What happened
On August 27, 2004, at 03:52 local time, a Cessna 208-B, registration EC-IHD, was performing a domestic cargo flight from Palma de Mallorca to Ibiza Airport. During the landing roll, the crew applied reverse thrust to decelerate the aircraft. Shortly after, they noticed intense vibrations originating from the nose wheel. In response, the crew deactivated reverse thrust and attempted to decelerate using only the brakes, but the vibrations intensified.
Following a metallic noise, the nose of the aircraft dropped, causing the propeller to strike the pavement. The aircraft continued to slide on the forward section of the fuselage until it came to a halt a few meters further along the runway. The crew, who were uninjured, secured the aircraft and evacuated the plane safely. The incident resulted in minor damage to the nose gear, propeller, and forward fuselage.
The investigation
Following the incident, a visual inspection of the nose gear assembly revealed that the nose strut had pivoted forward and slightly to the left from its upper mounting. This movement occurred because the drag link, which serves as a strut and shock absorber, had become detached. Investigators found that the drag link is connected to the nose gear via two bolts; specifically, the right-hand bolt had suffered a complete fracture.
Further examination of the hardware revealed that neither bolt had been fully threaded into the ring housing. The broken bolt was short by 3.3 mm, while the bent bolt was short by 2.8 mm. Metallurgical analysis of the fractured bolt confirmed that the failure was caused by bilateral bending fatigue. The study showed that fatigue cracks had nucleated at the base of the first thread groove and propagated inward until the remaining material failed due to sudden overload.
Findings
- The nose gear collapsed because one of the bolts connecting the gear to the drag link failed.
- The primary cause of the bolt failure was insufficient tightening torque during installation, which subjected the bolt to bending stresses rather than the intended shear stresses.
- The secondary bolt had also begun to undergo a similar fatigue process, though to a lesser extent than the primary failed bolt.