What happened
On April 28, 2010, at approximately 1225 central daylight time, a Boeing 737-700, registration N242WN, operating as Southwest Airlines flight 1322, and a Bell 207, registration N6YJ, were involved in a near mid-air collision at William P. Hobby Airport (HOU) in Houston, Texas. The weather was daytime visual meteorological conditions (VMC) with a wind of 010/10kt and visibility of 10sm.
The Boeing 737 was departing runway 12R for a scheduled flight to Baltimore/Washington International Thurgood Marshall Airport (BWI) with 135 passengers and a crew of five. The Bell 207 was departing from the south helipad on a northbound departure route with one person onboard.
At approximately 1224, the local controller cleared the Boeing 737 for takeoff from runway 12R with instructions to turn left to the north. Roughly 26 seconds later, the Bell 207 requested a northbound departure route (cougar departure) from the south helipad. The controller advised the Bell 207 to use caution and subsequently informed the helicopter that it had "no restrictions." The pilot of the Bell 207 read back the instructions and proceeded.
Approximately 20 seconds later, the crew of the Boeing 737 reported to the tower that the helicopter was crossing their path, noting they had performed an evasive maneuver to avoid the aircraft. Simultaneously, the Bell 207 performed a sharp right turn to avoid the departing Boeing 737. The aircraft reached a minimum separation of approximately 125 feet vertically and 100 feet laterally at the departure end of runway 12R.
The investigation
Radar data from the ASR-9 sensor at HOU confirmed the close proximity of the two aircraft. In Class B airspace, the applicable separation standard between VFR and IFR aircraft is visual separation or 500 feet vertically and 1.5 miles laterally. At the point of closest approach, the aircraft were separated by only about 125 feet laterally and 100 feet vertically. The investigation found that the controller did not issue traffic advisories or instructions to establish visual separation.