Separation & Airspace Safety is a vast domain at the crossroad of many topics: separation standards, safety risks analysis, collision modelling, advanced mathematics and many more.

As far as Air Traffic Control is concerned, it normally starts with national authorities laying down vertical and horizontal separation standards to facilitate the safe navigation of aircraft in controlled airspace. Observance of these standards ensures safe separation from the ground, from other aircraft and from protected airspace. Separation standards may sometimes serve to reduce exposure to Wake Vortex Turbulence although there are many occurrences of significant wake vortex encounter at separations much greater than prevailing minimum separation.

National separation standards are based on the provisions of ICAO Doc 4444 (Procedures for Air Traffic Management), especially Chapter 5. Differences from these standards (if any) are published in national AIPs. The methods used to achieve separation are varied and complex, depending on the phase of flight and the relative trajectories of the aircraft involved (Skybrary, 2019), but they are generally classified in three categories: vertical, lateral, and longitudinal separation.

Separation can be achieved by distance or time reports and/or estimates (commonly referred to as procedural separation) or can be achieved through electronic means such as radar, ADS-B or multilateration (M-LAT) (commonly referred to as surveillance separation).

 

 

A SHORT HISTORY OF THE ICAO SEPARATION AND AIRSPACE SAFETY PANEL

With the advent of commercial turbo jet aircraft operating at high levels and the need to re-evaluate the vertical separation minimum used at that time, the Vertical Separation Panel (VSP) was created in 1954. Later on, the need to review other separation minima due to the fuel shortage in the 70s generated the need to expand the tasks of the Panel and in 1971 the Review of General Concept of Separation Panel (RGCSP) met for the first time. The Air Navigation Commission agreed in 2000 that the Review of the General Concept of Separation Panel (RGCSP) be changed to the Separation and Airspace Safety Panel (SASP). The Commission considered that the change of the panel would better reflect the broad scope of the panel’s work programme and provided an appropriate emphasis on ICAO’s primary objective to ensure airspace safety while improving efficiency of operations. (ICAO, 2014)

 

Separation Concept

In summary, is the concept of keeping an aircraft outside a minimum distance from another aircraft to reduce the risk of those aircraft colliding, as well as prevent accidents due to secondary factors, such as wake turbulence. Separation can also apply to terrain, obstacles, and controlled airspace, wherein an aircraft must stay at a minimum distance from a block of airspace.

Air traffic controllers apply rules, known as separation minima, to do this. Pairs of aircraft to which these rules have been successfully applied are said to be separated: the risk of these aircraft colliding is therefore remote. If separation is at risk of being lost between two aircraft, they are said to be in a conflict.

When an aircraft passes behind or follows another aircraft, wake turbulence minima are applied due to the effect of the wingtip vortices of the preceding aircraft on the following aircraft. These minima vary depending on the relative size of the two aircraft. This is acute on final approach with a smaller aircraft following larger aircraft. (Wikipedia, 2020)

What are ATC clearances for?

A clearance issued by ATC is predicated on known traffic. An ATC clearance means an authorization by ATC, for the purpose of preventing collision between known aircraft, for an aircraft to proceed under specified conditions within controlled airspace. The pilot-in-command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft. If ATC issues a clearance that would cause a pilot to deviate from a rule or regulation, or in the pilot’s opinion, would place the aircraft in jeopardy, it is the pilot’s responsibility to request an amended clearance.

