Date: 202104
Local time of day: 0001-0600
Light: Night
Aircraft: B757 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight phase: Parked
Second aircraft: B757 Undifferentiated or Other Model
Aircraft component: Antiskid System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Other / Unknown
Reporter qualification: Maintenance Powerplant; Maintenance Airframe
Human factors: Communication Breakdown
Second reporter function: Other / Unknown; Engineer
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Maintenance
When detected: Aircraft In Service At Gate
Result: General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Procedure; Human Factors; Aircraft; MEL
Primary problem: Procedure

Narrative: Prior to schedule departure of Aircraft X; ZZZ Maintenance NAME while conducting his pre-departure checks discovered a hydraulic leak in the left wheelwell that was out of limits. Upon further investigation; it was isolated to the Normal Anti-Skid Module. ZZZ Maintenance contacted B757 Maintenance Control and a replacement Anti-Skid module was ordered to be shipped on recovery Aircraft Y to ZZZ. After landing Aircraft Y flight crew generated a discrepancy concerning an Elevator Asymmetry EICAS Alert (with history).  ZZZ Maintenance couldn't clear and no MEL relief was available for the fault. Additionally; on Aircraft Y post flight Maintenance discovered the Flap/Slat Control Valve leaking and out of limits in the wheelwell. Given only 1 Tech was on duty with 2 out of service aircraft; ZZZ Maintenance suggested that capping the Normal Anti-Skid Module (Aircraft X) and to MEL the Anti-Skid System to move the Aircraft. [Suggest] all parties involved to fully evaluate and determine proper course of action in a safe efficient manner.


Second narrative: Report was submitted to Service Engineering on Date regarding leaking Normal Brake Antiskid Module. ZZZ Maintenance found leak coming from Normal Brake Antiskid Module at weep hole.  Mx decided to MEL antiskid system. Maintenance requested Engineering Authorization (EA) to remove and cap hydraulic lines to Normal Brake Antiskid Module to stop leaking during the MEL deferral period. I reviewed System Schematic Manual and Aircraft Maintenance Manual. According to my interpretation of the system; with the anti-skid system deferred and the leaking Normal Brake Antiskid Module isolated; left gear would still be pressurized by the left hydraulic system. There are secondary and tertiary redundancies in the system. In this case; the left hydraulic system would have provided metered pressure to the left gear via the left antiskid shuttle butterfly valve. Normally the left gear metered pressure would be provided by the right hydraulic system via the Normal antiskid valve module but it was leaking/isolated. There were X [number of] fight legs flown in this configuration without incident. I don't see how my EA would inop the left main landing gear. The MEL was to defer the total antiskid system and the normal antiskid module is a part of that system.


Synopsis: Technicians reported that an aircraft anti skid module was improperly placed on MEL and dispatched for service.