PA31 gear doors

[boofhead]

Anybody have experience with the PA31 without gear doors? I am thinking of removing the ones on our company Chieftan but we do fly high (relative) altitude and I heard that there is a performance penalty. Rigging the doors is a continuous problem, and removing them would save a lot of time in maintenance. Or not?

[SNS3Guppy]

By what authorization or modification of your type certificate do you intend to operate without the doors?

Not to dampen your enthusiasm, but modifying an aircraft isn't necessarily justified simply because you don't like adjusting the gear doors.

[MX Trainer]

In all the years of maintaining a Chieftan I have never had a problem with the landing gear doors if they were correctly rigged to begin with. For our operation that involved a lot of work on unimproved strips including ice strips the landing gear doors were never a high maintenance area. Some of the aircraft were very high time as well and had been ridden hard and put away wet by previous owners.

I wouldn't consider the aircraft to have as much issues with the doors as something like the Beech King Air mechanical door system that I found to need more attention than the PA31-350.

What will kill your doors is the leading edge not having preload against the wing skin. This allows the airflow to get between the door and the wing and will distort and vibrate the door resulting in lots of wear in a hurry. In addition it will warp the door making it harder to rig in the future as the bent door will now contact the aft face before the forward face and in some cases make it impossible to correctly rig the door.

Put your aircraft on jacks - retract the gear - and check the fit of your doors as they retract. The correct pattern should be the forward door skin contacting the wing skin first and then just after that the door should snug into the aft area with a minimum of space along the rear door to wing skin. It is acceptable to have a bit of space there but try to get full contact if you can. the air pressure during flight will push the door into the recess but not if there is a gap at the forward edge of the door.

I have flown once with the doors off - FERRY FLIGHT ONLY - to get the aircraft back to our base after it took out a gear door and a prop on some wildlife. There was no way to fit a new door without doing some extensive work so we opted to get a ferry flight permit to return home. We remove both doors on both sides to keep symmetry. The only thing I remember about that flight was that it was a bit noisy and I know we didn't get above 10,000 feet as our aircraft was not equipped with an oxy system. This was a long time ago - early 1980s and I believe we made a phone call to Piper to be sure we could do the flight - but I am not 100% positive on that.

My $0.02 worth - Check the current doors for fit - if they are badly bent - get some new ones. Rig them correctly with new hardware and check them on every preflight for fit. Don't fly the aircraft if the doors don't fit correctly and you should have solved your problem.

Another issue that I would have with taking the doors off would be as the above poster commented - your aircraft no longer conforms to the type certificate specs.

Something that most people don't think about is why there are gear doors on the aircraft to begin with. So 3 things come immediately to mind for me - the first is the doors are put there for looks - second the doors are put there for aerodynamic reasons - and third the doors are put there to keep the landing gear away from the elements - like flying in icing conditions and having ice build up in the landing gear well to the point that the gear will no longer extend on your next landing. And that would pretty much negate any reason for removing the doors.:O

Regards,

Mx

[Tinstaafl]

Is there an issue with your maintenance mob? Why are they having rigging issues? I manage a PA31, and may be managing another soon. We don't seem to have gear door rigging issues apart from once after a major repair. Since then no problems.

[stuckgear]

STC'd mod to replace gear doors with fairings..


Aircraft Restoration Corp. received STC approval to install an aerodynamic fairing in place of the inner main landing gear doors on the PA-31 series airplanes.

[boofhead]

