Early 337 rear engine screens

billsheila · #1 03-05-09, 05:38 PM

The screening on my rear engine cowls on my 1965 337 is starting to fail. According to the logs this happened once before and was repaired but original parts are now NLA. My understanding is that later models were built and sold sans screens -- is this correct? If so does anyone know what year the screens came off? Any idea what they were there for in the first place? I spoke to CPA and tech services there kindly sent me a document outlining how someone had previously taken them off, which may be my only option, but I thought I would just do a bit more research here before deciding what to do.

Thanks in advance for any insights.

hharney · #2 03-05-09, 06:08 PM

I chose to remove mine years ago after trying to repair and fix too many times. I really can't remember the last time I saw a Skymaster that still had them. I know there has been previous posts on this subject and to some extent there were comments made about airworthiness without the screens. The IA that removed mine way back when made an entry in the logs that they were removed.

They were originally on the cowling to keep feathered critters out. Mines almost always hangered so I don't worry about those little varmints.

billsheila · #3 03-05-09, 07:21 PM

I thought of the critter idea, but then couldn't figure why if they found the rear door locked (ie screens in place) why they wouldn't just so to the side door (cowl flaps) or the front engine (no screens unless plugged with a cowl plug I guess). I wondered if they might also be there in case something came loose in the rear engine bay, then with the screens it wouldn't be able make its way to the rear prop causing a greater catastrophe.

Sounds like removal and log entry is the way to go. Thanks.

JeffAxel · #4 03-06-09, 12:46 AM

Bill,
I was told the screens weren't for critter control, but to prevent FOD damage to the rear prop from loose stuff coming out of the rear cowl. My plane doesn't have them, but they would seem to have some benefit. I had never heard of them being a maintenance problem until your post, but I guess it makes sense. I guess it is a cost/benefit ratio question as to whether to keep them or not.

billsheila · #5 03-06-09, 06:53 AM

The problem appears to be caused by vibration. My A/P says if we could find some similar screening (he says welded at joints would be an improvement) he could replace it and sign off on the alteration. But it "will be a project" to use his words, which is code for "get out the wallet". He says removal is an option as well, so your post is exactly right I think.

tropical · #6 03-06-09, 08:12 AM

Quote:

Originally Posted by billsheila

The problem appears to be caused by vibration. My A/P says if we could find some similar screening (he says welded at joints would be an improvement) he could replace it and sign off on the alteration. But it "will be a project" to use his words, which is code for "get out the wallet". He says removal is an option as well, so your post is exactly right I think.

He will have to apply for a Field Approval with the local FSDO and do a Form 337 as well as a log book entry. Right now it's next to impossible to get the Feds to do Field Approvals.

Ed Coffman · #7 03-06-09, 01:24 PM

You can make your own parts if they match the original.

14 CFR Part 21 CERTIFICATION PROCEDURES FOR PRODUCTS AND PARTS.
Subpart K--Approval of Materials, Parts, Processes, and Appliances
Sec. 21.303 - Replacement and modification parts.

(a) Except as provided in paragraph (b) of this section, no person may produce a modification or replacement part for sale for installation on a type certificated product unless it is produced pursuant to a Parts Manufacturer Approval issued under this subpart.
(b) This section does not apply to the following:
(2) Parts produced by an owner or operator for maintaining or altering his own product.

Here is an expanded version:

A replacement part may be manufactured by an owner or operator as long as it does not result in an alteration of the product from the type design. It can only be made for use on your airplane and can not be sold for use by another.

The part has to be made of the same material(s) and equal to the original part in strength, fit, form, function, etc. If it is not the same, then it is an alteration. This would "normally" just require a 337 be filled out for the major repair and a logbook entry.

The owner or operator may have someone make the part as long as he is responsible for the design or quality control of the part. But, the person returning the aircraft to service (putting name and certificate number in the logbooks) is the one responsible to make sure it is appropriate for the application and meets the airworthiness requirements of the type design.

A part made to alter the airplane would require an STC or field approval prior to the alteration being done.
________
California Dispensaries

hharney · #8 03-06-09, 01:47 PM

http://www.337skymaster.com/messages...ead.php?t=2303

Paul Sharp · #9 03-31-09, 01:18 PM

Sammy at Air Services (Carrollton, GA) had some of that material - it was the official stuff - 6 or 7 few years ago. He may still have some. It isn't that cheap material you can get at the hardware store but the real thing. I bought some from him and the mechanics I had at the time re-fashioned the rear screen and said it wasn't really difficult at all. It really didn't cost all that much and I'm really glad to have it. I have always been told an considered it well worth the protection from FO damage to the rea prop.