Description

On 28 January 2019, an Embraer 170-200 (C-FEJB) being operated by Sky Regional Airlines on a scheduled international passenger flight from Toronto to Dallas Fort Worth as SKV7665 had been cleared to take off on runway 06L in normal day IMC when a convoy of snow clearance vehicles got lost and crossed a holding point for the same runway. The aircraft was instructed to reject takeoff having reached approximately 110 knots and stopped 60 metres from the lead vehicle which itself had stopped just clear of the actual runway after multiple ATC calls to do so following activation of an automatic incursion alert.

Investigation

An Investigation was carried out by the Canadian Transportation Safety Board (TSB) using data downloaded from the CVR and FDR of the aircraft involved and recorded ATC voice and radar data.

What Happened

A group of three snow plough/sweepers and one snow blower were engaged in taxiway snow clearance. Driver forward visibility was reduced due to blowing snow and there was accumulated snow on the manoeuvring area which had in places obscured surface paint markings and embedded centreline and holding position lighting. The GND controller was relying on their A-SMGS display for airside movement control and this uniquely identified all airside vehicle and aircraft positions based on their transponder transmissions. The snow clearance vehicles were operating as a group led by a vehicle using the call sign ‘Plough 862’ and the driver of this vehicle was responsible for ATC communications for the group although all vehicles had the same VHF radio capability and were able to monitor ATC communications. However, it was subsequently found that ‘Plough 862’ was actually transmitting its radar position identity as ‘Plough 170’ and this was therefore how it was shown on the GND controller’s radar display.

The snow clearance vehicle group was proceeding south on taxiway ‘E’ and was instructed to turn left onto Taxiway ‘C’, the eastbound taxiway parallel to runway 06L to continue snow removal operations there. The vehicles reached the taxiway ‘E’/’C’ intersection and briefly turned to the right to dump some of the snow near the southern edge of taxiway ‘C’ before beginning the left turn. However, the lead vehicle then failed to turn sufficiently left and instead inadvertently entered taxiway ‘C2’ and, followed by the other three vehicles continued towards runway 06L (see the illustration below).

The lead vehicle approached and then crossed the runway 06L holding point and was followed by the other vehicles in the group. All the drivers subsequently stated that they had not seen any of the associated lights or visual cues which mark the holding point. As this was happening, the Embraer 170 was cleared for takeoff from the beginning of runway 06L with the reported RVR being reported as 900 metres. Since the intersection of taxiway ‘C2’ and the runway was approximately 1370 metres ahead, the crew had been unable to see it from the threshold.

The actual and intended routes of the vehicle group at the taxiway ‘E’/‘C’ intersection. [Reproduced from the Official Report]

Shortly after the takeoff roll had begun, the RIMCAS (Runway Incursion Monitoring and Collision Avoidance) stop-bar overrun alert in the control tower was activated and the GND controller saw from their radar display that the snow clearance vehicle group was crossing the holding position on taxiway ‘C2’ led by a vehicle with the callsign ‘Plough 170’. He therefore instructed ‘Plough 170’ to hold position but the driver of ‘Plough 862’ did not recognise that this instruction was intended for him and when the vehicles did not stop, the GND Controller repeated his instruction, this time using the words “Plough 170 Stop”. When the vehicles still continued, he transmitted “Plough 862 Stop”, but in the absence of an immediate response and with three of the four vehicles having now passed the runway 06L holding point, he then repeated the instruction and the group stopped moving. The GND Controller then transmitted “you are on the runway, hold position there”. The lead vehicle was just over 80 metres beyond the holding point but still approximately 30 metres from the edge of the actual runway.

At about the same time as the GND Controller began to instruct the vehicle group to stop, the south TWR controller instructed the Embraer 170 to “abort”. Its crew subsequently reported that although they could not see the vehicle incursion ahead, having reached an airspeed of 110 knots, they had immediately taken action and had come to a stop on the centreline of the 60 metre-wide runway, approximately 60 metres before its intersection with taxiway ‘C2’. This put then about 60 metres laterally distant from the vehicles (see the illustration below).

The ground radar display as it showed the stopped aircraft and vehicle group. [Reproduced from the Official Report]

The Context

It was noted that all of the vehicle operators involved in this event had “several years of experience operating various equipment, including snowploughs, on the airport manoeuvring areas”.

