Vehicle, Singapore Changi Singapore, 2022

Vehicle, Singapore Changi Singapore, 2022

Summary

On 3 June 2022, an Airport Rescue and Fire Fighting Service utility vehicle inadvertently entered an active runway at night when intending to drive along its parallel taxiway after becoming confused about their routing. On reaching the clearly identified runway holding point but requesting permission to access the intended taxiway, the controller turned off the illuminated stop bar and the vehicle was briefly driven onto the runway before the driver realised their error and made a U turn to exit. The incursion activated visual and aural warnings but these were both inexplicably missed by the controller and their supervisor.

Event Details
When
03/06/2022
Event Type
HF, RI
Day/Night
Night
Flight Conditions
On Ground - Normal Visibility
Location - Airport
Airport
HF
Tag(s)
Procedural non compliance
RI
Tag(s)
ATC error, Accepted ATC Clearance not followed, Runway Crossing, Vehicle Incursion, Visual Response to Conflict
Outcome
Damage or injury
No
Non-aircraft damage
No
Non-occupant Casualties
No
Off Airport Landing
No
Ditching
No
Causal Factor Group(s)
Group(s)
Air Traffic Management
Airport Operation
Safety Recommendation(s)
Group(s)
Air Traffic Management
Airport Management
Investigation Type
Type
Independent

Description

On 3 June 2022, a utility vehicle being operated by the Airport RFFS failed to follow its planned route when transiting from one airside fire station to another in normal night visibility and having become lost was then given access to an active runway from which an aircraft was about to depart. The crew of that aircraft alerted the runway controller to the incursion and the vehicle eventually regained its planned route and reached its intended destination.  

Investigation

An Investigation was carried out by the Singapore Transport Safety Investigation Bureau (TSIB). Recorded information from A-SMGCS and other ATC sources was available. The 33 year old Runway Controller involved had 7 years experience as a controller of which five years had been at Changi. The 53 year-old TWR Supervisor had 28 years experience as a controller, all at Changi. The 30 year-old vehicle driver had held a Category 1 Airfield Driving Permit since 2018 and their 33 year-old passenger had been similarly qualified since 2015.

What Happened

The driver of an Airport RFFS Utility Vehicle with a passenger on board planned to travel from Fire Station 2 situated to the south of the mid-point of runway 02C/20C (Runway 2) to Fire Station 3 situated to the south of the mid-point of runway 02R/20L (Runway 3). Instead of taking their usual route using the west perimeter, north perimeter and south perimeter roads to access parallel taxiway MY, from which Fire Station 3 could be accessed, they decided to use the west and north perimeter roads to reach the perimeter fence road to then reach taxiway Y2 and then turn left onto parallel taxiway MY. The illustration below shows both the usual and planned routes.

Vehicle Singapore Changi 2022 driver route

The driver’s usual (green) and planned (red) routes. [Reproduced from the Official Report]

The slightly shorter planned route had only become available four months earlier following the completion of construction works and the driver had become aware of it by word-of-mouth from his colleagues and had not previously used it. He understood that access to the final (taxiway) part of the new route would involve contacting the runway 3 (02R/20L) controller via walkie-talkie to request permission to enter taxiway ‘Y2’ as well as for permission to then turn left onto taxiway ‘MY’ towards Fire Station 3 (see the enlarged diagram showing this use of taxiways to complete the journey below). Once on taxiway ‘MY’ and approaching the position marked ‘Holding Position A’ on this diagram (which has a directional red stop bar visible only to aircraft/vehicles coming the other way) the driver was then required to inform the Runway 3 Controller that they were about to leave their area of responsibility and continue along the main part of taxiway ‘MY’ which is the responsibility of a Ground controller. The driver then had to establish contact with the designated Ground frequency to obtain permission to continue travelling on Taxiway ‘MY’ to complete its journey to Fire Station 3.  

Vehicle Singapore Changi 2022 taxiways and route

The transition from taxiway ‘Y2’ to taxiway ‘MY’ showing the driver’s actual (red) and intended (green) routes. [Reproduced from the Official Report]

The driver obtained permission from the Runway controller to proceed on taxiway ‘Y2’ and then turn left onto taxiway ‘MY’ but instead of making the required left turn, he continued from taxiway ‘Y2’ onto taxiway ‘MY1’ and reached the illuminated red stop bar at the runway 3 (02R/20L) holding point. He then called the runway controller to say (incorrectly) that he was approaching the holding position on taxiway ‘MY’ (where he was required to change to the ground frequency). Without checking the position of the vehicle, the Runway controller informed the driver that “the stop bar lights had been turned off” but added nothing more. Without realising that he was entering an active runway, the driver then did so.

Having switched off the taxiway ‘MY1’ stop bar, the Runway controller then “shifted her attention to a departing aircraft that was travelling towards runway 3 (02R/20L) on taxiway A1 from the opposite side of the runway and gave it takeoff clearance". Immediately after crossing the now unlit red stop bar and whilst believing that he was on Taxiway ‘MY’, the driver stopped and contacted the Ground controller to request permission to continue along taxiway ‘MY’ to Fire Station 3 and received this clearance. Whilst the driver was talking to the Ground controller, the Runway controller “tried to contact the driver to request him to confirm that he was on the runway (but) the transmission was garbled and the request was missed by the driver”. For unknown reasons, the Runway controller “did not pursue her request to the driver for a response and turned to other tasks”.

