Lena, WI, USA
N75RM
BEECH B36TC
The flight departed from an airport near Fort Worth, Texas, and proceeded on a northeast course. The airplane was enroute to Missouri for an annual inspection. About 30 minutes after takeoff, the airplane leveled off near 15,500 ft mean sea level (msl). About 24 minutes after leveling off, as the airplane approached a line of thunderstorms, the airplane started to climb, and the flight path began to deviate consistent with an attempt by the pilot to maneuver around those thunderstorms. Isolated thunderstorm tops in the area were 20,000 ft to 24,000 ft. About 28 minutes after the climb started, the airplane leveled off about 24,500 ft msl and returned to a northeast course. Attempts by air traffic control to contact the pilot after the airplane climbed through 18,000 ft msl were not successful. After about 2 hours and 37 minutes, the airplane entered a descent from about 24,500 ft msl. About 2 minutes later, the airplane course became slightly erratic as the descent continued; however, the airplane ultimately returned to the northeast course. At that time, the airplane was in a stabilized descent of about 1,000 ft per minute (fpm), which continued until the data ended. The airplane impacted a cornfield about 480 ft northeast of the final recorded data point. The impact path was aligned with the final portion of the flightpath. The airplane impacted a corn field and slid about 150 ft before coming to rest. The landing gear and wing flaps were retracted. Flight control continuity was confirmed, and an engine examination did not reveal any anomalies consistent with an inability to produce rated power. Both fuel tanks appeared to be intact and about 35 gallons of fuel remained in the left tank; however, no fuel remained in the right fuel tank. The cockpit fuel selector was set to the right tank at the time of the on-scene examination. These findings were consistent with a loss of engine power due to fuel starvation. Just under 2.5 hours after the airplane reached 24,500 feet msl, the airplane was intercepted and the pilot was observed to be incapacitated. The time when the pilot most likely became incapacitated could not be determined. Nevertheless, flightpath deviations around weather and the pilot’s lack of communication with air traffic control during the climb indicated performance deficiencies that were inconsistent with the pilot’s skill and experience. Thus, the pilot likely became impaired when the airplane was below 18,000 ft but might not have been incapacitated when the airplane climbed into class A airspace. In other words, the pilot likely became impaired at an altitude below 18,000 feet, and later became incapacitated. The airplane was not pressurized, but it was equipped with an onboard oxygen system. Examination of the onboard oxygen system revealed a cracked fitting behind the left (pilot) sidewall, which caused a leak when the system was pressurized. Metallurgical examination of the fitting determined that it had a localized casting defect and that a portion of the fracture contained thread sealant embedded onto the surface, indicating that a crack was present at the time the fitting was installed. The investigation was unable to determine the oxygen supply onboard before the accident flight and was, therefore, unable to make any determination of whether the pilot was being adequately supplied with oxygen during the flight. Given the altitudes at which the airplane was operating and the accident circumstances, the possibility of altitude-related hypoxia must be considered. If the airplane’s onboard oxygen system was properly functioning and properly used, the system would have generally been expected to prevent significant hypoxia in a pilot operating below 18,000 feet. Even with the nasal cannula instead of a mask at 24,500 feet, a pilot would generally not likely experience significant hypoxia if the oxygen system was functioning properly. However, an impaired or incapacitated pilot might have a diminished ability to use the nasal cannula effectively. In addition, if the supplemental oxygen supply became exhausted while the airplane was at altitude, due to the crack in the fitting, hypoxia would have resulted. An average, healthy pilot’s performance is mostly unaffected by cabin altitudes below 10,000 ft but may seriously deteriorate within 15?minutes at a cabin altitude of 15,000 feet. The time of useful consciousness is the maximum time available for an average, healthy pilot to take protective action against hypoxia at a given cabin altitude. This time decreases rapidly with increasing cabin altitude; at 18,000 feet, it is 20 to 30 minutes; at 25,000 feet it is 3 to 5 minutes. Although the pilot’s toxicology results indicated that he had used a cannabis product, the THC level in his blood was very low and there were no detectable THC metabolites in his blood or urine, making it unlikely that cannabis effects contributed to the accident. The accident pilot’s impairment and/or subsequent incapacitation could plausibly have