The GND Controller involved had approximately 15 years’ experience of which the previous 18 months had been gained at Toronto. Given the reduced visibility and the addition to normal traffic of numerous snow removal vehicles working on the manoeuvring areas, his workload was assessed as having been “high and complex”. The TWR controller involved had 14 years’ experience of which 9 years had been gained at Toronto and it was the first time he had ever instructed a departing aircraft to reject a takeoff when at high speed.

The GND controller was used to mobiles not transponding with the same identity as their designated identity and it was noted that whilst the Unit OM describes controllers’ responsibilities and responses if an aircraft transponder tag on their radar display does not match its call sign, it contained no similar procedures if a vehicle transponder tag on screen does not match its call sign. It was further noted that prior to the introduction of the A-SMGCS, the (ASDE) ground radar display had been derived from primary radar with no vehicle identity tags and vehicle call signs input manually on a virtual progress strip embedded in the Extended Computer Display System (EXCDS) to which controllers could refer. This system had led to controllers becoming used to seeing vehicles without associated tags. Once A-SMGCS arrived and vehicles increasingly became equipped with transponders, ground radar display screens began to show vehicle tags or call signs. If a vehicle’s display tag was incorrect, “controllers simply referred to the EXCDS for the appropriate call sign”. They did not track the number of incorrect tags/call signs so there was no way of knowing how frequently this was happening. So when the GND Controller twice got no response to his ‘stop’ call addressed to ‘Plough 170’, he checked the EXCDS display, saw what the correct call sign for the lead vehicle was and addressed his third and fourth ‘stop’ calls to the vehicle group to with the prefix ‘Plough 862’.

The RIMCAS which was activated in this event when the holding point was crossed without clearance only provided an alert (both aural and visual) once the holding point illuminated stop bar had been crossed when illuminated red. At the time of the incursion, both the illuminated stop bar and the holding point markings were obscured by snow but the two elevated stop bar lights installed near each runway edge at the holding point and which were unobstructed were not seen by the lead vehicle driver although it was reported (but not confirmed) that only one light of each pair was working. It was noted that whilst the intensity of all airside lighting was adjustable from level 1 (lowest) to level 5 (highest), no records of the intensity set were kept, although the intensity setting at the time was reported to have been level 5.

In respect of the TWR Controller’s instruction to the Embraer 170 to “abort” its takeoff, it was noted that the crew response had been prompt and effective. However, it was found that the Manual of Air Traffic Services (MATS) stated that the qualification “immediately” should be used only “when immediate action is required for safety reasons” and did not specifically recommend using this phraseology to emphasise urgency in an instruction to abort a takeoff which had already been identified of more general concern. It was found that in the matter of rejected takeoffs, Canadian ATS phraseology, lacking any requirement for attention-getting enhancements such as use of the word “immediately” or repeating the instruction, was at variance with the corresponding phraseology contained in ICAO Doc 4444 PANS-ATM which uses both options (the emphasis is in the original) “STOP IMMEDIATELY (repeat aircraft call sign) STOP IMMEDIATELY”.

It was, however, noted that whilst the current Investigation was in progress, the TSB had, in the course of a Safety Issue Investigation into a group of 27 runway incursions at Toronto in July 2019, made Safety Recommendation A18-04 to ANSP NAV CANADA to amend its phraseology guidance for safety-critical instructions such as a high speed rejected takeoff to ensure it was “sufficiently compelling” to attract attention of flight crew. This Recommendation had since been addressed by a new requirement to include repetition as the means to emphasise urgency but it had not yet been introduced.

In respect of vehicle driver position awareness, especially in poor visibility conditions, it was noted that “they did not have access to any real-time navigation displays such as moving maps or a GPS to assist”. However, all the drivers involved had understood the ATC clearance they had been given and had known where they were and where they were supposed to go before making the incorrect turn onto taxiway C2. Each of the vehicles had a VHF radio capable of communicating with ATC and the operators also had handheld radios capable of communicating with each other yet still followed the lead driver onto the runway after listening to the GND Controller’s clearance.