Then, whilst the driver was stopped on taxiway ‘MY1’ after crossing the unlit stop bar and talking to the Ground controller to obtain permission to continue on taxiway ‘MY’, the ‘MY1’ stop bar lights were illuminated again automatically which caused the presence of the vehicle to be detected by the Microwave Barrier Detector (MBD) which resulted in the A-SMGCS generating a visual alert indicating a runway incursion on the control screens of both the Runway controller and her Supervisor. The A-SMGCS also generated anural “Runway Incursion” alert at these two positions. However, both controllers subsequently told the Investigation that “they were not looking at the A-SMGCS screen and did not hear any aural warning”.

The flight crew of the aircraft that had been given a takeoff clearance for runway 20L by the Runway controller then requested confirmation of this clearance and were told to ignore it and instead instructed it to line up and wait which was acknowledged. As this aircraft was about to enter the runway, its flight crew saw the vehicle and having stopped their aircraft on taxiway ‘A1’, they alerted the Runway controller to the presence of a vehicle on the runway. At about the same time, the vehicle passenger “suddenly realised that the vehicle was on the runway and pointed this out to the driver”, who then quickly made a U-turn in order to exit the runway. On being alerted by the departing aircraft flight crew, the Runway controller looked out of the window and saw the vehicle on the runway and tried contacting the driver via walkie-talkie but got no response.

After U-turning on the runway and before exiting it, the driver stopped before crossing the runway holding position marking and made four consecutive attempts to contact the Runway controller via walkie-talkie to obtain permission to cross it. The fourth attempt elicited a response from the Runway controller who instructed him to vacate the runway immediately and the driver then crossed the runway holding position marking and turned right onto taxiway ‘MY’. On finally reaching the position marked ‘Holding Position A’ on the second diagram, the driver then obtained the necessary permission from the Ground controller to continue on taxiway ‘MY’ to Fire Station 3. It was estimated that the lost vehicle had remained on runway 20L for about one minute. 

The Conclusions of the Investigation were, in summary, formally documented as follows:

  1. The runway incursion was a result of the vehicle entering the runway after the Runway controller turned off the red stop bar lights at the runway holding position on taxiway ‘MY1’.
  2. The driver lost situational awareness. He was not familiar with the roadways around the aircraft manoeuvring area at taxiways ‘Y2’ and ‘MY’ and did not prepare adequately for using roadways in an unfamiliar area.     
  3. There were markings on the ground and signs on either side of the red stop bar lights at the runway holding position on taxiway ‘MY1’ to indicate that runway 20L was ahead. However, the driver did not look out for the signage as he was referring to his hand held phone to see the communication wording needed for contact with the Runway controller. This showed that he had not prepared himself adequately before beginning his journey using a new and unfamiliar route.
  4. The aerodrome operator’s driving rules only allow the driver to operate the radiotelephony set in vehicles which prevents any passenger who is also the holder of a Category 1 Airfield Driving Permit and therefore constitutes a qualified and useful resource to the driver from assisting with ATC communications.
  5. The Investigation team could not understand the Runway controller’s actions in turning off the red stop bar lights at the runway holding position on taxiway ‘MY1’, in subsequently trying to contact the driver to request him to confirm if he was still on the runway and in not pursuing a response from the driver. It seems as though she was not paying attention to her tasks in respect of scanning the runway through the control room window and correlating this view with the traffic information displayed on the A-SMGCS display. The Runway controller also did not follow the standard operating procedures to scan the entire length of the runway before issuing take-off clearance to an aircraft.
  6. The A-SMGCS generated both an aural warning and a visual alert message for the runway incursion but these seemed to have limited effectiveness in alerting both the Runway controller and her Supervisor.

Safety Action taken as a result of this event was noted as having included, but not been limited to the following:

The Airport ANSP:

  • conducted a safety briefing for all its controllers with a focus on preventing runway incursions, the actions to be taken if one occurs, the need to scan the A-SMGCS display to enhance their situational awareness at night and the need to correlate the ‘out-of-the-window’ view with the A-SMGCS display.  
  • conducted simulator training sessions for all its aerodrome controllers covering runway incursion scenarios to refresh and enhance their ability to handle them.
  • increased the volume of the aural alarm at the Runway Control Supervisor’s position and at supervisory positions in other air traffic control cabins.

The Airport RFFS:

  • conducted training for all its drivers to refresh and enhance their ability to recognise signs and markings within the aircraft movement area.
  • imposed additional measures to control movement to and from Fire Station 3 which involve using only established routes and reporting any intended deviations; drivers using standard radiotelephony in communications with the service Watch Room prior to any vehicular movements and requiring Watch Room personnel to monitor the movements of all Fire Service vehicles in the aircraft movement area on their traffic movement display screen.
  • installed on all their vehicles operating airside a device that will alert drivers when their vehicles are near a runway.

The Airport Operator:

  • conducted a safety briefing for all its Category 1 Airfield Driving Permit holders on the occurrence and refreshed them on safe driving within the Aircraft Movement Area. 
  • published an ‘Airside Safety Notice’ about the investigated event and highlighted the importance of both route planning and the maintenance of situational awareness when driving airside.  

Three Safety Recommendations were made as a result of the Investigation findings as follows: 

  • that the Changi ANSP review its A-SMGCS alert system for the aural warning annunciation of a runway incursion to be more noticeable and repetitive. [TSIB RA2023-008]
  • that the Changi ANSP review its A-SMGCS alert system in respect of the aural and visual alerts for a runway incursion so that they cease only after being acknowledged by the user. [TSIB RA2023-009]
  • that Changi Airport Operator consider allowing a passenger who holds a CAT 1 Airfield Driving Permit to share a driver’s radiotelephony workload for better resource management. [TSIB RA2023-010]

The Final Report was published on 18 May 2023.

Related Articles

SKYbrary Partners:

Safety knowledge contributed by: