Introduction In order to better understand the safety environment in Class G airspace, this paper collects and analyses data on mid-air collisions within the UK FIR involving UK registered civil aircraft. The data was extracted from the CAA MORS database and merged with the BGA accident database. Details of known accidents to equivalent civil aircraft and gliders operated by military personnel were added.
Aim The aim of this paper is to inform discussion on Class G airspace safety.
Nature of Data The data spans the whole range of operations in Class G airspace but accidents involving aircraft that were deliberately flown close together such as in formation, in displays and in air racing, are not relevant to airspace safety. Although they are recorded in the data they are omitted from the analysis together with 2 collisions involving hang-gliders. The remainder of occurrences are relevant to the analysis of safety in Class G airspace. The accidents involving 3 Grob115 aircraft operated by the RAF are included as they were civil registered and are equivalent to civil aircraft. Gliders operated by Air Cadets are equivalent to civil gliders and a single known accident is included.
It is possible to categorise all MORS and BGA collisions into those that occur during take-off, landing, departure and approach and those that occur away from the airfield or site either in the cruise or manoeuvring in an operating area. The BGA data also categorises collisions involving gliders into those which occur in local thermals, on local ridges or in cross country thermals. Whilst aeroplanes and helicopters operate local flights the nature of their activity is generally closer to the cruise regime than to the local thermal or ridge flight of gliders. For analysis against phase of flight, gliders using local thermals and ridges are treated as a separate group. Gliders using cross country thermals are included in the “cruise” group together with aeroplanes and helicopters manoeuvring and performing non-display aerobatics.
For brevity, civil aeroplanes and helicopters, including SLMGs operating as aeroplanes, are referred to as powered aircraft in the data.
Data Analysis The data is set out in Annex A covering all known collisions between 1975 and 2011 (37 years). The first worksheet lists all collisions with those involving deliberate close flight marked in brown and the 2 hang glider collisions marked in blue; they are discounted from the subsequent analysis. The second worksheet analyses the remaining data by type of aircraft and by phase of flight. To properly analyse the interaction between different classes of aircraft it is necessary to consider the accident to each aircraft as the basic entity rather than to count the number of collisions. Readers should note the difference between the number of collisions and the number of aircraft involved.
There is no recorded collision involving a commercial air transport aircraft in Class G airspace. In the 37 years since 1975 a total of 218 aircraft have been involved in 108 mid-air collisions of which 45 involved 86 fatalities. Disregarding hang gliders and the events which are irrelevant to the analysis of airspace safety leaves 178 aircraft involved in 89 collisions, 38 of which involved 74 fatalities.
Of the 178 aircraft involved, 72 were powered aircraft, 6 were glider tugs, 96 were gliders, and 4 were military. The military aircraft were 2 Tornados, 1 Tucano and 1 A-10
Collisions by Type: The 72 powered aircraft collided with:
4 military aircraft.
The remaining 62 powered aircraft collided with each other.
The 6 glider tugs collided with:
The 96 gliders collided with:
6 powered aircraft.
6 glider tugs.
The remaining 84 gliders collided with each other.
The 4 military aircraft collided with:
4 powered aircraft.
For powered aircraft which are not glider tugs the overall collision rate is 1.95 individual aircraft per year and 0.62 fatalities per aircraft:
The rate of collisions with gliders is 0.16 aircraft per year.
The rate of collisions with other powered aircraft is 1.68 aircraft per year.
For gliders the overall collision rate is 2.59 individual gliders per year and 0.26 fatalities per aircraft:
The rate of collision with powered aircraft is 0.16 aircraft per year.
The rate of collision with other gliders is 2.27 gliders per year.
Collisions by Phase of Flight: Of the 72 powered aircraft:
There were no glider/glider collisions in the cruise phase of flight.
The 6 glider tugs collided with gliders in the vicinity of the launch point
The 4 military aircraft collided with powered aircraft in the cruise at low level.
Context To place these accident rates in context it is necessary to compare them with the overall GA accident rates calculated on a similar basis. CAP 667, the review of fatal accidents 1985 to 1994 notes that accidents occurred to over 250 GA aeroplanes per year, excluding microlights and gliders and there were 28 fatalities per year. Adding the average number of accidents to BGA gliders in the same period (154 accidents and 3.4 fatalities per year) provides an equivalent total of some 400 aircraft accidents with 31.4 fatalities per year. This compares with 4.73 aircraft involved in collisions with 2 fatalities per year; approximately 1% of all accidents and 6% of all fatalities.
Conclusion Predominately, powered aircraft collide with other powered aircraft and gliders collide with other gliders. In 37 years only 6 collisions occurred between powered aircraft and gliders, 3 during launch site/ATZ transits by powered aircraft, 1 during powered aircraft aerobatics and 2 in cruising flight.
Whilst 49% of powered aircraft collisions occur in cruising flight, only 3% of glider collisions occurred in the cruise, all with powered aircraft. No gliders have collided with other gliders in cruising flight.
Collisions appear to be closely related to traffic density with 56% of powered aircraft collisions occurring over or near an airfield and glider collisions being divided 91% over or near the launch site and 9% in cross country thermal or cruise
Collisions account for approximately 1% of all GA accidents and 6% of fatalities.