MD-11
Maintenance Airframe; Maintenance Powerplant
Confusion
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL
General Maintenance Action
Human Factors; Procedure
The flight crew reported a Level 1 Tire Differential Pressure Alert during pushback with #5 tire pressure fluctuating from 230 to 260 PSI. I was dispatched to recover the aircraft and evaluate the problem. After determining that the #5 tire pressure sensor was faulty; I consulted the flight crew and informed them of my intent to defer the #5 tire pressure using MD-11 MEL 32-46-01-02 Brake Temperature Monitoring (BTM) and Tire Pressure Indicating (TPI) system - Tire Pressure Indication. Once agreed; I began working on the maintenance portion of the MEL. Finding no plausible way to secure the harness as per step 2; I removed it; capped the sensor coupling with a shipping cap (to prevent leakage); tagged the harness; and stored it in the flight deck coat closet which I denoted in the write-up. I then obtained a control number; finished the paperwork; and dispatched the aircraft. Step 2 of the Maintenance section of this MEL states: 'Deactivate affected Tire Pressure Sensor by disconnecting the tire pressure sensor harness at the Main Wheel Transmission Unit (MWTU). Secure affected sensor harness to prevent damage to the harness and MWTU.' This is the only step provided pertaining to the deactivation of pressure sensor and is vague at best; leaving little information or illustration as to how to perform the task safely. I determined that that there was no plausible way to store the cannon plug under the hub cab without it interfering with wheel tachometer generator operation or causing damage to harness and/or axle nut. I also determined that securing the harness to the outside of the hub cap on the outer wheel surface would be extremely unsafe. The harness would be subjected to extreme heat; environmental conditions; and centrifugal forces that could cause catastrophic damage should it depart the aircraft. In the end; I determined that the only safe way to secure the harness was to remove it from the wheel assembly altogether and capping the sensor coupling with a shipping cap (which is used on the same wheel and tire assembly on our MD-10 for flight as it does not have a TPI system) to prevent leakage; and storing it in the flight deck coat closet. This MEL does not specifically instruct me on how to secure the harness. It simply says to do so in such a way as to prevent damage to the harness and Main Wheel Transmission Unit. It does not say I can remove the harness; but it does not say that I cannot either. Improve the MEL by either: 1) rewriting MEL 32-46-01-02 to include a more specific and detailed maintenance procedure on deactivating/securing tire pressure sensor on wheel (i.e. materials used; illustrations; attach points; etc.) 2) rewriting MEL 32-46-01-02 to include completely removing harness and capping sensor coupling 3) deleting MEL 32-46-01-02 altogether and deferring the whole BTM and TPI system as per MEL 32-46-01.
A Maintenance Technician found it difficult comply with a MD-11 MEL procedure and elected to remove the harness and store it in the flight deck closet. He suggests a revision to the MEL be considered.