On 23 July 2011, a Boeing 757-200 being operated by Thomson AW on a passenger flight from Verona Italy to Glasgow was involved in a near miss with a Discus Glider whilst descending through 3450 feet QNH in Class ‘E’ airspace east of Glasgow and under radar control in day Visual Meteorological Conditions (VMC). The glider was working a local aerodrome frequency and had been observed intermittently on radar but with insufficient continuity to do other than to provide a general alert to the 757.
An Investigation was carried out by the UK Airprox Board. It was established that both aircraft had been in compliance with the operating requirements applicable to Class ‘E’ airspace and that at the time of the conflict, the white-coloured Discus BT glider had been climbing in a thermal during a cross country VFR flight from and returning to a designated gliding site at Portmoak located 44 nm north east of Glasgow Airport. The in flight visibility was reported to have been around 30 km.
The airspace involved was beneath Class ‘D’ airspace which commenced above 6000 feet and constituted a narrow corridor between adjacent blocks of Class ‘D’ airspace which extended on both sides below 6000 feet. The significant difference in Class ‘D’ for VFR traffic was noted to be the requirement to work the controlling ATC Unit and obtain a VFR clearance to operate, whereas there is no requirement for VFR traffic to work any radio frequency in Class ‘E’ airspace. It was found that the glider had a local non radar-equipped aerodrome frequency selected and was listening out with no evidence that he had called this facility. The glider was not fitted with a transponder.
The Glasgow radar controller had been vectoring traffic ahead of the 757 in the sequence around the same Discus glider but as it was unknown traffic, this was noted to be good practice in the circumstances, but more than the requirements of the MATS Part 1 (general procedures). However, by the time the 757 was released for a visual contact approach, the radar return from the Discus was no longer reliable. The 757 had turned left towards the Glasgow final approach and the controller had advised the crew that the Discus radar return had faded in the area they were about to fly through and advised them to keep a good lookout. With the benefit of this assistance, they had spotted the glider about 1.5nm ahead at the same level and made a prompt turn to the right to avoid it, estimating separation achieved as 100 metres. The glider pilot reported not having seen the 757 until it passed by in the opposite direction.
It was noted that NATS, the Glasgow ANSP, had previously submitted an Airspace Change Proposal for a reclassification of the part of the Glasgow CTA involved from Class 'E’ to Class ‘D’ on the basis that such action would enhance safety by establishing the airspace as a known traffic environment where all aircraft must be in contact with the controlling ATC unit.
As a result of the occurrence, and whilst the formal Investigation was still being concluded, the CAA Director of Airspace Policy (DAP), considering that “a safety critical risk existed” within the existing Glasgow Class ‘E’ CTA where the conflict had occurred, authorised an interim reclassification of this airspace from Class ‘E to Class ‘D’ to take effect on 16 September 2011.
The formal statement of Cause was given as: “A conflict between IFR and VFR traffic in Class E airspace, resolved by the B757 crew.”
The ICAO AIRPROX Risk Category (the actual risk after any avoiding action) was assessed as ‘B’.
The Final Report of the Investigation was published on 26 October 2011. In the light of the Safety Action already taken, no Safety Recommendations were made.