It is a common mod, done under an STC.
The Chieftan has two hydraulic pumps that are not designed for continuous operation. When the gear is down, doors closed and handle returned to OFF, the pumps are set to run an open loop, with low pressure. When the gear is up, doors closed, handle OFF, the pumps again go to low load. If the gear does not come up all the way, or the doors remain open, the pumps run continuously and can quickly fail. Maybe a couple of hours will kill the pumps, and the damage is cumulative.
One problem with the system is the nosegear UP switch, which is set on a flimsy piece of steel that is easily bent. The gear has no UP limit block, and if it comes up too fast it is only stopped by the switch bracket. Did I mention that this bracket is flimsy? It is common for the bracket to bend and stop the signal that tells the main gear doors to close in sequence. There is no STC for a stronger bracket.
If the main gear doors do not close, the pumps will continue to run and the drag on the airplane is significant, perhaps 20 - 30 knots loss of IAS. In addition, the rigging of the main gear doors is time consuming, with failures of the door hinges a common problem. The pumps might continue to run because of either the nosegear or main gear door failure, but taking the doors off removes one of the reasons for the problem.
I fly two different Chieftans and they both have this problem from time to time, usually shown by the gear red light remaining on after gear is selected up after takeoff. Cycling the gear usually fixes it, but not always, and once it starts it gets progressively worse until the nosegear or main gear doors are readjusted, which in its turn requires the airplane to be put on jacks. I might have to cycle the gear several times before I get a clean indication, but next flight it will work perfectly.
I am not sure, but the gear down speed might be higher than the POH limit of 130 knots with the doors removed, which would also be of benefit, and it might not be so important to get the gear up immediately after takeoff, while the IAS is low, thus preventing the problem in the first place.
We already have an STC for the gear door hinges, but it makes it easier to handle the landing gear system if the doors are removed. I am looking for information about performance penalties and the pro/cons of this. There are lots of Navajos out there, and there is surely a wealth of knowledge.
My question was directed at those people, hence I did not think I needed to spell it out so completely, but obviously I was wrong.
Again, I am not looking for suggestions as to how to do it, just information from anyone who has done it with regard to performance of the airplane.

[stuckgear]

I did not think I needed to spell it out so completely, but obviously I was wrong.



Atch ! it's a surprise no-one's posted a METAR yet ! :p

[boofhead]

Mx, thanks for your reply.

[SNS3Guppy]

There are lots of Navajos out there, and there is surely a wealth of knowledge.
My question was directed at those people,...

Those people answered you. You weren't satisfied with the reply.

Perhaps you need better maintenance. You shouldn't need to be rerigging the gear on a regular basis, and the issues you describe shouldn't be common for you. They should be, at best, a rarity.

[boofhead]

I guess I am not as good at describing the problem as I thought. The usual cause of the gear fault rests with the nose gear, which I have been told cannot be changed from the original design and every PA31 I have ever flown has at some time or other given me a problem in that area because of the design and construction of the parts. The gear up switch is on the same plate that acts as the limiting buffer for the gear. There is no other physical Up Stop, which means if the gear comes up too fast or hits the plate too hard it can bend the plate a little, which stops the switch from making and stops the sequencing, leaving the main gear doors hanging open and the pumps running. The doors hang out in the airstream and cause an increase in drag and there is a speed restriction as well as a time restriction for continuing the flight. The flight crew cannot see the doors. An obvious fix is to strengthen the plate, or replace it, and we have done all we can legally do but it is still not enough. I have seen the damage, and experienced the effect. I am not impressed with the design or construction of this part. When we replace the plate it eventually fails again. Right now the airplane is in annual, the gear is out of the airplane. It would be a logical time to make the change.
Removing the doors is something that is done by some operators, and I have to assume it is done for a good reason. There are STCs out there for doing this; why would they exist if they were not needed?
I have professional mechanics and have no complaint against them, they are knowledgeable and experienced. I trust my life to their work every time I fly. Why would you think I would change my allegiance to a bunch of Opinionated Experts, some of whom are obviously only trying to pretend to know anything about the subject, and who might or might not have any experience?
What is the statement? A little knowledge is dangerous?
If I decide to take the doors off it will not be because it offends your sensibilities but will be a decision taken in consultation with people I respect and for a genuine benefit.
The only company in my area that has removed the doors does not fly above 10,000 feet and they report satisfaction with the mod. It saves them a lot of time in maintenance and has a negligible effect on IAS. It allows them to at least return to a suitable maintenance airport without the gear doors hanging open, which restricts the airspeed both for certification and drag reasons. They have not put the doors back on, so it must be true that they are satisfied.
The area we fly extends from Barrow to Clearwater, and from Shemya to New York, including Canada. We fly on short strips, gravel or sealed, dry or wet, ice or snow. Some of our landings are on one-way strips which puts a load on the brakes and gear as well. My pilots are good at what they do but are not infallible. Not all landings are perfect.
Sometimes we are in remote areas that have no fuel or maintenance. A stuck gear door can be a major problem. Part of my job is to anticipate difficulties and have procedures for my crews to use that keep us flying, safely and effectively.
It has not happened, but where would I stand if one of my crews had an engine failure on takeoff and the gear did not properly retract? What effect on rate of climb would the gear doors have under these conditions? If I know of a problem and do nothing to prevent it, am I not also culpable?
It must be nice to always be so sure of the correctness of one's opinions as some on this forum are. I cannot go further lest I be banned again!
Although it is not a regular occurrence, failures have happened in the past and will no doubt happen again.
We fly above 20,000 feet with our airplanes and I am concerned with the effect of the lack of the doors on drag, or possible icing problems with no protection for the wheels. But I do not know this is true, it might be negligible.
Now for the METAR:

