NTSB Factual Report

HISTORY OF FLIGHT

On July 29, 2017, about 1420 Pacific daylight time, a Cessna 172N airplane, N5381J, was substantially damaged after it collided with mountainous terrain shortly after departure from Big Bear City Airport (L35), Big Bear, California. The commercial pilot and passenger were fatally injured. The airplane was registered to and operated by Midfield Aviation under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and a flight plan was not filed for the personal flight, which departed about 1415 and was destined for Apple Valley Airport (APV), Apple Valley, California.

According to airport personnel, the pilot and his girlfriend arrived at L35 in the accident airplane the day before the accident. After they deplaned, the pilot proposed to his girlfriend on the airport ramp. The following day, an airport surveillance camera captured the airplane depart runway 08 normally and begin a climb. According to a witness located near the departure end of the runway, the airplane came into view about 100 ft above ground level. He stated that the airplane did not gain any altitude as it entered a nose-high attitude that he described as "hanging on the prop." Both he and his wife, who was with him at the time, yelled to the airplane to "lower the nose." The engine sounded smooth and continuous. As the airplane reached a park adjacent to the departure end of the runway, it turned to the crosswind leg of the airport traffic pattern momentarily before turning 90° to a tight downwind leg. The witness remarked that both turns appeared coordinated; however, the airplane maintained a nose-high pitch attitude. The airplane then sank slowly and the wings began to rock back and forth before the airplane disappeared behind the trees.

Another witness, located near the crosswind leg of the runway 08 traffic pattern, observed an airplane fly low toward the south over him. The airplane began a turn to the right, then disappeared over the back side of an adjacent hill. The witness reported that the airplane's engine sounded continuous.

PERSONNEL INFORMATION

The pilot, age 30, held a commercial pilot certificate with ratings for airplane single- and multi-engine land and instrument airplane. He also held ratings for rotorcraft-helicopter and instrument helicopter. The pilot's most recent Federal Aviation Administration (FAA) first-class medical certificate was issued on April 12, 2017, with no limitations. At the time of the exam, the pilot reported that he had accumulated 225 total hours of flight experience, with 0 hours in the previous 6 months.

According to his personal logbook , which was current as of July 10, 2017, the pilot accumulated a total of 225 total hours of flight experience. Most of the pilot's single-engine flight time was accrued in a Diamond DA-40 airplane. His logbook indicated that he had completed a total of three flights and accrued 13 hours of flight experience in the accident airplane make and model. The pilot also flew the UH-60 Black Hawk, a military rotorcraft equipped with twin turbine engines; this flight experience was not included in his personal logbook.

The pilot's personal logbook showed that he had previously flown to L35 in a Cessna 172 on May 10, 2017. This was his only prior flight to the high-altitude airport.

On May 1, 2017, the pilot received a checkout in a Cessna 172 owned by the flight school that owned and operated the accident airplane. According to the instructor who completed the checkout, the local flight included standard practice maneuvers such as slow flight and steep turns, and reviewed fuel/air mixture control leaning procedures, since the pilot was not as experienced in operating reciprocating engines as he was with turbine engines. The flight school's standard practice was to review mixture control leaning, since APV is located at an elevation about 3,000 ft mean sea level (msl) and the temperature is typically warmer than international standard atmosphere.

AIRPLANE INFORMATION

According to Federal Aviation Administration (FAA) records, the airplane was manufactured in 1980 and was powered by a Lycoming O-320-H2AD, 160-horsepower, air cooled, reciprocating engine. A review of the logbooks revealed that the airplane had accrued about 54 flight hours since its most recent 100-hour inspection, which was completed on July 2, 2017, at 4,252.6 hours total time in service. At the time of the accident, the engine had accrued about 643 total hours since its most recent overhaul, which was completed on October 23, 2015. The airplane had accrued 4,306.4 hours total time in service at the time of the accident.

The engine records showed that the engine was removed and reinstalled in 2016; the records stated the replacement was due to "camlobe and no. 3 cylinder." The logbook entry did not show the discrepancies with the camshaft lobe and No. 3 cylinder. The No. 3 cylinder was replaced during the airplane's most recent 100-hour inspection.

A fuel receipt recovered from an airport fueler showed that the pilot purchased 5.14 gallons of 100LL aviation gasoline at 1406 on the day of the accident. According to the airport staff, no fuel contamination or engine anomalies were reported by other customers who fueled their airplanes on the day of the accident.

