Accident Briefs: June 2018

Accident Briefs: June 2018

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These are official summaries from the NTSB. They are printed in their entirety and verbatim.

CESSNA 172N

Moss Beach, CA

Injuries: 1 fatal, 1 serious

The private pilot and a passenger were approaching the airport to land with a 70° right crosswind at 10 knots (kts) with gusts to 14 kts. The pilot reported that, on final approach, the airplane was configured with full flaps (30°) at an airspeed of 60 kts, and an altitude of 500 ft mean sea level (msl) when it began to encounter turbulence. The pilot then elected to conduct the landing approach at a higher airspeed and subsequently retracted the flaps from 30° to less than 20°. Immediately after reconfiguring the flaps, the pilot reported that he experienced strong turbulence that violently rocked the airplane and simultaneously felt a “strong downdraft” as the airplane entered a right bank. The pilot was unable to correct the airplane’s attitude, and the airplane subsequently descended into terrain, where it impacted a paved road, several vehicles, and two houses before coming to rest.

A weather study revealed that, at the time of the accident, a weak temperature inversion was present between 400 and 600 ft msl. The stable layer of air produced by the temperature inversion trapped any updrafts or downdrafts created by the wind flowing over nearby terrain. This created an environment favorable for the development of low level wind shear and turbulence below 600 ft msl. Although airplane performance data revealed that the pilot maintained an airspeed above the airplane’s stall speed throughout the landing approach, his decision to retract the flaps likely resulted in a sudden loss of lift. This loss of lift, combined with the low level wind shear and turbulent conditions, most likely resulted in the pilot’s loss of control during the approach for landing.

Probable cause: The pilot’s loss of airplane control following an encounter with low level wind shear and turbulence during final approach for landing. Contributing to the loss of control was the pilot’s decision to retract the wing flaps on final approach, which resulted in a sudden loss of lift.

MOONEY M20J

Lake Hughes, CA

Injuries: 1 fatal

The instrument-rated private pilot/owner regularly used the airplane to commute for work between his home airport and an airport located about 80 miles to the south. On the day of the accident, the pilot departed his home airport and, about 5 minutes after takeoff, established the airplane on a direct course towards an aeronautical navigation beacon that was located on a mountain peak about 28 nautical miles south of the airport, at an elevation of 5,793 ft mean sea level (msl). After takeoff, the airplane initially climbed to about 7,300 ft msl, then descended to about 6,500 ft msl, before ultimately descending to about 5,750 ft msl, where it remained for the last several minutes of the flight.

The pilot was not in radio communication with any air traffic control (ATC) facility during the flight, and had not filed a flight plan, but the airplane had been tracked by ground-based ATC radar. The ATC radar track data ended near the accident site. Both radar and the data from the pilot’s onboard GPS device showed that the airplane remained in about straight and level flight for at least 8 minutes before the impact. The wreckage was located about 70 ft below the mountain peak. Ground scars and airplane damage indicated that the airplane was in level flight, with significant engine power, at the time of impact. Examination of the airframe and engine did not reveal any evidence of pre-impact mechanical deficiencies or failures that would have precluded normal operation. Available medical information revealed no evidence of pilot incapacitation.

Meteorological conditions at an airport near the accident location suggested that an overcast ceiling of about 4,750 ft msl was present near the accident site. That ceiling would have obscured the peak, and would have been about 1,000 ft lower than the impact point elevation. It is likely that the pilot flew into instrument meteorological conditions (IMC), which obscured the peak from his view as he attempted to cross the mountain range. The investigation was unable to determine whether the pilot entered IMC intentionally or unintentionally, or how long the airplane was operating in IMC before impact.

The investigation was unable to determine why the pilot was operating on a track at an altitude that did not provide terrain clearance, even if he did intentionally enter IMC without operating under instrument flight rules. Because the ATC radar and GPS altitudes for the flight were congruent, altimetry malfunctions and errors can be eliminated as causal factors. The pilot’s GPS unit was capable of providing both visual and aural terrain/obstacle alerts, but the terrain and alert configuration settings of the GPS were not able to be determined. It is possible that the pilot either ignored or deactivated those features, and thereby deprived himself of those protection capabilities. Such a deactivation could have been the result of the pilot’s comfort level with flying in that region, or it could have been inadvertent. Although the investigation could not determine what assumptions, tools, or methods the pilot used to ensure adequate terrain clearance for the accident flight, the pilot Page 2 of 3 WPR17FA055 had sufficient and accurate information available, or potentially available, to enable him to avoid terrain.

All elements of this accident are consistent with a controlled flight into terrain (CFIT) event. Although the specific underlying reasons for the CFIT event could not be determined, it is likely that the pilot’s comfort with the route, combined with his determination to complete the flight to reach work, caused him to enter IMC. That entry into IMC, coupled with an improper route and altitude combination, resulted in the collision with the peak.

Probable cause: The pilot’s controlled flight into mountainous terrain while attempting to operate under visual flight rules in instrument meteorological conditions (IMC).

 

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