aircraft skin patches

[RUDAS]

was wondering,how do they go about putting a skin patch onto a damaged acft,and what specifications as far as pressurization have to be met? was walking around an ancient 727 yesterday and the thing was patched up like a sieve...

[A-FLOOR]

It's not a "patch" in that sense of the word, it's called a repair doubler, which means a repair consists of two "patches", one on the inside and one on the outside, fitted well around the damaged area.

If your plane's cabin gets hit but a truck, the damaged part is first sawn out to prevent growth of fatigue cracks and a repair is crafted to match the construction of the aircraft body precisely, including the internal stringers as far as they are concerned. These bits are fitted to the aircraft using double rows of rivets and in case of wings' torsion boxes and pressurized cabins have to meet very strict rules about how large they have to be, how many rivets have to be used, how far they are apart, etc.

:)

[Boss Raptor]

On older acft particularly 727 and 737-200 many of those patches you saw are likely to be 'doublers' which are structurally containing/strengthening straps fitted in accordance with one of the many 'Aging Acft' Airworthiness Directives or the SSID program as the acft reaches certain age/hours or cycles - the instruction dictates the size and design of the straps/patches however some operators (mx. facilities) have done better/tidier jobs than others (or in some cases an option is to re-skin which for economic reasons an operator may not wish to do)

In the case of a 'patch' this will be down to a hole in the integral pressure hull and/or similar structural surface damage - the requirements/limits for these repairs is contained in the appropriate aircraft's 'SRM' Structural Repair Manual which dictates the size of the patch and fixing etc. dependant on where on the fuselage it is going

[RUDAS]

hey guys,thanks for that info.what i saw was in fact quite different to the plates i'm familiar with usually found around doors and seems etc that i know as being strenghtening plates.

this was actually just a small bare metal plate about 2-3inces long by 1.5inces high which appeared not to be riveted or anything,just attached to the skin with a date and number engraved on.in this instance the aircraft was an old ex-delta 727-200 n8873z that has been in storage for the desert for a while and had just arrived at my home base airport for breaking up.saw it as i was doing my pre-flight so thought i'd go have a look and noticed the patch. acft is obviously in flying order,having come all the way from the usa with the patch?

anybody familiar with this technique?:ok:

[Boss Raptor]

no rivets - sounds like it's bonded...posh glueing to us plebs... :) - and by the size you describe covering a small puncture hole possibly - you dont say where it is but I would guess if you walked over and looked at it closely to see the numbers at or below eye level which is likely place for a bash by ground equipment

never seen one with date and number however with a recent AD requiring an inspection plan to be incorporated for all repairs and structural mods this could be to track the repair for ongoing inspection purposes - good idea actually - better than just referring to a position plan and would allow you to track replacement of the patch etc. :ok:

An ex Delta 727 will have posh patches and doublers - more than likely reskinned rather than patched, particularly if it's an old one as at 20 years and/or again at 60,000 cycles you reskin much of the belly in accordance with Aging Aircraft Mod. Program - you wanna see a less posh one with all the doublers and triplers all over the door frames, the roof, the chine line (eye level below windows) and above the window line...have to say it must scare the cra!p out of the pax :E

[RUDAS]

even as a pilot,i flew on an old 737-200 in india a few months back...the thing had about three layers of riveted plates around the rear right hand door,made me pray.:ok: :}

[Boss Raptor]

Now I know that one :) lot of cracks found around rear door frame

That is a specific Aging Aircraft related AD...just like the cockpit side window post doublers known as E-F posts (also seen on 707 and 727 after all is exactly the same fwd structure) and the one just below the DV window which is like a butterfly stitch or sometimes a rectangular doubler :ok:

[Genghis the Engineer]

There are a set of guidelines on applying such patches in ASA's "Aviation Mechanic Handbook", which is (a) cheap, and (b) often found in the corner of hangars. Worth taking a look in there.

G

[Lu Zuckerman]

Most aircraft companies in the preparation of structural repair manuals will include only those repairs that are common to pressurized or non pressurized aircraft including helicopters.

When the aircraft goes into service and structural problems occur that are not covered in the repair manual the company in concert with the operator will develop a repair procedure. This procedure will be entered into the structural repair manual when it goes into revision (usually every six months). If the repair is serious enough an AD will be issued to all operators to check the specific area to determine if the structure has been compromised. And if so, the repair procedure will normally be included in the AD or, if not the repair procedure will be furnished by the manufacturer under separate cover.

If the structural problem is serious enough the company will provide technical assistance to the operator.


:E :E