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On April 28, 2000, between 1500 and 1620 hours Pacific daylight time, a Cessna 172P, N216PB, collided with the surface of Lake Alamanor near Chester, California. The airplane was operated by Pacific Flight Services of Chico, California, and was rented by the pilot for a personal flight. The aircraft was destroyed in the collision sequence and sank. The private pilot and his three passengers sustained fatal injuries. The airplane was being operated under 14 CFR Part 91 as a personal flight when the accident occurred. The flight is believed to have departed the Chester airport between 1500 and 1530 for a local sightseeing flight around the lake. Visual meteorological conditions prevailed and a flight plan was not filed for the flight.
No witnesses to the accident were identified by either Safety Board investigators or investigating officers from the Pulmas County Sheriff/Coroner's Office.
Investigation disclosed that the pilot rented the airplane from the operator and departed from the Chico airport about 1430 and flew to the Chester airport, a distance of 47 miles. At the Chester airport, the pilot met with his fiance, her grandparents, and her younger brother. According to the fiance and other family members, the pilot loaded his fiancee's grandparents and her younger brother onboard the airplane to go sightseeing around the lake while the fiance waited for the group to return. This was the pilot's first flight with passengers since obtaining his fixed wing private pilot certificate 14 days prior to the accident.
The airport manager and owner of the local fixed base operation (FBO) on the field witnessed the group of people walk out to the accident airplane and get in. He said he was about 100 feet away from the airplane and he heard it start up and also heard the subsequent takeoff. He said that he owns a Cessna, and the engine sounded "typical" and normal. The airport manager said he is also an airframe and power plant mechanic with inspection authorization. While he did not note the exact time, he believes that the airplane took off somewhere between 1500 and 1530.
The airport manager said that pilots typically land on runway 34 and depart using runway 16 so that they fly over the lake and not the noise sensitive town of Chester. He said he could not be 100 percent certain, but he believed the pilot departed on runway 16 out over the lake.
Shortly after 1600, a motorist driving along the west shore of the lake observed the tail of an airplane sticking out of the water and went to the U.S. Forest Service ranger station across the street from the airport to report the sighting. According to Pulmas County Sheriff's office, the 911 emergency call from the U.S. Forest Service office reporting the aircraft wreckage sighting was logged at 1625.
The location of the wreckage was plotted on a USGS survey map by the responding search and rescue personnel from the Pulmas County Sheriff's office. The location as plotted was later determined to be about 4,600 feet on a magnetic bearing of 132 degrees from the approach end of runway 34 (or the departure end of runway 16). The location is 0.4 miles east of the lake's north-south oriented western shoreline. According to the airport manager, the position of the wreckage would be consistent with either a upwind to crosswind turn point for runway 16, or, a base to final turn point for runway 34.
The pilot's personal flight records, the operator's records, and the Federal Aviation Administration (FAA) airman and medical records files were reviewed. He held a private pilot certificate with ratings for rotorcraft helicopters and single engine land airplanes. The rotorcraft helicopter rating was issued on August 1, 1999, and the airplane single engine land add-on rating was issued on April 14, 2000. The pilot's most recent third-class medical certificate was issued without limitations on September 1, 1998.
According to the pilot's flight logbook he had 131 hours total time, with 68 hours in rotorcraft, and 63 hours in fixed wing airplanes. All of the fixed wing flight time was amassed in Cessna 172 aircraft between September 1999 and the accident. Over half of the flights, including the pilot's practical flight test, were listed in the accident airplane. Of the 63 fixed wing flight hours, 10 were recorded as pilot-in-command. No logbook entries were recorded between the pilot's fixed wing practical flight test on April 14 and the date of the accident. Based on the identifiers listed in the logbook for flight origin and destination points, the highest elevation airport used by the pilot was about 2,500 feet msl, and only one flight was recorded to that airport. The balance of the flight activity was conducted in the greater San Joaquin Valley of California at airport elevations below 1,000 feet msl.