The Investigation looked at how the lead vehicle transponder had come to be transmitting an identity which did not match the actual identity of the vehicle on which it was installed. It was found that the task of installing transponders on airport authority airside vehicles was outsourced to a contractor by the airport authority and that the transponder installed on Plough 862 had originally been installed on another snowplough, Plough 170 and had been removed and installed on Plough 862 six weeks prior to the investigated event. The Airport Authority SOPs for the contractor’s transponder installation task required that after installation of a previously installed transponder, its code must be checked to ensure that the transmitted signal was correct. In the case of the transponder on Plough 862, the necessary reprogramming and validation check had been omitted. There were also no procedures in place for ATC to report cases of transponder code/vehicle identity mismatch to the Airport Authority.

The Investigation was led to understand that when the vehicle transponder installation programme had first started, “controllers would often challenge a vehicle that had an incorrect or a missing transponder code” but as these instances were not recorded and less feedback was communicated to the Airport Operator, they “assumed that fewer errors were occurring”. It was noted that early on in the development of the vehicle transponder project a mismatch between vehicle identity and transmitted code had been identified as a risk with the appropriate corrective action being the development of robust SOPs.

Finally, it was noted that the TSB had carried out 10 Runway Incursion Investigations including the Safety Issue Investigation focused on the recurrent incursions at Toronto and had also initiated investigations into two other runway incursion events concurrently with this one. Whilst accepting that it is a long time (1978) since there has been an accident as a result of a runway incursion in Canada, it was observed that “the potential consequences of such a collision could be catastrophic.” It was noted that “the rate of runway incursions in Canada and the associated risks of collision will remain until effective defences tailored to address previously identified hazards are implemented at airports and in aircraft, vehicles, and air traffic service facilities across Canada”.

The five formally-stated Findings as to Causes and Contributing Factors were as follows:

1. The transponder installed on the lead vehicle was had not been updated to remove the code from the vehicle on which it had previously been installed. As a result, the incorrect code was shown on the ground controller’s display.
2. NAV CANADA did not have procedures in place to track or report vehicle transponder errors to the Greater Toronto Airports Authority.
3. Due to the reduced visibility in blowing snow, the operator of the lead vehicle was not aware that the vehicle was on Taxiway C2 as it approached the holding position. As a result, the operator was not looking for, nor expecting to see, any of the visual cues that would have alerted him that the vehicle was approaching an active runway.
4. Because some of the visual cues marking the holding position (which was crossed) were obscured by snow and others may not have been working, these cues were not conspicuous enough to alert the operator of the lead vehicle to its proximity to the runway. As a result, the vehicle and the two vehicles following entered the runway protected area.
5. The GND controller recognised the incursion by the lead vehicle and instructed it to stop 4 times; however, the first two instructions were addressed to the wrong callsign - Plough 170 rather than Plough 862. Immediately after the ground controller used the correct call sign, the lead vehicle came to a stop 10 seconds and 82 metres after crossing the holding point on Taxiway C2.

A formally-stated Finding as to Risk was also made as follows:

• If air traffic controllers use abbreviated phraseology when issuing safety-critical instructions, there is a risk that the instruction will not be recognized or followed by flight crews.

One ‘Other Finding’ was also made:

• The vehicle operators did not have access to any real-time navigation displays to assist with navigating the various taxiways and runways, such as moving maps or a global positioning system.

Safety Action taken as a result of the investigated event prior to the completion of the Investigation was noted as having included the following:

• The Airport Operator amended its SOPs relating to the changing of vehicle transponders to require that after installing a unit, the contracted service provider involved confirms with ANSP NAV CANADA that the vehicle's transponder call sign is correct and not mismatched when displayed on ATC systems.

The Final Report of the Investigation was authorised for release on 22 April 2020 and it was officially released on 12 May 2020. No new Safety Recommendations were made.

Related Articles

• Runway Incursion
• Rejected Take Off
• Rejected Take Off: ATC Considerations
• Standard Operating Procedures (SOPs)
• Transponder

Further Reading

• Air Transportation Safety Issue Investigation Report A17O0038: Runway Incursions Between the Parallel Runways at Toronto/Lester B. Pearson International Airport, Ontario, TSB Canada, 31 Jan 2019