Patches on 737
 

Whilst walking across the tarmac today en route to my flight I had a close look at a Fly Me 737 bound for Gatwick. I noticed several square "patches" at various points of the fuselage. Is it normal for aircraft to be patched in this way? How do they know which part to patch ?

External patches are normal, although they may not be used in some specific aerodynamically critical areas.

In the business they are called "scab patches" and most are the result of baggage and catering trucks striking the aircraft. Damage is repaired in accordance with a "Structure Repairs Manual" or SRM and, where damage exceeds the SRM limits, a special repair scheme may have to be produced - usually in consultation with the aircraft manufacturer.

External patch repairs are generally removed and replaced with a flush repair during heavy maintenance visits. Whenever a repair is done, the damage is recorded on a damage record chart, which is one of the records which stay with each aircraft for life.

If it is really old 737 and the patches are extensive and in areas like around the roof and windows, where catering trucks don't normally hit, it could be the big AD called the lap joint repair (or something like that). This resulted from that plane in Hawaii blowing its roof some years ago.

To add to Blacksheep's reply:
Repairs outside SRM limits accomplished by a Part 145 organisation - at least for EU registered aircraft involved in CAT (Commercial Air Transport) - must be designed and approved in accordance with EASA Part 21. As Blacksheep infers, this will usually be the TC holder but some minor repairs may be designed and approved by a "stand alone" Part 21 organisation.
As to whether the "patch" is replaced with a flush repair depends in some cases on lease return conditions and/or DTA (damage tolerance assessment) by the Part 21 organsiation.
Repairs should be mapped (I've reviewed such maps at Blacksheep's organisation; in fact it was part of his department).

My tongue hurts.

Check out this 737-200Adv with lap joint reinforcers and other misc patches.

http://www.b737.org.uk/lap_joint_patches.jpg

More info here.

A "tired old B737" indeed. Nevertheless, it appears to be an airworthy one.

Hi Bus, still in the QA business I suppose? I'm off to sub-Part G shortly...

Just dont look to hard for the scribe line damage. :ok:

Hi Blacksheep,
Yep, still QA related but have spent most of year doing Human Factors and regulations training. Also into SMS and Part M related work (allied with a Sub-Part G organisation in Sussex)