N248AT

On March 8, 1993, at 1337 central standard time, the minimum air traffic control separation was lost between N248AT, an ATR 72 being operated as Simmons Flight 4298 and a McDonnell Douglas MD-80, N427, operated as American Airlines Flight 1106. Both airplanes had departed on Runway 32L at the O'Hare International Airport, Chicago, Illinois, just prior to the loss of separation.

There was no damage or injuries reported as a result of this incident. Visual meteorological conditions prevailed and IFR flight plans were filed.

Both airplanes were under the control of the North Local Controller (NLC) when the loss of separation occurred. The controller was responsible for aircraft landing on runway 27R and aircraft departing on 32R and 32L at the T-1 intersection. The Air Traffic Control Handbook 7110 65G, 5-113 requires a minimum heading divergence of 15 degrees or more. The events of the loss of separation which resulted in a 10 degree heading divergence occurred as follows:

1335:01 The NLC cleared Simmons 4298 for takeoff on runway 32L T-1 with instructions to fly the runway heading.

1335:09 The NLC cleared American 1106 for takeoff on runway 32L with instructions to turn right heading 010 degrees.

1337:01 The NLC clears Simmons 4298 to turn right to heading 360 degrees.

Both aircraft were then instructed to contact departure control. The local controller was unaware of the loss of separation until the tower received a call from the TRACON questioning the 10 degree heading divergence.

The local controller stated that she had cleared a previous Simmons flight for takeoff on 32L and a turn to 040 degrees. During the turn she stopped the airplane at 030 degrees due to the wind conditions. American 1106 was next to takeoff and instead of issuing a normal heading of 020 degrees as she normally would have done, she issued 010 degrees to maintain separation with the first Simmons flight. She stated that when she cleared Simmons 4298 to a heading of 360 degrees, she failed to offset the heading to 350 degrees to maintain separation with American 1106.

See Air Traffic Control/Human Performance Group Chairman's Report and Attachments for CHI-93-I-A115.