A Crew Divided

The NTSB has released its final report on a 26 July 2021 accident in which a 16-year-old Bombardier CL-600-2B16, registration N605TR, was destroyed and the entirety of its occupants—six passengers and two pilots—lost their lives following an instance of loss of control in flight while attempting to land at California’s Truckee-Tahoe Airport (TRK).

The accident aircraft was operated as a personal flight under Part 91 of the Federal Aviation Regulations.

The Pilot In Command (PIC), Second In Command (SIC), and four passengers departed for Truckee, California on a non-revenue flight operating under Instrument Flight Rules (IFR). The departure, climb, and enroute portions of the flight were uneventful.

During descent into TRK, Air Traffic Control (ATC) advised the flight-crew to expect the Area Navigation (RNAV [GPS]) approach to runway 20. Throughout the approach and attempted landing, the PIC was the Pilot Flying (PF) and the SIC was the Pilot Monitoring (PV). The PIC stated and the SIC calculated and confirmed the aircraft’s landing weight required a runway of greater length than the TRK runway 20.

Rather than request a straight-in approach to TRK runway 11—the longer runway—the PIC advised the SIC they would accept the clearance for the RNAV approach to runway 20 and circle to land on runway 11. The SIC subsequently relayed the PIC’s intentions to ATC, which approved the requested procedure.

Notwithstanding checklist requirements calling for such, the flight-crew failed to formally brief the circling procedure.

ATC issued holding instructions with which the PIC was slow to comply. The SIC, presumably inferring imminent task-saturation of the part of the PIC, initiated the holding-pattern entry and informed ATC the aircraft was established in the hold. Approximately twenty-seconds later, ATC cleared the accident-aircraft for the approach.

Before the SIC confirmed the approach clearance, he inquired after the PIC’s readiness to commence the approach procedure. The PIC responded in the affirmative. The SIC subsequently noted aloud the aircraft’s excessive airspeed at the approach’s commencement, and suggested a 360-degree turn. The PIC gave no response to the recommendation and made no attempt to turn the aircraft.

Upon visually identifying the airport, the SIC advised the PIC to execute a 90-degree right turn to put the aircraft on an approximate heading of 290-degrees—essentially a reciprocal (downwind) course to runway 11 and consistent with Bombardier’s operating manual procedures for the downwind leg of a circling approach.

The SIC inadvertently instructed the PIC to roll out of the turn prematurely, however, and the PIC leveled the aircraft’s wings on a magnetic heading of approximately 233-degrees—some 57-degrees south-southwest of a parallel (downwind) course to runway 11. The early roll-out put the aircraft on a course requiring an excessively tight corrective turn.

Upon initiating the turn to final, the aircraft was approximately 1.3-nautical-miles outside the maximum circling radius established for the Challenger 600’s approach category. The SIC deployed flaps 45-degrees after confirming such with the PIC. Bombardier’s operating manual procedure for the downwind leg of a circling approach called for a flap-setting of 30-degrees, but stated 45-degrees could be used at the flight-crew’s discretion, provided the approach remained within the limitations prescribed in the Aircraft Flight Manual (AFM).

At the time, the aircraft’s airspeed was 44-knots above the landing reference speed (Vref) of 118-knots previously calculated by the flight-crew. The SIC advised the PIC: “I’m gonna get your speed under control for you.” The FO likely reduced power after making the aforementioned statement, as engine fan-speeds (N1) began to decrease from approximately 88-percent to 28-percent and the aircraft commenced slowing form 162-knots.  

After several attempts by the SIC to point out the airport, the PIC acknowledged he had the runway in sight. The PIC’s initial inability to sight the runway might have been attributable to reduced visibility occasioned by smoke in the area.

The SIC—who was 13-years older than the PIC and had logged 14,308 total hours and 4,410 hours in type to the PIC’s 5,680 total and 235 hours in type—continuously reassured and instructed the PIC throughout the circle-to-land procedure.

On the base leg to runway 11, and approximately 25 seconds prior to the aircraft's impact with the ground, the SIC began prevailing upon the PIC, asking repeatedly for control of the aircraft. Neither crew-member, however, verbalized the positive transfer of aircraft control required by the operator’s General Operating Manual (GOM). Ergo, the NTSB could not determine which pilot had control of the aircraft following the antecedent requests.