According to family members, the passenger in the right front seat did not have any prior aeronautical experience. No record of the individual was found during a review of the FAA airman and medical records database.
The Cessna 172P, serial number 17274440, was manufactured in November 1980, and had accrued a total time in service of 9,005 hours. The most recent annual inspection was completed on February 4, 2000, 156 hours prior to the accident. In addition, a 100-hour inspection was accomplished on April 5, 2000, 58 hours prior to the mishap. A Lycoming O-320-D2J engine, serial number L-1046-39A, was the original Cessna factory installed engine in the airframe and had accumulated the same total time in service as the airframe. The engine had accrued 1,052 hours since the most recent major overhaul. Annual and 100-hour inspections were accomplished on the dates noted for the airframe. In addition, a 50-hour inspection was completed the day prior to the accident. Review of the operator's aircraft status sheet and maintenance department records disclosed that there were no unresolved discrepancies at the time the pilot rented the airplane.
The operator's records revealed that the airplane was refueled on the morning of the accident with the addition of 15.1 gallons of 100LL aviation gasoline. The operator reported that the addition of the fuel topped the aircraft standard range tanks to capacity (43 gallons total, 21.5 in each tank). Another renter pilot flew the airplane for 1.2 hours before the accident pilot rented it; comparison of the recording hour meter reading at the accident site and on the operator's rental log sheet for the pilot's departure from Chico revealed that the accident pilot flew the airplane for a total of 0.6-hours. Using average fuel consumption rates in the airplane flight manual climb and cruise performance charts, investigators conservatively estimated that the airplane had about 20 gallons of fuel onboard at the time of departure from the Chester airport. The disposition of the fuel load between the two standard capacity wing tanks could not be determined.
As noted above, the recording hour meter registered 0.6 hours from the time the pilot took the airplane at Chico. Using the performance charts in the Cessna Aircraft Information Manual for the airplane, the flight time from Chico to the Chester airport was computed (the charts are appended to this report). The performance charts include adjustment factors for the takeoff and climb variances from cruise. A climb to 6,000 feet was assumed in the computations, along with a cruise at 75 percent power, and an additional 6 minutes was factored in for the start and taxi at Chico, and the taxi in to parking at the Chester Airport. The total elapsed time thus derived was between 32 and 38 minutes, or, 0.6 hours on the recording hour meter.
Weight and balance computations were made for the takeoff at Chester, and at a zero fuel condition. The airplane empty weight, total moment, and center of gravity were obtained from the operator's maintenance records. The takeoff condition used the previously estimated 20 gallons of fuel. The occupant weights and seating positions were obtained from the Pulmas County Coroner's office. The detailed computations are appended to this report. For the takeoff condition, the gross weight was 2,258 pounds and the center of gravity was 42.4-inches. For the zero fuel condition, the gross weight was 2,138 pounds, with a center of gravity at 42.1 inches. According to the weight and balance charts in the airplane's flight manual, the allowable center of gravity range for the determined weights was 37.86 inches to 47.3 inches. The maximum authorized gross weight is 2,400 pounds.
According to Cessna Aircraft engineering documents, the control surface travel range for the elevator trim tab is 19 degrees tab down (nose up) and 22 degrees tab up (nose down). During examination of the control system following wreckage recovery from the lake, the elevator trim tab jackscrew actuator was found at a 13-degree tab down (nose up) position (See Tests and Research section of this narrative). At the request of Safety Board Investigators, Cessna Aircraft conducted a series of flight tests with a similarly equipped Cessna 172P. The tests were conducted at a weight and center of gravity location replicating the condition of the aircraft when it arrived at Chester and during the subsequent accident flight takeoff. A normal full-flap approach and landing was made following the procedures specified in the Aircraft Information Manual; the elevator trim tab was then measured and found to be 3.9 degrees tab down (nose up). A 13-degree tab down position was established on the ground and the cockpit indicator marked to be able to return to that setting while in flight. The power off trim speeds at zero flaps and at 10, 20, and 30 degrees of flap extension were then established. At zero flaps, power off, the trim speed was between 53 and 60 knots. With 10 degrees of flaps, power off, the trim speed was 53 to 56 knots. At 20 and at 30 degrees of flaps, power off, the trim speed was 53 to 58 knots. With flaps up and starting at liftoff airspeed, full power was applied; the test pilot terminated the procedure when the nose lifted above 40 degrees.