resulted from known effects of hypoxia. Hypoxia might have resulted from supplemental oxygen depletion, diminished altitude tolerance due to disease, or a combination of those factors. If the supplemental oxygen supply was exhausted while the aircraft was at altitude, hypoxia would have resulted, as the pilot did not take action to descend. The aircraft was at 24,500 ft for almost 2.5 hours before the pilot was seen to be incapacitated. At that altitude, the time of useful consciousness without supplemental oxygen for an average, healthy pilot is about 3 to 5 minutes. The pilot’s autopsy identified cardiopulmonary disease that conveyed increased susceptibility to hypoxia as well as some increased risk of experiencing an impairing or incapacitating cardiovascular event such as arrhythmia or ischemic stroke. Without knowing the pilot’s usual altitude tolerance or when the supplemental oxygen supply was exhausted, there is no way to determine the likelihood that the pilot’s cardiopulmonary disease contributed to the accident. Given the airplane’s flight path after the pilot deviated around weather, it is likely that the autopilot was engaged during most of the final portion of the flight. The pilot likely became impaired at some point during the flight below 18,00 ft and subsequently became incapacitated. The exact timing and underlying cause of those events could not be determined. Based on the flight path after the pilot’s deviation around weather, it is plausible the airplane completed most of the final portion of the flight with the autopilot engaged. Once the fuel supply in the selected tank was exhausted, the engine lost power and the airplane entered an extended glide that continued until the airplane impacted the cornfield.
HISTORY OF FLIGHTOn October 27, 2021, at 1817 central daylight time, a Beech B36TC airplane, N75RM, was substantially damaged when it was involved in an accident near Lena, Wisconsin. The pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The airplane departed from Fort Worth Meacham Airport (FTW), Fort Worth, Texas, about 1357 and proceeded on a northeasterly course. The pilot’s mechanic stated that the airplane was destined for Camdenton Memorial – Lake Regional Airport (OZS), near Camdenton, Missouri, so that the airplane could undergo an annual inspection. About 1427, the airplane leveled off near 15,500 ft mean sea level (msl). About 1451, the airplane entered a climb; shortly afterward, its flightpath began to deviate as the airplane approached a line of storms. About 1519, the airplane leveled off about 24,500 ft msl and returned to a northeasterly course. Air traffic control attempted to contact the pilot after the airplane climbed through 18,000 ft and into class A airspace, but these attempts were not successful. About 1756, the airplane entered a descent from 24,500 ft msl; at the time, the airplane was about 25 miles west of Green Bay, Wisconsin. About 1758, the airplane’s course became slightly erratic as the descent continued; about 6 minutes later, the airplane returned to the northeasterly course and became established in a steady descent of about 1,000 ft per minute, which continued until the data ended. The final data point was recorded at 1817:11. The airplane impacted a cornfield about 480 ft northeast of the final recorded data point. The impact path was aligned with the final portion of the flightpath. PERSONNEL INFORMATIONThe pilot’s logbook was not located during the investigation. As a result, the pilot’s most recent flight experience and flight review could not be determined. At the time of the pilot’s most recent airman medical examination, conducted in October 2017, the pilot reported total civil flight time of 2,465 hrs. The pilot’s third-class medical certificate expired in 2019. In July 2020, the pilot completed a BasicMed comprehensive medical examination checklist and a BasicMed course. AIRCRAFT INFORMATIONThe airplane was not pressurized, but it was equipped with an onboard oxygen system that included a 76.5-cubic ft oxygen cylinder installed below the front seats and fitted with an altitude compensating regulator. The cylinder shutoff valve was controlled by a push-pull knob on the lower portion of the instrument panel. The oxygen supply was routed to receptacles on the left and right cockpit sidewalls for the pilot and copilot/front seat passenger, respectively. Receptacles were also located in the center cabin for any rear seat passengers. A gauge indicating the pressure within the oxygen system was located on the left cockpit sidewall, but the airplane had no independent indication of low oxygen system pressure. A pulse-demand oxygen delivery module in the airplane was connected to the right sidewall (copilot) oxygen receptacle. The module was fitted with two nasal cannulas, and first responders reported the pilot was found wearing one. The module was set to the “F10” mode, which supplied an oxygen flow rate equivalent to 10,000 ft above the pressure altitude sensed by the unit. The oxygen delivery module