ERA22FA114

The pilot’s impairment due to exposure to carbon monoxide as a result of undetected engine exhaust penetration into the cockpit, resulting in the pilot's failure to maintain a minimum controllable airspeed after partially securing an engine after takeoff.

The pilot was performing an aerial survey flight, and after completing a preflight inspection, he taxied toward the runway for engine run-up and surveying computer start-up. During taxi and the subsequent run-up, the airplane was positioned for about 8-10 minutes with a quartering tailwind. Track data revealed that shortly after takeoff, the airplane’s climb rate decreased, and its acceleration stopped. Shortly thereafter, the airplane began a 10°-bank-angle left turn at an airspeed of about 136 knots, followed by a rapidly descending right turn and impact with terrain. Postaccident examination of the wreckage revealed that the left fuel tank selector handle was in the OFF position, the left throttle was near idle, the left propeller control was near the feather position, and the rudder was trimmed to the right. These control positions were consistent with the left engine being partially secured, which would result in a lack of power and the loss of climb rate noted shortly after takeoff. Additionally, the right fuel tank selector handle was found in the left main fuel tank position. The examination of both engines revealed no evidence of any preimpact anomalies or malfunctions that would have precluded normal operation, and no reason for why the pilot might have partially secured the left engine. In the event of an engine failure during takeoff, the airplane manufacturer’s Pilot’s Operating Handbook (POH) assumes that the inoperative propeller is feathered and that 5° of bank toward the operating engine is used to balance the side force generated by a full rudder input. If these conditions do not exist, the airplane can quickly become uncontrollable at airspeeds much higher than the published single-engine minimum controllable airspeed (Vmc). The physical evidence, along with a performance analysis of the airplane’s flight track, showed that the left engine was not fully secured, the right engine fuel selector was set to the left tank, and the airplane banked 10° into the inoperative engine at an airspeed of about 136 kt shortly before the airplane entered a steep, descending right turn. This turn toward the inoperative engine would have dramatically increased the airplane’s minimum controllable airspeed above that assumed by the POH (80 knots), and the pilot's ability to maintain control of the airplane would have been significantly reduced. It is likely that during this left turn, the pilot allowed the airplane's airspeed to decrease below a speed for which the airplane would have been controllable, which resulted in a loss of control and led to the airplane's roll to the right and rapid descent toward the terrain. Postaccident toxicological testing performed by a state office of forensic science revealed that the pilot’s carboxyhemoglobin, a marker of carbon monoxide (CO) exposure, was elevated at 31%. Although the Federal Aviation Administration Forensic Sciences Laboratory toxicology results did not show elevated carboxyhemoglobin, these test results might have been misleadingly low if there was an actual postmortem decrease of carboxyhemoglobin in the tested blood. This may have occurred if the specimens were obtained from a collection site where blood intermixed with gastric acid. The carboxyhemoglobin percentage measured in the blood specimen tested by the state forensic science office was confirmed by a second distinct technique, and the probability is small that the elevated result was attributable to postmortem changes. Examination of the airplane’s combustion heater assembly revealed no defects that could have allowed the combustion biproducts to intermix with the ventilation air, and examination of the wreckage revealed no evidence of inflight or post-impact fire. A postaccident test with an exemplar airplane (the same make/model as the accident airplane) that was equipped with an electronic CO detector revealed that when taxiing and performing an engine run-up with a quartering tailwind, the exhaust from the left engine was able to penetrate the cockpit. Based on the observations from this test, it is possible that engine exhaust gasses containing CO could have entered the cockpit while the pilot was conducting his pre-takeoff tasks. Given that the airplane was equipped only with a disposable “spot” CO detector, the pilot would not have been alerted to increasing CO levels unless he had looked at the device and observed a color change. Given that the temperature on the day of the accident was 33° F, it is likely that the airplane’s heater was operating. It is possible that its fan could have drawn additional air containing engine exhaust gasses and CO into the cabin heater air intake, and then into the cockpit, which would have increased the pilot’s the level of CO exposure. No other source of abnormal CO was identified. Based on available operational and physical evidence, it is likely that the pilot was impaired due to CO exposure. It is possible that this impairment could have resulted in his perception of a left engine problem, and resulted in him partially securing it, as demonstrated by the postaccident positions of the engine controls. Ultimately, the turn into the partially secured engine resulted in a loss of control and impact with terrain.