As the Challenger crossed the runway extended-centerline while maneuvering for landing, the SIC noted that the aircraft was too high. One of the pilots (recorded flight data did not indicate which) deployed the Challenger’s flight-spoilers fully—likely for purpose of increasing the jet’s sink rate. In the CL-600, the flight-spoilers are actuated by means of a single control lever accessible to both pilots.

At the time the flight-spoilers were deployed, the aircraft’s airspeed was 135-knots, 17-knots above the Vref based on an erroneous Basic Operating Weight (BOW) programmed into the accident-aircraft’s Flight Management System (FMS). Approximately seven-seconds later, the left-bank attitude steepened further, and the aircraft’s Stall Protection System (SPS) stick-shaker and stick-pusher engaged. The PIC inquired aloud: “What are you doing?” The SIC again repeatedly entreated the PIC to “let me [the SIC] have the airplane.”

The stick-shaker and stick-pusher then briefly disengaged, re-engaging a few seconds later. The aircraft subsequently entered a rapid left roll, consistent with a left-wing stall, and impacted terrain. A post-impact fire consumed the majority of the wreckage.

Analysis of data retrieved from the accident-aircraft’s Flight Data Recorder (FDR) indicated the Challenger’s engines were functioning normally at the time of impact. Indications of neither flight-control nor system-malfunction were noted

The accident-aircraft’s flight-control linkages were destroyed by either high-energy impact forces or the post-impact fire, which precluded comprehensive examination of the wreckage.

Examination of the primary flight control surfaces revealed no pre-impact mechanical anomalies. Accident-flight engine data showed no power interruptions and suggested no powerplant mechanical anomalies.

The PIC and SIC were appropriately qualified to perform their respective duties. The accident-flight was the first crew-pairing of the two pilots noted in the operator’s duty and flight-time records. A review of the operator’s documentation revealed the accident flight complied with the requirements of Title 14 Code of Federal Regulations (CFR) Part 91, General Operating and Flight Rules, and was not conducted under the operator’s 14 CFR Part 135 certificate. Although toxicology testing detected ethanol in the SIC’s tissue, given the different concentrations of ethanol, the presence of n-propanol, and the state in which the body was found, it is likely the identified ethanol was from sources other than ingestion.

The flight-crew elected to conduct a circling approach to runway 11 and never requested (of ATC) the straight-in RNAV (GPS) approach to the desired runway. The crew failed, also, to brief the new circling approach after previously briefing the anticipated straight-in approach. The flight crew’s failure to brief the circling approach connoted poor Crew Resource Management (CRM) insomuch as the pair failed to prepare for adverse developments and contingencies germane to such. Lack of preparation occasioned the commission of critical errors during the flight’s approach phase which included:

• Flying the circling approach at a higher airspeed than the upper-limit specified for the CL-600’s approach category (C).
• Failing to establish the aircraft on the downwind leg of the circle-to-land approach.
• Failing to visually identify the landing runway early in the approach—likely due to obscuration by smoke.

The accident-aircraft’s excessive airspeed reduced the interval during which the flight crew was to have configured the airplane, assessed its position relative the runway, and made corrections to its trajectory. During the approach, the SIC repeatedly attempted to call the PIC’s attention to the aircraft’s high rate of speed. The PIC, however, rejected the SIC’s suggestion to execute a 360-degree turn early in the approach; such a maneuver would have provided additional time and distance in which to diminish the aircraft’s speed and stabilize the approach.

The accident-aircraft’s speed at the time of the circling-maneuver’s commencement was 160-knots—twenty-knots higher than the upper-limit of the circle-to-land approach speed established for Category C aircraft. What’s more, the aircraft’s speed didn’t drop below the Category C maximum until the flight-crew was preparing to commence the approach’s base-leg turn.

The aircraft’s proper alignment with the landing runway was precluded by the aircraft’s close proximity to the airport and the PIC’s failure to establish a proper downwind course. The PIC, in fact, did not establish the airplane on a downwind leg parallel to the destination runway, but instead flew a downwind leg convergent with the runway centerline, thereby tightening the pattern and forcing an overshoot of the runway centerline only 0.8-nautical-miles from the TRK runway 11. The atypical downwind and base legs impeded the flight-crew’s ability to properly orient the aircraft with the runway’s centerline during the accident-flight’s final-approach segment.

