What happened
On December 9, 2004, during a multi-engine piston (MEP) rating training flight at Perpignan Airport, the instructor of a Piper PA 44-180, registration F-GIDF, experienced a sudden loss of elevator control. While demonstrating a high-bank turn, the instructor noticed the controls had become soft. He immediately leveled the wings and stabilized the aircraft in a slight dive at 125 kt.
To manage the flight, the instructor instructed the student to move to the rear seats to shift the aircraft's center of gravity. By adjusting the trim, power, and weight distribution, the instructor successfully stabilized the aircraft at 2,600 ft. The crew proceeded with a long final approach for runway 33. Despite some pitch oscillations during the approach, the aircraft landed safely without a bounce.
The investigation
Post-flight inspection revealed that the end of the elevator control cable had broken. The aircraft had flown 212 hours since its last major overhaul, during which the cables had been visually inspected according to the manufacturer's maintenance manual without any anomalies being noted.
Laboratory analysis of the broken MS21260-S4 stainless steel (SAE AISI 303 Se) cable end identified machining scratches at the break point. While no fatigue cracks or obvious external pitting were visible, microscopic analysis revealed branched, intergranular, and transgranular cracking. The presence of chlorine within these cracks was confirmed, suggesting that the material had undergone localized embrittlement.
Findings
- The failure was caused by internal corrosion that developed within the metal without significant outward signs.
- The proximity of the airfield to the sea likely facilitated this process, as evidenced by the presence of chlorine.
- The maintenance organization's inspection method was insufficient to detect the subtle external marks of corrosion that were present.
- There was a lack of awareness regarding the manufacturer's updated inspection recommendations, partly because the information was distributed via a non-mandatory Service Letter rather than a mandatory directive.