The Commonwealth of Virginia Office of the Chief Medical Examiner, Western District, performed the pilot’s autopsy. According to the autopsy report, the cause of death was blunt force trauma of the head, torso, and extremities, and the manner of death was accident. The Virginia Department of Forensic Science (DFS) performed toxicological testing of postmortem pooled cavity blood from the pilot. Ethanol was detected at 0.012 g/dL. Carboxyhemoglobin, a marker of CO exposure, was elevated at 31%, as measured by spectrophotometry with confirmation by microdiffusion. The FAA Forensic Sciences Laboratory also performed toxicological testing of pooled cavity blood from the pilot. Ethanol was not detected at a reporting threshold of 0.01 g/dL. Carboxyhemoglobin testing was performed on five specimens using spectrophotometry. For three of these specimens, carboxyhemoglobin was not detected at a reporting threshold of 10%. The remaining two specimens were unsuitable for measuring carboxyhemoglobin. Postmortem ethanol production is made more likely by extensive traumatic injury and can cause an affected toxicological specimen to test positive. Carboxyhemoglobin is formed when CO binds to hemoglobin in blood, impairing the blood’s ability to deliver oxygen to body tissues (hypemic hypoxia). CO is an odorless, tasteless, colorless, nonirritating gas that can be produced during hydrocarbon combustion. Exposure to CO usually occurs by inhalation of smoke or exhaust fumes. Symptoms of low-level CO exposure are nonspecific and variable, and may include headache, nausea, and tiredness. Increasing levels of exposure may become impairing or incapacitating, causing more serious neurocognitive, cardiac, and/or vision problems, progressing to death above carboxyhemoglobin levels of about 50% (or lower if other serious medical conditions co-exist), although symptoms are not simply predictable from carboxyhemoglobin levels. Nonsmokers normally have carboxyhemoglobin levels of less than 1-3%, while heavy smokers may have levels as high as 10-15%. As with other causes of tissue hypoxia, CO poisoning may be insidious and difficult for an exposed person to recognize; there is no reliable physical sign of exposure. Review of maintenance records revealed that the airplane’s overhauled engines and propellers had accumulated 18.6 hours of operation before the accident. The airplane was equipped with an adhesive, disposable “spot” carbon monoxide (CO) detector. In the presence of CO, the spot would turn gray/black, and the spot would return to normal color after it is exposed to fresh air. The Pilot’s Operating Handbook (POH) and airplane checklist required the fuel selectors to be placed in the "main" position for takeoff. In the event of an engine failure during takeoff, the POH directed the pilot to feather the inoperative propeller and establish a 5° bank into the operating engine. With an engine shut down, in addition to the reduction in available power, the lateral/directional handling qualities of the airplane change significantly, and the indicated airspeed must be maintained faster than the Vmc of 80 knots to maintain directional control. The complete POH checklist for an engine failure after takeoff includes the following: 1. Mixtures - AS REQUIRED for flight altitude. 2. Propellers - FULL FORWARD. 3. Throttles - FULL FORWARD. 4. Landing Gear - CHECK UP. 5. Inoperative Engine: a. Throttle - CLOSE. b. Mixture - IDLE CUT-OFF. c. Propeller - FEATHER. 6. Establish Bank - 5° toward operative engine. 7. Wing Flaps - UP, if extended, in small increments. 8. Climb To Clear 50-Foot Obstacle - 92 KIAS. 9. Climb At Best Single-Engine Rate-of-Climb Speed - 106 KIAS at sea level 10. Trim Tabs - ADJUST 5° bank toward operative engine with approximately ½ ball slip indicated on the turn and bank indicator. 11. Cowl Flap - CLOSE (Inoperative Engine). 12. Inoperative Engine - SECURE as follows: a. Fuel Selector - OFF (Feel For Detent). b. Auxiliary Fuel Pump - OFF. c. Magneto Switches - OFF. d. Alternator - OFF. 13. As Soon As Practical - LAND. Cabin Heat System Review of maintenance records revealed that the cabin heat system was installed in December 2019 at an airframe total time of 5,878.3 hours. Records show that it was serviced and inspected in February 2020, April 2020, and January 2022. It had accrued 317.2 hours in service at the most recent servicing. According to the operator, the pilot had previously flown aerial surveying and had accrued 85 hours of flight experience in the same make and model of the accident airplane. The accident flight was his first solo aerial surveying flight for the company following several observation flights with the company’s owner. Interviews with friends and family of the pilot revealed that he was happy to have been hired by the operator, got along well with the company’s owner, and was pleased that the company’s airplanes were newer and better equipped than those at his previous surveying job. On February 1, 2022, about 1006 eastern standard time, a Cessna 310R airplane, N622QT, was destroyed when it was involved in an accident near Danville, Virginia. The commercial pilot was fatally injured. The airplane was operated by Sol Aerial Surveys as a Title 14 Code of Federal Regulations Part 91 aerial surveying flight. According to another company pilot, on the morning of the accident, he and the accident pilot arrived at the Danville Regional Airport (DAN), Danville, Virginia, conducted their flight planning together, and completed the preflight inspections of their respective airplanes. They then taxied their airplanes to runway 2 for engine run-up and surveying computer start-up. During the taxi and engine run-up, the accident airplane was heading 196º true (205° magnetic). The company pilot estimated that the accident pilot was on that heading for about 8-10 minutes while they completed these pre-departure tasks. The company pilot departed first, and the accident pilot departed several minutes later at 1003. A performance study was prepared based on automatic dependent surveillance-broadcast (ADS-B) data obtained from the Federal Aviation Administration (FAA). The study and ADSB-B data showed that that the airplane departed DAN and turned toward the southeast. Shortly after takeoff, the airplane’s climb rate decreased from 1,200 ft/minute to about 500 ft/minute, and the airplane’s acceleration stopped. The airplane reached an altitude of about 2,625 ft above mean sea level (msl) about 2 minutes into the flight and began a 10°-bank-angle left turn at an airspeed of 136 knots. About 10 seconds after turning left, the airplane returned to wings-level and then rolled right at a rate of about 3º/second while descending at a rate of more than 1,000 ft/minute. The last estimated bank angle was over 60° to the right at an altitude of 1,175 ft msl. The airplane impacted a wooded area about 4 nautical miles southeast of DAN. The wreckage was highly fragmented along the 382-ft debris path oriented on a true heading of 246°. The accident site elevation was about 488 ft mean sea level. There was a strong fuel odor but no evidence of fire. The largest portion of the wreckage, consisting of the empennage, an engine, and the remnants of the cockpit was located about 214 ft beyond the severed treetops at the base of a 16-in-diameter pine tree that was broken about 15-20 ft above the ground. A second engine was located about 150 ft farther along the debris path. Neither the wings nor the fuselage was intact. The flap setting could not be determined. The landing gear were fractured off from their mounts and located in various parts of the debris field. The landing gear actuator indicated the nose and main landing gear were in the retracted position at the time of impact. The pitch trim actuator indicated the elevator trim tab trailing edge was about 10° tab up.