Low-Altitude Maneuvering · NTSB WPR17FA023
CESSNA 172N — Moss Beach, CA
| Date | November 18, 2016 |
| Location | Moss Beach, CA |
| Aircraft | CESSNA 172N |
| Purpose of flight | Personal |
| Conditions | Day · Visual Meteorological Cond |
| Phase / occurrence | Maneuvering-low-alt flying Loss of control in flight |
| Pilot age | 64 |
| Pilot total time | 1,145 hrs · Experienced |
| Time in type | 884 hrs |
| Fatalities | 1, 1 serious |
Probable cause
NTSB findings
- Personnel issues-Task performance-Use of equip/info-Aircraft control-Pilot - C
- Environmental issues-Conditions/weather/phenomena-Wind-Windshear-Effect on operation - C
- Environmental issues-Conditions/weather/phenomena-Turbulence-Terrain induced turbulence-Effect on operation - C
- Aircraft-Aircraft oper/perf/capability-Performance/control parameters-Lateral/bank control-Attain/maintain not possible - C
- Aircraft-Aircraft oper/perf/capability-Performance/control parameters-Descent rate-Attain/maintain not possible - C
- Personnel issues-Task performance-Use of equip/info-Use of equip/system-Pilot - F
- Personnel issues-Action/decision-Info processing/decision-Decision making/judgment-Pilot - F
- Aircraft-Aircraft systems-Flight control system-TE flap control system-Incorrect use/operation - F
What happened
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.