What happened
During ground operations, a local controller assigned Simmons 4058 to runway 9L and subsequently positioned Simmons 4158 (the subject aircraft) on runway 4L. After positioning the second aircraft, the controller returned to Simmons 4058, stated a runway number, and issued a takeoff clearance.
Before the crew of Simmons 4058 could respond to the instruction, the crew of Simmons 4158 acknowledged the clearance. The pilot of Simmons 4058 then queried the clearance, noting the discrepancy. Upon realizing the confusion and observing the movement of Simmons 4158, the controller canceled the takeoff clearance for Simmons 4058. The crew of Simmons 4058 responded to the cancellation by stating, "We thought that was gonna happen."
At the time of the event, a pilot-related work slowdown was occurring. Controllers reported that pilots were taxiing more slowly than usual and frequently appeared lost or confused while navigating the ground.
Findings
The investigation identified flight call sign confusion as a primary factor in the incident. The safety board issued recommendations to address similar instances of call sign confusion in air traffic control communications.