Section 6. Airport Surface Detection Procedures

  1. The operational status of ASDE systems must be determined during the relief briefing, or as soon as possible after assuming responsibility for the associated position.
  2. Use ASDE systems to augment visual observation of aircraft landing or departing, and aircraft or vehicular movements on runways and taxiways, or other parts of the movement area.
  1. ASDE systems with safety logic must be operated continuously.
  2. ASDE systems without safety logic must be operated:
  1. Continuously between sunset and sunrise.
  2. When visibility is less than the most distant point in the active movement area, or
  3. When, in your judgment, its use will assist you in the performance of your duties at any time.
  1. To identify an observed target/track on an ASDE system display, correlate its position with one or more of the following:
  1. Pilot/vehicle operator position report.
  2. Controller's visual observation.
  3. An identified target observed on the ASR or CTRD.
  1. An observed target/track on an ASDE system display may be identified as a false target by visual observation. If the area containing a suspected false target is not visible from the tower, an airport operations vehicle or pilots of aircraft operating in the area may be used to conduct the visual observation.
  2. After positive verification that a target is false, through pilot/vehicle operator position report or controller visual observation, the track may be temporarily dropped, which will remove the target from the display and safety logic processing. A notation must be made to FAA Form 7230-4, Daily Record of Facility Operation, when a track is temporarily dropped.
  1. ASDE system derived information may be used to:
  1. Formulate clearances and control instructions to aircraft and vehicles on the movement area.


FAA Order JO 7210.3, Para 3-6-2, ATC Surveillance Source Use.

  1. Position aircraft and vehicles using the movement area.
  2. Determine the exact location of aircraft and vehicles, or spatial relationship to other aircraft/vehicles on the movement area.
  3. Monitor compliance with control instructions by aircraft and vehicles on taxiways and runways.
  4. Confirm pilot reported positions.
  5. Provide directional taxi information, as appropriate.



  1. Do not provide specific navigational guidance (exact headings to be followed) unless an emergency exists or by mutual agreement with the pilot.


It remains the pilot's responsibility to navigate visually via routes to the clearance limit specified by the controller and to avoid other parked or taxiing aircraft, vehicles, or persons in the movement area.

  1. Do not allow an aircraft to begin departure roll or cross the landing threshold whenever there is an unidentified target/track displayed on the runway.

When the system generates an alert, the controller must immediately assess the situation visually and as presented on the ASDE system display, then take appropriate action as follows:

  1. When an arrival aircraft (still airborne, prior to the landing threshold) activates a warning alert, the controller must issue go-around instructions. (Exception: Alerts involving known formation flights, as they cross the landing threshold, may be disregarded if all other factors are acceptable.)


The intent of this paragraph is that an aircraft does not land on the runway, on that approach, when the safety logic system has generated a warning alert. A side-step maneuver or circle to land on another runway satisfies this requirement.


FAA Order JO 7110.65, Para 3-8-1, Sequence/Spacing Application.
FAA Order JO 7110.65, Para 3-9-6, Same Runway Separation.
FAA Order JO 7110.65, Para 3-10-3, Same Runway Separation.

  1. When an arrival aircraft activates a warning alert to a taxiway, the controller must issue go-around instructions.
  2. When two arrival aircraft, or an arrival aircraft and a departing aircraft activate an alert, the controller will issue go-around instructions or take appropriate action to ensure intersecting runway separation is maintained.


FAA Order JO 7110.65, Para 3-9-8, Intersecting Runway/Intersecting Flight Path Operations.
FAA Order JO 7110.65, Para 3-10-4, Intersecting Runway/Intersecting Flight Path Separation.

  1. For other safety logic system alerts, issue instructions/clearances based on good judgment and evaluation of the situation at hand.

Radar-only mode is an enhancement of the ASDE-X and ASSC systems which allows the system to stay operational with safety logic processing, despite a critical fault in the Multilateration (MLAT) subsystem. The system stays in full core alert status under radar-only mode without data block capability.