B737-800
Maintenance Powerplant; Maintenance Airframe
Maintenance Technician 25
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Maintenance
General Maintenance Action
Procedure; Manuals; Company Policy; Aircraft
Currently [Maintenance] is working a skin change on a 737 forward cargo door. While drilling up a pre-shaped skin it was realized that this skin was not fabricated for use on this MPN or model door. During discussions about the discrepancy with the crew; it came up that one of these pre-formed skins had been used in the past for a same model; MPN door.A review of the records shows that earlier this year; [Maintenance] produced a 737-800 cargo door by installing a skin fabricated by Engineering Order and drawing 52-XXXX-XXX.The skins fabricated per the Engineering Order and drawing are for a different model aircraft. This alone does not make these skins unusable but the fact that engineering based their approvals on a different aircraft model type; when approving the material substitution; does.The original substitution approvals were for an original skin bonded from two layers of 036 2024-T3; substituted for one single thickness skin of .071 2024-T42; for the aft cargo door of a 737-200/300.We installed this .071 2024-T42 on a forward cargo door where the original skin was .071 2024-T3. The Engineering Order; as stated; does not cover forward cargo doors or 737-800s. To use the Structural Repair Manual material substitution chart in an effort to allow for the substitution of a -T42 skin vs a -T3 skin requires additional thickness due to the different heat treat properties.Therefore the skin installed is an out of compliance situation.
Technician reported that material substitutions during a skin replacement were found to be out of compliance.