Description

On 14 January 2011 a Boeing 767-300 being operated by Air Canada on a scheduled passenger flight from Toronto to Zurich and in the cruise at FL350 about halfway across the Atlantic Ocean experienced a sudden pitch excursion in Visual Meteorological Conditions (VMC) at night from which recovery was achieved but during which 16 of the 103 occupants were injured. After receipt of advice on the extent of the injuries, the flight was continued to the planned destination without further event and upon arrival, seven of the injured passengers were hospitalised.

Investigation

An Investigation was carried out by the Canadian Transportation Safety Board. DFDR data was available but the 2 hour Cockpit Voice Recorder (CVR) had not been stopped after the event and had consequently been overwritten. It was noted that a two pilot crew was operating the flight in accordance with the prevailing crewing agreement.

It was established that soon after the First Officer had been woken from a long period of in-seat ‘controlled rest’ by a routine radio call made by the aircraft commander and soon afterwards had been appraised by him of expected opposite direction traffic 1000 feet below, a USAF C17, which was evident as a Airborne Collision Avoidance System (ACAS) target on the ND. The First Officer then apparently mistook the planet Venus for an oncoming aircraft but was re-advised by the aircraft commander of the traffic 1000 feet below.

When the aircraft commander, who was the designated PF for the sector, sighted the opposite traffic soon afterwards, he exchanged a flash of the aircraft landing lights with it but when the First Officer subsequently sighted the same traffic, he believed, on the basis of visual perception only, that it was above and descending towards them. Despite being PM, he reacted suddenly to what he perceived was an imminent collision by pushing hard forward on the control without reference to the PF with the result that pitch attitude changed quickly from 2º nose up to 6º nose down. The PF responded promptly by disconnecting the AP and restoring the original pitch attitude. The excursion extended to 400 feet below the cleared cruise level to 400 feet above it with an initial speed gain of 7 knots then a speed loss of 14 knots before cruise speed was regained. At no time was a TCAS TA or RA triggered. The push force exerted on the control column by the First Officer was found to have been 80 pounds, considerably more than the 24 pound threshold which is required to override an engaged autopilot.

The cabin injuries caused were all of the soft tissue variety with some occupants sustaining lacerations. Two of the cabin crew (one in the rear galley and one in a toilet) and 14 passengers, all of whom were in economy class, were injured. The seat belt sign had been illuminated for around 40 minutes at the time of the excursion but although a visual inspection of seat belts was reported to have been made when the sign was switched on, the passenger injuries were not compatible with a seat belt being secured at the time. The promulgated Air Canada procedure for ‘controlled rest’ was examined and it was found that the rest taken prior to the excursion had failed to comply with it in a number of respects:

• The senior member of cabin crew had not been informed as required and therefore could not (as also required) “call the flight deck at a specific time” to provide a status check on the flight crew.
• The maximum permitted rest period is 40 minutes whereas the rest prior to the incident had been for 75 minutes.
• The amount of rest to be taken must be agreed in advance of its commencement but it was not.
• After a rest period has been completed, the awakened pilot “should be provided (with) at least 15 minutes without any flight duties to become fully awake before resuming normal duties. An operational briefing shall follow.” The attempts at both providing and gaining situational awareness were self-evidently premature.

The Investigation considered that “each of these actions was consistent with common misunderstandings among Air Canada pilots” rather than an exceptional example of procedural non-compliance. It was found that the operator’s pilots “understood that they were required to call cabin crew prior to taking a controlled rest, but they tended to rely on their own assessment of the sleepiness of the non-resting pilot in order to decide whether the cabin crew needed to be told that rest was being taken”. It was claimed that “one of the reasons (why pilots) were reluctant to inform cabin crew was that they knew cabin crew were not entitled to controlled rest themselves.”

It was also found that there was considerable misunderstanding amongst the operator’s pilots about the reason why controlled rest was limited to 40 minutes. “Some pilots believed that 20 - 40 minutes could not provide appreciable benefits and believed that what was really required was a significant sleeping period - 90 to 120 minutes. Some were unaware that by sleeping longer than 40 minutes there was a high risk of entering slow-wave sleep and increasing the severity of sleep inertia.”

It was found that “the training provided by Air Canada on controlled rest was limited to repeating the procedure in the (Operations Manual) to the trainees, and did not explain or emphasize why the boundaries of the procedure are critical to safety.” A recent article in the safety magazine had described some of these issues but it was considered that “this form of training does not reliably lead to the level of training required” and was “insufficient to ensure that pilots fully understood and carried out the controlled rest procedures”.

However, in respect of the wider context for potential fatigue, both crew advised that they had reported for duty prior to the flight feeling “well rested” and no evidence that any generic fatigue concerns existed at Air Canada in respect of flights like the incident one was found.

The formal statement of Findings as to Causes and Contributing Factors was as follows:

1. The interrupted sleep obtained by the first officer prior to the flight increased the likelihood that rest would be needed during the overnight eastbound flight.
2. The first officer slept for approximately 75 minutes which likely placed the first officer into slow-wave sleep and induced longer and more severe sleep inertia.
3. The first officer was experiencing a circadian low due to the time of day and fatigue due to interrupted sleep which increased the propensity for sleep and subsequently worsened the sleep inertia.
4. By identifying the oncoming aircraft, the captain engaged the first officer (FO) before the effects of sleep inertia had worn off.
5. Under the effects of sleep inertia, the first officer perceived the oncoming aircraft to be on a collision course and pushed forward on the control column.
6. The frequency of training and depth of the training material on fatigue risk management to which the flight crew were exposed were such that the risks associated with fatigue were not adequately understood and procedures for conducting controlled rest were not followed by the flight crew.
7. Although the seatbelt sign was on and an announcement about potential turbulence was made, several passengers were injured during the event because they were not wearing their seatbelt.

The formal statement of Findings as to Risk was as follows:

1. North American-based pilots flying eastbound at night towards Europe are at increased risk of fatigue-related performance decrements.
2. The use of multiple safety occurrence reporting systems may result in some safety issues not being properly identified and analyzed.
3. Some passengers may not be aware of the inherent risks in not wearing a seatbelt at all times when seated.

Safety Action taken by Air Canada in response to the Investigation findings - the issue of a series of crew reminders and the initiation of research on crew alertness eastbound on the incident route - was noted.

The Final Report of the Investigation: Aviation Investigation Report A11F0012 was authorised for release on 29 February 2012. No Safety Recommendations were made as a result of the Investigation.

Further Reading

• Loss of Control
• Pilot Perception
• Fatigue
• Information Processing
• Situational Awareness