What happened
On June 10, 2016, during a scheduled heavy maintenance inspection (D2+C14+CPCP+12KHRS+A155+EO+R/I) at the LOTAMS technical base (EPWA), an incident occurred involving a Boeing 737-400 operated by PLL LOT SA. While personnel were performing tasks related to the installation and adjustment of the forward passenger door, the door skin sustained damage near the upper hinge. The damage, consisting of a tear approximately 13 mm in length, was caused when a protective hinge strip was not unscrewed during the adjustment process, causing it to snag the door skin.
The investigation
The investigation established that the maintenance tasks were being performed by personnel who held valid certifications but lacked specific training on the B73 and lacked sufficient experience for these particular procedures. While the work was being conducted under the supervision of B1-rated personnel, the investigation found that the oversight was inadequate. The technical staff failed to correctly interpret the Aircraft Maintenance Manual (AMM) instructions regarding the removal of the hinge cover strip.
Findings
- Human error involving the incorrect interpretation of the Aircraft Maintenance Manual (AMM) by the maintenance personnel.
- Organizational failure in technical management, specifically the assignment of complex door installation and adjustment tasks to personnel lacking the necessary type-specific training and experience.
- Inadequate supervision by the B1-rated certifying staff overseeing the task.
Safety action
Following the incident, the operator notified relevant stakeholders and implemented several corrective measures:
- Information regarding the incident was disseminated to maintenance area managers for cascading notification to all maintenance staff.
- The incident was shared with the technical personnel training section to be used as a case study in periodic human factors and aircraft type training.
- On-the-job training was mandated for the personnel involved, focusing on the correct use of technical documentation and the specific supervisory responsibilities of B-level personnel.
- Human factors training programs were updated to include topics related to this type of occurrence.
- The event was recorded in the LOTAMS safety database to monitor aviation safety indicators.