Air Tractor AT-502B Excursion Caused by Nose Gear Lock Failure

Casualties unknown • DOURADOS, MS, BR

An agricultural aircraft veered off the runway at a private airfield in Mato Grosso do Sul after a mechanical failure prevented the nose gear from locking.

What happened

On December 28, 2021, an Air Tractor AT-502B, registration PR-TZA, was performing a local agricultural spraying flight at Fazenda Paraíso Aerodrome (SD23) in Dourados, Mato Grosso do Sul. During the mission, the pilot identified a failure in the spraying system and decided to return to the airfield after the aircraft reached its maximum landing weight.

Upon landing on the unpaved runway, the pilot lost directional control of the aircraft, causing it to veer off the right side of the runway. The aircraft sustained substantial damage, though the pilot remained uninjured.

The investigation

CENIPA investigators examined the nose gear locking mechanism, which uses a mechanical system involving a lever, cables, and a spring-loaded plunger to secure the nose gear fork. The investigation focused on why the system failed to engage despite the pilot having moved the control lever to the locked position.

Investigators found that the nose gear lock was misaligned with the aircraft's longitudinal axis during the landing roll. A physical inspection of the mechanism revealed a significant accumulation of dirt and debris within the locking assembly. This contamination prevented the plunger from completing its full travel and inhibited the spring from properly engaging the lock.

While the pilot had performed the pre-flight checks, they admitted to not specifically performing the manual verification of the nose gear lock as prescribed in the Airplane Flight Manual (AFM). Furthermore, while the aircraft had undergone a 100-hour inspection recently, the continued operation on unpaved surfaces likely contributed to the contamination of the lubrication system.

Findings

  • The nose gear locking mechanism failed to function correctly due to dirt accumulation in the assembly.
  • The pilot did not perform the specific manual verification of the nose gear lock during the pre-flight walk-around as required by the AFM.
  • The aircraft was operating on unpaved runways, which likely led to the contamination of the mechanical components.
  • The nose gear lock lever was in the correct position, but the internal components were physically obstructed by debris.

Probable cause

The nose gear lock failed to engage because accumulated dirt prevented the mechanical plunger from fully seating, leading to a loss of directional control during landing.

Frequently asked questions

What happened in the 2021-12-28 aircraft accident near DOURADOS, MS, BR?

An agricultural aircraft veered off the runway at a private airfield in Mato Grosso do Sul after a mechanical failure prevented the nose gear from locking.

What aircraft was involved and where did it happen?

The accident on 2021-12-28 involved a aircraft, registration PRTZA, at DOURADOS, MS, BR.

What was the probable cause of the accident?

The nose gear lock failed to engage because accumulated dirt prevented the mechanical plunger from fully seating, leading to a loss of directional control during landing.

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