Decatur, TX, USA
N6797L
CESSNA 421C
After takeoff, the pilot proceeded about 30 miles and climbed to an altitude of about 2,200 ft mean sea level (msl). About 8 minutes after takeoff, the airplane entered a descending left turn that continued until impact. A witness observed a twin-engine airplane at a low altitude and in a descent. After the airplane descended below the tree line, a fireball emerged followed by some smoke; however, the smoke was thin and dissipated quickly. A second witness observed the airplane at a low altitude and in a slow, descending turn. The flight path was steady and the wings “never dipped.” Shortly after the airplane descended out of sight, he observed an explosion. Both engines were on fire when he arrived at the accident site, and there was a fuel leak from the right engine toward the cockpit area. He used a fire extinguisher to keep the fire off the fuselage until first responders arrived. The airplane impacted a utility pole and terrain. Burned vegetation was present over portions of the accident site. The left wing was separated outboard of the engine and was located near the utility pole. A postaccident examination revealed that the left main fuel tank was partially consumed by the postimpact fire; therefore, the amount of fuel in the tank could not be determined. The left engine nacelle was discolored consistent with the postimpact fire. The left nacelle fuel tank appeared intact, and no fuel was visible in the left nacelle fuel tank. However, the amount of fuel in the left nacelle fuel tank at the time of impact could not be determined. The right main fuel tank appeared intact, and about 1 gallon of fuel was drained from the tank during recovery of the airplane. While the postimpact fire was consistent with fuel present onboard the airplane at the time of the accident, the lack of an extensive and sustained ground fire suggested that a limited amount of fuel was present. The left and right engine cockpit fuel selectors were both positioned to the “RIGHT MAIN” fuel tank. The left fuel selector valve, located in the engine nacelle, was in the “OFF” position at the time of the exam. The right fuel selector was in the “RIGHT” fuel tank position. A teardown examination of the left engine did not reveal any anomalies consistent with a preimpact failure or malfunction. A teardown examination of the right engine revealed damage consistent with oil starvation throughout the engine. A teardown examination of the left propeller assembly revealed indications that the blades were at or near the feather pitch stop position during the impact sequence. A teardown examination of the right propeller assembly revealed indications that the blades were on or near the low pitch stop position during the impact sequence. The fuel flow indicator displayed the total fuel remaining as 8.3 gallons when powered up on a test bench. However, the fuel quantity indications are dependent on the pilot properly configuring the device when the airplane is refueled. The fuel flow indicator does not directly provide fuel quantity information. According to the airplane flight manual, the total unusable fuel for the airplane, with one engine nacelle fuel tank installed, was 7.8 gallons. Engine performance data recovered from the onboard engine monitor revealed a reduction in right engine power to near idle power. About 1 minute later, the airplane entered a descending left turn which continued until impact. About 3 minutes after the reduction in right engine power, the left engine completely lost power. Immediately afterward, right engine power increased to near full (takeoff) power. However, about 30 seconds later the right engine completely lost power. The airplane impacted the pole and the terrain a few seconds later. The pilot likely detected an impending failure of the right engine and intentionally reduced power. However, shortly afterward, the left engine lost power due to fuel starvation. At that time, the pilot likely set the left engine to crossfeed from the right main fuel tank to restore power. Unsuccessful, the pilot then decided to feather the left propeller and attempted to use any available power from the right engine, but the right engine immediately lost power as well. Whether the right engine lost power at that moment due to fuel starvation or oil starvation could not be determined. The pilot was obese and had hypertension, high cholesterol, and an enlarged heart with left ventricular thickening. While these cardiovascular conditions placed him at an increased risk for a sudden incapacitating cardiac event, the autopsy did not show any acute or remote myocardial infarction, and the flight path suggests intentional actions until the crash. Thus, the pilot’s cardiovascular disease was not a factor in this accident. Toxicology testing detected the muscle relaxant cyclobenzaprine and its active metabolite norcyclobenzaprine in the pilot’s femoral blood at low therapeutic levels. The sedative-hypnotic medication zolpidem was detected at subtherapeutic levels. While these substances are associated with side effects such as drowsiness and dizziness, the operational findings of this accident do not suggest performance issues related to fatigue. Thus, it is unlikely that the effects from the pilot’s use of cyclobenzaprine and zolpidem were factors in this accident.