Review of the Cessna Aircraft Information Manual for the Cessna 172P disclosed that 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, with a 470-foot-per-minute climb rate.
At an elevation of 4,500 feet mean sea level (msl), Lake Almanor 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 valley's long axis is oriented on a northwest to southeast line. The town of Chester 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, on average, surround the field.
The airport is on the shore of the lake at an elevation of 4,528 feet msl, and it has two runways. The traffic pattern altitude is 5,528 feet msl.
Composed of a gravel surface, runway 5/23 is 5,320 feet long by 120 feet wide. The departure end of runway 23 has obstacles consisting of trees, power lines, and a road. The departure end of runway 5 has trees for obstacles. A departure on runway 23 would be toward rising mountainous terrain, while a departure on runway 5 would be toward the lake's shoreline.
Runway 16/34 is asphalt surfaced and is 5,000 feet long by 100 feet wide. The departure end of runway 34 has obstacles consisting of trees, power lines, and a road. The town of Chester is immediately north of the airport and a departure on runway 34 would be over the residential and business districts, and toward rising mountainous terrain. A departure on runway 16, or an arrival to runway 34, would be over the lake and without obstructions. Runway 34 has right-hand traffic.
According to the airport manager, because of the surrounding 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.
The US Forest Service maintains an automatic weather observation station near the airport. The 1500 observation recorded a temperature of 56 degrees Fahrenheit, with 33 percent humidity, and winds from 273 degrees at 7 mph with peak winds at 18 mph. The 1600 observation recorded a temperature of 54 degrees Fahrenheit, with 35 percent humidity, and winds from 289 degrees at 9 mph with peak winds at 23 mph. The system only records the highest peak wind during the hour-long observation period; however, it does not record the time of the wind peak. Other wind speed transients between the steady state value and the highest peak value would not be recorded.
Based on the recorded temperature and station pressure at the Forest Service observation unit, the density altitude was calculated to be about 5,400 feet during the probable time frame for the accident.
The airport manager said the weather on the day of the accident was "breezy" with temperatures in the mid 50's. No unusual meteorological phenomena were observed in the vicinity of the lake, or reported by any pilot arriving at the airport on the day of the accident.
The closest official aviation weather observation stations are: Red Bluff, California, 55 miles west of the site; Chico, 47 miles southwest; and Blue Canyon, California, 73 miles southeast. All of these stations are separated from Lake Almanor by one or more mountain ranges. During the probable time frame of the accident, the stations were reporting westerly winds below 12 knots. The upper air soundings from the Reno, Nevada, and Medford, Oregon, reporting stations were showing northwesterly wind flows at 15 knots or less below 10,000 feet.
FAA Advisory Circular 00-6A, "Aviation Weather," and the textbook "Weather Elements," (Blair/Fite, 1975, Prentice-Hall, Inc., Englewood Cliffs, New Jersey) were reviewed regarding the effects of surface friction and Coriolis deflection on surface winds. According to both sources, protuberances in the surface induce a frictional slowing effect on wind velocity close to the surface; the rougher the surface (the more and larger the trees, buildings, etc.), the more pronounced the slowing effect. While the velocity change depends on many factors (including the terrain roughness, existence of a inversion layer, and the lapse rate of the atmosphere, among the most typical), the average velocity change is on the order of a 10 mph increase as you leave the frictionally affected layer. The boundary zone where the frictional effects rapidly decrease is usually in the 300- to 500-foot agl range. The Coriolis effect induces a change in the direction of the wind flow to the right (clockwise) in the northern hemisphere as you move away from the surface; at the boundary zone between the frictionally affected wind layer and the free air layer, the directional change is in the 10- to 20-degree range. Katabatic winds occur in mountainous areas and result from cold heavy air masses that flow down mountain slopes into valleys. As the Katabatic wind flow moves down a mountain slope, it is heated and dried, and will displace the warmer air masses in the valleys. If an inversion layer is present, the Katabatic wind may flow over the lower layer.
