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HAWK21M
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Lightening Diverter Strips

Tue Feb 15, 2005 6:46 pm


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Photo © Allan Martins Antunes


Do other Aircraft have Lightening diverter strips similiar to the B737.
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MEL
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jetstar
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RE: Lightening Diverter Strips

Tue Feb 15, 2005 11:04 pm

Because fiberglass is an insulator, not a conductor all fiberglass radar domes have metal diverter strips to form a path for the electrical current to flow into the metal frame of the radar dome and then into the airframe in case of a lightening strike to the radar dome. Some of these metal strips are more readily visible on some aircraft than others.

On the JetStar, they were molded directly into the radar dome and hardly visible unless you were real close to the radar dome. But to repair or replace them required the radar dome be removed and unless you had a spare radar dome the airplane was out of service until the repair was finished.

On this photo of the 737, it appears the metal diverter strips are on the surface and can be replaced or repaired very easily without removing the radar dome.
 
troubleshooter
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RE: Lightening Diverter Strips

Tue Feb 15, 2005 11:40 pm

The ERJs use the same system. The stripes are bolted to the outer radome surface. I think this is the most common type of installation.
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HAWK21M
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RE: Lightening Diverter Strips

Wed Feb 16, 2005 4:57 pm

How frequent are they replaced on the B737.I've never seen one done for over 13 yrs now.
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MEL
I may not win often, but I damn well never lose!!! ;)
 
tbanger
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RE: Lightening Diverter Strips

Wed Feb 16, 2005 5:31 pm

How frequent are they replaced on the B737.I've never seen one done for over 13 yrs now.

When they fail there resistance check I guess. If power wont flow through them, then they change them.


 
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HAWK21M
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RE: Lightening Diverter Strips

Thu Feb 17, 2005 1:10 am


Quoting Tbanger (reply 4):
When they fail there resistance check I guess. If power wont flow through them, then they change


That would need a Severe Lightening strike to have occured  Smile
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
airplay
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RE: Lightening Diverter Strips

Thu Feb 17, 2005 8:26 am

How frequent are they replaced on the B737.I've never seen one done for over 13 yrs now.

Lightning diverter strips are typically subject to periodic visual inspection. The strips are usually comprised of a row of segments of diamond shaped or slot shaped conducting surfaces.

A common inspection criteria calls for replacement if any 2 adjacent segments are missing or if a certain amount are missing in total.

The replacement is normally specialized maintenance that is done by an authorized facility, normally a radome repair facility. Even if you've never seen diverter strips replaced in 13 years, chances are quite probable that the radome has been replaced or repaired at which time the diverter strips were either maintained or replaced.

Because fiberglass is an insulator, not a conductor all fiberglass radar domes have metal diverter strips to form a path for the electrical current to flow into the metal frame of the radar dome and then into the airframe in case of a lightening strike to the radar dome. Some of these metal strips are more readily visible on some aircraft than others.

Just like anything in the unpredictable world of airplanes...there are exceptions. A great many smaller aircraft that use fibreglass radomes are not fitted with lighting diverter strips.
 
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HAWK21M
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RE: Lightening Diverter Strips

Thu Feb 17, 2005 8:06 pm


Quoting Airplay (reply 6):
Even if you've never seen diverter strips replaced in 13 years, chances are quite probable that the radome has been replaced or repaired at which time the diverter strips were either maintained or replaced.


Something which I suspected too.  Smile Thanks.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
CRJ200Mechanic
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RE: Lightening Diverter Strips

Fri Feb 18, 2005 5:59 pm

Quoting HAWK21M (reply 3):
How frequent are they replaced on the B737.I've never seen one done for over 13 yrs now.


The strips on the CRJ are the same as they are on the ERJ. I have to inspect them every night at my job. We only replace them when parts of the strip are missing. Segments tend to separate during a lighting strike (which it should). We they have to be replaced it's generally easier to replace the entire radome. The CRJ's are glued down and a pain in the rear to remove. I don't know how it is done on other aircraft
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HAWK21M
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RE: Lightening Diverter Strips

Sat Feb 19, 2005 12:04 am

Quoting CRJ200Mechanic (reply 8):
The CRJ's are glued down and a pain in the rear to remove.

You mean The strips are glued down in addition to Hardware,or only Glued down.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
CRJ200Mechanic
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RE: Lightening Diverter Strips

Sat Feb 19, 2005 11:15 am

HAWK21M

They do have two screws on each end of the strip, but glue is the primary means of holding them down

Thanks for bringing that to my attention, I forgot about the screws
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CRJ200Mechanic
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RE: Lightening Diverter Strips

Sat Feb 19, 2005 2:52 pm

I need to correct myself

I looked at the strips closer and they only have one screw on the aft section of the strip
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bsergonomics
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RE: Lightening Diverter Strips

Sat Feb 19, 2005 3:30 pm

For the uninitiated:

If you think that a lightning strike on an aircraft is a 'minor' occurrence, check out:

http://www.fugly.com/media/download....869&sort=&order=&rating=&per_page=

(In case the link doesn't work, do a Google search on "Plane_fast", which will give you the link)

It's a .gif 'movie' file that shows the strike in real time. There's also a slow version that show's the strike at a slower speed (do a search for, "plane_slow" and you should find it).