Similarly, if a pilot prefers to follow a different course of action, such as make a 360 degree turn for spacing to follow traffic when established in a landing or approach sequence, land on a different runway, take off from a different intersection, take off from the threshold instead of an intersection, or delay operation, the pilot is expected to inform ATC accordingly. When the pilot requests a different course of action, however, the pilot is expected to cooperate so as to preclude disruption of traffic flow or creation of conflicting patterns. The pilot is also expected to use the appropriate aircraft call sign to acknowledge all ATC clearances, frequency changes, or advisory information. (FAA, 2020)

For more information, visit one of the following WIKIFATCA pages:

Separation & Airspace Safety 175

  1. A Further Study into Interactions Between Remotely Piloted Aircraft Systems and ATC
  2. AAS 1.11 “FLY-BY” AND “FLY-OVER” WAYPOINTS
  3. AAS 1.14 SPACE-BASED AUTOMATIC DEPENDENT SURVEILLANCE – BROADCAST
  4. AAS 1.15 CONCEPT OF GNSS-BASED ALTITUDE
  5. AAS 1.21 UNMANNED AIRCRAFT SYSTEM (UAS) TRAFFIC MANAGEMENT (UTM)
  6. AAS 1.22 RPAS ASSUMPTIONS
  7. ADME 2.1 CONVERGING RUNWAY OPERATIONS (CROPS)
  8. ADME 2.4 SURFACE MOVEMENT GUIDANCE & CONTROL SYSTEMS
  9. ADS-B Operations
  10. Aerodrome – Land and Hold Short Operations
  11. Aerodrome – Converging Runway Operations
  12. Air Traffic Control Separation Monitoring Tool (ASMT)
  13. Air Traffic Control Separation Monitoring Tool (ASMT)
  14. Air Traffic Control Separation Monitoring Tool (ASMT)
  15. Airborne Separation Assurance
  16. Aircraft Flying with ‘Due Regard’
  17. Airspace Design and Procedures Controller Involvement
  18. Amendment to Current Policy on RNAV Procedural Separation Minima
  19. ASAS-TN2 – Airborne Separation Assistance System Thematic Network 2
  20. ATC Collision Avoidance Techniques
  21. ATS – Study Restrictions in the Enroute Environment
  22. ATS 3.15 (ADVANCED) STRATEGIC LATERAL OFFSET PROCEDURES
  23. ATS 3.16 THE USE OF SAFETY NETS IN ATM
  24. ATS 3.18 SHORT TERM CONFLICT ALERT
  25. ATS 3.19 MINIMUM SAFE ALTITUDE WARNING SYSTEMS
  26. ATS 3.21 SURVEILLANCE: IN-TRAIL PROCEDURES ITP
  27. ATS 3.29 MERGING AND SEQUENCING CONCEPTS
  28. ATS 3.32 RECATEGORIZATION OF AIRCRAFT FOR WAKE TURBULENCE
  29. ATS 3.34 TERRAIN AND OBSTACLE CLEARANCE RESPONSIBILITIES
  30. ATS 3.35 TERRAIN AND OBSTACLE CHARTING
  31. ATS 3.36 EMERGENCY DESCENT PROCEDURES
  32. ATS 3.4 STANDARDISATION OF REGIONAL TRANSITION ALTITUDES
  33. ATS 3.42 HELICOPTER OPERATIONS
  34. ATS 3.46 SECTORLESS ATM
  35. ATS 3.8 RADAR MONITORING
  36. ATS 3.9 GLOBAL COMPATIBLE FLIGHT LEVEL SYSTEMS
  37. Blended Airspace
  38. Co-operative Separation
  39. COM 4.11 RADIO MANDATORY ZONES / TRANSPONDER MANDATORY ZONES
  40. Concept of GNSS-Based Altitude
  41. Conspicuity and ATS Surveillance
  42. Cooperative Separation – Transfer of Control Functions to Pilots
  43. Deactivation of Safety Nets
  44. Development of Policy on Formation Flights Within Controlled Airspace
  45. Developments in the use of Global Navigation Satellite Systems (GNSS) as an Approach Aid
  46. EATCHIP ATM Procedures Development Sub-Group
  47. Emergency Descent Procedures
  48. En-route Wake Turbulence
  49. General Considerations on the Implact of U-Space Dynamic Airspace Reconfiguration on ATS Units
  50. Harmonised Transition Altitude
  51. High Altitude Operations (HAO)
  52. Interactions ATC/ACAS
  53. Interactions Between Unmanned Aircraft Systems and Air Traffic Control