Early in the approach, the SIC received updated weather information—including an advisory of reduced visibility due to heavy smoke in the vicinity of TRK—from an Automated Weather Observation System (AWOS). The SIC did not, however, relay the visibility advisory to the captain. The smoke likely restricted the PIC’s ability to visually identify the landing environment.

Throughout the approach, the SIC counseled the PIC to remain calm, stating time to maneuver the aircraft for a stabilized approach was plentiful, when—owing to the overly fast and tight circling-maneuver—it was not.

The SIC’s counsel and reassurances evinced his awareness of the adverse effects of self-induced pressure to perform. Nevertheless, the SIC exhibited the selfsame self-induced pressure to salvage a deteriorating approach. Moreover, the PIC, in addition to improperly setting up the approach, failed to request additional time in the holding-pattern and rejected the SIC’s suggestion to slow the aircraft by means of a 360-degree turn. In the absence of external pressure to land the aircraft, the PIC’s actions indicated self-induced pressure to perform without benefit of assistance or correction.

The accident-aircraft, after turning on to the base leg, was not in a position from which it could align with the runway without overshooting the centerline, nor could the pilots execute a normal descent to the runway. Furthermore, the Challenger’s airspeed was neither on nor approaching the targeted 118-knot Vref speed. The stabilized approach criteria spelled out in the operator’s GOM required the certificate-holder’s aircraft to be in a position to execute a normal descent to the landing runway, and airspeed to be on or approaching target no later than five-hundred-feet above field-elevation in Visual Meteorological Conditions (VMC). Having failed to meet subject criteria, the accident-approach was, by definition, unstabilized.

Upon realizing the approach had destabilized, the flight-crew should have, but did not initiate a go-around. The operator’s GOM empowered both pilots to perform a go-around, and the circumstances of the accident-approach did not preclude such. In any case, the SIC—contrary to the requirements of his role as spelled out in the operator’s GOM, made no callout for a go-around after the exceedance of the operator’s stabilized approach criteria. The flight crew’s continuation of the unstabilized approach, rather than going-around, was at once consistent with self-induced pressure to perform and degraded decision making.

Some eight-seconds after his first verbalized request for control of the aircraft, the SIC stated: “We’re gonna go through it and come back okay?” The statement likely pertained to the runway centerline, and evinced intent to salvage the unstable approach. As the accident-aircraft crossed the centerline, the PIC set forth: “It’s here”—also likely in reference to the runway 11 centerline. The SIC subsequently responded: “Yes, yes it’s here we are very high.” The utterance indicated the SIC was aware the aircraft was not in a position to make a normal approach to the runway. Contemporaneously, the Challenger’s flight-spoilers were deployed. The NTSB surmised—based on the SIC’s stated intention to overshoot and return to the runway centerline and his cognizance of the aircraft’s excessive altitude—that the SIC had deployed the flight-spoilers in an attempt to descend expediently toward a nominal glidepath to the landing runway.

Upon crossing the extended runway 11 centerline, the accident-aircraft approached a stall—as evinced by the stick-shaker’s engagement. The SIC again repeatedly requested control of the aircraft, likely motivated by a desire to continue the approach. The CVR, however, recorded neither a positive-transfer of aircraft control nor any indication the PIC had relinquished aircraft control to the SIC.

Throughout the accident-flight, the SIC acted as a de facto instructor to the PIC. His awareness of such might, in the NTSB’s estimation, have driven his desire to assume control of the aircraft as the approach deteriorated. The NTSB further posits—in light of the SIC’s desire to continue the approach and his multiple requests for control of the jet—that he improperly attempted to take control of the Challenger without the PIC’s consent and inadvertently increased the left banking attitude and precipitated the ensuing stall.

