Southwest B737 at Chicago on Dec 1st 2011, ATC error causes runway incursion

Last Update: November 8, 2012 / 12:16:18 GMT/Zulu time

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Incident Facts

Date of incident
Dec 1, 2011

Classification
Incident

Airline
Southwest Airlines

Aircraft Type
Boeing 737-700

ICAO Type Designator
B737

The NTSB released their factual report stating that a VIP arrival was planned later the day, which would effectively shut down the airport and thus put a lot of pressure onto the tower to get as many departures and arrivals through as possible.

One tower controller was handling the regular traffic as part of his normal duties, a second tower controller was plugged in as "ground control 2" monitoring the tower frequency and working the VIP arrival checklists. The monitoring controller later said he was not really listening to the communication on the tower frequency, he was confident of the actual controller's ability and thus did not see necessary to monitor him prior to the VIP arrival.

The controller had two business jets to depart from runway 31C, upon suggestion by his assistant the two departures were redirected to runway 31R however, Southwest Airlines flight 844 was cleared to land on runway 31C, 6 seconds later both business jets were cleared to cross runway 31C at the approach end.

After working several other aircraft and a a helicopter, about 107 seconds after the landing clearance for WN-844 (SWA844), the controller cleared the first business jet for takeoff from runway 31R immediately followed by the instruction to WN-844 to turn right, cross runway 31R and contact ground.

The monitoring controller recognized the conflict of the two instructions and queried the controller twice whether he would hold WN-844 short of runway 31R, however received no reply. The controller said later he wasn't sure which aircraft the monitor was referring to as his sight was blocked by tower equipment and other controllers standing.

The controller's assistant assumed the runway incursion occurred because the crew of WN-844 did not adhere to the hold short instruction. He had been listening to the monitor's VIP briefing and thus had not heard the takeoff clearance on runway 31R and the clearance to cross runway 31R. However, he noticed the business jet departing and saw the 737 taxi at high speed on taxiway B and queried the controller whether the 737 would stop short of runway 31R.

According to FAA analysis the business jet rotated 1196 feet short of the 737, the closed point of lateral separation was 287 feet with a vertical separation of 62 feet.

The NTSB continued: "At 09:07:59 (editorial note: 2:29 minutes after the landing clearance) the pilot of SWA844 called the tower and advised that “we just had a plane take off from 31R and you cleared us to cross.” The local controller responded “SWA844 cross 31R, contact ground.” SWA844 responded with “Ok if you just copied you cleared us to cross a runway where there was a plane taking off.” The local controller continued to work other traffic and at 09:08:52 (editorial note: the crew) again called the tower and asked the local controller for a telephone number to call and was directed to contact ground after which the pilot of SWA844 asked the local controller to acknowledge that they had been cleared onto a runway which a plane was taking off. The local controller responded with “contact ground please”."

The monitoring controller initiated the relief of the controller and directed the review of the control tapes. The controller was relieved 4:40 minutes after the landing clearance. The controller said, he was convinced he had cleared the 737 to hold short of runway 31R until he heard the tapes that confirmed he had cleared the 737 to cross runway 31R. The controller could not explain this action.

The Southwest crew got a phone number from ground control, talked to another controller on the tower indicating they would file a report about being cleared to cross a runway that another traffic was departing from. The controller assured this was not a normal event and the tower would file a report as well.

On Nov 8th 2012 the NTSB released their final report concluding the probable cause was:

The tower local controller did not ensure that the runway was clear of conflict before directing the B737 to cross the runway, and other air traffic control personnel did not effectively intervene when the separation between the two airplanes became questionable.
Incident Facts

Date of incident
Dec 1, 2011

Classification
Incident

Airline
Southwest Airlines

Aircraft Type
Boeing 737-700

ICAO Type Designator
B737

This article is published under license from Avherald.com. © of text by Avherald.com.
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