Casualties unknown

Loss of Separation Between Simmons 4085 and United 556 After Takeoff (N374MQ)

Chicago, IL, US

On March 21, 1993, a DE Havilland SHD-6 (registration N374MQ) operated by Simmons was involved in an aviation accident near Chicago, IL. Investigators recorded the probable cause as: THE LOCAL CONTROLLER'S FAILURE TO MAINTAIN 3 MILES RADAR SEPARATION BETWEEN TWO AIRPLANES. A FACTOR RELATED TO THE INCIDENT WAS THE LOCAL CONTROLLER'S DELAY IN REMEDIAL ACTION. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive; 3 related events involving the same aircraft type or operator are linked below.

Sourcesthe U.S. National Transportation Safety Board (NTSB) historical archivePrimary reportUpdated 2026-06-10Data APIEditorial standards

A controller issued takeoff clearances to Simmons 4085 and United 556. United's pilot did not turn to the assigned heading, leading to a loss of radar separation. The controller stopped United's climb in an attempt to prevent overtaking.

Incident

A loss of separation occurred between two aircraft after takeoff. The controller had issued a takeoff clearance to Simmons 4085 to fly the runway heading. United 556 was next in line and received a clearance to fly a heading of 140 degrees after takeoff.

Sequence of Events

The pilot of United 556 did not immediately turn to the assigned heading of 140 degrees. The controller made several attempts to contact the flight but received no response. In an effort to prevent United 556 from overtaking the slower Simmons 4085, the controller instructed United 556 to stop its climb. However, by the time the climb was stopped, radar separation of 3 miles had already been lost.

Aftermath

The incident resulted in a loss of radar separation between the two aircraft. No further details regarding injuries, damage, or subsequent actions were provided in the source.

Investigation report by the U.S. National Transportation Safety Board (NTSB) historical archive. Original record: https://carol.ntsb.gov/event/20001211X11943. This page is a structured re-presentation; facts and quotes are in the National Transportation Safety Board (NTSB), United States.