Date: 201505
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Aircraft component: Wing Leading Edge
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Other / Unknown
Detector: Person Passenger
When detected: In-flight
Result: General Maintenance Action
Contributing factors: Aircraft; Procedure; MEL; Human Factors; Chart Or Publication
Primary problem: Human Factors

Narrative: A departing passenger brought to my attention a section on the left wing top where he thought some rivets may not have been secure.  He had cell phone photos showing what appeared to be the area in question separated in flight.  (This gentleman is a pilot; non-company; who said he had seen this separation before).  Maintenance was summoned to the aircraft and confirmed that the rivets were not holding.  The aircraft was taken out of service.  The area in question is on the wing top; immediately inboard of the [left] engine pylon; just forward of the black paint line (that describes the 'okay for frost' area) and was six or seven rivets long.  For several years; on originators; I have made a point to inspect the upper wing surfaces from the overwing exits.  I did so this morning and did not detect any abnormalities.  The damage described in this report could not be detected by normal preflight duties; a ladder would be required.  Parked at gate; post flight. The only action that could prevent this issue is more frequent maintenance inspections of the compromised area.  This area is not adequately inspect-able from the ground or the cabin.

Callback: Reporter stated that from the cabin window; one can clearly see the area that the passenger/pilot was referring to. You just could not see the condition of the rivets unless a ladder was available. From the description by the passenger; the rivets were lifting in flight. Maintenance inspected the upper wing leading edge skin immediately inboard of the left engine pylon area and took the aircraft out of service. Maintenance Control however; released the B737NG with a Repetitive Inspection MEL and a 100-hour time limit when fastener repairs had to be accomplished. He felt the Maintenance Release was improper and believed the fasteners should have been replaced prior to the next flight. No information whether or not Maintenance will increase their surveillance of that wing area on their other B737 aircraft during overnight checks.



Synopsis: A Captain was informed by a passenger departing their B737-700 aircraft that rivets appeared to be loose on the upper wing skin leading edge area; just inboard of the left engine pylon. Maintenance determined passenger's observations were correct and the attach fasteners were loose.  Maintenance Control approved a 100-hour MEL deferral with Repetitive Inspections.