Pilot Debrief

ANTENOR VELAZCO LANCAIR EVOLUTION near Parker, CO — 2021-06-16

Final reportCEN21FA272
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Date
2021-06-16
Location
Parker, CO, USA
Airport
APA
Aircraft
ANTENOR VELAZCO LANCAIR EVOLUTION
Registration
N704AK
Category
Airplane
Highest injury
Fatal
Fatalities
2
Phase of flight
Approach

Probable cause

The pilot’s diversion of attention following an asymmetric flap deployment, which resulted in a descent and collision with powerlines. Contributing to the accident was maintenance personnel’s failure to properly secure the flap control rod attachment bolts, their failure to identify that the bolts were improperly secured during the subsequent condition inspection, and the pilot’s inadequate preflight inspections.

Contributing factors

Contributing to the accident was maintenance personnel’s failure to properly secure the flap control rod attachment bolts, their failure to identify that the bolts were improperly secured during the subsequent condition inspection, and the pilot’s inadequate preflight inspections.

NTSB narrative

The pilot and copilot were established on an instrument approach to the destination airport in visual meteorological conditions. About 3 miles from the end of the runway, the airplane began a left descending turn, during which the controller queried if the pilot was performing a 360° turn. The copilot replied that the airplane’s autopilot had failed. The airplane continued the left turning descent until ground impact. Several witnesses near the accident site saw the airplane flying low before the left wing impacted powerlines. The airplane came to rest on a hillside and was mostly consumed by postcrash fire. Examination of the airplane revealed that the left flap control rod end and associated attachment bolt were missing from the assembly. The threads for fastening the missing flap control rod attachment bolt were intact in the attachment bracket. The area around the threaded hole was rubbed, consistent with off-axis contact with the outboard end of the flap control rod attachment bolt. Corresponding off-axis contact deformation was observed at the edge of the control rod attachment bolt through-hole on the inboard side of the bracket. A piece of the right flap control rod remained attached to the bracket with an intact control rod attachment bolt. Like the left attachment bracket, the aft attachment bolts for the right flap control attachment bracket were secured with safety wire. While the head for the right flap control rod attachment bolt was drilled for use with safety wire, no safety wire was observed attached to the control rod attachment bolt. A review of maintenance records showed that paint work was performed on the airframe about 2 years before the accident, during which the flight control surfaces were removed. A follow-up entry noted that, “flight controls were balanced and installed with new hardware.” The airplane’s most recent condition inspection was completed about 8 months before the accident. Based on the available evidence, it is likely that when the flight controls were reinstalled after the paint work, the left flap and right flap control rod attachment bolts were not installed with safety wire. The use of safety wire on these bolts is mandated per the airplane build manual. These anomalies were not detected by the mechanic following the reinstallation or during the subsequent condition inspection nor were they detected during multiple preflight inspections by the pilot. The undamaged threads in the attachment for the left flap control rod indicated that the bolt likely backed out due to vibrations and the lack of the required safety wire. With that attachment lost, only the right flap would have deployed when the pilot was preparing to land, causing a flap asymmetry and the resulting turn to the left. It is likely the pilot was distracted by the misdiagnosis of the handling issue as an autopilot anomaly. During the subsequent turn away from the approach path, the pilot failed to maintain altitude, which resulted in impact with powerlines and terrain.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Pilot could have checked flap operation before approach to prevent loss of control.

NTSB coding

Evidence available

  • ADS-B / radar
  • Photos
  • 22 docket documents
View NTSB final reportView NTSB docket

Docket documents22

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