N300ER - 2013 BOMBARDIER INC BD-100-1A10 - Complete Aircraft History & Registry Information

March 03, 2023 - Windsor Locks, Connecticut

Damage Level

Minor

Description

The flight crew flew the passengers to their destination the day before the accident, and were conducting the return flight the following day. During the exterior preflight inspection, the second-in-command (SIC) was interrupted by line personnel delivering ice to the airplane and inadvertently failed to remove the right side pitot probe cover. The flight crew completed the remainder of their preflight activities, boarded the passengers, and taxied for takeoff. During takeoff, the SIC observed an anomaly with his right side primary flight display (PFD) airspeed indicator and he called for the pilot-in-command (PIC) to abort the takeoff. The PIC aborted the takeoff and taxied the airplane off the runway onto a taxiway. The SIC suspected that he may have forgotten to remove the pitot probe cover, and while stopped on the taxiway with the right engine running, he exited the airplane and removed the cover. Data recovered from the airplane’s flight data recorder (FDR) indicated that the crew aborted the takeoff 16 seconds after thrust application, and the airplane reached a maximum speed of 104 knots (kts) as indicated by the left PFD airspeed indicator. The right PFD airspeed indicator data was consistent with the pitot probe remaining covered. While on the taxiway, the PIC began troubleshooting a Crew Alerting System (CAS) cyan (blue) “RUDDER LIMITER FAULT” advisory message. He also noticed that the flight director was stuck in a pitch mode. He conducted multiple avionics stall tests, which had cleared the message on past flights; however, he was unable to clear the advisory message. The SIC initially indicated that he would call maintenance control; however, after a short discussion with the PIC, both flight crew members agreed to continue the flight with the advisory message posted. The flight crew did not consult the airplane’s “Go/No-Go” guide, but if they had, they would have found that the Rudder Limiter Fault advisory message was a “No-Go” item, and that the Minimum Equipment List provided no relief to depart with that message displayed. During the subsequent takeoff, the SIC noticed that the airplane’s V-speeds were no longer referenced (“bugged”) on the airspeed indicator, and he called the speeds from memory. When the airplane passed through about 400 ft radio altitude, an amber (yellow) caution “MACH TRIM FAIL” CAS message posted. The PIC turned the airplane on course and shortly after takeoff, turned on the autopilot (AP), after which the CAS immediately displayed an additional amber “AP STAB TRIM FAIL” caution message. During the climb to cruise altitude, the pilot disconnected the autopilot via his use of the horizontal pitch trim control wheel button. Following his trim adjustments and the resulting disconnect of the autopilot, he subsequently reengaged the autopilot two additional times. With each disengagement and reengagement, all AP-related caution messages would clear, and then reappear upon autopilot reengagement. Furthermore, during the second and third engagements, an additional “AP HOLDING NOSE DOWN” caution message was displayed as airspeed increased in the climb. According to the cockpit voice recorder (CVR), the SIC asked if the autopilot was failing to off, or if the PIC was disengaging the autopilot. The PIC informed the SIC that he disengaged the autopilot, but during the subsequent disengagements and reengagements, he never announced to the SIC that he was turning the autopilot on or off. The SIC advised the captain to not use the autopilot during the climb, to which the PIC agreed. Shortly after receiving the amber CAS caution messages, the PIC called for the SIC to “get the checklist,” but did not call for a specific checklist by name. The flight crew then became fixated on reprogramming the V-speeds into the Flight Management System (FMS), as the SIC believed that the caution messages may have been related to a configuration problem with the V-speeds and FMS since they had cleared following the aborted takeoff. About 8 minutes after the PIC called for the checklist, the SIC located the quick reference card (QRC) and the “PRI STAB TRIM FAIL” [Primary Stabilizer Trim Failure] checklist. The SIC reported in a postaccident interview that he selected this checklist because it was the only trim failure checklist on the QRC, and it seemed to address the root cause of the problem. Although there were multiple CAS messages displayed, he did not consider using any other checklist. The SIC reported that he visually showed the PIC the checklist, and they agreed to execute the checklist. The first action item was to move the stabilizer trim switch (“STAB TRIM”), located on the center console, from “PRI” (Primary) to “OFF.” The SIC read the checklist item aloud and subsequently moved the switch to off. Flight data recorder (FDR) information indicated that, as soon as the switch position was moved, the autopilot disconnected, and the airplane, which had been in a 3° nose-up attitude, rapidly pitched up to 11° in one second. The normal acceleration then rapidly rose to 4g. The PIC then pushed the control column forward with at least 90 lbs of force, the airplane pitched down to a near nose-level attitude, and the normal acceleration was reduced to -2.3g. The control column was subsequently pulled back through neutral, and the airplane rapidly pitched up to over 20° nose-up and more than 4g of normal acceleration. The FDR then stopped recording as the inertial g switch was triggered by the loading. As a result, the full extent of the pitch event was not recorded. The airplane’s maneuvering load factor limitation was +2.6g. The PIC reported that, immediately before the pitch oscillations, his left hand was on the flight controls and his right hand was guarding the right side of the flight controls. He reported that he did not anticipate the airplane pitching up so rapidly, but he did expect the autopilot to disconnect upon turning the stabilizer trim switch off. Shortly after the in-flight upset, the flight crew were alerted to a passenger that had been seriously injured. The SIC exited the flight deck to check on the passenger and to provide medical attention. He subsequently informed the PIC that there was a medical emergency and that they needed to land. About 17 minutes after the in-flight upset, the flight landed at the diversion airport. Later that day, the passenger