Air Traffic Bulletin

Issue 99-4 *SPECIAL* SEPTEMBER 1999



/*T/ The primary purpose of the ATC system is to separate aircraft and to organize and expedite the flow of traffic. Additional services sometimes play an important part in accomplishing this primary purpose. Controllers must provide additional service procedures to the extent that higher duty priorities permit. Traffic volume, frequency congestion, controller workload and other factors may limit time available for additional services.

A Near Midair Collision (NMAC) involving an IFR Boeing 737 and a VFR Beech 99 might have been prevented by the provision of additional services and merging target procedures. The Beech 99 departed an airport on a VFR flight plan in Class B airspace requesting an altitude of 10,500. The ATCS terminated the Beech 99’s radar service as the aircraft was leaving Class B airspace climbing through 7,200 feet. Approximately 45 seconds later, an arriving Boeing 737 contacted the approach controller and was assigned a heading toward the Beech 99 and descent to 10,000 feet. One minute later, the controller issued traffic to the crew of the Boeing 737, "twelve o’clock three miles opposite direction, altitude indicates nine thousand three hundred."

FAAO 7110.65 allows controllers to terminate radar advisory service to aircraft when they leave class B airspace areas, however, additional services are required when the work situation permits. Paragraph 2-1-2 outlines responsibilities and duty priority.



  1. Give first priority to separating aircraft and issuing safety alerts as required in this order. Good judgment shall be used in prioritizing all other provisions of this order based on the requirements of the situation at hand.
  2. Provide additional services to the extent possible, contingent only upon higher priority duties and other factors including limitations of radar, volume of traffic, frequency congestion, and workload.

FAAO 7110.65 paragraph 2-1-6 discusses safety alerts, priorities and controller requirements.


Issue a safety alert to an aircraft if you are aware the aircraft is in a position/attitude which, in your judgment, places it in unsafe proximity to terrain, obstructions, or other aircraft. Once the pilot informs you action is being taken to resolve the situation, you may discontinue the issuance of further alerts. Do not assume that because someone else has responsibility for the aircraft that the unsafe situation has been observed and the safety alert issued; inform the appropriate controller.

  1. Terrain/Obstruction Alert – Immediately issue/initiate an alert to an aircraft if you are aware the aircraft is at an altitude which, in your judgment, places it in unsafe proximity to terrain/obstructions. (NOTE: Paragraph 2-1-6(a) is not applicable to this NMAC.)

  1. Aircraft Conflict/Mode C Intruder Alert – Immediately issue/initiate an alert to an aircraft if you are aware of another aircraft at an altitude which you believe places them in unsafe proximity. If feasible, offer the pilot an alternate course of action.
  2. When an alternate course of action is given, end the transmission with the word "immediately."

FAAO 7110.65 paragraph 5-1-8 discusses merging target procedures and controller requirements.

  1. Except while they are established in a holding pattern, apply merging target procedures to all radar identified:

  1. Aircraft at 10,000 feet and above.
  2. Turbojet aircraft regardless of altitude.
  3. Presidential aircraft regardless of altitude.

b. Issue traffic information to those aircraft listed in subpara a. whose targets appear likely to merge unless the aircraft are separated by more than the appropriate vertical separation minima.

Class B airspace is the most complex terminal airspace in the United States. Air Traffic controllers are required to provide additional services outside Class B airspace, to the edge of their area of responsibility, when the work situation permits. In the NMAC described above, a crewmember was seriously injured as the Boeing 737 maneuvered to avoid the Beech 99. Termination of radar service, timely traffic advisories and safety alerts are causal factors that reduced the controller’s ability to prevent this accident. (ATP-100)


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