(sorry not available at this time, although the outside temp is currently -7F)

MX Trainer has given me good advice, although my people know this already it is good to have it supported and shows me he/she is qualified to at least discuss the gear system.
I am not asking IF I should do it, that is not your decision it is mine.
However it does not answer my question, which I will put down again here in case there is someone out there who is qualified to answer it:

If anyone has done it, what has been the effect on performance, particularly at altitude?

[SNS3Guppy]

The area we fly extends from Barrow to Clearwater, and from Shemya to New York, including Canada.

Some long trips in Navajos. Just curious: when did you last make that trip to Shemya in your Navajo, then turn back to fly to New York.

You're not the aerial photography outfit, are you?

I have professional mechanics and have no complaint against them, they are knowledgeable and experienced. I trust my life to their work every time I fly.

Very brave of you, given that according to your own comments, they don't seem to be able to properly rig the gear doors. If the doors require frequent rigging, you DO have a maintenance problem. Possibly several.

What is the statement? A little knowledge is dangerous?

One wonders whether this applies more to you, or to your mechanics. Perhaps both.

The usual cause of the gear fault rests with the nose gear, which I have been told cannot be changed from the original design and every PA31 I have ever flown has at some time or other given me a problem in that area because of the design and construction of the parts.

That's interesting, because not one of the navajos I've flown has ever given me that problem, or given anyone else flying them, that problem. That includes cargo, weather modification, charter, and tour operations in Chieftans and Panther Navajos.

My pilots are good at what they do but are not infallible. Not all landings are perfect.


That's really special, but has nothing to do with the gear doors now, does it?

[boofhead]

Guppy,
Yes it is photo work. Do I know you? Are you someone I rejected for a job? What is your motive for your demeaning comments?
We did not get to Shemya this year, the closest we got was Dutch.
Impune me all you want but lay off my mechanics. I never said they do not do good work, and the problem is not a continuous one but something I am doing a cost/benefit analysis on. I will probably not go forward with it, for cost or time, but do want to make sure it is considered before laying it to rest.
My last comment on landings was added because it might have some connection with the problem, I sure don't know and am not going to rule out anything. I do know it is affected by airspeed, both retraction and extension.
I don't have much time on PA31 airplanes, have only flown three or four of them, all for different outfits, but all of them required the occasional second or even third attempt to retract the gear before the handle went to neutral and the red light went out. Are you telling me that this is unique, that nobody else in the history of the PA31 has had this problem? Please...
I have had to manually extend the gear on only three airplanes, and the PA31 was one of them (not caused by the same part though) so I might be a little paranoid.
I enjoy technical discussions and respect your knowledge, even if I don't always agree with you. I hope I do not show you the same disrespect you show me. If your motive is to get under my skin, you win!

[SNS3Guppy]

Impune me all you want but lay off my mechanics.

So long as you own up to being the one who's doing all the constant rigging of the gear doors. You're the one who said "Rigging the doors is a continuous problem, and removing them would save a lot of time in maintenance." Your interest, expressed as the opening sentiment to the thread, is reducing maintenance costs due to the "continuous problem" of "rigging the doors." So is it you that get them rigged right, or your mechanics? If it's you, then by all means, let's lay off the mechanics. If it's not you, then it must be those "professional mechanics" that can't rig the doors properly. One, or the other.

Yes it is photo work. Do I know you? Are you someone I rejected for a job? What is your motive for your demeaning comments?

Demeaning? I quoted you.