succumbed to her injuries sustained during the in-flight upset. Postaccident download of the horizontal stabilizer trim electronic control unit (HSTECU) non-volatile memory found that, during the aborted takeoff, the speed mismatch between Air Data Computer 1 (ADC1) and ADC2 exceeded 20 kts for more than 5 seconds (due to the covered right pitot probe). This scenario resulted in key faults being recorded in the HSTECU. A review of the logic for these fault messages showed that the HSTECU latched an "ADC1/ADC2 Miscompare," indicating an airspeed data mismatch between ADC1 and ADC2, resulting in the HSTECU posting the Rudder Limiter Fault advisory message. In addition, a “Confirmed Mach Valid” latched to FALSE, which resulted in the Mach Trim Failure message, and the HSTECU inhibiting the autopilot trim function of the stabilizer. The manual stab trim operated at a reduced rate of movement, but was functional. The series of faults introduced into the HSTECU following the aborted takeoff resulted in the crew receiving the “AP STAB TRIM FAIL” CAS caution message upon autopilot engagement, due to the HSTECU inhibiting the autopilot trim function of the stabilizer. With the autopilot engaged and the trim function inhibited, the autopilot subsequently alerted the flight crew to “AP HOLDING NOSE DOWN,” which was meant to alert the crew that the autopilot was on, but that the airplane was out of trim and the autopilot was holding additional load on the flight controls. According to the airplane manufacturer, the “MACH TRIM FAIL” caution message was inhibited by the airplane’s avionics system and was not displayed to the flight crew on the CAS until the airplane was in the air (weight off wheels) and above 400 ft radio altitude. Flight testing of the accident scenario conducted after the accident, in a like make and model airplane, confirmed that the series of CAS messages likely presented in-flight were “MACH TRIM FAIL” (at 400 ft radio altitude), “AP STAB TRIM FAIL” (upon autopilot engagement), and “AP HOLDING NOSE DOWN” (upon speed deviation from where the AP was engaged). The testing confirmed that the AP-related CAS messages would clear and then reappear upon autopilot engagement and airspeed changes. The data indicated that there was no HSTECU malfunction other than the faults related to the ADC1 and ADC2 airspeed discrepancy during the initial takeoff. Additionally, there were no faults that would have produced a “PRI STAB TRIM FAIL” CAS message. Both the AP STAB TRIM FAIL and the AP HOLDING NOSE DOWN QRH checklists provided warnings about the airplane’s out-of-trim condition when those messages were displayed and also warned that abrupt changes in control forces may be experienced when disconnecting the autopilot. The checklists required the flight controls to be held firmly and provided a caution to minimize changes to airspeed and configuration to minimize the out-of-trim state. It is likely that the accident would have been prevented had the pilots completed one of the AP-related checklists; however, the SIC and PIC agreed to complete the PRI STAB TRIM FAIL checklist, despite the CAS not displaying this message. The crew displayed inadequate crew resource management on a number of occasions, beginning with their actions following the aborted takeoff, when they failed to recognize the “RUDDER LIMITER FAULT” message as a No-Go item. Had the flight crew called their maintenance control as required, they would have been instructed to power down the airplane, which likely would have cleared the HSTECU faults latched during the takeoff as a result of the airspeed discrepancies between ADC1 and ADC2 due to the right pitot probe still being covered. Then, despite the SIC questioning the decision to continue the climb to cruise after receiving the cascading CAS messages, the PIC continued the flight as planned. Additionally, the PIC failed to communicate with the SIC regarding his continued use of the autopilot during the climb even after receiving a warning from the SIC to not use the autopilot and agreeing with the SIC’s comments. The PIC’s continued use of the autopilot likely contributed to the SIC’s difficulty in selecting the correct checklist, given that the AP-related caution messages would disappear each time the autopilot was disconnected, but would reappear once reengaged. The PIC did not call for a specific checklist to address the CAS messages, and when the SIC showed the checklist to the PIC for agreement before they completed it, neither identified the chosen PRI STAB TRIM FAIL checklist as incorrect. According to the CVR transcript, shortly after regaining airplane control, both crew members acknowledged that the autopilot should not have been used during the climb. The fatally injured passenger’s seatbelt was not fastened at the time of the in-flight upset. The PIC reported that the seatbelt sign was on for the entire flight, and that his regular practice was to never turn it off. The in-flight upset occurred near 23,000 ft, about 9 minutes into the flight. It is likely that the passengers had no expectation for the seatbelt sign to be turned off at any time during the flight, given that they regularly flew with this flight crew. As a result, the passengers had to use their own judgement regarding whether it was safe to get up and move about the cabin. Had the flight crew chosen the correct QRH checklist, they would have been warned of the possible abrupt change in control force upon autopilot disengagement and could have ensured that the passengers were seated with seatbelts fastened before completing the non-normal procedure. Then, even if an in-flight upset occurred, serious injury likely could have been avoided entirely by each passenger simply being seated with their seatbelt fastened. There were no other serious injuries reported from any other occupant on board. The sequence of events that ultimately led to the accident originated with the flight crew’s failure to remove the right pitot probe cover before takeoff and their subsequent decision to depart with a No-Go CAS message. Although the message was advisory and not cautionary in nature, the airplane was indirectly alerting the flight crew to additional faults that had been introduced into the airplane’s systems following the aborted takeoff. The crew’s continuation of the flight with an unairworthy airplane directly contributed to the subsequent series of CAS messages, which the crew mis-diagnosed during the climb, resulting in the in-flight upset and loss of airplane control.