Story ID: 
AINsight: Recent Bizav Accidents Are Head-scratchers
By: Stuart “Kipp” Lau
Caption: Mishaps started with flight crews not responding correctly to flight control warnings on takeoff
Word Count: 1763
Two recently published accident reports have left me scratching my head. In both cases, the pilots of business jets attempted to troubleshoot maintenance issues “on the fly.” One was literally on the takeoff roll without consulting approved aircraft quick reference handbooks or manuals or seeking guidance from maintenance personnel.
The first accident led to an in-flight upset that killed a passenger, while the second resulted in a serious runway incursion where two aircraft collided at a runway intersection.
As a pilot and safety investigator, “Monday morning quarterbacking” is not my forte (I hate it!). But in this case, after digging through the two NTSB reports, I’m a bit perplexed as to why these professional pilots would attempt to take off and go fly with cockpit alerts related to flight control issues. All I can say, at this point, is, “C’mon Man!”
Unlike ESPN’s widely popular “C’mon Man”—a humorous segment on Monday Night Countdown featuring bloopers from professional football players—these two accidents were much more serious. The outcome of these events was tragic: one passenger was killed, three aircraft were damaged, and there was a potential to cause harm to many others.
Below are excerpts from the applicable NTSB reports.
Fatal Inflight Upset
In December, the NTSB published its final report on the fatal March 3, 2023 in-flight upset accident of a Bombardier Challenger 300. This event occurred on a Part 91 flight from Keene, New Hampshire, to Leesburg, Virginia.
According to the NTSB report, on the day of the accident, the second-in-command (SIC) of the flight was distracted and failed to remove the pitot probe cover on the right side of the aircraft.
During the takeoff roll, the SIC reported that the airplane accelerated normally, but he observed that the right primary flight display (PFD) airspeed indicator did not agree with the left-side airspeed indicator. This prompted the pilot-in-command (PIC) to reject the takeoff.
Following the rejected takeoff, the PIC exited the runway onto a taxiway. The left engine was then shut down, and the SIC opened the main cabin door and walked to the front of the airplane, where he found a “red pitot probe cover” installed on the right-side pitot probe. He then removed the cover, noticing no damage, and returned to the cockpit. 
The PIC then restarted the left engine and resumed the taxi for another takeoff attempt. Shortly after the engine started, the crew reported that a “RUDDER LIMIT FAULT” advisory message was annunciated on the crew alerting system (CAS). The PIC attempted to clear the message using an avionics “stall test” switch, which failed to work. At this point, the crew discussed calling maintenance control but decided to continue the flight since it was an advisory message and not a caution or warning message.
The flight crew did not consult the airplane’s guide in the quick reference handbook (QRH). On Bombardier business aircraft, the go/no-go guide is a table that provides guidance for non-normal advisory messages—either go with minimum equipment list relief or a no-go outcome. The “RUDDER LIMIT FAULT” advisory message is listed as a no-go item and would have grounded the flight.
During the second takeoff, the SIC noticed that the V-speeds were not set, but the acceleration was normal. From memory, the SIC called V1 and go/no-go rotate. During the subsequent climb, at 400 feet agl on the radar altimeter, flight data indicated a “MACH TRIM FAIL” caution message. Afterward, the PIC engaged the autopilot, and the “AP STAB TRIM FAIL” caution message was displayed.
The PIC would disengage and re-engage the autopilot several times—without advising the SIC—causing the autopilot caution messages to clear and then reappear as the autopilot was engaged. As the airspeed and altitude increased, the “AP HOLDING NOSE DOWN” caution message illuminated.
After receiving the amber caution messages, the PIC called for the SIC to “get the checklist” but did not call for a specific checklist by name. According to the report, the crew then became fixated on reprogramming the V-speeds in the FMS, believing that the caution messages were related to problems encountered following the rejected takeoff.
Approximately eight minutes later, the flight crew agreed to execute the “PRI STAB TRIM FAIL” checklist located on the quick reference card (QRC)—a CAS message that was not displayed. The SIC chose that checklist since it was the only trim-related checklist on the QRC, and he did not consider using any other checklist.
However, the correct checklist was available in the QRH and would have warned of the possible abrupt change in control force upon autopilot disconnect. It also would have ensured that passengers were seated with seat belts fastened.
According to the NTSB report, the first step in the “PRI STAB TRIM FAIL” checklist is to move the primary trim switch from primary to off. As the Challenger 300 crew switched this to off, removing power from the primary stab trim and disconnecting the autopilot, the aircraft abruptly pitched up to 11 degrees aircraft nose up, resulting in a load of four gs. Then the pitch decreased and the vertical acceleration changed to -2.3 gs, the NTSB said. Next, the control column was moved aft and the aircraft pitched up to 20 degrees with a resulting four-g load.