incorporated several annunciations, which included a flow fault, an apnea event, and low-battery warnings. The flow fault provided a red light indication and an aural alarm if no oxygen was flowing to the unit. An apnea event provide an amber light indication and an aural alarm when a “valid inhalation event” was not detected within 30 seconds. Neither warning was intended to indicate to the pilot that the system was out of oxygen. The NTSB did not perform an evaluation of the salience of the audible alarms when presented in the cockpit with background engine noise and when a pilot was using an aviation headset. According to the mechanic that had performed the most recent annual inspection, the pilot contacted him a few weeks before the accident to inquire about an annual inspection. The mechanic was expecting the pilot to bring the airplane to his facility in Camdenton, Missouri, on the day of the accident. There was no record that showed when the oxygen system was last serviced, refilled, or used. A specific maintenance record is not required when refilling the oxygen cylinder. Similarly, routine use of the system during flight is not required to be logged. Although that airplane was equipped with an autopilot, there was no data specific to its use during the flight, or any modes that may or may not have been selected. METEOROLOGICAL INFORMATIONThe National Weather Service composite radar mosaic at 1450 depicted a line of rain showers and thunderstorms across the airplane’s flightpath. The line ran from near Wichita, Kansas; southeast to Tulsa, Oklahoma; and past Hot Springs, Arkansas. Individual thunderstorm cell tops were indicated from 20,000 to 24,000 ft msl. AIRPORT INFORMATIONThe airplane was not pressurized, but it was equipped with an onboard oxygen system that included a 76.5-cubic ft oxygen cylinder installed below the front seats and fitted with an altitude compensating regulator. The cylinder shutoff valve was controlled by a push-pull knob on the lower portion of the instrument panel. The oxygen supply was routed to receptacles on the left and right cockpit sidewalls for the pilot and copilot/front seat passenger, respectively. Receptacles were also located in the center cabin for any rear seat passengers. A gauge indicating the pressure within the oxygen system was located on the left cockpit sidewall, but the airplane had no independent indication of low oxygen system pressure. A pulse-demand oxygen delivery module in the airplane was connected to the right sidewall (copilot) oxygen receptacle. The module was fitted with two nasal cannulas, and first responders reported the pilot was found wearing one. The module was set to the “F10” mode, which supplied an oxygen flow rate equivalent to 10,000 ft above the pressure altitude sensed by the unit. The oxygen delivery module incorporated several annunciations, which included a flow fault, an apnea event, and low-battery warnings. The flow fault provided a red light indication and an aural alarm if no oxygen was flowing to the unit. An apnea event provide an amber light indication and an aural alarm when a “valid inhalation event” was not detected within 30 seconds. Neither warning was intended to indicate to the pilot that the system was out of oxygen. The NTSB did not perform an evaluation of the salience of the audible alarms when presented in the cockpit with background engine noise and when a pilot was using an aviation headset. According to the mechanic that had performed the most recent annual inspection, the pilot contacted him a few weeks before the accident to inquire about an annual inspection. The mechanic was expecting the pilot to bring the airplane to his facility in Camdenton, Missouri, on the day of the accident. There was no record that showed when the oxygen system was last serviced, refilled, or used. A specific maintenance record is not required when refilling the oxygen cylinder. Similarly, routine use of the system during flight is not required to be logged. Although that airplane was equipped with an autopilot, there was no data specific to its use during the flight, or any modes that may or may not have been selected. WRECKAGE AND IMPACT INFORMATIONAfter impacting the cornfield, the airplane slid about 150 ft before coming to rest. The landing gear and wing flaps were retracted. The lower fuselage structure was damaged due to impact from the airplane nose to the mid-cabin area. Flight control continuity was confirmed from each control surface to the cockpit. An engine examination revealed no anomalies consistent with the engine’s inability to produce rated power. Both fuel tanks appeared to be intact. About 35 gallons of fuel remained in the left tank; no fuel remained in the right tank. The cockpit fuel selector was found set to the right tank. Examination of the onboard oxygen system revealed that the oxygen cylinder was intact. The altitude compensating regulator and overpressure relief valve attachment fittings were damaged due to impact. The cylinder valve was in the ON position, and