Aviation Accident Summaries

Aviation Accident Summary ANC18FA028

Petaluma, CA, USA

Aircraft #1




The pilot was departing the non-tower-controlled airport on an instrument flight rules (IFR) flight plan. He received his IFR clearance before departure but the pilot never contacted air traffic control after takeoff. The wreckage was located about 4 hours later about 1 mile from the departure airport. A witness located at the departure airport watched the airplane depart and climb to about 300 ft above ground level (agl) before it initiated a shallow left turn and disappeared into the fog. The witness reported that there were no unusual sounds from the airplane during the takeoff, and that the engine sounded normal.  Instrument meteorological conditions (IMC) were present in the vicinity of the accident site at the time of the accident. In addition, AIRMETs were valid that warned of IFR conditions due to precipitation and mist and moderate turbulence below 10,000 ft. A possibility of light low-level wind shear (LLWS) was identified between the surface and 100 ft agl at the accident site. Multiple pilot reports in the area indicated cloud ceilings around 400-700 ft agl with moderate turbulence. However, the pilot obtained weather information about 6 hours before takeoff, which only included the AIRMETs and not the PIREPs indicated the cloud ceiling and turbulence. A postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. The damage to the airplane indicated that it impacted the ground in a nose-down, near-vertical attitude consistent with an aerodynamic stall. Given the weather information available for the accident site around the time of the accident, the pilot likely encountered IMC with areas of turbulence and LLWS almost immediately after takeoff and did not maintain sufficient airspeed for these conditions, which resulted in an exceedance of the airplane's critical angle of attack and an aerodynamic stall.

