Pilot Debrief

MOONEY M20F near Watsonville, CA — 2011-07-08

Final reportWPR11FA316
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Date
2011-07-08
Location
Watsonville, CA, USA
Airport
WVI
Aircraft
MOONEY M20F
Registration
N7759M
Category
Airplane
Highest injury
Fatal
Fatalities
4
Phase of flight
Initial climb

Probable cause

The pilot's decision to take off toward a nearby low cloud layer and the subsequent turn, stall, and spin during the pilot’s attempt to avoid the cloud layer. Contributing to the accident was the pilot's failure to avoid the stall. His ability to avoid the stall was hindered by an inaudible stall warning system of questionable accuracy.

Contributing factors

Contributing to the accident was the pilot's inability to recognize an incipient stall, and prevent the full stall. His ability to recognize and prevent the stall was hindered by an inaudible stall warning system of questionable accuracy.

NTSB narrative

The pilot departed from his home airport situated about 3 miles east-northeast of the ocean with a low-lying stratus cloud layer. The takeoff was conducted while it was still daylight. Eyewitness and photographic evidence indicated that the stratus layer was nearby, to the southwest, south and southeast of the airport at the time of the takeoff. The airport was non-towered, and was equipped with two similar-length runways, designated as 2/20 and 8/26. Airplane performance, and terrain and obstacle clearance considerations did not preclude a takeoff from any of the four possible runway options. However, the takeoff was conducted from runway 20, directly towards the cloud layer. Eyewitnesses and recovered GPS data indicated that the airplane began a sharp left turn prior to reaching the end of the runway, at an altitude of about 400 feet above ground level (agl). That turn was consistent with an effort to avoid the cloud layer, but contrary to published airport noise abatement guidance that prohibited departure turns prior to the airport boundary, or at altitudes below 900 feet agl. The airplane did not enter the cloud, but during the turn, the airplane stalled, entered a spin, and descended rapidly to the ground. The airplane struck a parking lot and building less than 700 feet from the departure runway. Post-accident examination of the airplane and engine did not reveal any anomalies or failures that would have precluded normal operation. At least two headsets, one of which was a noise cancelling unit, were located in the wreckage. According to the airplane co-owner, the vane-activated, electrically-powered stall warning horn was inaudible to a pilot wearing a headset, and the owners' attempts to rectify that situation were unsuccessful. Post-accident testing of the vane switch and warning horn indicated that they were functional, but the horn volume was not measured or compared to any known standard. During airplane manufacture, the final position of the stall warning vane and switch assembly on the wing is determined during the production flight test of each individual airplane, in order to ensure system activation at the proper angle of attack. No records of the as-delivered vane position were available, and the as-delivered position of the vane could not be discerned by examination of the wreckage. Examination of the vane assembly revealed that it had been modified, and was not installed in accordance with the manufacturer's design drawings. In addition, no information regarding the accuracy of the modified stall warning system was located. The investigation was unable to determine whether the system would have provided sufficient, or even any, notification of a stall, presuming the horn was audible to the pilot, which in this case it was not. Despite three other runway alternatives, the pilot knowingly and intentionally decided to depart from the runway most closely aligned towards the stratus layer, with the apparent plan to turn to avoid it once airborne. While his runway choice may have been influenced by habit pattern, existing traffic, or a previous taxi event at that airport, the investigation was unable to determine why the pilot chose that runway, instead of using any of the other three alternatives which would have taken him away from the cloud layer. He then inadvertently stalled and spun the airplane during the avoidance turn, at an altitude which did not allow recovery.

Analysis

Primary failure mode
Spatial disorientation
First missed decision gate
Pilot could have aborted takeoff due to low ceilings and fog conditions.

NTSB coding

Evidence available

  • FDR / data
  • ADS-B / radar
  • 31 docket documents
View NTSB final reportView NTSB docket

Docket documents31

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