WRECKAGE AND IMPACT
The location of the wreckage was plotted on a USGS survey map by the responding search and rescue personnel. The location was later determined to be about 4,600 feet on a magnetic bearing of 132 degrees from the approach end of runway 34 (or the departure end of runway 16). The geographic coordinates of the airplane wreckage were west longitude 121 degrees 13.8 minutes by north latitude 40 degrees 15.8 minutes. As plotted on a USGS 7.5-minute chart, the approach end of runway 34 was west longitude 121 degrees 14.38 minutes by north latitude 40 degrees 16.56 minutes.
According to the Pulmas County Sheriff's Office, two of the passengers (the fiancee's Grandparents) had a residence on the western lakeshore in the 100 block of Kokanee Trail. Review of a chart disclosed that the house was just under a mile southeast of the airplane wreckage location.
Search and rescue divers from the Pulmas County Sheriff's Office documented the wreckage at the time the occupant remains were recovered. A diagram prepared by the diver is appended to this report. In pertinent part, the diver reported that the airplane was inverted and nosed into the bottom sediments about a 75-degree angle in 16 feet of water. About the aft most 3 feet of the tail was protruding from the surface of the water. The tail of the airplane was oriented to the north toward the airport. Both wings were attached to the fuselage and were displaced forward with the tips resting on the bottom. The nose landing gear was displaced rearward and to the right. More damage was evident on the right wing than the left. The right main landing gear was missing from the fuselage and was not visible in the immediate area. The left cockpit door and the baggage door were found open. The engine cowling was present and crushed. The divers noted a strong smell and taste of gasoline in the water around the wreckage during the initial response dives to check on the occupants.
After the aircraft was floated and lifted from the water, the following major components were not present: 1) right main landing gear strut and wheel; 2) upper engine cowling; 3) right aileron; 4) right control yoke; and 5) left cabin door.
TESTS AND RESEARCH
The aircraft wreckage was recovered from the lake on April 29, 2000, by an aircraft retrieval/salvage firm, Plain Parts, Pleasant Grove, California. A cursory examination was conducted at that time. The recovered wreckage was examined in detail by Safety Board investigators on May 1, 2000, at the facilities of Plain Parts.
The cabin fuselage from the propeller spinner aft to just behind the rear baggage compartment bulkhead was crushed, distorted, and disrupted. The cabin windows on the front, right side, and rear were broken; the left rear side window was intact. The empennage section was displaced to the right and slightly tail up, with compression wrinkling evident on the right-hand side all the way back to the horizontal stabilizers. The predominant pattern of crush fold lines was noted to be about 45 degrees to the longitudinal axis and 20 degrees to the lateral axis, with the right side deformed more than the left. The fairing around the left main gear strut was hydraulically accordioned rearward about 70 degrees to the horizontal.
The left wing remained attached to the center section carry through structure and was undamaged outboard of the lift strut attachment point. The entire left wing was bent downward at a 25-degree angle, with the bend point located just outboard of the fuel tank's left edge. The lift strut was pulled out of both the wing structure and the fuselage attach point. The aileron and flap remained attached to their respective hangar and hinge assemblies. No fuel was found in the left fuel tank, only lake water.