the control cable from the cylinder valve to the instrument panel control knob was intact and continuous. The oxygen lines appeared intact with the exception of a right-angle fitting common to the left (pilot) sidewall receptacle. With the system pressurized, a noticeable leak was identified behind the left sidewall. The fitting was cracked at the supply end. Metallurgical examination of the fitting revealed that one side of the fracture surface exhibited an area with Teflon thread sealant embedded onto the surface. The sealant was in the area of the first three threads and did not extend along the full width of the crack. A portion of the fracture surface was smooth and showed no fracture features, such as ductile dimples, which was consistent with a casting defect in that area. The remaining portion of the fracture surface exhibited ductile dimples, consistent with an overstress fracture. Examination of the oxygen cylinder valve revealed no anomalies. Examination of the altitude compensating regulator revealed that the regulator exhibited minor deviations from the test requirements; however, none of these discrepancies were consistent with the system’s inability to provide the required oxygen. Examination and testing of the pulse-demand oxygen delivery module and associated in-line pressure regulator revealed no anomalies from the required test parameters. Testing of the oxygen system pressure gauge located on left cockpit sidewall revealed no anomalies. When oxygen pressure was applied, the gauge indicated the correct supply pressure. ADDITIONAL INFORMATIONHypoxia occurs when a person is deprived of adequate oxygen. Impairing effects from hypoxia can include confusion, disorientation, diminished judgment and reactions, worsened motor coordination, difficulty communicating and performing simple tasks, and a false sense of well-being. The brain is particularly sensitive to hypoxia, and it can be difficult for a pilot to recognize the danger of hypoxia and take protective action before impairment or incapacitation occurs. Failure to take protective action can be fatal. MEDICAL AND PATHOLOGICAL INFORMATIONThe 67-year-old male pilot had his last aviation medical examination on October 5, 2017. He reported having occasional asthma symptoms associated with seasonal allergies. He reported using fluticasone/salmeterol, a combination of two asthma medications which generally are not considered impairing. The aviation medical examiner (AME) noted that the pilot met the Conditions AMEs Can Issue (CACI) criteria for his asthma. No significant issues were identified. The Office of the Dane County Medical Examiner performed the pilot’s autopsy. According to the autopsy report, his cause of death was blunt force injuries. and the manner of death was accident. A summary comment from the Medical Examiner who performed the autopsy stated: “It is my medical opinion that [the pilot] died as a result of blunt force injuries of the head, torso and extremities complicating hypertensive and atherosclerotic heart disease. The minimal injuries and hemorrhage present at autopsy suggest that the decedent died of natural causes before the crash. However, the contribution of these injuries to an unconscious state, and immediate death, cannot be excluded. As such, the manner of death in this case is ruled accident.” The autopsy identified an enlarged heart. The heart weighed 530 grams (upper limit of normal is roughly 510 grams for a male of the pilot’s body weight). The thicknesses of the left ventricular wall, right ventricular wall, and interventricular septum of the heart were 1.6 cm, 0.4 cm, and 1.6 cm, respectively (upper limits of normal are roughly 1.6 cm, 0.6 cm, and 1.8 cm, respectively). The remainder of the heart examination was unremarkable; cross sections of the coronary arteries revealed no atherosclerosis. The kidneys showed chronic changes typical of high blood pressure. The lungs showed evidence of pulmonary hypertension, with plexiform lesions of the bifurcation to the pulmonary arteries. The autopsy examination did not identify other significant natural disease. Toxicology testing by NMS Labs detected delta-9-tetrahydocannabinol (commonly known as THC) at0.63 ng/mL in the pilot’s subclavian blood; no THC metabolites were detected. Toxicology testing by the Federal Aviation Administration Forensic Sciences Laboratory detected loratadine (a nonsedating antihistamine medication) and its metabolite desloratadine in the pilot’s subclavian blood and urine; no THC or THC metabolites were detected.
Impairment and subsequent incapacitation of the pilot for reasons that could not be determined. The incapacitation resulted in a loss of engine power due to fuel starvation. Likely contributing was pilot hypoxia due to altitude exposure, possibly worsened by effects of undiagnosed pulmonary hypertension, by premature depletion of the supplemental oxygen supply, or by a combination of those factors.
Source: NTSB Aviation Accident Database
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