I should add that we design both military and civil aircraft for such an occurrence and normally the only damage is to the pilots' underwear....
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HAWK21M
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RE: Lightening Diverter Strips

Sat Feb 19, 2005 5:10 pm

Quoting CRJ200Mechanic (reply 11):
I looked at the strips closer and they only have one screw on the aft section of the strip


Odd to have it at the Aft end rather than the Front [To avoid Peelback].
Is there a special mounting slot that the Diverter stips slides into & held locked by the Screw at the Aft end.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
CRJ200Mechanic
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RE: Lightening Diverter Strips

Sat Feb 19, 2005 5:34 pm

All I could find in the manuals, (I have limited access to the SRM's) was a temporary repair

I have pasted portions below. It sound like the only slot they slide into would be the edge created by the paint.
If you would like more I will send. I just don't want the message to get too long. It's a pretty lengthy process

NOTE: THE INFORMATION PROVIDED IS FOR INFORMATION ONLY

1. General
This subject contains approved specific repairs for replacing and bonding of the nose radome lightning diverter strips.
2. LimitationsA. Temporary Repair is limited to 450 Flight hours maximum
B. All edges of each lightning strip must be completely bonded to the radome with no gaps, separations or pinholes.
C. The work area must be clean and well ventilated, with ambient temperature 20°C to 30°C (70°F to 90°F), and humidity not more than 75%.
D. Do not use power tools to abrade resin or surface of radome.
E. Use clean wax-free containers to mix the adhesive.
F. The adhesives must not be thinned.
A. Remove the nose radome, refer to the Aircraft Maintenance Manual (AMM).
B. Remove the hardware at the lightning strip termination, at the aft end.
C. Peel off the lightning strip from the surface of the radome.
D. Remove the old adhesive with a clean cloth dampened with methyl ethyl ketone.
E. Use pressure-sensitive mylar tape to mask off the area where the lightning strip is to be bonded. NOTE: The area must extend 0.125 inch (3.175 mm) beyond the edges and the ends of the lightning strip to form a fillet.

CAUTION: INSTALL THE LIGHTNING STRIP DIRECTLY ONTO THE PRIMED SURFACE OF THE RADOME ONLY.
F. Remove all the polyurethane topcoat in the lightning strip recess faying surface area by abrasion with #400 grit abrasive paper.
G. Lightly abrade the primer in the radome faying surface area using Scotchbrite pads to remove the glaze. NOTE: Damaged or missing primer must be replaced with one coat of primer CMS565-01 (refer to Chapter 51).

CAUTION: DO NOT ABRADE THE CENTER PORTION OF THE LIGHTNING STRIPS.
H. Abrade the faying surfaces of the lightning strips with #80 grit abrasive paper to remove all resin or paint glaze.
I. Clean the faying surfaces with a clean cloth dampened with methyl ethyl ketone. NOTE: The cleaned parts must be handled with clean white cotton gloves.

J. Mask off the external surface of the lightning strip with pressure-sensitive tape.
K. Prepare the Amicon CT-5047-2 A/B conductive adhesive by mixing one hundred parts by weight of A with six parts by weight of B. Part B shall be fully mixed into Part A in a clean, wax-free container. Do not thin the adhesive. NOTE: Mixed conductive adhesive remaining must be discarded after 45 minutes.

CAUTION: MAKE SURE THAT THE ADHESIVES ARE NOT APPLIED TO THE SEGMENTED SURFACES OF THE DIVERTER STRIPS.
L. Apply conductive adhesive to the strip termination attachment and the radome faying surfaces. Make sure that the faying surfaces are fully covered with a 0.005 inch (0.127 mm) layer of conductive adhesive, 0.360 inch (9.144 mm) forward of the termination attachment end, as shown in
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CRJ200Mechanic
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RE: Lightening Diverter Strips

Sat Feb 19, 2005 6:21 pm

HAWK21M
I found a good picture of the strips for you. I'm not sure if I can get it attached to message right. I have the pic saved if I screw up



Here are some pictures of the tail skid


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Click here for bigger photo!

Photo © Airwim



View Large View Medium
Click here for bigger photo!

Photo © Freight-Dawg



Its just a small bumber on the seam of the tail cone. I apologize for the pics, it was the best I could do. Maybe someone else has some better pictures
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CRJ200Mechanic
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RE: Lightening Diverter Strips

Sat Feb 19, 2005 6:26 pm

HAWK21M

Sorry I can't figure it out. here is the link

http://www.jetphotos.net/viewphoto.php?id=149906
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airplay
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RE: Lightening Diverter Strips

Sat Feb 19, 2005 11:53 pm

Odd to have it at the Aft end rather than the Front [To avoid Peelback]..

