Green Circle Demolition Textron Aviation Inc 510 accident

A Raytheon Hawker 850XP, N269AA, operated by DuPage Aerospace, collided with a Textron Aviation Inc 510 Citation Mustang, N510HM, at the intersection of runways 13R and 22 at William P. Hobby Airport (HOU) in Houston, Texas. N510HM was rolling after landing on runway 13R, and N269AA was on its takeoff roll on runway 22. About the time of lift-off, the left wingtip of N269AA struck the left side of N510HM’s tail cone, resulting in substantial damage to N510HM. N269AA continued its takeoff, and during initial climb advised the HOU air traffic control tower (ATCT) that they needed to return to the airport. The local control (LC) controller provided vectors to runway 13R, where N269AA landed uneventfully. About 4.5 minutes prior to the collision, the LC controller cleared N510HM to land while it was on a 9-mile final. About 2.5 minutes before the collision, N510HM reported a 4-mile final. About 2 minutes prior to the collision the LC controller cleared N269AA to “line up and wait” (LUAW) on runway 22. The pilot monitoring (PM) correctly readback the clearance with “line up and wait uh, two two uh, six nine Alpha Alpha”. During post-accident interviews, the PM recalled hearing the LUAW clearance and a subsequent clearance for takeoff, and the pilot flying (PF) recalled hearing only a clearance for takeoff. However, a review of the certified air traffic control voice recordings revealed that there was no takeoff clearance issued to N269AA (or other airplanes) at that time. 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. Both Hawker pilots recalled that near the time of the LUAW clearance, the programmed V-speed references were no longer displayed on their instruments. They discussed the issue, and the PM began re-entering data into the flight management system to restore the speeds. The PF stated he felt “a little bit rushed” due to the perceived takeoff clearance and he did not want to delay on the runway. The crew discussed the speeds and elected to proceed with the takeoff. This activity may have distracted the pilots and exacerbated their expectation bias. Additionally, when the LC controller issued the LUAW clearance, they did not provide a traffic advisory to either airplane, which is a required procedure. A traffic advisory would have provided more context and awareness for both crews about the location and activity of the other airplane. However, the PM correctly acknowledged the LUAW clearance, which should be sufficiently clear that a delay was required before takeoff could commence, regardless of the reason. Therefore, it is unlikely that the lack of a traffic advisory contributed to the outcome. The N269AA crew taxied onto the runway and began the takeoff without a clearance from the ATCT. The ATCT controllers observed its movement and the Airport Surface Detection Equipment – Model X (ASDE-X) in the ATCT sounded a warning of a perceived collision. The LC controller twice instructed N269AA to stop and hold position but received no response. The pilots recalled that as they began the takeoff roll, two events occurred. First, they noticed that the rudder bias system had activated, which they resolved by adjusting the thrust such that both engines were set to similar power setting. The PF did this, and the rudder bias system deactivated. Second, the elevator trim warning system activated, and the PM then adjusted the pitch trim (by rolling it nose down about 1/16 inch) which extinguished the warning. These activities likely distracted the pilots and prevented them from recognizing the instructions from the LC controller to stop. They continued their takeoff roll, and both pilots recalled that they did not see N510HM until about 1 second before the collision. According to the chief pilot of DuPage Aerospace, company policy and training (and as part of every takeoff briefing) specify that takeoffs should be aborted for “any fault or failure” below 80 knots. He elaborated that if a fault were indicated on the annunciator panel [which is where the elevator trim warning system indictor is displayed], “then you should be aborting.” He further stated that “it depends what the fault or failure is” and described that if the elevator trim warning activated during takeoff, while the trim setting was very near either end of the takeoff range, that he would re-trim the airplane and then move the throttles back into the takeoff position and make sure the warning did not reactivate. If it were to reactivate, he would then abort the takeoff. Similarly, the PM noted during his interview that the elevator trim warnings are common in the Hawker, particularly when the trim setting was at or near the very aft mark of the [takeoff range] of the trim indicator. He said that typically a slight roll forward of the trim wheel would extinguish the light. This suggests there is some discrepancy or exceptions between the operator’s policy and at times, the in-practice procedures, with regard to conditions that warrant an aborted takeoff. In this case, the elevator trim warning (and the activation of the rudder bias) was temporary and easy to quickly remedy, though it happened to occur at a critical time as ATC was attempting to stop the takeoff roll. Separately, the chief pilot stated that it was company policy (and an element of the before start checklist) to test the cockpit voice recorder (CVR) prior to every flight. After the accident, the CVR was found to be inoperative due to activation of the impact or G switch, which interrupts electrical power to the CVR and its control unit in the cockpit. This can occur for several reasons, including hard landings or during maintenance operations. Review of the recording revealed audio consistent with maintenance activities. The CVR does not record date and time, however it likely became inoperative at some time prior to this crew’s pairing, which began two flights prior to the accident flight. Post accident testing of the CVR and the impact switch revealed they operated as designed. 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 1) pressed the CVR test button and 2) noticed that none of the indicator lights on the CVR control unit had illuminated, because the control unit (and CVR) were not powered. Normally, the indicator lights show the progress of the self-test, and whether the test passes or fails. However, during normal operation (no faults, and not in self-test mode) none of the indictor lights on the cockpit voice control unit are illuminated. Therefore, the control unit would look the same if 1) the CVR was running normally, or 2) if it was completely unpowered by the activated inertial switch. The only methods for the flight crew to determine if the unit is functioning are to use the self-test function, or by monitoring the audio through the headset jack on the control panel. Since the CVR was inoperative, the relevant crew conversations that would have provided additional insight to the investigation were not captured. This demonstrates the importance of properly testing the CVR before each flight.

Verbatim NTSB analysis and probable cause from the NTSB dataset