and found an o-ring that was damaged. He replaced that and problem solved. We believe that at one point we used the emergency gear drop with the gear switch in the up position and the pump breaker in. The pump runs whenever the switch is in the "up" position and the pressure sensor reads low pressure. In flight the gear is held up by pressure. If a hose or seal blows, the gear drops by gravity/spring pressure. The emergency lever just dumps the pressure and allows the gear to fall. By working the lever with the pump running, the flowing oil damaged (cut or dislodged, I don't remember) that o-ring.

I don't know what prevents that from happening when the auto-extender drops the gear. Maybe it does and that's your problem? The override position just prevents the diaphragm from operating the Hoof valve. The important thing in my mind is to make sure the pump breaker is pulled before using the emergency drop lever.

The indicator light system and pump are completely separate systems. The only function of the micro-switches at the gear is to light up the three lights. The pump is controlled by the gear lever, the pressure switch, and the weight-on-wheels switch.

I hope this helps. It sounds like your issue is similar, with the added complication of the auto-extender. I'd yank that thing while I'm in there if I were you.

Yes, I have considered yanking the auto-extender in the past. I don't know if it contributed to this recent issue or not. My biggest beef with the auto-extender is that it is dialed way up on airspeed. It won't let you raise the gear unless you are flying over 100kts. That's nuts considering vx/vy of 77/87. Every takeoff that thing gets disabled by me.

Insurance-wise it is a wash. Agent tells me it has caused as many accidents as saves. Removal requires about a grand to Piper for the paperwork.

 

[Dan Thomas]

My biggest beef with the auto-extender is that it is dialed way up on airspeed. It won't let you raise the gear unless you are flying over 100kts. That's nuts considering vx/vy of 77/87. Every takeoff that thing gets disabled by me.

That sure sounds like a misrigged system. No surprise; in almost every airplane I worked on for the first time I found flight and/or engine controls badly out of rig. Seems that mechanics never consult the service manuals. I've had owners ask me what I did to make the airplane fly so nicely now. AllI did was set things as per the instructions.

 

[Datadriver]

I worked with my mechanic today on my Arrow IV's "gear indicator lights circuit breaker trippin". It turns out a recent avionics install had left a live wire dangling down in the engine compartment. When the nose gear came up it was mashing the wire causing the tripped breaker.

ALSO: in this airplane if the gear lights breaker is tripped the gear handle does NOT activate the pump. I don't know if all '79 Arrow IVs are wired that way but mine is.

 

[Rgbeard]

Looking at the hydraulic diagram for the piper arrow gear system with the auto extend feature, I was wondering if the emergency gear extend valve being open or partially open would allow fluid to flow back into the gear up side of the actuators as well as the gear down side preventing gear extension through the emergency valve. If the auto extend diaphragm got stuck, maybe the emergency valve would be stuck partially open. Could this lead to a failed gear extension? I don’t have access to an airplane with this system to test it, but has anyone ever tried to put the gear down with the emergency valve open and the hydraulic pump running in the gear down direction? Is this why the checklist says to put the emergency gear valve in override first before emergency gear extension? I guess that would fully close the valve so no back flow will occur.

No. What you’re proposing isn’t a specific risk. What’s your intent with the question?