Notwithstanding the SIC’s alleged attempt to usurp control of the aircraft, the PIC should have, but failed, to take decisive action to retain control of the aircraft—so stated the NTSB. In addition, both the SIC’s attempt to salvage the unstabilized approach and the PIC’s failure to assert his command authority evinced degraded crew-performance and vigilance. During the accident-flight’s final ten-seconds, the CVR captured reactive statements from both crew-members, including the SIC’s multiple requests for control of the aircraft, suggestive of the pair’s failure to cooperate. The PIC’s lack of assertiveness, both crew-member’s failures to recognize their respective psychological stresses, and the pilots’ mutual disregard for safety while attempting to salvage an approach gone terribly wrong point in unison to improper Crew Resource Management (CRM) in the accident-flight’s final moments.

Failures in CRM generally connote a lack of clear communication between crew-members and collective failure to recognize degraded performance and diminished vigilance in the cockpit. Poor CRM contributed to the degraded performance of the accident-flight’s crew and their competition for control of the aircraft—which resulted, ultimately, in a disastrous stall and loss of both life and property.

Examination of the accident-aircraft’s maintenance logs revealed the weight-and-balance figures entered into the Challenger’s FMS units had been incorrect. Approximately ten-months prior to the accident-flight, a maintenance facility serviced the accident-aircraft’s FMS units in compliance with scheduled battery replacement schedules. While the facility reinstalled the required databases—which included approach-speed and performance data—a weight specific to the aircraft was not input. The NTSB deduced the accident-aircraft had likely been operating with an incorrect empty-weight since the maintenance. Records indicated the operator had conducted four flights in the aircraft since acquiring such in May 2021.

The erroneous default empty weight entered into the FMS was approximately three-thousand-pounds lighter than the estimated actual empty weight of the aircraft at the time of the accident-flight. Owing to the inaccuracy, the FMS computed an erroneous Vref of 118-knots—six-knots slower than the correct Vref speed of 124-knots. Although the oversight instantiated a want for attention to detail on the operator’s part, the NTSB determined the weight-and-balance discrepancy did not contribute to the stall insomuch as the accident-aircraft—during its final moments—was flying several knots above the correct Vref speed.

Accident data and the NTSB’s performance study revealed full-deployment of the flight-spoilers some 12-seconds prior to the accident had a significant effect on the accident-aircraft’s stall-margin in the seconds prior to impact. Performance analysis showed the Challenger’s stick-shaker would have engaged at a bank-angle of approximately 36-degrees and a Calibrated AirSpeed (CAS) of 130-knots. Had the flight spoilers been stowed at the antecedent airspeed, the stick-shaker would not have engaged until the accident-aircraft reached a calculated bank-angle of 50-degrees. The Challenger’s stall-margin, therefore, was significantly reduced by the deployment of the flight-spoilers.

As mentioned, CVR evidence suggested the SIC most likely deployed the flight-spoilers. The NTSB was unable to determine whether any of the statements recorded by the CVR at the time of flight-spoiler deployment were related, specifically, to that action. While the CVR captured the PIC questioning an action undertaken by the SIC just prior the stall warning; it remains unclear whether the PIC’s inquiry was in response to a specific control input made by the SIC, or to the SIC’s continued and repeated requests for control of the aircraft.

The NTSB theorizes the recorded momentary disengagement of the accident-aircraft’s stall-warning system is attributable not to the flight-crew, but to Angle-Of-Attack (AOA) recovery occasioned by the stick-pusher’s activation.

The combination of the SIC’s improper deployment of the flight-spoilers and the accident-aircraft’s bank-angle and airspeed resulted in an exceedance of the critical angle-of-attack followed by an asymmetric stall of the Challenger’s left wing, a rapid roll, and impact with terrain.

The National Transportation Safety Board determined the probable cause(s) of the described accident to be:

• The SIC’s improper attempt to salvage an unstabilized approach by executing a steep left turn to realign the airplane with the centerline of the landing runway.  
• The PIC’s failure to intervene after recognizing the SIC’s erroneous action.
• Both pilots’ failure to heed warnings issued by the accident-aircraft’s stall-warning systems, which resulted in a left-wing stall and subsequent impact with terrain.

Contributing to the accident were the SIC’s improper deployment of the flight-spoilers, which decreased the accident-aircraft’s stall-margin.

• The PIC’s improper setup of the circling approach.
• The flight-crew’s self-induced pressure to perform.
• Degraded decision making resultant of poor crew resource management.

FMI: www.ntsb.gov