Date: 201208
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Light: Night
Aircraft: B737-400
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Parked
Aircraft component: Fuselage Main Frame
Reporter organization: Air Carrier
Reporter function: Lead Technician
Reporter qualification: Maintenance Powerplant; Maintenance Airframe
Human factors: Situational Awareness; Confusion; Communication Breakdown
Second reporter function: Technician
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural FAR
Detector: Person Maintenance
When detected: Routine Inspection
Result: General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Procedure; Human Factors; Aircraft; Chart Or Publication
Primary problem: Human Factors

Narrative: Aircraft X; a B737-400; was found with corrosion on the intercostal at the aft end common to Body Station (BS) 986.50 floor beam. This corrosion was visible while standing on the ground looking up through the open Outflow Valve. This was written up [in the logbook]. At this time it was believed the corrosion was more then simple surface corrosion and extended between the floor and the floor beam; extensive photos were taken by Inspection at this time. The area in question also contained some re-work; a roughly trimmed cutout in the intercostal that had been made for the Hi-Lok to clear. The job was turned from graveyard [shift] to dayshift at the morning meeting. At this meeting it was understood by the off-going shift that the aircraft was to be ferried elsewhere for the repair of the floor beam due to the extensive nature of the work.After the turn over it was noted that the Dayshift Manager and the Dayshift Airframe Supervisor were at the aircraft and observing the area of the discrepancy. The sign-off of the discrepancy was done on a write-up. The corrosion removal was done by a Graveyard Mechanic who had stayed over for an engine run on another aircraft. This Mechanic said he did not see any rough re-work area and only removed surface corrosion from the area. A Dayshift Mechanic signed-off the painting of the area and another Dayshift Mechanic signed-off the entire job. There is no documentation that the Airframe Shop had evaluated or worked this discrepancy. [Later] in the evening; it was noted by the Graveyard Mechanics that the aircraft was in revenue service and apparently the corrosion issue and the rough rework area had not been addressed. The original write-up did provide sufficient detail of the discrepancy and the turn over at the morning [meeting] did not adequately cover the defects. The Mechanic who removed the corrosion and the Inspector were not aware of the detailed photos of the area.


Second narrative: I was performing a walkround on a B737-400 aircraft that was on a Routine Overnight (RON) [check]. I looked up in the Outflow Valve and noticed corrosion on the floor support and an incorrect blend out on the edge. I notified my Lead and Supervisor to the damage and documented the corrosion. I thought that the write-up was adequate to address the corrosion and did not document the blend out when it had corrosion also. I stated the wrong Body Station (BS) - it should be Body Station 967 to 986.50 instead of the 986.5 to 1006 that I wrote. My Lead and Supervisor were shown the location and the next shift was shown the location. At the beginning of my shift; I was informed that aircraft was put back into service instead of being ferried back to a vendor for repair as previously told to me.I work Graveyard [Shift] and I documented the corrosion. My Lead and Supervisor knew of the corrosion at the morning turnover meeting. My Lead and Supervisor notified the oncoming shift of the damage and corrosion and that it needed to be addressed. In the morning meeting; they stated that the Ferry permit was being worked on; my write up was sufficient; and a turnover was not required. The Dayshift Lead and Supervisor knew about the damage. Somewhere there was a breakdown in communication: the edge damage and corrosion was not addressed. We have an Airframe Shop who is supposed to work on corrosion; they were not the people that removed the corrosion. A Graveyard Technician that was working on a different airplane in a different hangar and walking through was given the assignment to remove the corrosion instead of having the next shift Airframe Shop address the write-up.My Lead notified Maintenance Control that there was a discrepancy that may not have been addressed correctly. Maintenance Control grounded the plane; flight cancelled; and flew it back for Inspection. A better turnover meeting between shifts involving technicians; supervisors and leads could eliminate some miscommunications. Using the Airframe Shop to address elements in their work scope rather than [using] an inexperienced Technician. The other item that could help eliminate errors is a large graphic to see Body Stations and some training on how to read Body Station charts. Supervisors or Leads should review the write-ups to insure locations and descriptions are accurate.


Synopsis: A Lead Line Aircraft Maintenance Technician (AMT) and another AMT report about their involvement with a B737-400 aircraft that was released with known corrosion on the internal fuselage aft end; at the outflow valve area common to Body Station (BS) 986.50 floor beam. Aircraft later grounded and flight canceled.