Date: 201303
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: Q400
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Cruise
Aircraft component: Oil Cooler
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Powerplant; Maintenance Airframe
Human factors: Communication Breakdown; Situational Awareness; Time Pressure
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted; General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

Narrative: On a March 2013 morning; Mechanic Y and I; as Mechanic X; took a turnover from graveshift mechanics on the replacement of the #2 Engine Oil Cooler shroud. The installation was done; only remaining steps were to apply firewall sealant and close engine cowling and do Operational and Leak Checks. The cooler was only removed to Facilitate Maintenance; same Serial Number cooler re-installed. We read the task for Oil Cooler Installation; and printed it off along with the task for Engine Leak Check. (Paragraph-5D); not realizing we had failed to notice the Task for Oil Pressure Check and adjustment (Paragraph-5E). I thought we had put the task copies on the aircraft before we pulled out of the hangar; and didn't realize we didn't have them onboard until we were running the engines. In the interest of time; we decided that it was a standard leak check and proceeded with the runs; warming the oil. We had several other checks to do. From reading the Task earlier; I incorrectly remembered the oil temperature (temp) called for in the task as being 60 degrees. As I recall; we achieved an oil temp in the low to mid 60's. We missed the part about the 80% NH. We monitored oil pressure being in the normal range as part of standard run procedures. After shutdown; Mechanic Y performed a Leak Check of the cooler; with no leaks noted; then he signed-off the Non-Routine [Write-up/ Task Card] while I cleaned our mess in the hangar. In-flight enroute; the pilot reported oil pressure fluctuations; then a steady decline in oil pressure along with oil pressure caution light. The engine was not shutdown; and the flight diverted. On-call Maintenance reported large quantities of oil on cowling and no oil showing in quantity sight gauge or dipstick. The event occurred because an O-ring was cut on installation of the inboard oil cooler line at the oil cooler. The cooler shroud has sharp edges. The leak did not happen until the aircraft was in-flight; approximately 25-minutes from [my divert airport] is my understanding. I and a fellow Mechanic were sent to [my divert airport] to investigate what happened. We began engine removal and when the suspect line was removed; it was noted that the oil O-ring had a slice out of the outer edge. Me and Mechanic Y; (who was also in [my divert airport] for the engine replacement); were notified by a Supervisor that the Flight Data Recorder (FDR) and or Engine Monitoring Unit (EMU) download showed that we had missed a step. We then reviewed the associated task involved and realized the mistakes that had been made. We should have taken the time to shutdown the engines and get the printed task; complacency.

Callback: Reporter stated he and Mechanic Y did not run the PW150A turboprop engine up to 80% NH; which is the rotational speed indication of the High Pressure Compressor (HPC). The previous shift had Removed and Reinstalled (R/R) the same Air/ Oil Cooler in order to replace the oil cooler shroud. That shroud tends to crack a lot and mechanics have to remove the Oil Cooler to gain access to the shroud. The shroud edge is very sharp and the O-Ring on the oil line was apparently cut and went unnoticed when the oil cooler line was attached to the oil cooler. The oil line connection began leaking approximately 25-minutes after departure.



Synopsis: A Line Mechanic reported a damaged O-Ring seal for an Air/Oil Cooler line on #2 Engine had caused an inflight diversion of a company Q-400 aircraft; due to a steady loss of oil pressure and oil quantity.