No, you never rejected me for a job, ruskie. I wouldn't apply there.

Especially as you're using mechanics who can't rig a gear door.

Are you telling me that this is unique, that nobody else in the history of the PA31 has had this problem? Please...

I said nothing of the sort? Can you think for yourself without putting words in others mouths? Perhaps nobody in the history of the PA31, flying for a reputable company, with good maintenance. Perhaps that's what you intended to say I said.

I don't have much time on PA31 airplanes, have only flown three or four of them, all for different outfits, but all of them required the occasional second or even third attempt to retract the gear before the handle went to neutral and the red light went out.

Obviously you don't have much time on PA31 airplanes. Perhaps you have extraordinarily bad fortune (and judgment) in choosing employers that can't maintain airplanes. Who knows?

If you're having to try several times to retract the gear, ever stop to think that perhaps you shouldn't be retracting it in the first place?

I have had to manually extend the gear on only three airplanes, and the PA31 was one of them (not caused by the same part though) so I might be a little paranoid.

A little?

Do svidania.

[Big Pistons Forever]

I have a lot of time on Navajo's. The handle should return to neutral after retraction everytime. If it does not and the gear handle has to be reselected to make the gear work than the system is unservicable and should be repaired. If this is a recurring issue on an aircraft in your the fleet than it would appear that there is a problem with the maintainance as the gear is not being rigged correctly. I am not making any value judgement here just relating what in my experience are the facts of the case presented.

[717tech]

At the risk of being shot... wouldnt the STC kit have new performance/limitation figures to plan with?

[boofhead]

I ask a simple question, none of you can answer it, but some cannot resist taking the time to be snarky.

I guess my posts have been too long for many to read them or take the time to understand them before replying. Thanks anyway, it has been interesting.

Big Pistons, thank you for your comment. I am fully aware of the implications of the problem.

[SNS3Guppy]

I guess my posts have been too long for many to read them or take the time to understand them before replying.

Not at all. It's the reason you were quoted, and it was via those same quotes to which you were replied.

[boofhead]

No, you are wrong. I intended to have a serious conversation but did not realise the children from Jetblast were lurking. OK I was wrong to use the word continuous in my initial post, but I cleared that up early in the exchange. Yet you will not let it go.

I am not interested in your opinions of my or my mechanic's professionalism.
If you are not interested in helping me, please don't waste my time.

I have researched the airplane and there is abundant information out there concerning the landing gear system and its problems. I am being proactive by trying to learn more, and in so doing prevent future problems, perhaps in the field where my pilots will not have direct maintenance support.

The STC does have some information, but as usual with these things there is nothing concrete regarding performance, nor is there a price quoted. It does suggest an increase in the gear speeds might be available, which is worth having. I will need to call I guess.

Stuckgear, thank you for your lead.

[411A]

One problem with the system is the nosegear UP switch, which is set on a flimsy piece of steel that is easily bent.
Easily solved.
Fabricate a new bracket that is stronger.
Call it an owner produced part, and install.
Perfectly legal, so long as the airplane is operated under 14CFR91.
If not, fabricate one anyway and install, with no log entry...or get a field approval.

[SNS3Guppy]

It must be nice to always be so sure of the correctness of one's opinions as some on this forum are. I cannot go further lest I be banned again!

You wouldn't want to be banned again, then.

The STC does have some information, but as usual with these things there is nothing concrete regarding performance, nor is there a price quoted. It does suggest an increase in the gear speeds might be available, which is worth having.

There's always the press release...

Aircraft Restoration Corp. received STC approval to install an aerodynamic fairing in place of the inner main landing gear doors on the PA-31 series airplanes. The cost of this modification will pay for itself the first time you need to replace a door, hinges or actuators. It is a simple modification that reduces maintenance and parts costs. The number of moving parts is decreased AND the recurring AD note to inspect the door hinges is no longer required. The potential of gear door sagging or coming open in flight is eliminated. Split and leaking hoses and worn out actuators are a thing of the past.

One of our customers said, "One of the best things there is about this modification is that there is no performance penalty and no vibration! The landing gear retracts and extends faster and now I never have to worry about the doors coming open in flight, my payload was increased too".

