NTSB Revises Probable Cause of 2018 Citation Crash

The aircraft was equipped with Tamarack Aerospace Group’s active technology load alleviation system (ATLAS), which operated independently of other airplane systems.

The system included the installation of Tamarack active camber surfaces (TACS), which are aerodynamic control surfaces mounted on the wing extensions that either hold their position in trail with the wing or symmetrically deploy trailing edge up or trailing edge down to alleviate structural loads. The TACS are actuated by the TACS control units (TCUs) and are not controlled by the pilot.

The winglets are designed to improve aircraft stability and fuel efficiency. 

According to the NTSB report, on November 30, 2018, the Citation took off from Clark Regional Airport (KJVY) in Jeffersonville, Indiana, en route to Chicago Midway International Airport (KMDW). There was one pilot and two passengers on board.

IMC prevailed, and the flight was on an IFR flight plan. Data provided by the aircraft’s ADS-B showed the airplane climbing to an altitude of about 1,400 feet then turning left to the assigned fix and continuing to climb. 

The pilot contacted ATC and was assigned 10,000 feet. The pilot then activated the autopilot and selected the assigned altitude as the aircraft continued to climb. As it passed through 3,000 feet, it began rolling to the left at a rate of approximately 5 degrees per second.

After the onset of the roll, the airplane was at an airspeed of about 240 knots. When the airplane reached about 30 degrees of left bank, the autopilot disconnected, accompanied by an aural alert. The autopilot was designed to automatically disconnect at 45 degrees of bank.

One second later, the cockpit voice recorder (CVR) recorded a statement by the pilot consistent with surprise, which the NTSB determined was likely made in response to the autopilot disconnect or the bank angle. The NTSB surmised that based on the pilot’s reaction, the roll to the left was uncommanded.

Both the climb and bank angle continued until an altitude of about 6,100 feet, then the aircraft entered a rapid descent, and the bank angle increased to almost 90 degrees.

The CVR picked up the airplane’s enhanced ground proximity warning system, including eight “bank angle” annunciations and one “overspeed warning” annunciation. 

About 23 seconds after the autopilot disconnected, the pilot made a mayday call, shouting that he was “…in an emergency descent unable to gain control of the aircraft.” The final ADS-B data point indicates the airplane was at an altitude of about 1,000 feet, airspeed of about 380 knots, and 53-degree left bank. The airplane impacted terrain in a wooded area about 8.5 miles northwest of the departure airport. The total time from the beginning of the uncommanded roll to impact was about 35 seconds.

In the initial final report issued in 2021, the NTSB cited the probable cause of the accident as the “asymmetric deployment of the left wing load alleviation system for undetermined reasons, which resulted in an in-flight upset from which the pilot was not able to recover.”

Tamarack took issue with the agency’s findings, saying in particular that the report suggested the devices moved in a manner that is physically impossible, and witness marks found on the wreckage were caused by impact damage.

As previously reported by FLYING in 2022, Tamarack Aerospace Group presented this information to the NTSB. However, the manufacturer alleges the safety board did not consider the information and instead released the probable cause of the accident four days later.

Tamarack filed a petition challenging the NTSB findings that suggested the company’s winglet design contributed to the accident. In its petition Tamarack alleged the agency made “erroneous findings that are unsupported by the factual record, inconsistent with engineering principles or proven to be physically impossible.” 

The petition also questioned the NTSB’s inability to determine the experience level of the pilot in command (PIC). The PIC had an airline transport pilot certificate and a Cessna 525 (Citation) type rating. But since the pilot’s logbook was not located, his experience could not be determined.

By failing to locate his logbook, Tamarack suggests the NTSB did not follow its own published recommended procedures used on all aircraft accidents.

Tamarack called on the NTSB to reopen the investigation in order to “reconsider and modify its findings.” The agency complied.

On February 23, the NTSB published a revised aviation investigation final report. It noted that after the autopilot disconnect, the "pilot’s statements were consistent with startle and surprise and, although he made no statements that described actions he was taking, his statement in the mayday call of ‘unable to gain control’ is likely consistent with the pilot having taken some actions to regain control but an increasing recognition that they were not effective."

Investigators noted that, according to a supplement to the flight manual emergency procedures, during an ATLAS inoperative condition in flight, the pilot is to move the throttles to idle and extend the speedbrakes to reach an airspeed below 161 knots. Warnings indicate that speed reduction is the first priority in these failure conditions, and large aileron input may be required if an ATLAS failure at high indicated airspeed includes a TACS runaway.

Investigators stated that the aircraft continued to climb after the autopilot disconnect, consistent with the engine being at a high power setting. During the descent, airplane systems warned of an overspeed condition, and the last data point revealed the airplane was traveling about 380 knots.

"Thus, it is unlikely that the pilot moved the throttles to the idle position as directed by the flight manual supplement," the NTSB report said.

The report also pointed out the pilot did not reduce engine power or deploy the speedbrakes. The probable cause of the accident is listed as the "pilot’s inability to regain airplane control after a left roll that began for reasons that could not be determined based on the available evidence."

Tamarack president Jacob Klinginsmith said the company was “very pleased” the NTSB decided to grant its petition for reconsideration. 

“[The NTSB has] taken steps to correct multiple technical errors in the original investigation," said Klinginsmith. "This reversal shows the NTSB has the courage, professionalism, and proper process to make these corrections, and for that we applaud the NTSB."