Factual Information

HISTORY OF FLIGHTOn April 6, 2018, about 1710 Pacific daylight time, a Mooney M20J airplane, N9133Z, was destroyed when it was involved in an accident in Petaluma, California. The private pilot sustained fatal injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. About 1657, the pilot contacted Flight Service to request an instrument flight rules (IFR) clearance from Petaluma Municipal Airport (O69) to Fallbrook Community Airpark (L18), Fallbrook, California. The pilot reported that he would be departing runway 29 and was ready for an immediate departure. The pilot received his IFR clearance at 1700 with a void time of 1710. A pilot-rated witness familiar with operations at O69 was on the deck of the airport office monitoring the airport's common traffic frequency when he heard the accident pilot broadcast that he was taxiing to runway 29. He then observed the airplane taxi to runway 11. He stated that the airplane remained in the runway 11 runup area for about 15 minutes. About 1700, the pilot announced, "Petaluma traffic, Mooney departing Runway 29"; the witness then transmitted "Runway 11" to which the pilot replied, "Thank you. I appreciate the help." He observed the airplane depart runway 11 and climb to an altitude about 300 ft above ground level before initiating a shallow left turn and disappearing into the fog. The witness reported that there were no unusual sounds from the airplane during the takeoff and that the engine sounded strong, smooth, and normal. Another witness reported that the accident airplane landed at O69 around 1645 the day before the accident and taxied to the fuel island. He stated that he helped the pilot obtain fuel, observed him sump the airplane's fuel tanks after refueling, and instructed him where to park for the evening. He stated that the accident pilot queried a FedEx pilot on the appropriate instrument departure procedure for runway 29. The accident pilot returned to the airport about 1645 on the day of the accident and walked to his airplane to begin preflight preparations. About 1700, as he was leaving the airport, he saw the airplane in the runup area for runway 11. He returned to the airport about 1800 to aid in the search for the missing airplane. The pilot never established radio contact with the Oakland Air Route Traffic Control Center (ZOA) after takeoff. At 1723, ZOA received an emergency locator transmitter signal report in the vicinity of O69; an alert notice was issued by the FAA at 1803. Aerial search operations were hindered by weather; however, a ground search was conducted by local law enforcement and first responders. The wreckage was located about 2200 about 1 mile north of O69. METEOROLOGICAL INFORMATIONThe National Weather Service (NWS) surface analysis chart for 1700 depicted station models around the accident site with air temperatures low- to mid- 60°F, dew point temperature near 60°F, with temperature-dew point spreads of 2°F or less, a south wind of 5 to 10 knots, moderate rain, and overcast skies. The NWS Storm Prediction Center (SPC) constant pressure charts depicted a low-level trough northeast of the accident site over northern California. Troughs typically act as lifting mechanisms where enhanced lift, gusty winds, fronts, clouds, and precipitation can occur. Troughs and a frontal boundary close to the surface and near mountainous terrain also act to aid in the mixing of low-level air, allowing for the possibility of low-level wind shear (LLWS) and turbulence. AIRMETs Sierra and Tango were valid for the accident site at the accident time. The AIRMETs were issued at 1345 and warned of IFR conditions due to precipitation and mist, mountain obscuration conditions due to clouds, precipitation, and mist, and moderate turbulence conditions below 10,000 ft mean sea level (msl). A High-Resolution Rapid Refresh model sounding was created for the accident site for 1700. The sounding wind profile indicated a surface wind from 163° at 5 knots with the wind becoming westerly through 5,000 ft and increasing to 25 knots. A possibility of light LLWS was identified between surface and 100 ft agl in addition to a possibility of light to moderate clear air turbulence in several layers between 2,000 ft and 14,000 ft. Publicly-disseminated pilot reports (PIREP) from about 2 hours before the accident to about 2 hours after the accident indicated cloud ceilings in the area around 400 to 700 ft agl with moderate turbulence. In addition, an urgent PIREP was made at 1438 near San Francisco International Airport (SFO) located about 43 miles south of the accident site; the pilot of an Airbus A320 at an altitude of 1,900 ft while on final approach to runway 19 at SFO reported LLWS +/- 15 knots. WRECKAGE AND IMPACT INFORMATIONThe accident site was located in a muddy mustard field with rolling hills at an elevation of about 307 ft msl. The airplane impacted in a near-vertical attitude on a heading of about 200° and a postcrash fire ensued. All the airplane's major components were located at the accident site. Both wing fuel tanks were ruptured. The cockpit and cabin area were largely consumed by postcrash fire. The aft fuselage exhibited extensive accordion-style crushing. The right wing was displaced from the fuselage and came to rest on the right side and forward of the fuselage. The right fuel cap was in place and secure, but the fuel cap seal sustained thermal damage. The right aileron remained attached to its respective attach points but sustained impact damage. The right flap separated from its attach points and was bent up at both ends about midspan. The left wing sustained extensive accordion-style leading edge crushing near the tip, lessening in severity toward the wing root. The left fuel cap was in place and secure; however, the fuel cap seal exhibited cracks around the circumference of the seal. The left aileron and flap remained attached to their respective attach points and were relatively undamaged. The left flap was in the up position. The left main landing gear was in the retracted position. The right main landing gear separated from its attach points but remained attached to its operating linkage. The vertical and left horizontal stabilizer, left elevator, and rudder remained attached to the empennage and were relatively free of impact damage. The right horizontal stabilizer and right elevator remained attached to their respective attach points, but sustained impact damage. Flight control continuity was verified from the cabin to the rudder. Elevator control continuity was established from the elevator via the push/pull tube to the aft fuselage to the cabin area, where it was melted due to postcrash fire. Left aileron control continuity was established from the aileron to the wing root area. Right aileron control continuity was established to the wing root area, where the push/pull tube was fractured and exhibited features consistent with overload. Examination of the airframe revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. The engine and propeller separated from the airframe and were buried in about 3 ft of soft mud. The engine sustained extensive impact damage to the front, underside, and accessory case. The propeller remained attached to the crankshaft and the blades remained attached to the propeller hub assembly. Both blades exhibited leading edge polishing. The engine was manually rotated using a drive tool at the vacuum pump accessory drive. The engine rotated freely and compression was produced in all four cylinders. Valve train and gear train continuity was confirmed during the engine rotation. The single-drive dual magneto separated from its mounting pad and suffered impact damage to its case. When the coupling was rotated by hand, blue spark was observed on only one lead at each rotation of the coupling; however, blue spark was observed on all leads at the left distributor in rotational order. The vacuum pump was removed and disassembled. The carbon rotor fractured into three pieces; however, all the vanes were whole and in position. The drive coupling was intact and undamaged. A liquid consistent with water was present in the fuel flow divider under the diaphragm in a proportion estimated to be half of that of remaining liquid that was consistent with 100LL aviation fuel. MEDICAL AND PATHOLOGICAL INFORMATIONAn autopsy was conducted under the authority of the Sonoma County Coroner, Petaluma, California. The cause of death for the pilot was attributed to multiple blunt force and thermal injuries. The FAA Forensic Sciences Laboratory performed forensic toxicology testing on specimens from the pilot. According to the toxicology report, testing for carbon monoxide and cyanide was not performed, and no ethanol was detected in the urine. The testing identified 2.184 µg/ml doxylamine in the urine and 1.877 µg/ml in the liver. Doxylamine is a sedating antihistamine used to treat cold and allergy symptoms and available over-the-counter as a sleep aid.

Probable Cause and Findings

The pilot's failure to maintain adequate airspeed while departing in instrument meteorological conditions, moderate turbulence, and low-level wind shear, which resulted in the airplane exceeding its critical angle of attack and a subsequent aerodynamic stall.


Source: NTSB Aviation Accident Database

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