Urgent technical advise required (Bonding Jumper on B737-400)?

Question

While on duty attending/performing an Aircraft Search on a long-layover aircraft earlier today (a B737-400) @ Landing Gear door R/H FWD, I have found the bonding jumper to be disconnected (as if it was being cut).

Upon informing the LAE to witness the condition, I was being told that it is 'normal' (in a sense that it occurs normally) that it 'snapped'.

Here the question that I would like to ask is if it is really 'normal' for bonding jumpers to 'snap' (since bonding jumpers aren't fixed on high tension)? If its true, what is the frequency/chances of it to happen in such a way?

It was a long-layover aircraft and engineering maintenance/services had been underway for several times during the night and since if it was supposed to be a 'normal' condition, why wasn't it changed/checked at that time?

As I have understood, it is required by the Civil Airworthiness regulations (usually in most nations) to change the bonding jumpers if found to be faulty.

Answer 1

Broken bonding jumpers absolutely no big deal.  

They do serve a purpose--to reduce static on the radios by conducting electrical charges between components like gear doors, flight controls, etc.  Because these components move relative to fixed structure, they have to flex, but like anything else that's made of metal that has to flex, eventually it will work-harden and break.  And they do, from time to time.   Typically they'll have a frayed appearance.  But if the jumper got caught or pinched between two moving components, it may appear to have been cut.

However, with most flight controls (which do most of the moving and flexing) there's more than one, so there's a  redundancy built in.  Besides, there's a metal-to-metal interface through the attach fittings and bolts that attach these components to the airplane structure.

In fact, back in 1972, Boeing issued a service bulletin for the 727 (SB727-51-0016, which was also approved by the FAA) that allowed operators to delete all landing gear door bonding jumpers and all but one on each of the flight controls.  In the text of the SB Boeing stated that service tests had established that when redundant jumpers were removed, radio noise did not increase appreciably.

Yes, the maintenance manuals for whatever airplane will say to replace them if they're missing or defective.  But it's not as if it's primary structure, or an engine attach fitting, or something that's truly critical.  The airplane will fly just fine with a bonding jumper broken.  Should it have been caught and changed?  Yes, it should.  But it may have been that they had more important things to worry about than a single bonding jumper on a nose gear door, given the length of time they had to work on the airplane.  Or perhaps the task cards they had to work did not call for inspecting the bonding jumpers.

Answer 2

Bonding straps flex during normal use and break.  There are usually multiple bonding straps per bonded component so this item can be deferred.  This is no big deal.

Answer 3

I hate looking up the AMM so u do it so see if you're correct or the LAE. Trust your instinct it might save lives.

Me i will look the AMM even though as you say it is in the RH LG DOOR area hey you didn't say if it is the NOSE or MLG.

Answer 4

Aircraft structures are bonded to each other to reduce radio noise (caused by static build up as the plane flies) and to allow a lightning strike to travel though the aircraft without damaging critical components.

In all likelihood, this one strap will not be a significant safety problem, but should be fixed as soon a practicable.  It doesn't take very long to repair and they can usually be made from bulk items.

The aircraft's airframe maintenance manual (AMM) and configuration deviation list (CDL) will give you information whether this item can be deferred or not.

A bonding jumper can easily be broken if it is installed incorrectly, if it is too old and has flexed too many times, or has been damaged by moving components or careless mechanics.  I've seen tons of them broken on heavy jets during checks.