Entering Controlled Airspace
Infringement of controlled airspace, danger and restricted areas and prohibited areas is a serious aviation hazard and occurs when an aircraft enters such airspace without necessary permission.
A significant cause of airspace infringement is that some pilots are not familiar with the correct procedure for entering controlled airspace and do so without clearance. This article deals with international regulations concerning entering controlled airspace.
National regulations may differ in detail but will follow the same general rules.
ICAO Annex 2: Rules of the Air
The Rules of the Air state that clearance must be obtained before an aircraft enters controlled airspace (with the exception of a VFR aircraft entering class "E" airspace). All aircraft wishing to enter controlled airspace must file a flight plan, either on the ground before flight, or in the air, and the air traffic services involved must receive the request at least 10 minutes before the expected time of entry. (See ICAO Annex 2, Chapter 3, Section 3.3)
Getting clearance may take a little time; the controller has other jobs to do and may be dealing with a more urgent task - perhaps on another frequency, and he/she has to check the position and level of other aircraft before giving clearance. That is why the request must be made at least 10 minutes before entry time.
- An aircraft must not enter controlled airspace until clearance has been received.
- It is not sufficient that the pilot has informed the controller of his/her request; entry must await receipt of formal clearance;
- The aircraft must stay clear of controlled airspace while awaiting clearance.
How to Ask for Clearance
A pilot wishing to enter controlled airspace should call the ACC responsible for the controlled airspace concerned using the frequency specified in the AIPs or Flight Information Publication.
The initial call should be made at least 10 minutes before the point of entry, and should consist of the aircraft call sign followed by a brief statement of the request.
“Zenda Control ABCDE, request crossing of A1 at Benton”.
The controller will reply, saying either:
“ABCDE, Zenda Control, Standby”, or
“ABCDE, Zenda Control, pass your message”.
If the reply was “Standby”, then clearance has not been given and the aircraft must wait, keeping out of controlled airspace.
If the reply was “pass your message”, then the following information should be passed:
- aircraft call sign and type,
- present level,
- flight conditions,
- crossing position,
- requested crossing level, and,
- estimated time at the crossing position.
“Zenda Control ABCDE is a Cessna 172, 25 miles West of Benton heading 100, FL 70 VMC, request crossing clearance of airway A1 at Benton FL 70 at 1023.”
Clearance may not be granted straight away, because the controller has to check the position and levels of other traffic. Until clearance is received, the aircraft must stay clear of controlled airspace.
When the controller passes the crossing clearance, the pilot must read it back so that he/she can check that it has been copied correctly.
The clearance may not be exactly the same as was requested, but it must be obeyed. For example, if the clearance was at a different flight level from that requested, the aircraft must climb or descend to the cleared level before entering controlled airspace. If the pilot is unable to comply with the clearance (e.g. if doing this will cause a VFR flight to enter IMC or due to the aircraft being unable to climb), they must advise the controller and receive an alternative clearance. The aircraft must remain outside controlled airspace until the process is complete.
Accidents and Incidents
This section contains events where aircraft entered controlled airspace without obtaining ATC clearance.
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.
On 27 January 2005, two USAF-operated McDonnell Douglas F15E fighter aircraft, both continued to climb and both passed through the level of an Embraer 145 being operated by British Airways Regional on a scheduled passenger flight from Birmingham to Hannover, one seen at an estimated range of 100 feet.
On 15 October 2008, following participation in a military exercise over East Anglia (UK), a formation of 2 foreign Eurofighters entered busy controlled airspace east north east of London without clearance while in the process of trying to establish the required initial contact with military ATC, resulting in loss of prescribed separation against several civil aircraft.
On 19 December 2002, a Piper PA-46 Malibu, after takeoff from Son Bonet Aerodrome, penetrated the control zone (CTR) of Palma de Mallorca tower. The pilot was instructed to leave the CTR and the aircraft headed towards mountainous terrain to the north of the island where the flight conditions were below the VFR minimum. In level flight the aircraft impacted terrain at an altitude of 2000 ft killing all three occupants.
- ICAO Annex 2: Rules of the Air, Chapter 3, Section 3.3;
EUROCONTROL Airspace Infringement Initiative
EUROCONTROL Guidance Notes for GA pilots