Date: 201212
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Parked
Aircraft component: Powerplant Lubrication System
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Other / Unknown
Human factors: Communication Breakdown; Situational Awareness; Time Pressure; Troubleshooting
Second reporter function: Technician
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Departure Airport; General Maintenance Action
Contributing factors: Procedure; Incorrect / Not Installed / Unavailable Part; Manuals
Primary problem: Procedure

Narrative: Aircraft came in with a [logbook write-up] stating the left [engine] oil bypass light came on at landing. The crew who flew the plane in stated to the mechanics working the plane that the light flickered. Later that night the mechanics came to me and told me about the [logbook write-up] and the verbal from the crew. They stated they had inspected the Delta P (differential pressure switch) and it had not popped for the oil filter; they also tried to remove the filter bowl to replace the filter and it was stuck. I got into the IPC (Illustrated Parts Catalog) to see if we had the next higher component; the module that the filter bowl attaches to and we did not have one. In the meanwhile the mechanics went to the plane and cleaned the cannon plug and ran the engine and the bypass light did not re-illuminate. They came back in and told me about the situation and I dialed up Maintenance Control to tell them what was going on with the plane. I told Maintenance Control that the filter bowl was stuck and we would destroy it if we forced it any further plus we did not have the module 'next higher assembly'. Since we cleaned the plug; ran the engine and no delta P indication we; myself the Mechanic and the Controller; felt it was an indication issue; and we made the decision to clear the [logbook write-up]. I did not pull up the FIM (Fault Isolation Manual) that night and assumed that the mechanics did which I should have questioned when I reviewed the [logbook write-up] because of no mention of a FIM or MM (Maintenance Manual) used to come to this conclusion. The plane left the next morning and while on climbout at 25;000 FT the light came on and the plane returned to the field. Once back day shift removed the module and cut the filter bowl off and the filter was clean. They then looked at the chips [detectors] and found the gearbox detector had debris and the engine was changed.


Second narrative: #1 Engine oil filter bypass light flickered enroute to (STA) on (date). There was no history of any other indications or engine problems reported; and the light was extinguished upon arrival. I believe that the determination was that this was the product of an intermittent electrical anomaly. (STA) MX performed an engine run with no other indications illuminating. The aircraft was dispatched out of (STA). The bypass light illuminated once again resulting in an air return. Upon further inspection; the oil filter showed evidence of debris and the engine was replaced.


Synopsis: While troubleshooting an engine oil filter bypass light write up on a B737-700; Maintenance personnel were unable to remove the oil filter bowl. With no module available; they were hesitant to damage the filter bowl and concluded that the problem was indication only. The next flight; when the light came on again; the flight crew returned to the field. During the subsequent troubleshooting; the module was removed and the filter accessed; only to be found clean. However; when the chip detectors were checked; they contained material; leading to an engine change.