On 11 March 2013, the crew of an Embraer 190 (C-FLWH) being operated by Air Canada on a scheduled passenger flight (ACA178) from Edmonton to Toronto in night Visual Meteorological Conditions (VMC) and on approach to runway 24R at destination did not hear two ATC instructions to go around given at 200 feet agl and then again at 125 feet agl issued because an unoccupied vehicle had just been detected moving across the runway. As a result, and without becoming aware of the vehicle, they completed the landing, fully clearing the vehicle in the process.
An Investigation was carried out by the Canadian TSB. Recorded data relevant to the Investigation was overwritten on both 2 hour Digital Voice Data Recorders (DVDRs) after instructions from the TSB to isolate the recorder failed to achieve this in time, apparently because "the guidance provided to maintenance crews regarding the procedure to isolate the digital voice–data recorders was unclear".
The vehicle incursion and subsequent over flight of the slowly moving vehicle was found to have occurred at 2340 local time when the airport traffic situation was quiet. One GND and one TWR controller were providing ATS from the TWR cabin and a third controller had remained "for post handover monitoring". It was established that the installed ASDE equipment in the TWR cabin provided some capability for controllers to supplement visual observation of airside ground movements. However, the vehicle beacon was found not to meet the standard mandated for airside use which decreased the chances of it being seen by ground personnel, the flight crew or air traffic control. The initial movement of the van (for 700 feet) was not displayed on the ASDE until the vehicle reached intersection 'DV' (see the diagram below).
Shortly after the vehicle began to show, GND controller looked at his ADSE display and saw "an unexpected slow-moving target...and considered that it was possibly a false target". He continued with other duties for two minutes before returning to check the ASDE display by which time, a target was observed on the displaced threshold of Runway 24R which was pointed out to the TWR controller who was also looking at the ground controller’s ASDE display. "Both controllers quickly scanned the electronic flight progress strips and looked outside in an attempt to identify or confirm the target" and "the third controller scanned the area with binoculars." However, since the threshold was approximately 1.4 nm distant, and at night the view is impeded by terminal lighting, visual identification was not possible. The TWR controller, realising that there was an aircraft about to land on the same runway transmitted “Air Canada 178 pull up and go around, sir” and six seconds later, having had no response to the first call, he again instructed “Air Canada 178 pull up and go around”.
The controllers "watched the aircraft land and saw the ASDE target disappear off the side of the taxiway on the far side of the runway" and the van was subsequently located in the grass.
The Investigation noted that the RIMCAS system incorporated in the ADSE was configured to provide alerts at both TWR an GND controller positions. At the time of the incident, runway 23 was being used for departures and runway 24R for arrivals. The GND controller's ADSE display - the one which was being watched by both controllers during the incursion - was found to have been configured for RIMCAS in respect of runway 23 only and so no alerts were generated by the driverless vehicle . The TWR controller's display was configured for RIMCAS in respect of arrivals on both runways and departures on runway 23 and had therefore received a stage 1 (visual only) alert 23 seconds before the conflict and a stage 2 (aural and visual) alert 2 seconds before the conflict.
The track taken by the vehicle in relation to the landing aircraft (reproduced from the Official Report)
The pilots of the E190 had acquired the airport visually at approximately 7nm out and saw the preceding aircraft vacate the runway when they had approximately 5nm to run. Operator SOPs including the requirement to maintain a sterile flight deck environment were followed. It was established that the first air traffic control go around instruction had been masked by a concurrent Terrain Avoidance and Warning System (TAWS) automated callout of "two hundred" and the crew did not hear it. As the aircraft reached approximately 120 feet agl, the crew heard part of a radio transmission containing the words “go around” but after communicating between themselves, they "decided that the call could not have been for them". The Investigation concluded that the rapid commencement of the controllers transmission after pressing 'transmit' and the poor pronunciation of the aircraft call sign prefix led to the latter being absent from the received transmission. It was considered that a go-around transmission in the absence of other supporting cues such as the sight of an obstacle had meant that "the communication was insufficient to challenge the flight crew’s mental model of the situation, or their expectation of an uneventful landing". It was established that the aircraft had cleared the van by approximately 35 feet before touching down on Runway 24R, approximately 1500 feet past the displaced threshold.
It was noted that fatigue had not been a factor and that both pilots were experienced and had carried out many go arounds both on ATC instructions and otherwise although all of these had been "at least partially anticipated". The limited response of the crew to the two go around calls given that neither had see the van ahead despite the fact that it should, in theory , have remained visible from their flight deck until approximately 55 feet agl, was attributed by the Investigation to a process described in the "Recognition-primed Decision Making (RPD)" model that seeks to "explain how people make quick, effective decisions when faced with complex situations". The subject is discussed in the Investigation Report.
In respect of the detection of clipped ATC transmissions at the point of receipt, it was noted that the type of voice recording equipment in use at Toronto ATC recorded very marginally more speech than would be received by an aircraft crew. Whilst this would not normally be a significant matter, in this case it had contributed to what could have been a potentially erroneous understanding of what would have been heard if not recognised.
Safety Action taken as a result of the Investigation was documented as including a reiteration by the Airport Operator of an existing prohibition on "leaving vehicles idling and (not secure) on the airside" and action by them to ensure vehicle beacons were operative and effective, the latter by improving clarity on the required minimum luminosity.
The Investigation also noted that although upgrading of the ASDE system to an A-SMGCS with an enhanced RIMCAS component occurred at the end of the summer in 2013, this change was not a consequence of the investigated event. However, it was noted that the new system did bring a reduction in false targets and integration with other sensors such as those enabling vehicle tracking and multilateration as well as a more effective RIMCAS.
The Final Report was authorised for release by the Board on 21 May 2014 and officially released on 30 July 2014. No Safety Recommendations were made as a result of the Investigation