What happened
On Sunday, September 18, 2005, at 11:19 h local time, a Beechcraft 95-B55, registration EC-HZB, was performing a private flight near Tenerife Norte Airport. After a 25-minute local flight without prior incident, the aircraft began its approach to runway 12. During the touchdown phase, the aircraft began to drift and veer toward the right. The aircraft eventually exited the runway, striking a runway edge beacon approximately 1,578 meters from the threshold of runway 12. The aircraft came to a stop roughly 35 meters from the runway centerline, oriented at approximately 210°, resting on its right wing, nose gear, and left main gear. The right main gear remained retracted. There were 3 occupants on board (one pilot and two passengers), all of whom sustained no injuries.
The investigation
The investigation focused on the mechanical state of the landing gear and the maintenance history of the aircraft. Post-incident inspections revealed that while the nose and left main gears were properly extended and locked, the right main gear remained retracted with the doors closed. The inspection of the landing gear components showed significant deformation in the right main gear's extension/retraction drag bar, which had buckled and struck the retraction box structure, causing two rivets to fail.
Investigators also examined the locking mechanism, which relies on a cable, a spring, a bracket, and a roller. The inspection found that the locking roller was completely seized, preventing the necessary rotation for the gear to unlock. Furthermore, the inspection revealed that the springs and cables in both gear assemblies showed signs of oxidation, and the locking bracket showed signs of erosion due to excessive friction against the seized roller.
Findings
- The primary cause of the runway excursion was the failure of the right main landing gear to unlock during the approach.
- The failure to unlock was caused by the seized state of the retraction structure roller, which prevented the gear from descending.
- The mechanism's failure was exacerbated by increased resistance within the assembly due to corrosion on the springs and cables.
- The aircraft's operation in the Canary Islands, an environment with high salinity and humidity, likely accelerated the corrosion of the landing gear components.
- While a maintenance inspection had been performed six months prior, there was no evidence that the known history of corrosion (noted in 2003) had prompted more frequent inspections to mitigate the effects of the corrosive maritime environment.