# NTSB CHI93IA127: de Havilland SHD-6, N374MQ, Chicago, IL, March 21, 1993 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: March 21, 1993, 08:06 local (14:06 UTC) - Place: Chicago, IL - Location: 41.8500° N, 87.6501° W: Placed by OpenAirDocs: center of Chicago, IL, within about 9 miles (OpenAirDocs) - Nearby events: https://openairdocs.org/map.md?lat=41.8500&lon=-87.6501&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 3 uninjured - Status: Completed, report December 2, 1994 - Report: Approved by Office Director - NTSB case key (mKey): 9191 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI93IA127 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/9191/pdf - Page: https://openairdocs.org/ntsb/CHI93IA127 ## Probable cause 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. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Miscellaneous/other, climb - to cruise - radar separation - not maintained, atc personnel(lcl/gnd/clnc) (cause) - remedial action - delayed, atc personnel(lcl/gnd/clnc) (contributing factor) ## Analysis THE CONTROLLER ISSUED A TAKEOFF CLEARANCE FOR SIMMONS 4085 TO FLY THE RUNWAY HEADING. UNITED 556 WAS NEXT TO TAKEOFF AND WAS ISSUED A CLEARANCE TO FLY A HEADING OF 140 DEGREES AFTER TAKEOFF. THE PILOT DID NOT TURN IMMEDIATELY TO 140 DEGREES AND SEVERAL ATTEMPTS BY THE CONTROLLER TO CONTACT THE FLIGHT WERE TO NO AVAIL. IN AN ATTEMPT TO PREVENT THE UNITED FLIGHT FROM OVERTAKING THE SLOWER SIMMONS FLIGHT, THE CONTROLLER STOPPED UNITED FROM CLIMBING. RADAR SEPARATION OF 3 MILES HAD ALREADY BEEN LOST BY TIME THE UNITED FLIGHT STOPPED ITS CLIMB. ## Factual narrative On March 21, 1993, at 0806 central standard time, minimum air traffic control separation was lost between N374MQ, a DeHavilland SHD-6, operated as Simmons Flight 4085, and N361UA, a Boeing 737, operated as United Airlines Flight 556. Both airplanes had departed on Runway 22L at the O'Hare International Airport, Chicago, Illinois, just prior to the loss of separation. Visual meteorological conditions prevailed and IFR flight plans were filed. There were no injuries or damage reported as a result of this incident. Both airplanes had departed runway 22L which was being controlled by the South Local Controller (SLC). This controller was responsible for arrivals on runway 27L and depatures from runway 22L and 32L T-1 intersection. The events which resulted in the loss of separation occurred as follows: At 0802, Simmons 4085 was cleared for takeoff and instructed to fly the runway heading. At 0803, Simmons 4085 was instructed to fly a heading of 200 degrees. At 0804, United 556 was cleared for takeoff and instructed to fly a heading of 140 degrees. United 556 was instructed not to delay it's takeoff roll. At 0805, Simmons 4085 was instructed to contact departure control. At 0806, United 556 is instructed once again to fly a heading of 140 degrees. Twelve seconds later, United 556 is instructed to maintain 4,000 feet. Ten seconds later, the flight is instructed to contact departure control. (The controller stated she stopped United's climb at 4,000 feet because without turning to 140 degrees, it would have over taken the slower Simmons flight ahead of it. However, by this time the loss of separation had already occorred.) Air Traffic Control Handbook 7110.65G, paragraph 5-72 states, "Separate aircraft by the following minima: a.1. when less than 40 miles from the antenna-3 miles." According to radar data, lateral separation between Simmons 4085 and United 556 decreased to 2.25 miles with 400 feet of vertical separation. See Air Traffic Control/Human Performance Group Chairman's Factual Report and Attachments for CHI-93-I-A115. ## Aircraft - Registration: N374MQ (not matched to a registry record) - Reported make and model: de Havilland SHD-6 - Category: Airplane - Engines: P&W PT6A 620 horsepower turbo prop - Damage: No damage - Flight: Part 121 - Operator: Simmons - Registered owner: Security Pacific Equipt Leasin - Airworthiness certificate: Standard, Transport - Departed: ORD - Destination: DEC, DECATUR, IL - Flight plan: IFR - Airport: ORD, O'Hare Int'L Airport ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 37; airline transport, commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: left; flight hours: 10,000 total ## Weather - Conditions: Visual (VMC), Day - Wind: 250° at 6 knots - Visibility: 5 statute miles - Lowest ceiling: 3,700 ft overcast - Temperature: 34 °F, dew point 30 °F - Altimeter: 30.00 inHg - Observed at: ORD From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.