METEOROLOGICAL INFORMATION

The 1615 recorded weather observation at L35 included wind from 090° at 7 knots, 10 statute miles visibility, scattered clouds at 8,500 ft, temperature 25°C (77° F), dew point 5°C (41° F), and an altimeter setting of 30.33 inches of mercury.

An NTSB weather study showed a density altitude of 9,138.9 ft msl about the time of the accident. The pressure altitude at the time of the accident was 6,362.2 ft.

AIRPORT INFORMATION

L35 was located at an elevation of 6,752 ft above mean sea level and was equipped with one asphalt runway in a 08/26 configuration. The L35 northwest airport departure procedure for runway 08 stated that the pilot should execute a 10° left turn at the end of the runway. The graphic depiction shows a course line that continues about 1.5 nm northeast of the airport before turning to the south for about 1 nm. The course continues west for several miles before turning northwest.

At the end of each runway are digital signs that show the current density altitude. The density altitude is also announced over the airport's automatic weather observation system.

WRECKAGE AND IMPACT INFORMATION

The airplane came to rest in a wooded area about 0.5 nautical miles south of L35. The initial impact point (IIP) was identified by a tree scar near the top of a 45-ft-tall tree and the left wingtip, which was co-located with the tree. An additional scar was found on another tree about 20 ft forward of the initial tree strike signature. The right elevator remained attached to its horizontal stabilizer and was located 20 ft forward of the second tree. The main wreckage, which was oriented on a 085° heading and marked by multiple broken tree branches, was positioned in a 40° nose-down angle about 40 ft past the IIP heading of 227° and comprised the engine, fuselage, wings, and empennage.

The right wing was displaced forward a few degrees relative to the fuselage and displayed a depression at the leading edge adjacent to the wing root. A cluster of dents was observed near the outboard leading edge. The left aileron exhibited buckling and compression and the flap displayed some compression wrinkles. Tree impact signatures were located throughout the right wing. Multiple dents and compression wrinkles were found on the upper and lower right wing skins.

The left wing separated from the wing root and exhibited an approximate 10-inch depression at the outboard leading edge. Aft bending was observed at the outboard portion of the wing's leading edge and aft compression was found at the inboard leading edge portion of the wing.

The fuselage was intact with the exception of the engine, which had separated from the engine firewall.

The vertical stabilizer, rudder, and left horizontal stabilizer were secured to the empennage, which remained attached to the aft fuselage. The right horizontal stabilizer separated at the stabilizer root, came to rest in the wreckage path, and displayed a depression at the leading edge consistent with tree impact.

The rudder, aileron, and elevator cables were traced from the cockpit to their respective control surfaces. Both the flap indicator and flap handle indicated that the flaps were extended 10°; however, the flap jackscrew did not display any threads, consistent with a flaps-retracted position. The throttle was broken and the mixture control knob was in the full rich position.

Both wing fuel tanks were breached and contained an odor consistent with 100 low lead aviation grade gasoline. Fuel line continuity was confirmed from the wing fuel lines to the engine through the fuel selector valve, which rotated normally through each detent. The fuel gascolator bowl was removed and contained traces of foreign debris.

Rotational continuity was established throughout the engine and valve train when the engine crankshaft was manually rotated using a hand tool. Thumb compression and suction were obtained for all four cylinders. The engine was disassembled and the cylinder combustion chambers and barrels were examined visually; the cylinder bores, valve heads, and piston faces displayed normal operation and combustion signatures. The cylinder overhead components, including the valves, springs, push rods, and rocker arms, exhibited normal operation and lubrication signatures.

An examination of the top and bottom spark plugs revealed signatures consistent with normal wear. The oil filter did not display any metallic particles and the oil sump did not contain any metallic particles.

The carburetor throttle linkage remained attached to the throttle arm and the mixture linkage remained attached to the throttle plate. Trace amounts of fuel was observed in the plunger within the float valve chamber. The internal components appeared normal, including both the needle valve carburetor floats, which were normal in appearance.

The engine was equipped with a single-drive dual magneto, which rotated normally by hand, but did not seat during each turn. Spark was observed at each of the eight ignition harness leads when the unit was manually actuated by hand.

The two-blade, ground adjustable propeller was attached to the propeller flange. Both blades exhibited chordwise scratches. One blade displayed forward bending and the other blade displayed tip curling.

