Narrative:

A B737-700 aircraft; aircraft X; was in ZZZ for a heavy C-1 (HC1) check. I; inspector X; was assigned to heavy tail inspection. I found two each cracks on the left-hand (left/H) horizontal stabilizer lower inspar skin. Mechanics started the repair per structural repair manual (srm) xx-xx-01-2R-11; repair 11. Per the srm repair; table 201 calls out the repair doubler to use 2024-T3 and table 202 calls out for the doubler to be .090' thousandths of an inch thick. As the night went on I stopped by to verify metal type and thickness and saw the x-colored tag (form) showing [2023]-T3; .090' thick on the 16'x16' inch piece on metal the mechanics had. I told them to carry on with the repair and parts fabrication (fab). During the fab of the repair parts; it was time to turn over [the work] to dayshift. At that time; I and the mechanics signed-off the steps on the (form). The graveyard shift ended and the mechanics went home. I stayed and worked the aircraft. Dayshift mechanics took over the repair part fabrication and continued to install. At one point during the dayshift; the mechanics working the repair asked if the doubler was in fact [2024]-T3; I responded; 'yes.' I saw the x-colored tag (form) during the night shift. Mechanic X stated that it didn't appear correct; but with the information I told him; he continued on with the repair. With all solid fasteners installed and waiting on an engineering authorization (east/a) from engineering for two blind fasteners to be installed; I then turned the aircraft over. [Several shifts later]; the dayshift mechanic X that installed the repair on left/H horiz stab lower inspar skin on aircraft X; needed some metal from the sheet metal (south/M) shop. He then noticed that a sheet of [2024]-0 was mislabeled as [2024]-T3. He brought this to my attention and we realized that this was the same metal used on aircraft X. At this time; we called the company hot line and the aircraft was grounded. [Recommend] better vendor quality control (Q/C).

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Original NASA ASRS Text

Title: An Aircraft Maintenance Inspector; a Parts Receiving Inspector; and an Aircraft Maintenance Technician (AMT) report about a Structural Repair Doubler that was inadvertently fabricated and installed from a mislabeled sheet of 2024-0 aluminum instead of the harder 2024-T3 ALCLAD aluminum material. Doublers are being installed over the Horizontal Stab skin cracks found on many B737-700 aircraft.

Narrative: A B737-700 aircraft; Aircraft X; was in ZZZ for a Heavy C-1 (HC1) Check. I; Inspector X; was assigned to Heavy Tail Inspection. I found two each cracks on the Left-Hand (L/H) Horizontal Stabilizer lower inspar skin. Mechanics started the repair per Structural Repair Manual (SRM) XX-XX-01-2R-11; Repair 11. Per the SRM repair; Table 201 calls out the Repair Doubler to use 2024-T3 and Table 202 calls out for the Doubler to be .090' thousandths of an inch thick. As the night went on I stopped by to verify metal type and thickness and saw the X-colored Tag (Form) showing [2023]-T3; .090' thick on the 16'x16' inch piece on metal the mechanics had. I told them to carry on with the repair and parts fabrication (fab). During the fab of the repair parts; it was time to turn over [the work] to dayshift. At that time; I and the mechanics signed-off the steps on the (Form). The graveyard shift ended and the mechanics went home. I stayed and worked the aircraft. Dayshift mechanics took over the repair part fabrication and continued to install. At one point during the dayshift; the mechanics working the repair asked if the Doubler was in fact [2024]-T3; I responded; 'Yes.' I saw the X-colored tag (form) during the night shift. Mechanic X stated that it didn't appear correct; but with the information I told him; he continued on with the repair. With all solid fasteners installed and waiting on an Engineering Authorization (E/A) from Engineering for two blind fasteners to be installed; I then turned the aircraft over. [Several shifts later]; the dayshift Mechanic X that installed the repair on L/H Horiz Stab lower inspar skin on Aircraft X; needed some metal from the Sheet Metal (S/M) Shop. He then noticed that a sheet of [2024]-0 was mislabeled as [2024]-T3. He brought this to my attention and we realized that this was the same metal used on Aircraft X. At this time; we called the company Hot Line and the aircraft was grounded. [Recommend] better Vendor Quality Control (Q/C).

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.