The right wing remained attached to the center section carry through structure. It was crushed and hydraulically distorted from leading edge to trailing edge over the entire span. The outboard third of the wing was smoothly twisted leading edge down about 10 degrees. The lift strut was pulled out of both the wing structure and the fuselage attach point. The flap remained attached to its hangar and hinge assembly, and was deformed in a spanwise direction. No fuel was found in the right fuel tank, only lake water; the tank was hydraulically bulged and deformed from the inside out. The fuel cap vent was clear.
The right aileron was not recovered. The aileron hinges remained attached to the wing, with small torn out sections of aileron skin affixed to the aileron side of the hinges.
The left and right horizontal stabilizer and elevators remained attached to the empennage. The left horizontal stabilizer and elevator assembly was undamaged. The right horizontal stabilizer and elevator was hydraulically deformed and distorted. The elevator trim tab jackscrew measured 0.75-inches extension, which according to Cessna equals a 13-degree tab down setting.
The fuel selector valve was found in the "BOTH" detent. No fuel was found in the lines from the tanks to the engine, only lake water. The strainer bowl and filter screen, and the carburetor finger screen, were clean. The fuel system vent lines were found open.
The left cockpit control yoke exhibited a fracture of the left control yoke horn, and the tube was bent to the right. The right cockpit control yoke was missing and the tube was pulled out of the "T" bar assembly. Control system continuity was established from the cockpit "T" bar and rudder pedals to the control surface bell cranks. The flap actuator jackscrew was found in the fully retracted position.
The electric clock was found stopped at 3:13. The throttle and mixture controls were found in the full power and full rich positions, both in the cockpit and at the carburetor. The carburetor heat control was in the cold position, both at the cockpit control and at the induction air box.
The propeller remained attached to the engine crankshaft flange and was undamaged. The spinner was crushed without apparent torsional distortion.
The engine remained attached to the engine mounts and to the firewall. Crankshaft rotation yielded thumb compression in each cylinder, with accessory gear and valve train continuity established. The valves operated an equal amount in proper cylinder firing order with crankshaft rotation. The magnetos were wet and would not produce a spark; however, they rotated freely. The spark plugs were wet and exhibited ash gray coloration. Water was drained from the Nos. 1 and 3 cylinders, while deposits of silt and mud were found in the Nos. 2 and 4 cylinders. No particulates were found in the oil filter or on the suction screen.
The carburetor was fractured circumferentially near the throat and the throttle valve was full open. The single piece venturi was intact. The bowl was clean and did not contain fuel. The metal floats were intact and undamaged.
MEDICAL AND PATHOLOGICAL INFORMATION
All of the occupants sustained fatal injuries and post mortem examinations were conducted by the Pulmas County Coroner's Office. Specimens from the pilot were retained for toxicological testing by the FAA's Civil Aeromedical Institute in Oklahoma City, Oklahoma. The results of the toxicological tests were negative for alcohol and all screened drug substances.
Sheriff's rescue divers recovered the occupants from the submerged aircraft cabin. The individual identified as the pilot was found in the left front seat, and the person identified as the fiancee's grandfather was in the right front seat. The grandmother was in the right rear seat and the younger brother was recovered from the left rear seat. The pilot and the left rear occupant were retained in their seats by their seatbelts. The right front and right rear occupants were not retained by seat belts.
The pathologist who examined the victim's remains reported that all four had abdominal injuries consistent with seat lap belt usage, with no evidence of shoulder harness use on anyone. The cause of death for all four was ascribed to multiple traumatic blunt force injury. The pathologist reported that the pilot did not present any fractures of the extremities. The right front seat passenger; however, had compound fractures just above both ankles and compound fractures of both wrists, in addition to other compound comminuted fractures of the right leg and upper arm bones. Neither the pilot nor the right front seat passenger presented lacerations or fracture/dislocations of the thumbs or fingers of either hand.
The wreckage was verbally released to representatives of the registered owner on May 2, 2000, at the conclusion of all component examinations. When released, the wreckage was located at the facilities of Plain Parts, Pleasant Grove. No parts or components were retained. A formal written release was executed on October 20, 2000.