Entering Controlled Airspace
Entering Controlled Airspace
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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. Pilots should be aware that:
- 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,
- position,
- heading,
- 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 complied with. 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 28 May 2022, the crew of a Boeing 737-800 which had just taken off from Palma in good daylight visibility observed a light aircraft approaching from the right at high speed on a collision course and immediately initiated evasive action, achieving a minimum separation subsequently found to have been 116 feet vertically and 1,200 metres laterally and passing behind it. ATC radar showed that the other aircraft had not taken any action and it was found to have been operating on a VFR flight plan in controlled airspace without complying with the requirements for such access or listening out.
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.
Further Reading
ICAO
- ICAO Annex 2: Rules of the Air, Chapter 3, Section 3.3;
EUROCONTROL Airspace Infringement Initiative
- European Action Plan for Airspace Infringement Risk Reduction;
- Airspace Infringement Risk Analysis Part II;
- Watch your R/T checklist poster
EUROCONTROL Guidance Notes for GA pilots
- Rules for VFR flight;
- Flight preparation;
- Getting aeronautical information before flight;
- Reading and understanding NOTAMS;
- Getting meteorological information before flight;
- Reading and understanding weather reports and forecasts;
- Using meteorological information for planning;
- Visual navigation;
- VOR/DME/ADF Navigation;
- GPS Navigation;
- Getting aeronautical and meteorological information in flight;
- Entering controlled airspace;
- Getting the most out of your transponder;
HindSight Articles:
UK CAA
- Airspace & Safety Initiative
- General Aviation Safety Sense Leaflets
- On Track - A Confidential Airspace Infringement Project;
- CAP 1535: The Skyway Code, September 2017
Other
- IFR / VFR – Air Traffic in Airspace E, Sympathetic Cooperation, by BFU, December 2011
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