A Line Mechanic reports finding B737 Classic seat row and seat belts installed on a B737NG aircraft. Mechanic also reports that more than one Data Part Number (P/N) placard have been found on the forward support tube of numerous seat rows that have been through third party Repair Station Overhaul Vendors. Multiple P/N placards contribute to incorrect seat belt and seat row installations.
Synopsis
A Line Mechanic reports finding B737 Classic seat row and seat belts installed on a B737NG aircraft. Mechanic also reports that more than one Data Part Number (P/N) placard have been found on the forward support tube of numerous seat rows that have been through third party Repair Station Overhaul Vendors. Multiple P/N placards contribute to incorrect seat belt and seat row installations.
Narrative
While the Technician was replacing a seatbelt in Row 11-CDE; he noticed that all three seatbelts in Row 12- CDE were 737 Classic belts. While he was changing out those belts with new B737NG belts; he wrote down the Part Number (P/N) for the seat row. When he came back to the office he looked up in the Illustrated Parts Catalog (IPC) and found that the P/N for that seat row should have been Manufacturer (MFG) P/N 87822002. On the aircraft was MFG P/N 87525022; this P/N is applicable for a B737 Classic aircraft. He subsequently removed the seat row. While waiting for the new seat row to show up; we noticed that the seat we removed had four different P/N placards. We figured out that a new P/N placard is placed onto the seat forward bottom tube each time it is modified. This still leads to a great deal of confusion; especially when the writing on the placards is worn away. We were then asked to verify the P/N's of all the seats on the aircraft. When we were done; we had 10-seat rows that had illegible P/N placards and found one seat row (15-DEF) with the completely wrong P/N even though the seat was properly configured for that location. After we removed the seat assembly in Row-12 we found extensive damage to the seat tracks in the floor. It appears that some sort of sharp object had been used to remove the seat at some previous time and serious nicks and gouges were seen on the surface of the seat track. The difficulty removing the seat may have been caused by the different cross section of the seat track two inches forward of seat Row-12 DEF; aft leg position. I believe that the procedure for changing the P/N of a seat should include some sort of way of showing on the Original Data Plate that the P/N has been changed and that the Previous P/N Placards should be removed or shown to be no longer effective to that seat assembly. The fact that the seat assembly is allowed to have more than one Data/ P/N Placard should be avoided to prevent confusion. We also found many Placards on that aircraft that were worn to the point where we were unable to ascertain what the proper P/N was. Also seat Row-15 DEF was completely the wrong P/N; but it was evident that someone had 'changed' the P/N on the newest Placard with some sort of marker.
NASA callback
Reporter stated all the affected seats on their B737NG aircraft had been through a third party Vendor seat overhaul Repair Station. How a B737 Classic seat row ended up being installed on their 737NG has not been resolved. The B737-700 and B737-900s have the same seat; but not the B737-800 aircraft. The seats are heavier on the B737-800s and as a result require thicker seat belts. Special seat belts with airbags are now required at passenger rows facing the forward bulkhead in first class and coach. Seat belts with airbags have a cable running from the seat belt down under the seat into a box that controls the airbag deployment under certain G-loads. Although the airbag belts are stiffer; passengers still manage to twist the belt with the airbag facing into their lap and stomach areas.Reporter stated there are specific Maintenance Manual procedures describing the correct procedure for marking an identification placard for the seat row that includes a Mylar protective film or a Clear-coat finish to the placard. Many Original Data placards are a metal placard with embossed Manufacturer (MFG) Part Numbers (P/N). The placards identifying the MFG Part Number are placed on the forward support tube of the seat assembly. But most seat rows are now sent out (contracted) to third party Repair Stations for overhaul; or repair; or modifications. Third party repair Vendors apply their own placards on the same support tube. Reporter stated there is a real ongoing nightmare for mechanics when they have to change a seat belt for wear; or damage; or body fluids and must use the Part Number referenced on the seat placard under the seat cushion to determine the correct seat belt for that seat row. A standard seat row assembly in coach is three seats. Many seats have gone through more than one overhaul; modification or repair and have just as many placards attached along the entire length of the seat support tube. Changes to the seat assembly means changes to the Part Numbers on the placards. The placards are covered by the seat cushions. If a Mechanic lifts up only one cushion and uses the Part Number he sees on the placard to determine a replacement seat belt; he could easily install the incorrect belt; unless he pulls up all three seat cushions to see if other more current placards are also installed.Reporter stated a Seat Shop Mechanic may be able to visually determine the differences in seat rows; but a Line Mechanic has to rely on the seat assembly identification placard for Part Numbers in order to determine which seat belt goes where; or if the correct seat row is installed.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.