Following the upset, the flight crewmembers were alerted by a passenger that another passenger had been injured. The SIC exited the cockpit to check on the passenger and provide medical attention. Soon afterward, the SIC advised the PIC that there was a medical emergency and they needed to land. The passenger would later die at the hospital from her injuries.
The NTSB’s analysis of the horizontal stabilizer trim electronic control unit (HSTECU) non-volatile memory found that during the rejected takeoff, the speed mismatch between air data computer 1 (ADC 1) and ADC 2 exceeded 20 knots for more than five seconds due to the covered pitot probe. This scenario induced several fault messages, such as “ADC 1/ADC 2 miscompare,” into the HSTECU system logic that ultimately resulted in a “RUDDER LIMITER” fault and subsequent and cascading autopilot/trim failures. Flight testing of an exemplary Challenger 300 confirmed these findings.
Sadly, according to the report, the HSTECU faults could have been cleared if the unit—via circuit breaker or the entire airplane—was powered down and then back up before takeoff.
The NTSB determined that the probable cause of the accident was “the flight crew’s failure to remove the right-side pitot probe cover before flight, their decision to depart with a no-go advisory message following an aborted takeoff, and their selection of the incorrect non-normal checklist inflight, which resulted in an inflight upset that exceeded the load factor limitations of the airplane and resulted in fatal injuries to a passenger whose seatbelt was not fastened.
“Contributing to the severity of the inflight upset were the PIC’s decision to continue to climb and use the autopilot while troubleshooting the non-normal situation, and the PIC’s pilot-induced oscillations following the autopilot disconnecting from the out of trim condition. Also contributing to the accident was the crew’s inadequate crew resource management.”
Houston…We Have a Problem
On Oct. 24, 2023—seven months after the Challenger in-flight upset—the crew of a Hawker 850XP on takeoff roll struck a Cessna Citation Mustang that was landing on a crossing runway at Houston Hobby Airport (KHOU). Both aircraft were substantially damaged, but fortunately, none of the occupants were injured.
According to the NTSB preliminary accident report (the final report has not been published), the tower controller instructed the pilots of the Hawker to “line up and wait” on Runway 22, while the Citation Mustang was cleared to land on Runway 13R. In a post-accident interview, the Hawker pilots said they believed that they were cleared for takeoff when they took off.
According to the Hawker pilots, prior to reaching the runway, the V-speeds were no longer displayed on the flight display screens. This created a distraction, along with “RUDDER BIAS” and “PITCH TRIM” alerts that were displayed during the takeoff roll. Remarkably, the Hawker pilots were attempting to “resolve [these alerts] as they were on the takeoff roll.”
According to the report, as the Hawker approached Runway 22, it unexpectedly began its takeoff roll. At this point, a controller in the tower working clearance delivery noted the Hawker’s movement and notified the tower controller. The tower controller immediately instructed the Hawker crew to “stop, hold your position.” There was no response. Again, the tower controller yelled, “Hold your position, stop,” to which there was no response.
Less than two minutes after beginning its unauthorized takeoff, the Hawker’s left wingtip struck the empennage of the Citation. Both pilots of the Hawker stated that they did not see the Citation until about one second before impact, and they described the feeling as a “thud.” The Citation pilot said he did not see the Hawker and described the impact as a “sound similar to a truck tire blowing.”
After the aircraft hit each other, the Hawker crew continued their takeoff and immediately returned to land on Runway 13R. The Citation cleared the runway.
A post-accident examination revealed significant damage to the Hawker’s left winglet and wing leading edge surfaces. The Citation had significant damage to its empennage, including the tail cone, rudder, and other structural elements.
Conclusion
To me, as a fan of business aviation for more than 40 years, these accidents are unsettling. Is this a “Bedford moment”—the 2014 accident of a Gulfstream IV that killed seven people? Are these isolated events or is this a systemic issue in business aviation?
In each case, pilots during takeoff were confronted with cockpit alerts related to flight control issues. Guidance from approved aircraft manuals or insightful maintenance personnel would require these pilots to take a time out to reflect on the safety and legality of their flights.
In hindsight, in each case, the safest course of action would have been to simply clear the runway, set the parking brake, and pick up the QRH or phone a friend such as a maintenance manager or chief pilot.
The opinions expressed in this column are those of the author and are not necessarily endorsed by AIN Media Group.