Expectation Bias, Distraction Led to Runway Collision

Crew “expectation bias and distraction” led to a Hawker 850XP taking off without a clearance and colliding with a landing Cessna Citation Mustang on an intersecting runway at Houston Hobby Airport (KHOU) on Oct. 24, 2023, according to the NTSB final report. The Mustang—on landing rollout—was substantially damaged when, on lift off, the Hawker’s left wingtip struck the left side of the Citation’s tail cone. The Hawker, with minor damage, returned to land. Daylight VMC prevailed.

There were no injuries to the two pilots and one passenger aboard the Hawker, which was operating under Part 135, or to the one pilot and three passengers aboard the Mustang being operated under Part 91.

Some 4.5 minutes before the collision on a nine-mile final, Mustang N510HM was cleared to land on Runway 13. About 2.5 minutes before the collision, N510HM reported a four-mile final. Two minutes later, Hawker N269AA was cleared to “line up and wait” (LUAW) on Runway 22. The pilot monitoring (PM) correctly read back the clearance, but both pilots told accident investigators that they also recalled hearing a subsequent clearance for takeoff. However, a review of ATC recordings revealed that there was no takeoff clearance issued to N269AA or any other aircraft at that time.

The NTSB determined this discrepancy was likely due to the pilots’ expectation bias, a cognitive phenomenon where individuals perceive what they expect to hear or see and act accordingly. But the Safety Board also concluded that the Hawker pilots may have been distracted initially by instrumentation issues at the time of the LUAW clearance and then warning alarms on the takeoff roll.

With the Hawker in position for takeoff, the crew noticed the programmed V speed references were no longer displayed. They discussed the issue, and the PM began re-entering data into the flight management system. The pilot flying (PF) stated he felt “a little bit rushed” due to the perceived takeoff clearance and did not want to delay on the runway. “This activity may have distracted the pilots and exacerbated their expectation bias,” said the final report.

Controllers twice instructed N269AA to stop and hold position but received no response. The NTSB believes the Hawker crew may “not have recognized the instructions” because they were likely distracted by two warning messages as they began the takeoff role. First, they noticed that the rudder bias system had activated, which they resolved by adjusting thrust. Second, the elevator trim warning system activated, and the PM rolled the pitch trim slightly nose down which extinguished the warning. Both pilots recalled that they did not see the Mustang until about one second before the collision.

Investigators also discovered that the Hawker’s cockpit voice recorder was inoperative due to activation of the impact or G switch. This can occur for several reasons, but the NTSB said, “The flight crew should have been aware of the CVR’s nonoperational status during the before start checklist prior to the accident and the two previous flights, had they pressed the CVR test button and noticed that none of the indicator lights on the CVR control unit had illuminated.”