What happened
On March 15, 2018, a Piper PA-42 Cheyenne III, registration OB-1630, operated by Servicios Aéreos Tarapoto E.I.R.L., landed at Chachapoyas Airport in the Amazonas region of Peru. Following a successful landing, the crew began a 180-degree turn on the left main gear axis to head toward the parking apron. During this maneuver, the crew felt intense vibrations in the left main landing gear and noted significant resistance to forward movement while attempting to straighten the aircraft's heading.
The crew notified air traffic control and requested permission to shut down the engines to perform a visual inspection. The inspection revealed that the bolt head of the left main gear lower link assembly had fractured, and the fork of the lower shock strut was also broken, causing the tire to tilt. All nine passengers and two crew members evacuated the aircraft safely without any injuries.
The investigation
The investigation conducted by the CIAA established that the aircraft had been operating in the Peruvian Amazon, where frequent 18/0-degree turns on narrow or irregular runways are common. Laboratory analysis of the failed components indicated that the fracture of the bolt head was caused by material fatigue, aging, or pitting corrosion. Furthermore, the investigation found that the subsequent damage to the shock strut fork was the result of excessive bending stresses caused by the initial failure of the bolt.
Findings
- The primary cause of the incident was the fracture of the left main landing gear lower link assembly bolt and the shock strut fork due to material fatigue.
- The aircraft's maintenance program and manual did not include non-destructive testing (NDT) or equivalent methods to inspect these specific components for cracks, corrosion, or fatigue.
- Frequent 180-degree turns on narrow runways and landings on potentially irregular surfaces contributed to the accumulation of structural stress on the landing gear components.
Safety action
The investigation issued recommendations to the operator to evaluate including magnetic particle inspection (a type of NDT) in their Approved Maintenance Program to detect cracks or corrosion in bolts exposed to high shear stresses. Additionally, it was recommended that the inspection of the landing gear bolts and shock strut forks be incorporated into required inspection items (RII) during routine maintenance checks.