20000428005799A

(-23) Cessna 172, N216PB collided with lake almanor under unkown circumstances. The private pilot and his three passengers received fatal injuries. The aircraft was being operated under the provisions of FAR part 91 as a personal flight when the accident occurred. The pliot departed chico, CA airport frlw to Chester California, where the accident occurred. Visual meteorolgist conditions prevailed and a flight plan was filed. (.4) there were no witnesses to the accident. A passing motorist saw the tail of the aircraft sticking out of a lake and notified authorities. Crush lines on the recovered wreckage disclosed that it impacted the water right wing low with a pitch attitude in excess of 45 degrees nose down. No preimpact mechanical malfunctions or failures were identified. The pilot rented the airplane and flew 47 miles to the mountain resort airport, landed, met some of his future in-laws, and loaded three of them onboard for a local sightseeing trip around the lake. He obtained his fixed wing private certificate 2 weeks prior to the accident, and this was the first flight with passengers. During training, he had only 1 flight involving a high-density altitud e airport, with the balance of his training conducted at airports with elevations less than 1,000 feet MSL. The density altitude at the accident site was 5,400 feet. The lake is in an oval shaped mountain valley 25 miles long by 15 miles wide surrounded by mountains, which rise 3,000 to 4,000 above the water's surface. The town and the airport are at the northwest end of the lake. The town borders the airport to the north, and mature pine trees that are 50 to 60 feet in height surround the field and provide obstacles for an approach or departure on any runway but 16/34. The airport manager said that because of the terrain and obstacles, and the proximity of the noise sensitive town to the north, pilots typically land on runway 34 and takeoff on runway 16. While he could not be certain, the airport manager believes the airplane departed on runway 16. The location of the wreckage would be consistent with an upwind to crosswind turn point for runway 16. The aircraft was found in a takeoff and initial climb configuration. Based on the aircraft's recording hour meter and the stopped electric clock, the accident occurred in the initial climb from takeoff on runway 16. The performance data data for the airplane establishes it would have climbed to between 400 and 500 feet AGL as it reached the accident location. Using flight planning charts for the airplane, the elapsed time on the recording hour meter does not support a conclusion that the pilot completed a run-up or had any appreciable ground run time prior to the accident takeoff. Between 1500 and 1600, the airport's automatic weather observation station recorded winds from 289 degrees at 9 mph with peak gusts to 23 mph. The system only records the highest peak wind gust during the hour-long observation period; however, it does not record the time of the wind peak. Surface winds are affected by friction and coriolis deflection, which will produce an average increase in wind speed of 10 mph at the boundary between the layer next to the surface and the free flow layer above, which is typically about 400 feet AGL. Coriolis deflection will cause the wind direction to change clockwise at the boundary, with a typical direction change of 10 to 20 degrees. Katabatic wind effects in mountainous areas can result in a rapidly moving air mass, which if an inversion layer is present, may flow over the lower layer. Therefore,the takeoff roll on runway 16 would have been with a right quartering tailwind, which moved closer to a direct tailwind and increased in speed as the aircraft climbed through 400 feet. Considering the recorded peak wind speed, it is likely the aircraft encountered a rapid change in wind velocity by as much as 25 to 30 mph. The flaps-up stall speed at zero degrees of bank is 44 knots indicated airspeed (KIAS) and 47 KIAS with 30 degrees of bank angle. Normal initial climb segment airspeed is 74 KIAS at 5,000 feet MSL.