What happened
On February 4, 2009, an EMB-721C, registration PT-EQI, was performing a flight from Urbano Santos to São Luís, Brazil. During the approach to runway 06 at Marechal Cunha Machado Airport (SBSL), the pilot noticed that the nose gear indicator light showed the gear was not locked down. After requesting a visual inspection from the tower controller, the pilot confirmed the nose gear was stuck in a mid-position.
Despite attempting emergency procedures to lock the gear, the pilot proceeded with the landing. To mitigate the risk of the nose gear collapsing, the pilot instructed the five passengers to move to the rear of the aircraft to shift the center of gravity. Upon touchdown, the aircraft initially maintained control, but during the landing roll, the left main landing gear retracted. This caused the aircraft to veer 18/0 degrees to the left, resulting in the aircraft exiting the runway. All six occupants (one pilot and five passengers) were uninjured, though the aircraft sustained light damage to the landing gear, flaps, and left wingtip.
The investigation
CENIPA's investigation revealed several critical mechanical and maintenance failures. Investigators found that the nose gear assembly had been incorrectly assembled, with components such as the bushing, drag link, and washers installed in the wrong sequence. Additionally, a steel washer with an incorrect diameter was used. This improper assembly allowed the drag link to detach from its support.
Furthermore, the investigation found that the hydraulic power pack was inoperable due to being burnt out. This likely occurred because the nose gear failed to complete its cycle, preventing the automatic shutdown of the hydraulic pump. The investigation also noted that the main landing gear lock clearances were below the manufacturer's specifications, which may have caused the green lights to indicate the gear was locked when it was not actually secured.
Findings
- Improper maintenance assembly: The primary cause was the incorrect sequence of assembly in the nose gear mechanism and the use of non-specification hardware.
- Maintenance supervision failures: There was a lack of adequate oversight regarding maintenance records, as previous services performed on the landing gear system were not documented.
- Inadequate gear lock adjustments: Main landing gear lock clearances were out of tolerance, contributing to misleading cockpit indications.
- Inoperable hydraulic component: The hydraulic power pack had failed due to excessive operation time caused by the incomplete gear cycle.