Flight operations in remote areas such as Canada's North–west Territories often are unconventional when compared with those in areas crisscrossed with busy airways, airports with precision approaches at both ends and border-to-border radar coverage. In the hinterlands it is not uncommon for the pilot of a scheduled commercial flight to manage all flight dispatch duties himself.

Such was the case at Air Tindi. The operator provides scheduled passenger and freight flights to and from its base in Yellowknife, Northwest Territories, using Cessna Caravan 208Bs under CAR Subpart 703. In addition, it's authorized to use single-engine aircraft for transportation of passengers under IFR and day and night VFR.

The company's self-dispatch system delegates operational control of flights to the pilot-in-command. In October 2011, crews were afforded latitude to conduct scheduled passenger operations under VFR. Under this system, the PIC was responsible for ensuring that appropriate documents including flight plans are prepared and filed prior to departure.

At 0800 on Oct. 4, 2011, a young Air Tindi pilot flew Cessna Caravan C-GATV on a regularly scheduled flight from Fort Simpson, Northwest Territories (CYFS) to Yellowknife as Air Tindi Flight 222. The VFR commercial flight arrived at 0919 without incident despite spotty marginal weather and a possible violation of airspace rules.

Fort Simpson weather at 0800 recorded visibility of 6 mi. in light rain and mist, broken clouds at 300 ft. and an overcast at 1,500 ft. The Caravan entered clouds shortly after takeoff and remained in clouds cruising at 3,900 ft. for most of the flight. Thus the trip was flown in IMC above the floor of controlled airspace at 2,200 ft. AGL in which an IFR clearance was required.

The next leg for this pilot was to depart Yellowknife with three passengers at 1100 for a regularly scheduled flight to Lutsel K'e located some 106 mi. due east. The company operations manual contained a published route with a minimum IFR altitude of 3,100 ft. ASL. This provided a minimum of 2,000 ft. of terrain clearance from the highest elevation of 1,100 ft., which was about 26 mi. west of Lutsel K'e. Most of the route lay in uncontrolled airspace, and an ATC clearance was not required. The airport was served by an RNAV instrument approach with a minimum straight-in LNAV descent altitude of 1,160 ft. ASL, or 567 ft. AGL. It was left to the pilot to decide whether to go VFR or file IFR.

The Yellowknife-Lutsel K'e region that day was under the influence of a trough of warm air aloft. The system generated overcast layers from 2,000 to 4,000 ft. ASL with tops at 24,000 ft. ASL. Scattered altocumulus castellanus topped at 22,000 ft. ASL. Predicted localized visibilities were from 3 sm to more than 6 sm in light rain showers and mist, and patchy ceilings were from 800 to 1,500 ft. AGL. Moderate mixed icing was predicted above the freezing level at 5,000 ft. AGL.

The terminal forecast for Yellowknife, valid for 24 hr., from 0600 was available to the pilot before departure. For the period of the flight, the forecast called for wind, 120 deg. at 12 kt.; visibility, more than 6 sm in light rain; a few clouds at 600 ft. AGL and a broken cloud cover at 1,500 ft. agl. Occasionally, the visibility was to be 3 sm in light rain and mist, with clouds broken at 600 ft. AGL. A revised forecast, issued at 1102, predicted essentially the same conditions, with a temporary lower broken cloud height of 500 ft. AGL.

The 1100 METAR for Yellowknife reported wind, 110 deg. at 12 kt., gusting to 18 kt.; visibility, 3 sm in light rain and mist; sky condition, 500 ft. AGL broken, 1,000 ft. AGL overcast; temperature 6C, dewpoint 5C. Stratocumulus covered most of the sky.

When Air Tindi 200 departed Yellowknife at 1103 under a VFR clearance, the visibility was at the VFR minimums of 3 sm. VFR operations within the control zone were allowed without requiring a special VFR clearance. Once en route, clear of the Yellowknife control zone and below 1,000 ft. AGL, the aircraft was required under Canadian Aviation Regulations to remain clear of clouds with flight visibility not less than 2 sm. Investigators would determine later that the flight to the Lutsel K'e area was conducted on a direct track at low level, below a low, ragged cloud base into reducing visibility.

The last radio call heard from the Caravan was a position report indicating the flight was about 20 mi. from Lutsel K'e. The pilot reported none of the usual information such as arrival intentions and estimated time of arrival. The crew of another aircraft that also was inbound to Lutsel K'e from Yellowknife heard this radio report.

The Air Tindi Caravan failed to arrive at its scheduled time of 1145. The company's representative at Lutsel K'e alerted the Yellowknife operations center at 1223. The last known position appearing on the Air Tindi headquarters SkyTrac database indicated that C-GATV had stopped short of Lutsel K'e, and the company emergency response plan was activated at 1245. Two company fixed-wing aircraft were dispatched on visual and electronic searches. Neither the Joint Rescue Coordination Center nor search aircraft received an ELT signal.

Ultimately, a rescue crew in a float-equipped de Havilland DHC-6 located the wreckage at 1420 and landed on nearby Great Slave Lake. The crew hiked into the accident site and arrived at 1530. The pilot and one passenger were dead. Two passengers suffering serious injuries were shuttled by helicopter to the floatplane and evacuated to Yellowknife at 1800.

The aircraft had crashed some 26 nm west of Lutsel K'e near the crest of Pehtei Peninsula. There was no post-impact fire.

Investigators from Canada's Transportation Safety Board (TSB) surveyed the scene and wreckage. The terrain between Yellowknife and Lutsel K'e consists of gently rolling, tree-covered Canadian Shield rocky outcrops, with interspersed lakes. Ground elevation on the route varied from 600 ft. to 1,100 ft. ASL. The accident site was near the highest point on the route, rising about 500 ft. from the surface of Great Slave Lake. The peninsula is oriented nearly perpendicular to the aircraft's flight path to Lutsel K'e. The first point of impact was at an elevation of 1,013 ft. ASL, about 38 ft. below the top of the peninsula and 20 ft. above the face of a vertical cliff.

At impact, the aircraft was in a nearly level attitude in pitch and roll. First ground impact was by the landing gear, followed by the belly cargo pod and the propeller, all of which separated from the aircraft at this point. The airplane continued up a 10-deg. slope over the top of the hill, became airborne and came to rest inverted 477 ft. down the eastern slope of the peninsula. The cockpit was crushed, and the forward passenger cabin was distorted, with the forward cabin bulkhead mostly dislodged from its attachments. The left wing had folded back and rested on the ceiling of the cabin.

The airplane had been equipped with a SkyTrac GPS-based flight-following system that transmitted aircraft position, altitude, groundspeed and track via satellite link to the company at subscribed 15-min. intervals. The onboard equipment recorded this data at 5-sec. intervals. The 5-sec. interval data were extracted by the TSB laboratory and used to reconstruct the accident flight. The last SkyTrac transmission at 1140 showed the aircraft at rest, indicating the time of the accident.

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.

Studies have established the relative risk of road accidents involving cannabis-impaired versus sober drivers as “odds ratios.” A blood delta9-THC concentration of 6 to 8 ng/ml correlated with a blood alcohol level of 0.05%, and an odds ratio of 1.5 to two times the risk of accident for a sober person. Drivers who were under the influence of cannabis tended to compensate consciously by operating more cautiously.

The duration of THC effects is variable, subject to a number of conditions. Generally, after a single dose of marijuana, there will be some impairment for up to 6 hr. Experiments have suggested significant carry-over impairment in complex human/machine performance such as flying, up to 24 hr. after a moderate dose of THC via inhalation. This influence can occur after an individual ceases to be aware of any influence of the drug.

Although some clients of aviation operators in Canada require pre-employment and periodic drug and alcohol screening, said the TSB, there are no Canadian regulations requiring persons employed in federally regulated transportation industries to submit to toxicological testing. U.S. federal transportation law requires drug and alcohol testing of all employees in safety-sensitive transportation positions, including aviation.

The TSB’s Analysis

The TSB determined the airplane and its systems were working properly before the crash. What follows is from the TSB analysis of the incident:

When C-GATV departed for Lutsel K'e, the weather at Yellowknife was marginal for VFR flight. Low clouds persisted for the entire flight, which was flown at low level so the pilot could maintain visual contact with the ground. The descent during the last 2 min. of the flight suggests that the ceiling had become lower.

The conduct of the flight and the nature of the impact were characteristic of a CFIT event: the aircraft struck rising terrain under the pilot's control at cruise speed, with a wings-level attitude and a heading generally consistent with the direct track to the destination. Because no effective evasive maneuvers were made before impact, it is likely that the crest of the Pehtei Peninsula was obscured in fog and not visible to the pilot. The application of increased engine power immediately before impact was likely made when the terrain in front of the aircraft suddenly became visible.

When the pilot transmitted a position report 6 nm closer to Lutsel K'e than the actual position, it is possible that he believed that the shoreline of Great Slave Lake had been crossed and that open water at about 500 ft. ASL lay ahead. Since GPS was likely the primary navigational aide, there should have been little ambiguity in position, unless the unit was set to a waypoint associated with the RNAV approach at Lutsel K'e. However, the location of the site and the wreckage trail track indicate that the aircraft was proceeding directly to the airport. If an instrument approach had been planned, the aircraft should have been navigating toward a waypoint associated with the approach, and at an altitude no lower than 3,100 ft. in accordance with the company-published route.

A TAWS installation in C-GATV could have warned of the impending collision with the ground, possibly in sufficient time to prevent the accident.

Investigators could not determine why the pilot chose to fly the trip under VFR. Conditions were suitable to enable operation under IFR at altitudes providing safe terrain clearance. The pilot, the aircraft and the company were qualified to operate the trip under IFR. The en route weather was suitable, and with the freezing level well above the minimum IFR route altitude, icing was not a factor to preclude IFR flight. The cloud base was above the minimums required for successful completion of an approach and landing at Lutsel K'e. Before departure, the forecast weather was such that Yellowknife could be filed as an IFR alternate.

The fuel load was not considered to be a factor in the pilot's decision to fly the trip under VFR rather than IFR. Fuel was readily available at Yellowknife, and there was adequate time between the arrival from Fort Simpson and the departure for Lutsel K'e to bring the fuel quantity to IFR requirements under the supervision of dispatch personnel.

Although the pilot had gained experience in an IFR environment during his flying as a copilot in multiengine aircraft, he had limited experience in single-pilot IFR operations. This may have led to reluctance to file an IFR flight plan on the accident flight, and the decision to remain visual in marginal VFR weather conditions. The route lay mostly in uncontrolled airspace, and when flight visibility deteriorated, the pilot had the option of climbing without ATC clearance to a safe altitude, and conducting an instrument approach at Lutsel K'e. The pilot apparently was willing to fly in cloud as indicated by the earlier flight from Fort Simpson to Yellowknife, albeit on a VFR flight plan in controlled airspace.

Decision-making and THC Effects

On the day of the accident, aspects of the pilot's planning, flying technique and decision-making were inconsistent with regulatory and administrative requirements, the company operations manual policy and safe flying practices. These included VFR flight in marginal visual weather conditions, flight in IMC on a VFR flight plan, and overwater flight beyond gliding distance of land. The quantity of psychoactive components in the pilot's system is considered to have been sufficient to result in impairment of cognitive processes. This would likely have had an effect on planning and conduct of the accident flight. It is possible that the pilot, under the influence of cannabis, avoided the higher workload of IFR flight in IMC, choosing to remain visual for the trip to Lutsel K'e.

Overwater Flight Risk

The company did not provide personal floatation devices in the land-plane fleet, and management expected single-engine aircraft to remain within gliding distance of land at all times. The pilot was familiar with the route, and given the low cloud en route and the current weather at Lutsel K'e, it is likely that a diversion to the south to remain within gliding distance of land would have to be made well before arriving at the shoreline near the accident location. The direct flight track flown toward Lutsel K'e suggests that, after crossing the Pehtei Peninsula, the pilot was prepared to overfly 11 nm of open water at low level, increasing the risk to the aircraft and its occupants. Overflight of Great Slave Lake on the earlier flight from Fort Simpson to Yellowknife indicated a willingness on the part of the pilot to accept that risk.

Findings

Rather than issue a “probable cause,” Canada's Transportation Safety Board issues “Findings as to Causes and Contributing Factors,” “Findings as to Risk” and “Safety Actions.”

In this case, the TSB issued the following:

Findings as to Causes and Contributing Factors:

(1) The aircraft was flown at low altitude into an area of low forward visibility during a day VFR flight, which prevented the pilot from seeing and avoiding terrain.

(2) The concentrations of cannabinoids were sufficient to have caused impairment in pilot performance and decision-making on the accident flight.

Findings as to Risk:

(1) Installation instructions for the ELT did not provide a means of determining the necessary degree of strap tightness to prevent the ELT from being ejected from its mount during an accident. Resultant damages to the ELT and antenna connections could preclude transmission of an effective signal, affecting search and rescue of the aircraft and occupants.

(2) Flying beyond gliding distance of land without personal floatation devices on board exposes the occupants to hypothermia and/or drowning in the event of a ditching.

Other Findings:

(1) Earlier on the day of the accident, the pilot flew the route from Fort Simpson to Yellowknife in cloud on a VFR flight plan in controlled airspace.

(2) With the ELT unable to transmit a usable signal, the SkyTrac system in C-GATV was instrumental in locating the accident site. This reduced the search time and allowed for timely rescue of the seriously injured survivors.

Safety Actions

Operators in Canada and the U.S. were warned to be sure ELTs secured by hook and loop systems are appropriately retained. Air Tindi issued several company directives including these:

Dispatch limitations:

All scheduled flights will be dispatched under IFR. VFR flight may only be conducted if authorized by operations management personnel.

No company aircraft may be operated on any scheduled passenger flight when the observed weather is at, or forecast to be lower than, the alternate minima for the destination airport.

The airline also instituted changes to the operational control system of scheduled passenger flights to ensure adequate flight following and timely reporting of departure and arrival times to the company System Operations Control Center.

The company has also begun installing Appareo Vision 1000 Systems cockpit imaging and flight data monitoring devices in its Cessna 208B fleet. The data recorded by this equipment can be helpful in incident/accident investigation.

Finally, the company has revised the existing drug and alcohol policy to include random testing of employees in safety-sensitive positions. These positions include pilots, maintenance engineers and dispatch personnel.

Modern Times

The use of marijuana in its various forms is under considerable debate in the U.S. Some states have nullified federal law and are allowing marijuana to be sold legally for medical purposes. Other jurisdictions have decriminalized marijuana held for personal use and, at worse, made its possession a simple violation similar to failing to signal a turn while driving.

It is important for pilots to understand that substances containing THC can reduce cognitive functioning. Not only is physical performance degraded, but judgment can be affected for long periods after THC enters the bloodstream. And, more important, the user may not realize the effects remain more than 24 hr. after its use.

As the general public and even laws become more tolerant of THC-containing substances, pilots must remain especially wary of their use for medical or recreational purposes.