A complete report of the examination is available in the public docket associated with this case.

MEDICAL AND PATHOLOGICAL INFORMATION

The Sheriff-Coroner of the County of San Bernardino, San Bernardino, California, conducted an autopsy on the pilot. The cause of death was listed as "multiple blunt force injuries, seconds." The autopsy described an enlarged heart with 70% narrowing of the left anterior descending and right coronary arteries and 40% narrowing of the left circumflex artery. A blood sample taken by the coroner's office detected 21 mg/dL of ethanol in the chest blood, 10 mg/dL ethanol in the vitreous fluid, and a blood alcohol concentration of 0.021 g/100mL. The report did not indicate the presence of any drugs of abuse.

The FAA's Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma, performed toxicology testing on specimens from the pilot. The testing detected 27 mg/dL ethanol in urine, 18 mg/dL ethanol in cavity blood, and propanol in urine and cavity blood. It is likely that some or all of the identified ethanol was from sources other than ingestion.

TESTS AND RESEARCH

Aircraft Performance

Airplane weight and balance computations were performed using the occupant weights at the time of the accident as captured by the coroner: 199 lbs (pilot) and 177 lbs (passenger). A baggage weight of 66 lbs was also provided by the coroner's office. The calculation was completed using an airplane empty weght of 1,473 lbs and two separate fuel weights: 120 lbs (fuel tanks at half capacity) and 240 lbs (full fuel). The airplane's gross weight with half and full fuel was 1,969 lbs and 2,089 lbs, respectively. According to the pilot's operating handbook (POH), the airplane's maximum gross weight was 2,300 lbs. A weight and balance record is available in the NTSB public docket.

The airplane's takeoff distance was calculated using a performance chart from the POH. According to the chart, at an ambient temperature of 30°C, the airplane required a ground roll distance of 980 ft at a gross weight of 1,900 lbs and 1,245 ft at a gross weight of 2,100 lbs.

The POH contained a table that showed the airplane's maximum rate of climb at various pressure altitudes at the airplane's maximum gross weight. According to the chart, at a pressure altitude of 6,000 ft, and a temperature of 20°C, the airplane's rate of climb would have been about 440 ft per minute (fpm).

Surveillance Video Study

The surveillance videos retrieved from the airport office were analyzed by the NTSB vehicle performance division. The videos recorded by three surveillance cameras were used to estimate speed, altitude, rate of climb, and pitch angle. Shortly after rotation, the airplane's estimated airspeed was about 60 kts, the rate of climb was about 780 fpm, and the pitch angle was about 8.5°. These values subsequently declined when the airplane was about 90 ft above the runway. After about 10 seconds, the airspeed decreased to about 49 kts, the rate of climb was about 340 fpm, and the pitch angle was about 5°.

ADDITIONAL INFORMATION

High Density Altitude

The hazards associated with high density altitude operations are outlined in FAA Pamphlet FAA-P-8740-2, Density Altitude. The publication states,

Whether due to high altitude, high temperature, or both, reduced air density (reported in terms of density altitude) adversely affects aerodynamic performance and decreases the engine's horsepower output. Takeoff distance, power available (in normally aspirated engines), and climb rate are all adversely affected.

At power settings of less than 75 percent, or at density altitude above 5,000 feet, it is also essential to lean normally-aspirated engines for maximum power on takeoff (unless the aircraft is equipped with an automatic altitude mixture control). Otherwise, the excessively rich mixture is another detriment to overall performance.

According to the FAA Airplane Flying Handbook (FAA-H-8083-3B), "under conditions of high-density altitude, the airplane may be able to become airborne at an insufficient airspeed, but unable to climb out of ground effect. Consequently, the airplane may not be able to clear obstructions."

The FAA Pilot's Operating Handbook (FAA-H-8083-25A) states that,

due to the reduced drag in ground effect, the aircraft may seem capable of takeoff well below the recommended speed. As the aircraft rises out of ground effect with a deficiency of speed, the greater induced drag may result in marginal initial climb performance. In extreme conditions, such as…high density altitude…a deficiency of airspeed during takeoff may permit the aircraft to become airborne but be incapable of sustaining flight out of ground effect.

NTSB Probable Cause

The pilot's exceedance of the airplane's critical angle of attack during takeoff in high density altitude conditions, which resulted in an aerodynamic stall, loss of control, and subsequent impact with terrain.