Incident Overview
On September 23, 2016, during a scheduled C14+CPCP+15MO maintenance check at the LOTAMS technical base at Warsaw Chopin Airport (EPWA), technicians discovered serious cracks on the left inner middle flap rib of a Boeing 737-400 aircraft, registration SP-LLF, operated by Polskie Linie Lotnicze LOT S.A.
Aircraft and Component Details
The affected component was the left inner middle flap rib, part number 65C26310-25, serial number 2054. The rib had been removed from the aircraft prior to the inspection. The cracks were documented as severe.
Maintenance Actions
In response, the damaged flap rib was replaced with a new unit. LOTAMS subsequently notified the operator's engineering department (OTE PLL LOT).
Investigation Findings
The investigation, overseen by Tomasz Makowski, was conducted by the operator. The cause of the cracking could not be determined. No injuries were reported, and the aircraft was not involved in an accident; the event was classified as an incident.
Preventive Measures
The event was recorded in the operator's SMS database and classified according to LOT's criteria. It will be included in safety performance indicators monitored under the company's Safety Management System.
Commission Recommendations
No safety recommendations were issued.