  54. Introduction of RVSM on a Trial Basis in the North Atlantic Region
  55. Investigate Applications of Provision of Area Proximity Warnings
  56. Investigate interactions between Traffic Collision Avoidance System and Mode S
  57. Investigate Minimum Safe Altitude Warning Systems (MSAW)
  58. Investigate Navigation and Surveillance Provided by a Single Position Information System
  59. Investigate Potential Applications of ADS-B
  60. Investigate Route Conformance Monitoring System
  61. Investigation of the Nomenclature used in the Acronyms CIB & CIC
  62. LM 7.1.3 TRANSFER OF CONTROL FUNCTIONS – LEGAL ASPECTS
  63. Longitudinal Separation Anomalous Interpretations
  64. Management of Mixed Mode Operations
  65. MLS Operational Procedures
  66. Monitor the Application and Implementation of RNAV
  67. Monitor the Developments in the Operational use of ASAS
  68. Monitoring TIBA
  69. NATSPG
  70. Navigation – Magnetic vs True
  71. Off–Set Tracking in the North Atlantic (NAT)
  72. Policy Review: Strategic Lateral Offset Procedures (SLOP)
  73. Policy Review: Terrain and Obstacle Clearance
  74. Produce a Definition of Area Proximity Warning System
  75. Produce a Definition of Conflict Detection Tools
  76. Produce a Definition of Controller Tools
  77. Produce a Definition of Minimum Safe Altitude Warning Systems
  78. Produce Definition of Short Term Conflict Alert
  79. Produce Definitions of “Fly-by” and “Fly-over”
  80. Produce Definitions on Spacing, Separation and Segregation
  81. Professional and Legal Aspects of Downlinking TCAS RAs (TCAS Resolution Advisories)
  82. Radar Monitoring in the En-route Phase
  83. Radar Monitoring Procedures in TMAs
  84. Radio Mandatory Zones / Transponder Mandatory Zones
  85. Rating for Automatic Dependent Surveillance Control
  86. Reduced Vertical Separation Above FL 290
  87. Reduced Vertical Separation Minima (RVSM)
  88. Reduction in Vertical Separation Above FL290
  89. Reduction of Non-radar Separation Standards Using ADS
  90. Removal of Ground Based Aids
  91. Report of Visual Approach Procedures
  92. Responsibility For Terrain And Obstacle Clearance During Weather Avoidance
  93. Review ATS 3.36 – Recategorization of Aircraft for Wake Turbulence
  94. Review Continuous Descent Operations Manual
  95. Review Existing Policy and Develop Further Policy on Simultaneous IFR Operations on Intersecting / Converging Runways
  96. Review Issues in the Application of Cockpit Display of Traffic Information (CDTI) in Advanced Surface Movement Guidance System (A-SMGCS) Operations
  97. Review Issues Regarding ATC Systems Capability to Monitor Relevant Controller Intervention Buffer (CIB) Parameters
  98. Review of Lateral and Longitudinal Separation
  99. Review of Lateral and Longitudinal Separation
  100. Review of LM (Legal Matters) – Professional Policy of the TPM
  101. Review of Policy in Regards to TCAS RA Downlink
  102. Review of Policy on Area Navigation
  103. Review of Policy on Ground Based Safety Nets
  104. Review of Policy on Precision Area Navigation
  105. Review of Policy on Surface Movement Radar
  106. Review of Policy: Non-plannable Level in the NAT-Region
  107. Review of Policy: Resumption of Separation Following a TCAS RA
  108. Review of Policy: Short Term Conflict Alert (STCA)
  109. Review of Provisional Policy – ATM Safety Monitoring Tools (ASMT)
  110. Review of TCAS Policy
  111. Review of WC (Working Conditions) – Professional Policy of the TPM
  112. Review of WC 10.2.11 – The Free Flight Concept
