Date: 201201
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Light: Night
Aircraft: B757-200
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Parked
Aircraft component: Trailing Edge Flap
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Lead Technician
Reporter qualification: Maintenance Powerplant; Maintenance Airframe
Human factors: Communication Breakdown; Confusion; Other / Unknown
Second reporter function: Technician
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Maintenance
When detected: Other After Aircraft Released
Result: General Maintenance Action
Contributing factors: Chart Or Publication; Aircraft; Human Factors; Manuals; Incorrect / Not Installed / Unavailable Part
Primary problem: Human Factors

Narrative: [During a] light C-Check; on addressing a discrepancy relating to loose hardware (6-each bolts) on the left-hand inboard flap track; I misread the blueprint and ordered 6-each new bolts (6-point type) from the parts list. The Part Number (P/N) used was listed for one bolt only (a 6-point bolt); the other five bolts (12-point bolts) were a different part number (and were listed below the one P/N used). I gave the Aircraft Maintenance Technician (AMT) the six [bolts] and they were installed. The AMT questioned the fact that all six bolts were 6-points and I told him I got the part number from the blueprint; so he installed and torqued them [on Aircraft X; a B757-200].In the process of getting the part numbers for the bolts [for Aircraft X]; I had looked at the parts list on the [blueprint] drawing and saw the first number listed; (the 6-point bolt); and incorrectly assumed that all six on the assembly were the same; so I ordered them. All installation procedures were followed per specifications; re-torqued and sealed. Approximately four weeks later; while addressing a similar discrepancy on Aircraft Y in C-Check; I ordered the one 6-point and the five 12-point bolts. This jogged my memory of the parts installed on Aircraft X. That same day I checked and found Aircraft X was currently undergoing maintenance in another airport and generated [made] a Non-Routine [write-up] to have the installation checked for the correct hardware; listing the correct parts and the orientation of the bolts. The bolts were consequently replaced with the correct Part Numbers (P/N). Suggest slowing down and be extra vigilant to small script on blueprints - don't assume.


Second narrative: There were 6-each bolts Removed and Replaced (R/R) on Aircraft X; on an electronic Non-Routine [write-up] in our maintenance computer. I feel that during the 'completion' phase; the Non-Routine having an RII closing should have prompted a parts verification in the maintenance computer and that the installation of the 6-each bolts should also have been an RII buy-back [verified].


Synopsis: A Lead Mechanic and another Mechanic report about installing five (6-point type) bolts for the left-hand inboard flap track during a C-Check on a B757-200 aircraft. The Lead Mechanic had misread the parts list on an engineering blueprint.