Lingering Effects

By Richard N. Aarons
Source: Business & Commercial Aviation

After takeoff from Yellowknife, the pilot flew a direct track to Lutsel K'e with slight variations in groundspeed and track. Altitude varied between 850 ft. and 1,470 ft. ASL. Aircraft height above ground level varied between 129 ft. and 600 ft. One minute before its impact, the aircraft was at 1,325 ft. ASL, or 500 ft. AGL, 136 kt. ground speed and tracking 091 deg. Immediately before impact, altitude was 1,060 ft. ASL, the ground speed was 141 kt. and track was 098 deg.

The Pilot

Air Tindi employed a pilot-in-waiting program in which newly licensed pilots would work as ramp attendants for a period of time before moving into a pilot position. Under that arrangement, the pilots would gain operations experience, and the company would benefit from assessing the suitability of prospective pilots. Initially, they would fly as copilots on multiengine aircraft and be mentored by experienced pilots. This was followed by type training on the Cessna 185 or Cessna 208 for day VFR operations and line indoctrination to scheduled service destinations.

The accident pilot progressed through this program after obtaining a commercial pilot license - airplane in 2004. He worked as a ramp attendant until 2007 and then began flying as a copilot on the de Havilland DHC-6, acquiring approximately 1,500 hr., primarily in VFR operations. In 2010, he began flying as copilot on the Beech King Air 200, on which he acquired approximately 450 hr. of IFR flying. In February 2011, he began training on the Cessna 208, completing a VFR pilot proficiency check ride in March 2011, followed by company line indoctrination on type.

He did not pass a renewal Group 3 (single-engine) IFR check ride due to difficulties with GPS use, but after additional training, he passed a second IFR check ride on Aug. 18, 2011. All the pilot's revenue flights in the C208 as captain were under VFR. The pilot was qualified for the flight and had a valid instrument rating as well as medical and pilot proficiency certification. The pilot's flight and duty time limits were not exceeded. The pilot had just returned to work after three days off, and there were no indications that fatigue affected the pilot's performance.

Cannabinoids (Marijuana)

Post-mortem toxicological screening revealed the presence of cannabinoids in the pilot's system. Femoral blood contained 50.1 nanograms per milliliter (ng/ml) of delta9- tetrahydrocannabinol (delta9-THC), and 21.6 ng/ml of carboxy-THC. Pleural fluid contained 11.9 ng/ml of delta9- THC, as well as 41.8 ng/ml of carboxy-THC. Urine contained 272 ng/ml of carboxy-THC.

Delta9-THC is the principal psychoactive cannabinoid found in marijuana, hashish, hash oil and certain hemp products. Delta9-THC is metabolized in the liver, with the formation of psychoactive and inactive compounds. THC compounds are stored in fatty tissue, reaching peak concentrations in four to five days. Metabolic products are eventually excreted and total elimination of a single dose may take up to 30 days.

A number of factors complicate accurate determination of the recency of cannabinoid use including the mode of intake (smoking versus eating), concentration of cannabinoids, and individual variations. Delta9-THC blood plasma concentrations in live subjects of over 2 to 3 ng/ml have been shown to indicate marijuana smoking within 6 hr. Dispersal and redistribution of cannabinoids occurring in the post-mortem interval before sampling for toxicological analysis can alter the presence of cannabinoids in tissues and fluids. This increases the difficulty in the application of formulas to establish accurate usage time frames.

Effects of THC

The TSB reviewed flight simulator experiments on the effects of THC on pilot performance. They demonstrated “that THC has wide-ranging effects on human performance, including impairment of working memory, coordination, tracking, perceptual-motor performance, temporal perception and vigilance.” The effects of impairment increase with the complexity of the task, said the TSB. A blood delta9-THC concentration over 5 ng/ml is the threshold considered to be necessary for possible impairment.

“Even allowing for a reasonable margin of error in the toxicology results, the amount of THC present in this occurrence is considerably greater than the threshold that resulted in degraded pilot performance in studies on the impairing effects of THC,” said the investigators.

Comments On Articles