Yosemite Valley, CA, USA
N9524M
MOONEY M20F
The instrument-rated pilot departed on a visual flight rules cross-county flight. Review of radar data showed the airplane departing and then proceeding on a northeasterly heading toward the intended destination. For the first 35 minutes of flight, the airplane remained below 10,000 ft mean sea level (msl). The airplane then ascended to a maximum altitude of 17,000 ft msl, initiated a descent, and turned north. As the airplane continued to descend through 14,300 ft msl, it turned west. (The airplane operated above 10,000 ft msl for 1 hour 8 minutes.) The data then showed the airplane perform a series of 360-degree descending turns. During the series of turns, the airplane descended to 6,200 ft msl and then ascended while turning east. The last recorded radar target was located about 12 miles west of the accident site at an altitude of 9,800 ft msl. Examination of the accident site revealed that the airplane impacted mountainous terrain just below the top of a ridgeline at an altitude of about 10,679 ft msl. Airmen's meteorological information for instrument meteorological conditions (IMC), mountain obscuration, and moderate turbulence conditions below 18,000 ft were in effect throughout the area about the time of the accident. Satellite imagery depicted a layer of low clouds over the area with a thick, overcast layer of clouds over the accident site. Weather radar imagery depicted scattered echoes within the immediate vicinity of the accident site, which indicates that precipitation was falling over the area. However, due to the possibility of beam blockage from the higher terrain, the full extent and intensity of the precipitation over the accident site could not be determined. It could not be determined if the pilot obtained a weather briefing before the flight. A postaccident examination of the airframe and engine revealed no evidence of preimpact mechanical malfunctions or failures that would have precluded normal operation. Wreckage impact signatures and radar data were consistent with continued flight toward the intended destination before the accident. It is likely that the pilot was attempting to maneuver around the IMC but did not maintain situational awareness and sufficient altitude above the mountainous terrain and entered IMC at the time of the accident. As noted, the airplane operated 1 hour 8 minutes over 10,000 ft msl; this included 42 minutes over 14,000 ft msl. The Federal Aviation Administration requires pilots to use supplemental oxygen when flying over 14,000 ft msl; however, no evidence was found that supplemental oxygen was available to or used by the pilot. The duration of flight at these altitudes without supplemental oxygen could have resulted in the pilot experiencing hypoxia, which can cause various symptoms, including headache, decreased reaction time, impaired judgment, euphoria, visual impairment, and drowsiness. The pilot's decision-making was likely significantly impaired during this period, and the radar track showed that the airplane turned away from and flew northwest beyond the intended destination. However, the data then showed the airplane descend and remain below 10,000 ft msl for the last 17 minutes of recorded data as the flight track changed direction back toward the original destination. During this period, it is likely that the symptoms of hypoxia would have largely abated.
HISTORY OF FLIGHT On December 17, 2012, about 1234 Pacific standard time, a Mooney M20F airplane, N9524M, was destroyed when it impacted terrain while maneuvering near Yosemite Valley, California. The airplane was registered to and operated by the pilot under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91. The private pilot, sole occupant of the airplane, sustained fatal injuries. Visual meteorological conditions prevailed, and a flight plan was not filed for the personal flight. The flight originated from the Santa Ynez Airport (IZA), Santa Ynez, California, about 1027 with an intended destination of Mammoth Lakes, California. A family member of the pilot reported the airplane overdue to local law enforcement the evening of December 17, 2012, after becoming concerned when the pilot had not arrived at his intended destination. The Federal Aviation Administration (FAA) issued an Alert Notification (ALNOT) for the missing airplane at 2309. An emergency locator beacon signal was not reported during the search and rescue operation. Search and rescue operations by Civil Air Patrol and local authorities were suspended on December 21, 2012. The wreckage was located by a visitor to the Yosemite National Park on July 7, 2013, near Vogelsang Peak. Review of radar data provided by the FAA revealed that following departure from IZA, the flight flew in a north easterly direction while ascending to about 8,500 feet mean sea level (msl). The data showed that the flight remained at 8,500 feet for about 22 minutes before initiating an ascent. About 4 minutes into the ascent, the flight ascended above 10,000 feet msl and leveled off at 14,500 feet msl 17 minutes later. The flight remained at altitudes around 14,500 feet for about 11 minutes before initiating an ascent. The data showed that about 18 minutes later, the flight leveled off at 17,000 feet msl, and remained there for about 1 minute before starting a descent as the flight initiated a left turn to a north westerly heading. The radar data further depicted that the flight turned to a westerly heading while descending through 14,300 feet about 10 minutes following the start of the descent. About 19 minutes into the descent, the data showed that the flight began to perform several descending 360-degree turns over the course of about 12 minutes, of which the lowest recorded altitude was 6,200 feet msl. The data further depicted that the flight began an ascent and turned to a south easterly course at an altitude of 8,800 feet msl. The flight continued an ascent for about 8 minutes until radar contact was lost. The last recorded radar target was located about 12 miles west of the accident site at an altitude of 9,800 feet msl. PERSONNEL