Accident
The aircraft, an ATR72 operated by TRIP Linhas Aéreas, was on a scheduled passenger flight from Belém-Val de Cans Airport to Altamira with 47 passengers and 4 crew members. The approach was conducted under visual flight rules, and the aircraft was stabilized. Landing was smooth with gradual deceleration using only ground idle. After the 70-knot callout, a strong noise was heard, and the left main landing gear collapsed, causing the aircraft to veer left off the runway and come to rest in a grassy area. One passenger sustained minor injuries.
Investigation
The investigation determined that the left main landing gear assembly (part number D23189000-19, serial number MN1700) collapsed due to failure of the aft pivot pin (part number D61000, serial number 25). The pin failed from fatigue, and the onset of fatigue was facilitated by a machining process carried out in the pin's section transition region.
The landing gear had accumulated 5,130 cycles since its last overhaul. The maintenance program required overhaul every eight years or 18,000 cycles. The gear had been removed on 27 February 2009 and sent for overhaul to AV Indústria Aeronáutica Ltda. on 9 March 2009, at which time it had 31,684 cycles since new and 18,095 cycles since the last overhaul. AV Indústria Aeronáutica Ltda. was certified for such inspections but outsourced some tasks because it lacked technical knowledge and appropriate machinery for reconditioning the aft pivot pin. Two of the three outsourced companies were not certified by the civil aviation authority. AV Indústria Aeronáutica Ltda. conducted external audits but these were insufficient to identify that the contractors lacked qualified personnel, manuals, and machinery. Additionally, the technical manager did not supervise the overhaul inspections and services performed by the contracted companies.
Findings
The failure analysis report stated that the aft pivot pin fractured due to fatigue, with onset facilitated by a machining process in the section transition region. The manufacturer's maintenance manual did not reference any machining work in that region. The only stage where machining was required was grinding of chromium. The lack of training and qualification of subcontractors led to inadequate machining during maintenance. Inadequate supervision by TRIP Linhas Aéreas, AV Indústria Aeronáutica Ltda., and the civil aviation authority allowed latent failures to persist. The pin exhibited fracture surfaces with a ±45° inclination and a flat area with multiple initiation sites indicative of fatigue. Scratches from inadequate machining were observed near the fatigue fracture, and the machining had produced a depression altering the pin's profile.