In most cases this kit costs less than the parts you will replace when a component fails. Some of the problem parts are no longer available or the used replacement parts you purchase are no better than the ones you are replacing. It takes 25 to 30 man-hours labor to install. There is no added pilot workload.

As an additional improvement to this STC we are working with the FAA to allow a POH supplement to increase the gear extension speed to 153 Knots (180 MPH) on the early Navajo's, the same as all of the late model Navajo's and Cheyenne's. The faster extension speed allows the ability to slow the airplane more rapidly, thereby helping the pilot to fit in seamlessly when operating near busy airports AND in the case of the Navajo's allows the ability to slow the airplane down using the gear, this will reduce the chance of shock cooling the engines when steep descents are required by ATC.

The STC, you'll note, intends to offer an increase in extension speed to match most PA31's, and only then on early models, and only with the provision that ARC is supplicating the FAA for the increase.

I am not interested in your opinions of my or my mechanic's professionalism.

That's a shame, because you did say "Impune me all you want but lay off my mechanics." You asked, you see.

If you are not interested in helping me, please don't waste my time.

Come on, now, buffy. I'm very much interested in helping you. The first thing you need is an understanding that you seem to have problems following you in your very limited experience with the airplane that don't plague others. These continuous gear problems you experience aren't typical. These failures you experinece: not at all typical. The idea of rigging landing gear is that you don't have to keep adjusting it once it's rigged properly. If you have to keep adjusting it, either the gear hasn't been rigged properly, or there are other gear component problems. Either way, if the problem continues, then you have a maintenance problem, end of story.

You describe having to attempt to raise the gear multiple times. Clearly, most evidently, and without question you have a major maintenance problem, starting with your own denial that there's a maintenance problem. Impune you, you implore, but not your saintly wrenches. These angels can do no wrong. They're professionals. They don't make mistakes. They're a step from walking on water, so don't impune them. Impune you, you pray, the sacrificial lamb of piperdom.

Newsflash, sacrificial boofy-lamb: your gear should come up the first time you move the handle. The handle should center. You shouldn't have to keep adjusting the gear doors. The gear works fine. So do the doors. Helping you first requires that you recognize the problems that you're having (or that you perceive as having, as you haven't any experience in the Navajo, or so you say).

If you're seeking to solve the problems of gear not retracting, of doors hanging, of gear failures, or door failures, and other such problems, rather than seeking the removal of the doors, why not simply maintain them properly in the first place?

You may be seeking a solution that's in search of a problem.

[717tech]

Navajo Inner Gear Door Removal STC (http://www.colemill.com/SA00555DE.php)

First link I found trying to find a picture of this STC. Would I be right in saying that the fairing they are talking about is similar to the B737 in the way of a rubber ring forming a seal in the wheel well?

[boofhead]

Thanks for that, it looks good. The other STC does not have this detail of the finished kit, and that makes a difference in presentation. The price is not too bad either. Maybe I will go for it after all. I still would like some info from someone who has had it done, especially in regard to high altitude performance.

411, I already asked about an improved bracket, but there is not one approved and my maint guy will not do anything that is not fully legal. If I can find paperwork covering it I can go in that direction as well. Field approvals are not easy any longer.

We have replaced the bracket already, but the new one does not seem any stronger. The system works well if you follow all the servicing requirements, including lubrication and door ADs, as well as regular rigging during major inspections. Removing the doors would reduce this work as well as remove the AD requirements, so it has an advantage. I would like to allow the airplane to fly back to maintenance if this problem developed in the field. I would not be happy to authorize a takeoff if the gear doors were not retracting properly in case there was a problem with an engine at the same time. I know that would be highly unlikely, but it would be hard to justify at an accident inquiry.

Anyway, thanks for the information, it has been helpful. I might have enough now to make a case for it. I am glad there were some adults here after all.

[717tech]

Have you asked about the maint org designing an Engineering Order? I would have thought that if this was a wide spread problem there would be a replacement bracket available?

[411A]

I would have thought that if this was a wide spread problem there would be a replacement bracket available?

Or, hire a DER to design/approve a new/stronger bracket.

[boofhead]

I will price that out. There is an engineering firm on the field. We have the gear out right now and this would be a good time to do it.
My quick fix has always been the main gear doors, but it makes sense to go after the real problem first.