OSTROTH THANE L COZY MK IV — Half Moon Bay, CA

What happened

The pilot departed under visual flight rules while instrument meteorological conditions were reported at the airport, with a broken cloud layer at 300 ft above ground level (agl). A witness who was dining outside north of the departure airport initially heard the airplane and saw it shortly after. The witness said that the sound of the engine was similar to the sound of coughing and that the airplane appeared to increase in speed while it dipped and turned. The sound of the engine then “cut out,” and the airplane appeared to have banked toward the shoreline. Shortly thereafter the witness lost sight of the airplane’s lights.

Flight track data showed that the airplane departed to the north and entered a left turn just beyond the departure end of the runway. The data showed that the airplane had ascended to a maximum altitude of 250 ft mean sea level (msl), with groundspeed fluctuating between 87 and 91 knots. The last data point was recorded about 4,900 ft north of where wreckage was observed floating in the Pacific Ocean.

Postaccident examination of the airplane revealed that the fuel lines attached to the fuel flow divider remained attached but were loose when moved with a wrench. No evidence of fuel staining or leaks was observed. Postaccident examination of the airplane revealed no other evidence of a potential mechanical malfunction that would have precluded normal operation.

An editorial "what led to it / how to avoid it" analysis for this accident is generated separately and will appear here.