  113. Review policy of ACAS / TCAS
  114. Review Policy on Formation Flights within Controlled Airspace
  115. Review Policy on Interception of Civil Aircraft
  116. Review Policy on Separation Lateral and Longitudinal
  117. Review policy on Surface Guidance Movement and Control Systems
  118. Review the Issue of ASAS Separation when less than the Relevant ATC Separation, e.g. Radar
  119. Review the Issues Concerning Controller Intervention Buffer
  120. RNAV – Monitoring its Implementation
  121. RNAV Procedural Separation – Amendment of Current Policy
  122. RNAV Procedural Separation – Longitudinal Distance Standard Minima
  123. RNP for Approach and Landing
  124. RVSM
  125. Safety Components in a Separation Minima
  126. Sectorless ATM
  127. SEP 5.1 USE OF 1000FT VERTICAL SEPARATION ABOVE FL290
  128. SEP 5.2 LATERAL AND LONGITUDINAL SEPARATION
  129. SEP 5.3 AIRBORNE SEPARATION ASSISTANCE SYSTEMS (ASAS) AND COCKPIT DISPLAY OF TRAFFIC INFORMATION (CDTI)
  130. SEP 5.4 CONTROLLER INTERVENTION BUFFER
  131. SEP 5.5 DYNAMIC RECONFIGURATION OF U-SPACE AIRSPACE
  132. Separation Between Departing and Arriving Aircraft – Cut-off Point (CoP)
  133. Separation Between Units Without Procedural Agreement
  134. Separation in Class E Airspace
  135. SICASP/WG2 Meeting
  136. Simultaneous Operations on Intersecting Runways
  137. Simultaneous Operations on Intersecting Runways
  138. Spacing, Separation and Segregation – Use in Future ATM Systems
  139. Study ADS-B Applications – Used in ITP
  140. Study Advanced Offset Procedures
  141. Study Automatic Dependent Surveillance (ADS) to Update IFATCA Provisional Policy
  142. Study Down Link of Traffic Collision Avoidance System Resolution Advisories
  143. Study Land and Hold Short Operations
  144. Study Merging and Sequencing Concepts
  145. Study Recategorization of Aircraft for Wake Turbulence
  146. Study Remote Towers Concept
  147. Study Reporting of TCAS RAs
  148. Study Strategic Lateral Offset Procedure
  149. Study Visual Separation on Approach
  150. Surveillance – Provide an update on ITP
  151. Surveillance Applications Policy – Applications of Radar Monitoring
  152. Surveillance Applications Policy – ASAS
  153. Surveillance Applications Policy – Review Policy on Radar Monitoring
  154. Surveillance Applications Policy – Review Policy on ADS
  155. Technical Aspects of Medium Term Conflict Detection
  156. Terrain and Obstacle Clearance Responsibilities
  157. Terrain Clearance and Airspace Design
  158. The Development of MLS Continues
  159. The Use of GNSS – ATC
  160. The Use of GNSS as a Runway Approach Aid
  161. The Use of Lateral Offsets
  162. The Use of Lateral Offsets
  163. The Use of Non-flight Plannable Levels in the Nat Region for Contingency
  164. The Use of Safety Nets in ATM
  165. Three Main Systems of Flight Level (FL) Determination
  166. TPM Review – ATS Editorials
  167. TPM Review – ATS (Major Edit)
  168. Transfer of Control Functions to Pilots (Legal Aspects)
  169. Transfer of Separation Functions to Pilots – Human Factors Aspects
  170. UAS Flight Rules
  171. UTM (Unmanned Aircraft System (UAS) Traffic Management)
  172. Vertical Spacing Between Controlled and Uncontrolled Aircraft at or near Airspace Boundaries
  173. WC 10.2.9 CO-OPERATIVE SEPARATION
  174. WC 10.7.7 SEPARATION BETWEEN UNITS WITHOUT PROCEDURAL AGREEMENT
  175. Weather Deviation Procedure in Asia-Pacific Region
Last Update: 28th January 2022
27th October 2019 2179 Jean-Francois LepageWIKI

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