HISTORY OF FLIGHTOn November 18, 2022, at 1510 central standard time, a Cessna 421C airplane, N6797L, was destroyed when it was involved in an accident near Decatur, Texas. The pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 positioning flight. ADS-B data documented two flights on the day of the accident. The initial flight departed Denton Enterprise Airport (DTO), Denton, Texas, at 1343 and landed at 1430. The flight consisted of multiple rectangular patterns within the vicinity of the airport. The accident flight departed DTO at 1459. The pilot proceeded about 30 miles west and climbed to an altitude of about 2,200 ft mean sea level (msl). About 1507, the airplane entered a descent and a left turn; both of which continued until the end of the data. The final data point was recorded at 1510:19. The airplane came to rest about 125 ft north-northeast of the final data point. A witness was about one-half mile east of the accident site when he observed a twin-engine airplane at a low altitude and in a descent. He did not observe any smoke or fire from the airplane. After the airplane descended below the tree line, a fireball emerged followed by some smoke; however, the smoke was thin and dissipated quickly. A second witness, also located about one-half mile east of the accident site, observed the airplane at a low altitude and in a slow, descending turn toward the north. The flight path was steady and the wings “never dipped.” Shortly after the airplane descended out of sight, he observed an explosion. Both engines were on fire when he arrived at the accident site, and there was a fuel leak from the right engine toward the cockpit area. He used a fire extinguisher to keep the fire off the fuselage until the fire crews arrived. AIRCRAFT INFORMATIONMaintenance records provided to the National Transportation Safety Board included standard booklet form records with entries ending in December 2018. They were accompanied by separate and unsigned copies detailing annual inspections completed in February 2020 and March 2021. According to the airplane flight manual, the unusable fuel for a Cessna 421 with 1 wing nacelle locker tank was 7.8 gallons total. AIRPORT INFORMATIONMaintenance records provided to the National Transportation Safety Board included standard booklet form records with entries ending in December 2018. They were accompanied by separate and unsigned copies detailing annual inspections completed in February 2020 and March 2021. According to the airplane flight manual, the unusable fuel for a Cessna 421 with 1 wing nacelle locker tank was 7.8 gallons total. WRECKAGE AND IMPACT INFORMATIONThe airplane impacted a utility pole and terrain. It came to rest upright about 165 ft from the utility pole, and a postimpact fire ensued. Burned vegetation was present over portions of the accident site. The left wing was separated outboard of the engine and located near the utility pole. It exhibited a semi-circular impression near the wing tip consistent with an in-flight impact to the pole. Airframe The fuselage was damaged consistent with impact forces. A postimpact fire partially consumed the left wing, left and right engine nacelles, and a small portion of the cabin. The flight controls remained attached to the airframe and no anomalies consistent with a preimpact flight control failure/malfunction were observed. Left- and right-wing flap control continuity was confirmed. The position of the actuator was consistent with the wing flaps being retracted at impact. The landing gear was retracted at the accident site. The left main fuel tank was partially consumed by the postimpact fire. The left engine nacelle was discolored consistent with the postimpact fire but appeared otherwise intact. The left nacelle fuel tank appeared intact, and no fuel was visible in the tank at the time of the on-scene examination. A right nacelle fuel tank was not installed. The right main fuel tank appeared intact, and about 1 gallon of fuel was drained from the tank during recovery of the airplane. The caps for the left and right main fuel tanks, and for the left engine nacelle fuel tank, were securely installed. The left and right engine cockpit fuel selectors were both positioned to the “RIGHT MAIN” fuel tank. The left fuel selector valve, located in the engine nacelle, was in the “OFF” position at the time of the exam. The right fuel selector was in the “RIGHT” fuel tank position and was unobstructed when air was blown through the valve. Left Engine The left engine remained in place relative to the left wing. The engine mounts were broken consistent with impact forces. The aft portion of the engine exhibited thermal damage consistent with the postimpact fire. The turbocharger exhibited thermal damage but appeared otherwise intact and was free to rotate. A teardown examination did not reveal any anomalies