Despite acknowledging ATC instructions to line up and wait (LUAW), the flight crew of a Bombardier Learjet 60 took off without clearance at Boston Logan International Airport (KBOS) and thus caused a near-collision with a JetBlue Embraer E190, according to the NTSB final report published yesterday.

The incident, which caused no injuries or damage, occurred at 6:55 p.m. on February 27. Runways 04R and 09 are intersecting, and BOS tower had instructed the flight crew of the Learjet, being operated as a Part 91 positioning flight by charter operator Hop-A-Jet, to LUAW on Runway 09 while the JetBlue had been cleared to land on Runway 04R.

The Learjet flight crew read back the controller’s instructions to LUAW, but they began the takeoff roll instead. After being alerted by the airport's surface-detection equipment, model X, the tower controller issued go-around instructions to the JetBlue crew, and they initiated the maneuver while over Runway 04R before reaching the intersection with Runway 09.

The closest proximity between the airplanes occurred when the E190 was about 30 feet agl during the landing flare, near the point where the runways intersected. As they entered the flare after crossing the threshold, the JetBlue pilots saw the Learjet cross 04R on Runway 09 but could not estimate how far away the airplane was.

The Learjet captain said they had heard a clearance that “seems to be line up and wait." He further stated that “he probably responded to the clearance, but in his mind, they were cleared for takeoff.” After departing, ATC provided a phone number to call upon landing. In that call, BOS tower told them that they had taken off without authorization and caused an airplane that had been cleared to land on Runway 04 to execute a go-around, passing about 400 feet above them. Both pilots filed NASA Aviation Safety Report System reports after ATC’s phone call.

“I cannot understand what happened to me during the clearance,” the pilot told the NTSB in a later interview. “The only thing that comes to my mind is that the cold temperature in Boston affected me. I was not feeling completely well and had a stuffed nose.” Said the copilot: “As we lined up, I asked my work partner if we were cleared for takeoff, and [he] said yes. We were both convinced that we were cleared for takeoff.”