NTSB Identification: WPR11FA316
14 CFR Part 91: General Aviation
Accident occurred Thursday, July 07, 2011 in Watsonville, CA
Probable Cause Approval Date: 12/02/2013
Aircraft: MOONEY M20F, registration: N7759M
Injuries: 4 Fatal.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The pilot departed from his home airport, which was located about 3 miles east-northeast of the ocean, in daylight conditions. Eyewitness and photographic evidence indicated that there was a low stratus cloud layer to the southwest, south, and southeast of the departure airport at the time of the takeoff. The airport, which had no air traffic control tower, 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 pilot took off on runway 20, directly toward the low cloud layer.
Eyewitnesses and recovered GPS data indicated that the airplane began a sharp left turn before 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 was contrary to published airport noise abatement guidance that prohibited departure turns within the airport boundaries or at altitudes lower than 900 feet agl. Witnesses stated that the airplane did not enter the cloud layer; however, during the left turn, the airplane stalled, entered a spin, and descended rapidly to the ground. The airplane struck a parking lot and a building less than 700 feet from the departure runway. Postaccident examination of the airplane and engine did not reveal any anomalies or failures that would have precluded normal operation.
Despite three other runway alternatives, the pilot departed from the runway with a departure path that would take the airplane closest to the low cloud layer, with the apparent plan to turn to avoid it once airborne. The pilot’s runway choice may have been influenced by habit, existing traffic, or a previous taxi event, but any of the other three runway alternatives would have taken him away from the cloud layer. The pilot then inadvertently stalled and spun the airplane during a turn to avoid the clouds at an altitude that did not allow for recovery.
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. Postaccident testing of the stall vane switch and warning horn indicated that they were functional.
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 to ensure system activation at the proper angle of attack. No records of the as-delivered vane position for the accident airplane were available, and the as-delivered vane position could not be discerned by examination of the wreckage. However, examination of the vane assembly revealed that it 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. Therefore, it was not possible to determine whether the system would have accurately provided sufficient, or even any, notification of a stall, presuming the horn was audible to the pilot, which in this case it likely was not.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: 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.
Full narrative available
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