consistent with a preimpact failure or malfunction. Right Engine The right engine remained in place relative to the right wing, and the engine mounts were broken consistent with impact forces. A teardown examination revealed damage consistent with oil starvation throughout the engine. The connecting rods and rod caps were discolored consistent with oil starvation. Additionally, the crankcase main journal bearings Nos. 1 to 4 were discolored and extruded consistent with overheating and oil starvation. The Nos. 1 and 2 crankcase bearings were dislocated, with the left side bearing positioned on the right side: one bearing on top of the other. Multiple metallic fragments were distributed throughout the engine. The interior faces of the crankcase displayed abrasion damage consistent with forward-aft movement of the crankshaft. The idler gears were out of position and unable to drive the magnetos. The magnetos themselves provided spark at all leads when removed from the engine and tested. Left Propeller Blade Nos.1 and 2 were bent forward near the tip; Blade #No. 3 was bent aft over the outboard one-half span. The hub was intact, and all blades were retained. The piston was positioned near the feather position. The root face of blade No. 1 exhibited a witness mark consistent with contact from the adjacent blade actuation pin during the accident sequence. The extent of the blade damage appeared consistent with low rotational energy at impact. Additionally, the witness mark location indicated the left propeller assembly was at or near the feather pitch stop during the impact sequence. Right Propeller Blade Nos. 1 and 3 were bent; Blade No. 2 appeared undeformed. The hub was intact, and all blades were retained. The piston was positioned near the low pitch. The root face of blade No. 1 exhibited a witness mark consistent with contact from the adjacent blade actuation pin during the accident sequence. Based on the witness mark, the right propeller assembly was on or near the low pitch stop position during the impact sequence. MEDICAL AND PATHOLOGICAL INFORMATIONThe 57-year-old male pilot held a first-class medical certificate with the limitation that he must have available glasses for near vision. At his most recent Federal Aviation Administration medical examination on May 27, 2022, he reported taking pantoprazole for gastric reflux, amlodipine and hydrochlorothiazide to treat high blood pressure, atorvastatin to treat high cholesterol, aspirin, zolpidem as a sleep aid, and fexofenadine to treat seasonal allergies. According to the autopsy report, the pilot’s cause of death was blunt force injuries, and the manner of death was accident. The medical examiner reported the pilot had an enlarged heart (510 grams) with left ventricular thickening and was obese, with a body mass index (BMI) of 39.43 kilograms per meter squared. Toxicology testing detected cyclobenzaprine at 8 nanograms per milliliter (ng/mL) in the pilot’s femoral blood and 41 ng/mL in his urine, norcyclobenzaprine at 15 ng/mL in his femoral blood and 59 ng/mL in his urine, and zolpidem at 9 ng/mL in his femoral blood and 12 ng/mL in his urine. The generally non-impairing substances amlodipine, atorvastatin, fexofenadine, azacyclonol, and tamsulosin were detected in the pilot’s femoral blood and urine, and albuterol was detected only in his urine. TESTS AND RESEARCHThe fuel flow indicator displayed the following information when powered up: 1. Total fuel used: 119.7 gallons; 2. Total fuel remaining: 8.3 gallons; 3. Left tank fuel used: 58.9 gallons; 4. Right tank fuel used: 60.8 gallons. The fuel quantity indications are dependent on the pilot properly configuring the device when the airplane is refueled. The fuel flow indicator does not directly display quantity information. Engine performance data recovered from the onboard engine monitor provided parameters for both engines including speed, fuel flow, manifold pressure, cylinder head temperature, exhaust gas temperature, and turbocharger temperature. The data revealed that about 1506, a decrease in right engine speed, fuel flow, manifold pressure, and temperatures consistent with an idle power setting. About 3 minutes later, the data depicted an abrupt decrease in all engine parameters consistent with a complete loss of left engine power. Immediately afterward, the right engine parameters increased consistent with a takeoff power setting. However, about 30 seconds later the right engine parameters all abruptly decreased consistent with a complete loss of right engine power. Data ended a few seconds afterward and appeared to coincide with the accident sequence.
A loss of power on the left engine due to fuel starvation and the subsequent loss of power on the right engine for undetermined reasons.
Source: NTSB Aviation Accident Database
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