Date: 201403
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Light: Night
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight phase: Parked
Aircraft component: Flap/Slat Indication
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Other / Unknown
Reporter qualification: Maintenance Airframe; Maintenance Powerplant
Human factors: Confusion; Communication Breakdown; Workload
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Other Post Landing
Result: General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Chart Or Publication; Manuals; Human Factors; Aircraft
Primary problem: Manuals

Narrative: B737-700 aircraft had a Proximity Sensor Electronics Unit (PSEU) light illuminated after landing in ZZZ1. I contacted Contract Maintenance and the Mechanic performed a PSEU BITE Check to see what was causing the light. The Fault Codes reported were 32-62014 (Landing Flap A and B disagree) and a 32-64004 (DO NOT DISPATCH). Because of the DO NOT DISPATCH message; I advised the Mechanic we had to look at the root cause which was the Flap Landing Warning Switch. I sent him the required Fault Isolation Manual (FIM) Task and he performed the task and inspected the switch. I advised him to clean and actuate the switch and do the FIM Task again. The Fault cleared and it was signed-off. Approximately 10 minutes after the logbook was signed; the PSEU light re-illuminated so I advised the Mechanic to perform another BITE Check on the PSEU. The same fault codes as before came back. Because of the DO NOT DISPATCH fault; I determined that the aircraft was now Aircraft On Ground (AOG). I asked the Mechanic if he could standby; while I began to search for a replacement part. He agreed to stay to help me. After determining that a part was not available locally and having two in our Air Carrier's stock in ZZZ; I began preparing for the aircraft to overnight in ZZZ1 until the part would arrive. Soon after; I found our Air Carrier's Maintenance Manual Supplement that allowed for the spare contacts in the switch to be used. I called the Mechanic and asked if he would be able to perform the Task and he again agreed to help me. I sent him the Maintenance Manual Supplement and the associated Boeing wiring Diagram Manual (WDM) and he performed the Task flawlessly and retested the Flap Landing Warning Switch System to confirm the repair. There were no faults; so I advised him that we could now sign-off the second write-up in the logbook. The last step of the Maintenance Manual Supplement states that company Maintenance Control will create a Deferred Maintenance Item (DMI) to track the use of the spare contacts in the switch. I knew that the [acronym] 'DMI' needed to be revised to Maintenance Tracking Item (MTI); since our Air Carrier implemented a new Maintenance Tracking and Compliance System and placed the spare contacts on MTI for tracking purposes with the mechanic. The aircraft departed three hours and 33 minutes late without incident. I discovered after the fact; the next night; that there is indeed an MEL for using the spare contacts for the S138 Switch; but I was unaware that MEL 32-21 existed. Because of the DO NOT DISPATCH message [that] the PSEU was faulting; I never checked the MEL to see if there was any relief because I considered the DO NOT DISPATCH message an AOG situation. After finding the Maintenance Manual Supplement to correct the problem (Air Carrier Supplemental Aircraft Maintenance Manual (SAMM) 27-51-00); I generated the tracking item that it called out for. I never considered that a repair to the [Flap Landing Warning Switch] System; with a satisfactory Operational Check would have required an MEL for a now perfectly operating system; so I never looked at the MEL. After reviewing the MEL the next night; the repair outcome of the MEL Dispatch Deviation Guide (DDG) Maintenance Procedure (MEL 32-21 and AMM 32-00-00-040) is the same as the Maintenance Manual Supplement (Air Carrier SAMM 27-51-00). A Company Maintenance request has been submitted to change the statement at the end of the SAMM to indicate to place the S138 Switch on MEL 32-21 rather than a DMI and change the DMI to MTI for the other two switches in the SAMM. I would also like it noted that the mechanics involved in this; performed everything under my advisement and should not be held accountable for my mistake. In order to prevent an event like this from happening again; I will remember to reference the MEL first to see if there is MEL relief available. I also would like to note that MEL 32-17 for the PSEU light does reference you to the 32-21 MEL in regards to; if you have a DO NOT DISPATCH message. Perhaps there could be a better way to make this more noticeable because DO NOT DISPATCH generally means an AOG situation and the MEL may not be looked at (i.e. my mistake). When you type in the fault code for the FIM reference; there is no mention of the MEL relief available for the S138 Switch. In my opinion; the manuals related to a S138 Switch failure do not guide you to this MEL; so if not consulting the MEL first; the MEL relief for this switch can easily be missed. MEL 32-17-C. 'DO NOT DISPATCH' message #32-64004 - dispatch is not allowed. If messages #32-62009; 32-62109; 32-62010; 32-62110; or 32-62014 are also displayed; refer to MEL Item 32-21; Flap Landing Warning Switch. The bottom line is; if all of the referenced Manual steps matched each other; or even referenced that MEL 32-21 should be consulted; if using the spare switch contact option; I think that it would not have been missed.

Callback: Reporter stated he is a Maintenance Controller and has 14-years experience on B737 aircraft. The PSEU light is located on the Overhead panel and a Master Caution Light 'Overhead' will also illuminate with a Flap Landing Warning Switch fault. The Flap Landing Warning Switch S-138 is located inside a drum-like unit that is part of the Flap Control Unit near the aft bulkhead in the Main Landing Gear (MLG) wheel well. There is a spare; or alternate S-138 switch available for Maintenance to connect to; by re-pinning the S-138 connector or cutting and splice connecting another wire to the spare switch; if the first S-138 switch contacts are inoperative. The PSEU and Master Caution light had illuminated after the landing rollout when the flight crew retracted the flaps.Reporter stated the Flap Landing Warning Switch S-138 is a common and continuing problem on all B737s models from the -200s up through the -900 series. He was informed he had violated their company General Maintenance Manual procedures by not using MEL 32-17 when the spare set of contacts for the S-138 Switch are used; because the time limit for repairing the first S-138 Switch contacts was ten days compared to 120-days when a Maintenance Tracking Item (MTI) is created. The Flap Landing Warning Switch was 100% functional with the S-138 switch in the spare contact position. His Air Carrier recognizes their manuals need revisions; especially since they have been merging a lot of data into a new Maintenance Tracking and Compliance software program provided by an outside contractor. The initial revision to cross-reference their manuals with their MEL did not go well. He helped with the second revision which seems to have a much better flow.



Synopsis: A Maintenance Controller was informed he should have applied MEL 32-17 to a B737-700 aircraft for a Flap Landing Warning Switch S-138 repair he had directed; instead of using their Maintenance Tracking Item procedures. The Proximity Sensor Electronics Unit (PSEU) light and Master Caution light had previously illuminated after landing.