The screw(s) are not there to hold the strips in place. They provide the path for the lightning to conduct to the primary airframe. In other words, they electrically bond the strips to the rest of the airplane.

If the screws were on the forward end, there would be no airframe to screw to.
 
CRJ200Mechanic
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RE: Lightening Diverter Strips

Sun Feb 20, 2005 7:55 am

Airplay

thanks for info, I didn't think of that. I don't really mess with the things doing line maintenance.
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HAWK21M
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RE: Lightening Diverter Strips

Sun Feb 20, 2005 2:10 pm

Quoting Airplay (reply 17):
If the screws were on the forward end, there would be no airframe to screw to.


Are you saying the radome on the CRJ cannot be screwd tight on the front but only on Aft,because of Airframe.Cant it be Connected from the Airframe to radome by bonding Jumpers.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
Santhosh
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RE: Lightening Diverter Strips

Sun Feb 20, 2005 9:35 pm

What sort of a metal is used to make the Diverter strips?

George
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CRJ200Mechanic
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RE: Lightening Diverter Strips

Sun Feb 20, 2005 10:38 pm

Quoting HAWK21M (reply 19):
Are you saying the radome on the CRJ cannot be screwd tight on the front but only on Aft,because of Airframe.Cant it be Connected from the Airframe to radome by bonding Jumpers.



The screws are connted to bonding jumpers on the inside of the radome. I guess if they were connected up front they would get in the way of the radar. Just a guess though
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airplay
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RE: Lightening Diverter Strips

Sun Feb 20, 2005 11:27 pm

Are you saying the radome on the CRJ cannot be screwd tight on the front but only on Aft,because of Airframe.Cant it be Connected from the Airframe to radome by bonding Jumpers.

You guys are overthinking this one a bit...

 Smile

Of course there are an infinite amount of ways to do this. However, you are killing two birds with one stone if you use the radome mounting screws to bond the lightning diverter strips to the airframe.

Can it be done any other way? You bet. And chances are someone can present us with evidence that it is done differently on some airplane somewhere.

As alluded to in another post, you really want to avoid as much metal as possible in front of the radar antenna.
 
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HAWK21M
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RE: Lightening Diverter Strips

Wed Feb 23, 2005 12:59 am

Why not just use bonding cables.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
airplay
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RE: Lightening Diverter Strips

Wed Feb 23, 2005 3:10 am

Quoting HAWK21M (reply 23):
Why not just use bonding cables.


If you had the choice between using a screw to bond the strips that you would have to install anyway to secure the radome or using bonding cables, why would you chose the latter?
 
avt007
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RE: Lightening Diverter Strips

Thu Feb 24, 2005 2:26 am

I worked on an aircraft where the customer complained that the radios completely failed in clouds. Obviously they had a P-static problem, so I checked the airframe with a test set that charges it with 25,000 volts through a wand. The cause was immediately obvious. When the radome was charged, the radios produced large amounts of noise. One of the diverter strips had cracked near the aft screw, and the static was arcing across the gap, creating a ton of RF noise. In this case they might have been better off removing the strip, but as they had no spare radome immediately available, they sanded the paint off the strip and bridged the gap with aluminium tape! Not a very elegant solution, but it was effective for the couple of days it took to get a new radome.
 
airplay
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RE: Lightening Diverter Strips

Thu Feb 24, 2005 5:01 am

Avt007,

Isn't it incredible, how a very small defect in the bonding has such a huge and serious effect on the airplane?

I've had similar experiences with broken or missing bonding straps on a single control surface or fuel panel. Also when a maintainer fails to install the proper conductive strip of paint after replacing a de-ice boot.

There are many private operators out there who blame crappy performance on their radios while the real problem is failure to maintain the airplane bonding and static wicks.
 
avt007
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RE: Lightening Diverter Strips

Thu Feb 24, 2005 7:35 am

Yes, something small and innocent looking can really mess up your day! On another occasion, a Falcon operator reported the loss of ADFs, Omega/VLF, and I think his coms too. It was scaring the heck out of them because they were doing approaches up north in some very mountainous areas. It was affecting the VOR as well, giving dubious needle indications. It took a bit to find, but it was the leading edge of the vertical stab that had been painted 4-5 times without being stripped. The layers of paint made for a great capacitor or something. Once it was stripped and painted properly, the problem went away.
Speaking of radomes, another customer said the glideslope was ok until they captured and started the descent, then it went weak and intermittent. I met the customer at the aircraft, and he was holding a new set of nav antennae. I said no,the GS antenna is really small, and probably in the radome. When we removed the radome, about a gallon of water poured out. Whoever had PRCd the dome had also sealed the water drains! Judging by the high tide marks, in level flight the antenna was dry, but when nose down, the GS was submerged.
Another customer had some physical damage to the radome, and in a misguided attempt to keep the water out of the honeycomb, he put a big piece of aluminium tape on the outside, smack in front of the radar. We were called in when the crew said the radar died. I wonder why?
Radomes look simple, but they can bite you..........

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