What happened
On March 11, 2011, a Boeing 757-200, operating as Delta Air Lines flight 2086, departed runway 27R at Hartsfield-Jackson Atlanta International Airport (ATL) for La Guardia Airport (LGA). Following takeoff, the flight crew failed to activate the aircraft's transponder and did not contact air traffic control for approximately eight minutes.
During this period, the aircraft N693DL traveled through one controller's airspace and entered another's without any coordination. Because the transponder was inactive, the aircraft's flight data block did not automatically appear on radar displays. Instead, the aircraft was visible only as an enhanced primary target lacking identification or radar altitude information.
While the aircraft was flying without a radar data tag, primary radar data showed that a loss of lateral separation occurred between the Boeing 757 and three other aircraft:
- A Beechcraft 55 (N36638), with a closest proximity of 1.44 miles.
- A Pilatus PC-12 (N825MK), with a closest proximity of 0.81 miles.
- An Atlantic Southeast Airlines CRJ-100, with a closest proximity of 2.36 miles.
There were no injuries reported on any of the flights involved. The incident occurred during daytime visual meteorological conditions (VMC).
The investigation
Investigation into the flight history revealed that the Atlanta Tower controller instructed the aircraft to contact departure control one minute after takeoff. Although the pilot read back the instructions correctly, contact with departure control was not made until roughly 1328 EDT.
At 1324 EDT, the Atlanta TRACON south departure controller noticed an unaccounted-for flight strip and inquired about the status of the flight with the tower. The Traffic Management Coordinator attempted to locate the target on the Traffic Situation Display but could not positively identify the aircraft due to the high number of primary targets in the area.
At 1326 EDT, the crew of N693DL contacted the tower to ask about their assigned altitude. Shortly after, the pilot reported that the transponder had been turned on, at which point the aircraft's radar data block appeared on the controller's display. The departure controller then expedited the aircraft's climb to 14,000 feet to maintain separation and handed the flight off to Atlanta Center.