INFORMATION The pilot, age 68, held a private pilot certificate with an airplane single-engine land and instrument-airplane ratings. A third-class airman medical certificate was issued on March 3, 2011, with no limitations stated. The pilot reported on his most recent medical certificate application that he had accumulated 3,000 total flight hours. Review of the pilot's logbook revealed that as of the most recent logbook entry dated October 16, 2012, he had accumulated 3,033.8 hours of total flight time, of which 0.2 hours were within the previous 90 days to the accident. No actual instrument or simulated instrument flight time was logged since April, 2009. AIRCRAFT INFORMATION The four-seat, low-wing, retractable-gear airplane, serial number (S/N) 670101, was manufactured in 1966. It was powered by a Lycoming IO-360-A1A engine, serial number RL-4167-51A, rated at 180 horse power. The airplane was also equipped with a Hartzell adjustable pitch propeller. The airplane logbook records were not located. METEOROLOGICAL INFORMATION A National Transportation Safety Board (NTSB) staff meteorologist prepared a factual report for the area and time frame surrounding the accident. The southwest section of the NWS Surface Analysis Chart for 1300 depicted a low pressure system at 1013-hectopascals (hPa) over northern Idaho with a cold front extending southwestward into Nevada and northern California, where some cyclonic circulation was noted and the front became stationary, before turning back into a cold front and extending southward along the California coast. A trough of low pressure extended over western Nevada into Arizona. The accident site was located in the warm air sector immediately ahead of the approaching cold front, and west of the trough over Nevada. A 6 to 9-hPa pressure gradient existed over the eastern California and Nevada in the general location of the accident, suggesting a strong localized pressure gradient over the mountains. The NWS National Radar Mosaic from the National Climatic Data Center (NCDC) for 1230 depicted several areas of precipitation associated with rain and snow showers were depicted over northeastern California along the Sierra Nevada Mountains and in the vicinity of the accident site. The upper air sounding at 1600 from the NWS Reno (KREV), Nevada, located approximately 110 miles northwest of the accident site indicated a surface wind from 250 degrees at 24 knots with little variation in direction with height through 18,000 feet. The mean 0 to 6 kilometer (or 18,000 feet) wind was from 259 degrees at 68 knots. With the level of maximum wind was identified at 300-hPa or 30,000 feet with a wind from 260 degrees at 156 knots. The wind profile was favorable for the development of mountain wave activity with a predominate wave near 8,900 feet capable of producing severe turbulence and updraft of 1,545 feet per minute (fpm). The Geostationary Operational Environmental Satellite (GOES)-15 visible image recorded at 1230 depicted a layer of low clouds with a thick overcast layer of clouds over the accident site. A defined edge of the clouds was in the vicinity of Mammoth Lakes and Bishop California, which did not change significantly, or move with time were identified with orographic type clouds. Other defined lenticular clouds perpendicular to the wind flow were identified over southern Nevada immediately downwind from the Sierra Nevada Mountains. The image for 1235 from the Weather Surveillance Radar-1988 (WSR-88D) located in Hanford, California, depicted a large area of scattered echoes along the windward side of the Sierra Nevada's and extended into the immediate vicinity of the accident site, with echoes of 10 to 35 dBZ, which suggests that precipitation was falling over the area. However, due to the possibility of beam blockage from the higher terrain, the full extent and intensity of the echoes over the accident site could not be accurately determined. An Airmen's Meteorological Information (AIRMET) was current for mountain obscuration and moderate turbulence below 18,000 feet over the route and the accident site. Review of recorded weather data from the Mammoth Yosemite Airport (KMMH), located 30 miles southeast of the accident site revealed at 1235 wind was from 320 degrees at 8 knots gusting to 19 knots, visibility unrestricted at 10 miles, scattered clouds at 5,000 feet, ceiling broken at 7,000 feet, temperature 5 degrees Celsius (C), dew point -4 degrees C, altimeter 29.96 inches of mercury. A review of the observations from 0800 through 1400 indicated strong southwesterly winds of 25 knots with gusts to approximately 40 knots prior to the accident, with VFR conditions prevailing at the airport. During the evening hours after 2100, the weather deteriorated with IFR conditions in light to moderate snow, which continued into the morning hours of December 18. Columbia Airport (O22), located approximately 53 miles west-northwest of the accident site at an elevation of 2,119 feet, recorded weather data at 1235 was wind from 160 degrees at 7 knots, visibility 1 ½ miles, Ceiling overcast at 400 feet, temperature and dew point 9 degrees C, altimeter 30.01 inches of Hg. For further information, see the weather study report within the public docket for this accident. It was not determined if the pilot obtained a weather briefing prior to the flight. WRECKAGE AND IMPACT INFORMATION National Park Service Rangers from the Yosemite National Park reported that the airplane came to rest upright on the northern base of an approximate 500-foot high vertical rock slope at an elevation of about 10,679 feet msl. All major structural components of the airplane were located at the accident site. Due to the remote and rugged location, representatives from the NTSB did not travel to the accident site. The wreckage was recovered to a secure location for further examination. MEDICAL AND PATHOLOGICAL INFORMATION The Stanislaus County Coroner conducted an autopsy on the pilot on July 11, 2013. The medical examiner determined that the cause of death was "…Multiple injuries." However, the autopsy was limited by the condition of the body when