History of the Flight
On 29 August 2006, a DHC-6 Twin Otter (registration G-BVVK) and an Embraer EMB-145EU (registration G-EMBV) were involved in a runway incursion incident at Glasgow Airport. The DHC-6 was operating a commercial passenger flight from Campbeltown and had landed on Runway 27, then backtracked and held at holding point Y1. The commander applied toe brakes but did not set the parking brake. The aerodrome controller cleared the DHC-6 to cross Runway 23 after the landing Embraer, and the clearance was correctly read back.
While waiting for the Embraer to land, the DHC-6 commander, a training captain, discussed training points with the co-pilot, requiring both to look inside the flight deck. After the discussion, the commander thought they had been stationary for some time and could not see the Embraer, concluding it had likely passed. He cautiously moved forward to cross Runway 23. As he approached the runway edge, he saw the Embraer about to touch down and immediately selected the power levers into Beta range, reversing the aircraft back toward Y1. The Embraer crew saw the DHC-6 just before touchdown but believed it was stationary and did not consider it a hazard, landing normally.
RIMCAS Operation
Glasgow Airport was equipped with a Runway Incursion Monitoring and Confliction Alerting Sub-system (RIMCAS) that monitored surface movements. At the time of the incident, visual operations were in progress, and only Runway 05/23 was active. The RIMCAS was set to Visual mode for Runway 05/23, which monitors only the runway surface area. Since the DHC-6 did not fully enter the runway and the Cross Runway or Low Visibility Procedures modes were not selected, no alert was triggered when the aircraft crossed the Y1 holding point. The controllers were unaware that in Visual mode, the areas between the holding points and the runway edge were not defined for monitoring, contrary to their perception.
Analysis and Conclusion
The AAIB analysis stated that the runway incursion was caused by the DHC-6 flight crew diverting their attention from outside monitoring to discussing training matters. When the commander looked up, he had a false sense of the time spent at the holding point and believed the Embraer had landed and passed. His cautious move forward and continuous lookout allowed him to see the landing aircraft and stop before entering the runway. The DHC-6's ability to reverse enabled the commander to move away from the runway.
The aerodrome controller had seen the DHC-6 stationary at Y1 and, when checking the runway before clearing the Embraer to land, the DHC-6 was still at the holding point. The controller did not notice the cautious forward movement, and because the aircraft did not fully encroach, the runway appeared clear. The controller expected a RIMCAS alert when the DHC-6 crossed Y1, but no alert occurred due to the selected mode.
Safety Action
Following the incident, NATS took immediate action to ensure controllers correctly understood RIMCAS capabilities, particularly the defined areas covered by different modes. NATS also extended awareness training to clarify that when only one runway is active in Visual mode, the monitoring area does not include the holding point zones.