At approximately 9 p.m. on Aug. 27, 2011, a privately-owned Robinson R44 Raven II helicopter left the aerodrome in Saint Ferdinand, Que., for a night flight to the nearby town of Saint-Nicolas, Que. In addition to the pilot, who was operating under visual flight rules, three passengers were on board.
It was dark, more than an hour after sunset, but the trip was supposed to be short—20 minutes for a family of four to return home after an evening spent visiting friends. Moreover, the nearest aerodromes reported good visibility; and the pilot had been licensed for six years with almost 900 hours of flight time, meeting the Canadian Aviation Regulations (CAR) requirements for a night rating. Yet nine minutes later, all four people were dead, the helicopter itself destroyed on impact after crashing in a wooded area barely a kilometre away.
In late September, the Transportation Safety Board (TSB) released its investigation report into the crash (Report A11Q0168). According to the findings, there was no evidence of mechanical failure, and the pilot probably lost control of the aircraft shortly after takeoff. The likely cause? Spatial disorientation. The aerodrome was not equipped with a lighting system, and TSB investigators concluded the pilot would have had few visual references outside the aircraft, thus leaving himself vulnerable to various night-flying illusions.
Several types of illusions can affect a pilot’s orientation, including vestibular illusions. These are the most complex and the most dangerous, in part because the inner ear is sensitive to both linear and angular acceleration. In the case of the former, a pilot who lacks visual cues may incorrectly perceive the aircraft to be pitching either nose-up or nose-down. (This occurs frequently just after takeoff.) The latter, meanwhile, can give a pilot who has just completed a turn the sensation that he is still turning, but in the opposite direction.
Most extreme among forms of vestibular disorientation is the Coreolis phenomenon, which can happen when the pilot turns his head to the front or to the back while the aircraft is turning. This can create the sensation of pitch, roll, and yaw all at the same time. In the absence of external illumination or other visual cues, a pilot who performs even simple actions, such as turning his head to the front to perform a task, or raising his head to look ahead while turning, can experience this. And while it doesn’t mean a crash will necessarily result, it can make the aircraft difficult to control.
The risks presented by spatial illusions, however, are known. And pilots who wish to fly at night—when these risks are greatest—must complete additional training as specified in the Canadian Aviation Regulations (CARs).
In this occurrence, the pilot held a night rating. The pilot had also logged six hours of night flight time as pilot-in-command during the previous six months, for a total of nine takeoffs and landings, and had therefore satisfied the recency requirements of the CARs. However, of note, all of these took place in areas where the surrounding environment was illuminated. This is not unusual: flight training schools are often located near populated areas, meaning training is often conducted in and around lit runways or heliports. Yet on the evening of the occurrence, the pilot was faced with a quite different set of circumstances. It was very dark: there was no visible moon, the roads next to the airport are not lit, and there are few nearby homes. Moreover, there are many trees in the direction of the planned destination. In short, the pilot would have been taking off from, and flying over, a “black hole” of near-featureless terrain—a challenging combination for any pilot, let alone one with little exposure to night flying outside metropolitan areas.
The TSB’s report, therefore, made this risk one of its key findings: pilots without extensive night flight experience outside of well-lit areas are at higher risk of spatial disorientation. Moreover, it is also possible that the minimum requirements to obtain a private pilot helicopter night rating may not be enough to adequately educate and demonstrate to private helicopter pilots the risks involved in night flying—including the visual illusions that can lead to spatial disorientation.
So what should pilots do to prevent these kinds of accidents from happening?
As it turns out, one of the best defences against succumbing to spatial illusions is awareness. Simply knowing that disorientation can occur—and conducting a proper instrument check—can help to prevent these problems. In fact, most of the strategies to reduce the risk of spatial disorientation involve pre-flight preparation. These include keeping cockpit lights low, so eyes stay adjusted to darkness and pilots can see clearly outside.
Helicopter flying is growing in popularity. Twenty-five years ago, there were just 210 licensed private pilots in Canada. By 2011, that number had more than tripled, to 637. As the numbers continue to grow—and with over 300 people currently holding student pilot permits—it is reasonable to assume that there will be an increase in night-rated pilots. It is difficult to predict the impact this could have on the number or rate of night flying accidents, but one thing is clear: with spatial disorientation accounting for between five and 10 per cent of all general aviation accidents—90 per cent of which are fatal—pilots need to be extra careful when flying at night.
That means being aware of the hazards and risks presented during night flying, and taking appropriate mitigation measures.
The TSB is an independent agency that investigates marine, pipeline, railway and aviation transportation occurrences. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability. For more information, visit our website at www.bst-tsb.gc.ca.