Airspace infringement occurs when an aircraft enters notified airspace without previously requesting and obtaining clearance from the controlling authority of that airspace, or enters the airspace under conditions that were not contained in the clearance.
Notified Airspace includes controlled airspace structures in ICAO airspace classes A to E, such as Airways, Terminal Control Areas (TMAs), Control Zones (CTRs) or aerodrome traffic zones (ATZ) outside controlled airspace, as well as restricted airspaces, such as danger areas, restricted areas, prohibited areas and temporary segregated/reserved areas.
It should be noted that VFR traffic cannot infringe class E airspace because, under ICAO rules, neither an ATC clearance nor radio communication is required to enter or operate within it, unless filed national differences call for one or the other (or both). Traffic following instrument flight rules (IFR) can infringe class E airspace when not in receipt of a clearance to enter it.
Although VFR flights do not require clearance to enter Class E airspace, serious incidents have occurred between VFR and IFR flights in such airspace due largely to limitations in the “see-and-avoid” principle. Therefore this type of incident is also being addressed by airspace infringement prevention initiatives.
All classes of aircraft are prone to airspace infringement, but the majority of incidents recorded involve General Aviation (GA). This is unsurprising, as most GA VFR flights are conducted outside controlled areas and zones, and are in general flown by less trained and less experienced leisure pilots; whereas IFR flights are usually conducted within controlled airspace and carried out under the supervision of ATC units.
- Mid-Air Collision
- Loss of Separation from other aircraft. An infringement leading to loss of separation may also cause Loss of Control due to wake vortex encounter and could result in injuries to passengers or crew when violent manoeuvres are needed to avoid the other aircraft.
- Disruption to flight operations. An infringement can significantly increase controller and pilot workload due to the need to break-off an approach, change aircraft sequence for landing or implement other contingency measures. Any disruption to flight operations is likely to have adverse environmental and economic impact due to increased fuel burn by aircraft, both in the air and on the ground, which are subject to delays .
- Exposure to danger from military hazards, e.g. radiation, gun-firing or manoeuvring high-performance aircraft.
- Perceived security risk of flight contrary to clearance which may result in a military response.
- Disruption of military or other special activities within restricted, danger or prohibited airspace.
- Enhanced Flight Information Service (FIS), based on the use of radar, provides services to VFR flights outside controlled airspace. Examples include Traffic Service (provides the pilot with traffic information on conflicting aircraft) and Deconfliction Service (provides the pilot with traffic information and deconfliction advice on conflicting aircraft) provided in the UK airspace.
- Accurate aircraft navigation systems, including conventional, BRNAV and PRNAV systems
- Hand held or mounted GPS equipment used in VFR flying on board light aircraft, provided that the pilot has a proper understanding of the right way to use it and is aware of its limitations.
- Use of aircraft transponders, especially those associated with encoding altimeters which enable ATC to identify traffic and can facilitate TCAS-based avoiding action.
- Ground based Safety Nets, such as Short Term Conflict Alert (STCA) and Area Proximity Warning (APW) that can alert controllers to hazardous situations and help mitigate the effects of infringements.
- Knowledge of and strict adherence to RTF procedures.
- Aircraft flying outside controlled or restricted airspace, etc. enters the airspace without clearance due to:
- Lack of awareness of existence of the airspace (lack of, or out-of-date maps, deficient briefing, etc.); or,
- Lack of awareness of the activation of airspace restriction; or
- Poor navigation performance (equipment or technique); or,
- Poor air-ground communication technique; or,
- Lack of understanding of procedure for obtaining clearance to enter.
- Aircraft flying outside controlled or restricted airspace enters it with or without awareness as a result of adverse weather avoidance
- Aircraft flying outside controlled or restricted airspace enters it as a result of misunderstanding or misinterpretation of ATC instructions or clearance.
- Poorly equipped aircraft (navigation and communication equipment).
- Inexperienced, inadequately trained or poorly performing pilots.
