Date: 201812
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Nacelle/Pylon
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Communication Breakdown
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew; Person Maintenance
When detected: Aircraft In Service At Gate; In-flight
Result: Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action
Contributing factors: Aircraft; Procedure
Primary problem: Aircraft

Narrative: During walk-around prior to flight; visible gap in top of engine 2 nacelle was visible from rear of engine. Item logged; maintenance responded and determined seal was missing. After diagnosis and discussion; item was deferred; new maintenance release document was issued; and flight departed. After takeoff and during handoff from tower controller to departure controller; ATC said they were contacted by company maintenance during our takeoff roll to notify us to return to the gate. PNF (Pilot Not Flying) contacted maintenance via VHF to ascertain what this was about. Maintenance said they were concerned about the deferral and whether it was appropriate; properly used; properly performed; and/or properly documented; and asked us to consider return to departure airport to resolve the issue. PNF clarified that we had departed and queried about the necessity to return to departure. Maintenance advised a return. All systems were normal from our perspective and concern in that moment was coming from maintenance; but given the nature of the deferral we shared concern about having proper deferral or maintenance action taken. Weighing the options of a return to departure airport with a currently healthy but potentially unairworthy airplane; or climbing up from pattern altitude and flying to destination on the assumption that maintenance's excessive caution was just that; we chose to divert to the maintenance base immediately below us [instead of] climbing to cruise altitude and proceeding to a non-maintenance base over an hour away. We were below any operational limit weights and the weather was excellent directly beneath us. Dispatch was advised. Dispatch objected to the protocol followed by maintenance and suggested we proceed to destination. We thought the more conservative choice was to return to departure airport. We returned to destination and flight ended uneventfully. Maintenance took the airplane out of service; we flew the flight on a new airplane; publicly embarrassed by the debacle but feeling that the safer course of action was taken.




Synopsis: A319 Captain reported an improper maintenance deferral of a potentially unairworthy aircraft; requiring flight to return to departure airport.