1. Traffic Processing Sequence — Tactical and Strategic Investigation of all the facts pertaining to the Air Traffic Services tactical and strategic traffic processing sequence should be considered an essential element in the reconstruction of the history of the flight. Information obtained, such as unauthorized horizontal and/ or vertical excursions and violations may also be relevant to specific Operations and Human Factors investigations. Because these aspects are often closely related, careful collection, collation and evaluation of the pertinent facts is required to achieve the best possible use of the information collected.

2. The tactical processing sequence will normally be recorded in some media and verified by careful analysis of data and personnel statements. The strategic processing sequence and planning may be a more difficult task and may require more selective in-depth interviewing techniques to ascertain anticipated traffic processing and expectations of outcomes.

3. Dependent upon the nature of the occurrence, some or all of the following items may be relevant to determining tactical (short term/ immediate) and strategic (long term/later) processing effects and outcomes: a) terminal airspace approach and departures b) enroute airspace c) holding and diversions d) traffic flow, speed control and level assignment/s e) on and off- airway flight paths f) air traffic information management g) air traffic sequencing and priorities

4. Traffic Disposition The Air Traffic Services investigation should try to establish and reconstruct the actual traffic disposition for a defined time prior to an occurrence and at the actual time of the occurrences. Recorded flight progress display data will normally provide all essential information to permit reconstruction of the horizontal and vertical traffic disposition for analysis.

5. It is equally important that the Air Traffic Services investigation not only reconstruct the actual traffic disposition, but that air traffic service personnel be given opportunity to present their views and/or estimation of the situation. For example, an aircraft may have unintentionally been assigned a heading or level different to that intended by the Air Traffic Service person with jurisdiction for the aircraft.

6. Dependent upon the nature of the occurrence, some or all of the following items may be relevant to reconstructing the traffic disposition and possible variations of actual and planned flight paths for each active aircraft: a) airspace jurisdiction b) ATS routes and waypoints c) range d) azimuth e) level f) track g) holding pattern h) meteorological effects i) vertical and horizontal separation minima

7. Information Flow Co-ordination and Aircraft Movement Messages The provision of safe, orderly and expeditious air traffic management is totally dependent upon exchange of timely and accurate information flow, co-ordination and distribution of aircraft movement messages throughout the Air Traffic Service system. This process is as important as the information and instructions provided to aircrew and forms an essential element of any Air Traffic Services investigation. It requires: a) a thorough understanding of mutual responsibilities b) careful application c) comprehensive training, and d) unambiguous communications

8. Dependent upon the nature of the occurrence, some or all of the following items may be relevant in ascertaining information flow, coordination and distribution of aircraft movement messages to, from, or between, co-located/remote Air Traffic Service personnel and units: a) unit responsibilities b) inter-unit communications c) intra-unit communications d) distribution of aircraft movement and control messages e) frequency change management f) phraseology g) readback/hearback errors and omissions h) flight progress display data and notations

9. Situational Awareness Numerous aircraft and operational displays, when combined with effective and efficient communications and facilities, provide Air Traffic Services personnel with the cues to devise and deliver essential instructions and information to aircraft. In some situations aircraft maintain predefined flight path trajectories on published airways and in others, the aircraft may be in user-preferred trajectory (4-D). In practice, any one Air Traffic Service unit may have jurisdiction of a mixture of aircraft moving in four dimensions. Understanding of the situational awareness forms an integral part of the Air Traffic Services investigation.

10. Information obtained, such as real or perceived differences in the Air Traffic Service personnel’s awareness of aircraft disposition and range may also be relevant to specific Operations and Human Factors investigations. Many of these aspects are often closely related and careful collection, collation and analysis of the information is required.

11. Dependent upon the nature of the occurrence, some or all of the following items may be relevant: a) active and pending traffic disposition b) flight progress display c) communications d) facility control and presentation settings e) aircraft performance f) actual and expected meteorological situation g) airspace operational configuration, instructions and limitations h) terrain and other obstructions

12. Separation Assurance Techniques Effective tactical and strategic air traffic management techniques, procedures and practices are essential elements for the implementation of separation assurance techniques in the Air Traffic Services system. Separation assurance as distinct from achieving separation becomes significant in any Air Traffic Service investigation where prescribed aircraft proximity standards have been violated due to human or system failures. There are many situations where aircraft proximity standards could be violated even where all aircraft comply with their given instructions or information.

13. For example, two aircraft operating at the same correct level may be converging on the same waypoint at the same estimated time. However, it is usually left to a matter of timing for Air Traffic Service units to recognize, respond and rectify potential aircraft proximity occurrences before a prescribed standard is violated. The Air Traffic Service investigation should establish if the required separation assurance was in place and if it could have been maintained in the event of failure of any single, or multiple component failure of the Air Traffic Service system, such as communications or surveillance facilities

14. Dependent upon the nature of the occurrence, some or all of the following items may be relevant to determining continuous effective planning and implementation of separation assurance techniques: a) selected procedure for vertical and horizontal separation b) tactical and strategic traffic processing including procedures for accommodation of non approved aircraft into RVSM airspace c) airways and available communications facilities d) conflict warning systems e) timely execution f) monitoring and surveillance of traffic g) re-evaluation of outcomes