Incident Summary
On November 23, 2018, at approximately 1733 Pacific standard time, the pilot of a Cessna 208B (registration N781FE) became incapacitated while taxiing near Bakersfield, California. The aircraft was operated by West Air, Inc. as a Title 14 CFR Part 135 on-demand cargo flight, owned by FedEx Corporation. The pilot, an airline transport pilot, sustained minor injuries; the airplane was not damaged.
Pilot Account
The pilot reported that during loading, he counted 68 boxes, 41 of which were labeled as containing 2 lbs of dry ice each. A FedEx dangerous goods representative approved the shipment without checking contents. The operator's internal policy allowed a maximum of 168 lbs dry ice in the cabin. The shipper's declared weight was within limits.
After starting the engine at 1729, while taxiing, the pilot experienced "strong sleepiness" and difficulty breathing. He stopped at the runway run-up area and closed his eyes. He failed to respond to air traffic control for 25 minutes. The tower controller alerted the fire department. A firefighter illuminated the cockpit, observed the pilot with head back and mouth open, placed wheel chocks, and boarded. After unsuccessful attempts to rouse the pilot, a sternal rub caused movement. The firefighter shut down the engine and electrical system. The pilot gradually became conscious, answered questions coherently, and exited the airplane. He was transported to the hospital.
Medical Findings
The pilot reported no medical conditions or medications at his last medical certificate on January 20, 2018. Months later, he was diagnosed with Valley Fever and treated with fluconazole, which is not generally cognitively impairing. He reported no side effects except drowsiness the first night.
Postincident medical tests (CT scan, cardiac catheterization, echocardiogram, lab work) showed no abnormalities. A few weeks later, a cardiologist concluded that symptoms were consistent with carbon dioxide (CO2) poisoning from dry ice. Excess inhaled CO2 is rapidly exhaled within minutes.
Dry Ice and CO2 Hazards
FAA Advisory Circular (AC) 91-76A describes dry ice hazards. Dry ice sublimates into gaseous CO2, potentially incapacitating aircrew. Tests showed sublimation rates average 2% per hour for packages containing 4.6–5.3 lbs. The AC states CO2 exposure should not exceed 0.5% (5,000 ppm). Symptoms include headache, dizziness, muscular weakness, drowsiness, and tinnitus. Removal from exposure results in rapid recovery.
The pilot had closed cockpit vents due to cold weather. The operator had no policy requiring ventilation with dry ice onboard at that time.
A subsequent NTSB sublimation study indicated that CO2 concentration in an unvented cabin would reach 1% in 5 minutes (twice the standard) and 6.37% by 30 minutes—levels consistent with loss of consciousness. At the correct weight of 81 lbs, concentration would reach 1% in about 10 minutes and above 4% when the firefighter opened the door.
Shipper Procedures
The shipper's standard practice was one scoop (2 lbs) of dry ice per box, but weight was not measured. The employee who packaged the dry ice on the incident flight normally used 2 scoops for larger boxes; on that day he used 1.5 to 2 scoops per box and marked "0.9 kg" (2 lbs) per label—the standard they always used. Postincident measurement showed one full scoop equaled 2.3 lbs. The declared total of 41 boxes was 81 lbs, but actual weight ranged from 122 to 162 lbs.
The shipper stated the incident shipment was an extremely high-volume, irregular order. They reassigned an employee who had not packaged hazardous materials in 17 months or completed training since September 2015.
Previous Similar Incident
On March 5, 2018, the same pilot experienced similar symptoms after picking up a dry ice shipment. After closing vents and starting taxi, he had difficulty breathing. A CO2 detector issued by the operator indicated 4,000 ppm after 200 ft. He opened three vents, turned back, and the detector reached 7,800 ppm. Opening the door reduced it to 6,450 ppm.