it was found. No internal organs were available for examination. The FAA's Civil Aeromedical Institute (CAMI) in Oklahoma City, Oklahoma, performed toxicology tests on the pilot. According to CAMI's report, no testing was performed due to putrefaction of the samples. TESTS AND RESEARCH Examination of recovered airframe and engine was conducted on December 11, 2013, at the facilities of Air Transport, Phoenix, Arizona, by representatives of the NTSB and Lycoming Engines. Examination of the recovered airframe revealed that the left and right wings were separated from the fuselage to facilitate wreckage recovery. The right wing was separated about 10 inches inboard of the fuel cap. The flap remained attached via the two outboard mounts, and the aileron remained attached via all of its respective mounts. The upper side of the wing from the flap and aileron junction was compressed downward, becoming more severe farther outboard. About 30 inches of the outboard portion of the leading edge was crushed upward with a circular impression, and the upper wing skin was crushed downward. The right fuel tank was breeched. The left wing was separated about 25 inches inboard of the fuel cap. The leading edge of the wing was crushed aft and upward throughout its entire span. The outboard 27 inches exhibited a slight 45-degree crush angle from the leading edge to the wingtip. The aileron remained attached via all mounts, and the flap remained attached via its outboard mount. The left fuel tank was breeched. The left forward side of the fuselage was severely bent and buckled throughout. The engine firewall was compressed aft to the forward seats. The forward floor and fuselage area was displaced aft and upward, slightly to the right. In addition, a large circular impression was observed on the left side of the floor board / cabin structure. The instrument panel was fragmented with numerous instrument displacements. The empennage was separated from the fuselage aft of the baggage area. The horizontal and vertical stabilizer remained attached. The rudder and elevators remained attached via all their mounts. Flight control continuity was established from the ailerons inboard to the area where the wings were separated and inboard to the center cockpit area. Control continuity was established from the rudder and elevators forward to where the empennage was separated and to the center part of the fuselage. No evidence of any portable or airframe equipped oxygen systems were located within the recovered wreckage. The Lycoming IO-360-A1A engine, serial number RL-4167-51A, remained partially attached to the airframe via wires and hoses. The vacuum pump, propeller governor, and fuel injection servo were separated from the engine. The right magneto was partially separated from the engine. The forward portion of the crankcase exhibited cracks and damage consistent with impact. The propeller was cut off using a saw aft of the propeller flange. The magnetos, top spark plugs, and rocker box covers were removed. The number two cylinder head exhibited impact damage, and the top portion of the cylinder head was separated. The remaining cylinders were intact. All of the intake and exhaust rocker arms were intact and oil coated. The crankshaft could not be rotated due to impact damage. Holes were drilled in the top of the crankcase in line with the rotation plain of each cylinder piston rod journal. Internal mechanical continuity was established using a lighted borescope. All internal engine components were free of mechanical damage and exhibited no evidence of heat distress. All four cylinders were examined internally with a lighted borescope, and found to be unremarkable. The left and right magnetos were intact. When the magneto drive shafts were rotated using a hand drill, both magnetos produced spark on all posts. The top spark plugs were removed and the electrodes remained free of damage. The top spark plugs exhibited uniform light gray deposits. The vacuum pump and drive coupling was displaced from the engine, and not located within the recovered wreckage. The propeller remained attached to the propeller flange. The propeller flange was partially separated from the crankshaft. One blade exhibited slight "S" bending and torsional twisting with a gouge on the leading edge. The opposing blade leading edge and trailing edge gouges with some chordwise striations and gouges on the forward face of the blade. No evidence of any preexisting mechanical malfunction that would have precluded normal operation was found during the examination. For further information, see the NTSB Airframe and Engine Examination Summary report within the public docket for this accident. ADDITIONAL INFORMATION The FAA Aeronautical Information Manual (AIM) notes that hypoxia is a "state of oxygen deficiency in the body sufficient to impair functions of the brain," and "the effects of hypoxia are usually quite difficult to recognize, especially when they occur gradually." The AIM also states that between 12,000 and 15,000 feet "judgment, memory, alertness, coordination and ability to make calculations are impaired, and headache, drowsiness, dizziness and either a sense of well-being (euphoria) or belligerence occur. The Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25A) adds that "one noteworthy attribute of the onset of hypoxia is that the first symptoms are euphoria and a carefree feeling." The Pilot's Handbook of Aeronautical Knowledge further states that symptoms are "Cyanosis (blue fingernails and lips), headache, decreased reaction time, impaired judgment, euphoria, visual impairment, and drowsiness." FAA regulations (14 CFR 91.211) require a pilot to use supplemental oxygen when operating above 12,500 feet msl in excess of 30 minutes and during the entire flight time when operating above 14,000 feet msl.
The pilot’s decision to continue flight into instrument meteorological conditions, which resulted in his failure to maintain situational awareness and sufficient altitude to clear mountainous terrain.
Source: NTSB Aviation Accident Database
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