- Poor pre-flight preparation (out-of-date or inappropriate maps, NOTAM briefing, etc.).
- Over-reliance on GPS equipment or failure to use it effectively
- Adverse weather.
- Airspace and Procedure Design which constrains uncontrolled air traffic into corridors of limited horizontal and/or vertical dimension.
- Unfavourable attitude of air traffic controllers to VFR flights, leading to poor comumnication.
- Routine (assumption that airspace restrictions on a familiar route will not change) or Complacency.
- Improve airspace infringement awareness;
- Improve pilot's navigation and communication skills by raising the standard of pilot training, emphasising the importance of and developing the ability to ensure:
- Enhance Flight Information Services to VFR flights based on the use of radar in areas where airspace infringement is common;
- Implement safety nets, such as APW that can alert controllers of potential or actual infringements;
- Improve the availability and accessibility of aeronautical and meteorological information to VFR flights;
- Review airspace design where repetitive airspace infringement occur with the objective of removing features which appear to have contributed to such incidents;
- Encourage or mandate the use of high quality aircraft systems for navigation and communication, including transponders;
- Improve cooperation at local level between ATS providers, GA establishments and the military.
Accidents and Incidents
The following events recorded on SKYbrary involved an incursion into controlled airspace:
On 13 October 2019, an Airbus A320neo inbound to Zurich had been cleared to the lowest available Class ‘C’ airspace level when a light aircraft crossing its intended track below in uncontrolled airspace began to climb into the same Class C airspace without clearance. An ATC Conflict Alert was activated and the controller put the A320 on an avoidance radar heading and safe separation was thereby achieved. The reason for the incursion was not determined but the event was considered yet another example of yet-to-be-addressed airspace infringement risk and a corresponding safety recommendation was made to the State Safety Regulator.
On 4 July 2019, the operator of an Alauda Airspeeder UAV lost control of it and it climbed to 8000 feet into controlled airspace at a designated holding pattern for London Gatwick before falling at 5000 fpm and impacting the ground close to housing. The Investigation was unable to establish the cause of the loss of control but noted that the system to immediately terminate a flight in such circumstances had also failed, thereby compromising public safety. The approval for operation of the UAV was found to been poorly performed and lacking any assessment of the airworthiness of the UAS.
On 20 July 2014, the pilot of a VFR Cessna 172 became distracted and entered the Class 'C' controlled airspace of two successive TMAs without clearance. In the second one he was overtaken by a Boeing 738 inbound to Copenhagen with less than 90 metres separation. The 738 crew reported a late sighting of the 172 and seemingly assessed that avoiding action was unnecessary. Although the 172 had a Mode C-capable transponder, it was not transmitting altitude prior to the incident and the Investigation noted that this had invalidated preventive ATC and TCAS safety barriers and compromised flight safety.
On 11 August 2012, the augmenting crew member in the flight deck of an Airbus A340 about to join final approach to Zurich in Class 'C' airspace as cleared suddenly saw a glider on a collision course with the aircraft. The operating crew were alerted and immediately executed a pronounced avoiding manoeuvre and the two aircraft passed at approximately the same level with approximately 260 metres separation. The Investigation attributed the conflict to airspace incursion by the glider and issue of a clearance to below MRVA to the A340 and noted the absence of relevant safety nets.
On 26 July 1999, an ATR 72-200 being operated by Mount Cook Airlines on a scheduled passenger flight from Christchurch to Queenstown entered the destination CTR without the required ATC clearance after earlier cancelling IFR and in marginal day VMC due to snow showers, separation was then lost against a Boeing 737-200 being operated IFR by Air New Zealand on a scheduled passenger flight from Auckland to Queenstown which was manoeuvring visually (circling) after making an offset VOR/DME approach in accordance with a valid ATC clearance.
EUROCONTROL Airspace Infringement Initiative
EUROCONTROL Guidance Notes for GA pilots