What happened
On September 29, 1998, an Embraer 120 Brasilia, registration F-GTSH, operated by Regional Airlines, departed Clermont-Ferrand for Pau. Approximately one minute after takeoff, while climbing through 3,600 feet during a left turn, the flight crew experienced a sudden heavy impact followed by intense vibrations throughout the controls.
The crew immediately decided to return to the airport, requesting priority and alerting air traffic control to prepare emergency services. While the crew could not identify the specific source of the disturbance, the vibrations slightly subsided as the aircraft slowed for landing and the crew extended the landing gear and flaps. The aircraft landed safely at 19:38 UTC, but upon inspection at the parking stand, it was discovered that the entire left leading edge of the horizontal stabilizer had been torn away. Despite extensive search efforts, the missing component was never recovered.
The investigation
The investigation focused on the structural integrity of the horizontal stabilizer and recent maintenance performed on the aircraft. The aircraft had recently undergone maintenance at Nantes Aéro S.A. to replace de-icing boots on several Embraer 120 aircraft, including F-GTSH, with the work completed on September 10, 1998.
Investigators examined the remaining fasteners on the stabilizer. On the upper surface (extrados), 25 screws were still present but were found to be loose. On the lower surface (intrados), no screws from the leading edge were recovered. Detailed analysis of the remaining hardware revealed significant discrepancies in the fasteners used during the recent maintenance. While some screws were the correct manufacturer-referenced parts, others were unreferenced, oxidized, or of different models. Specifically, several stainless steel screws were found that lacked the required centering cone and were not cadmium-coated like the original parts.
Findings
- The loss of the left horizontal stabilizer leading edge was caused by the failure of the fasteners holding the component to the stabilizer.
- The investigation identified the use of incorrect and non-standard hardware during recent maintenance work.
- Several unreferenced stainless steel screws were used on the upper surface of the stabilizer; these lacked the necessary centering cones and were not the specified cadmium-coated type.
- Some fasteners were found to be loose, and several nuts showed traces of fresh grease without evidence of being properly tightened.
- The investigation noted that the loss of the component likely originated from the inside of the structure and moved outward, as evidenced by the condition of the remaining hardware and the torn stabilizer structure.