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B752/GLID, vicinity Glasgow UK, 2011

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On 23 July 2011 a Boeing 757 in Class ‘E’ airspace east of Glasgow in VMC encountered a glider ahead at the same altitude and deviated right to avoid a collision. The glider, climbing in a thermal, had not seen the 757 until it passed during avoiding action. The closest proximity was estimated as 100 metres at the same level as the glider passed to the left of the 757 in the opposite direction. Since the circumstances were considered to have demonstrated a safety critical risk by the UK CAA, an interim airspace reclassification Class ‘D’ was implemented
Event Details
When July 2011
Actual or Potential
Event Type
Human Factors, Loss of Separation
Day/Night Day
Flight Conditions VMC
Flight Details
Aircraft BOEING 757-200
Operator Thomson Airways
Domicile United Kingdom
Type of Flight Public Transport (Passenger)
Origin Verona Villafranca Airport
Intended Destination Glasgow International Airport
Take off Commenced Yes
Flight Airborne Yes
Flight Completed Yes
Flight Phase Descent
Flight Details
Aircraft Various Glider
Operator Private
Type of Flight Private
Intended Destination XPMK
Take off Commenced Yes
Flight Airborne Yes
Flight Completed Yes
Flight Phase Manoeuvring
Location - Airport
Airport vicinity Glasgow International Airport
Tag(s) Airspace Design
Tag(s) Ineffective Monitoring,
Manual Handling
Tag(s) Required Separation not maintained,
Released to Own Separation,
Near Miss
Damage or injury No
Causal Factor Group(s)
Group(s) Aircraft Operation
Safety Recommendation(s)
Group(s) None Made
Investigation Type
Type Independent


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.

Safety Action

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.

Further Reading