The National Transportation Safety Board’s preliminary report into the plane crash that killed former NASCAR driver Greg Biffle, his family and three others determined that Biffle was not flying the plane owned by his GB Aviation Leasing LLC company when it crashed on Dec. 18.

Per the report released Friday, the plane was flown by Dennis Dutton, a pilot certified to operate numerous commercial aircraft, with his son Jack, in the right cockpit seat. Biffle, a licensed pilot with “civil flight experience that included over 3,500 hours of flight time,” was seated behind the two and is identified as the rear passenger in the report.

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However, neither Biffle nor Jack Dutton were licensed to fly the Cessna Citation. The report notes that Dennis Dutton was licensed to fly the Citation with a second-in-command on board, and even though Jack Dutton was a pilot himself he “was not qualified to perform second in command duties for the flight,” according to the NTSB, as he had just over 175 hours of single-engine aircraft experience.

Aero Consulting Experts CEO Ross Aimer told Yahoo Sports that Jack Dutton’s lack of qualification was “troublesome” and said the plane required two pilots.

“In this particular case, because it requires two pilots, and neither of those — Biffle or the young man — were qualified, they should have had a licensed pilot in that seat,” Aimer said.

Biffle, his wife Cristina, their son Ryder, Biffle’s daughter Emma, Dennis and Jack Dutton and Craig Wadsworth were aboard the plane as it attempted to land at Statesville (North Carolina) Regional Airport shortly after taking off from the same airport. They were flying to Sarasota, Florida.

The Cessna Citation 550 is a dual-engine aircraft, and the report states that issues with the plane started before the flight began. Here are the key takeaways from the NTSB’s findings.

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• The left engine initially did not start before both engines were powered on at approximately 9:53 a.m. ET. As the plane was taxiing for takeoff “the pilot and the two pilot-rated passengers discussed that a thrust reverser indicator light(s) for an unspecified engine was inoperative, but that the thrust reverser for the affected engine was working properly.”

• The plane took off at approximately 10:06 a.m. “During takeoff roll, the rear passenger commented that the left engine was producing more power than the right and indicated there may have been a faulty gauge. The pilot continued the takeoff.” The report states that it was overcast at approximately 5,000 feet for the entirety of the flight, though visibility dropped from 10 miles to five miles from 9:54 to 10:15.

• Early GPS data shows that the plane turned left as it climbed and that Dennis Dutton said he’d fly under visual flight rules before he was cleared to fly under instrument flight rules. After a 180-degree turn and reached 2,200 feet, it “continued to turn left and began to descend. The right-seat passenger attempted to contact” air traffic control “and activate the flight’s IFR flight plan between 10:08 and 10:10 but was unsuccessful due to the controller’s workload and associated radio communications.

• At 10:09, Dennis Dutton and Biffle discussed climbing higher even though they were supposed to continue flying under visual flight rules. The report states that “the pilot initiated a climb, and shortly after, the rear passenger noted a difference between the left and right engine interstage turbine temperature indications.” There were no other discussions that covered the instruments throughout the remainder of the [cockpit voice recorder] recording” and the autopilot disengaged — either intentionally or independently — just after 10:10.

• Seconds later, “the cockpit area microphone captured the pilot making remarks indicating his altitude indicator was not working properly and that additional left side flight instruments may not have been working properly.” The Garmin GPS on board had stopped recording airspeed data and heading data at around that time.

• At 10:11 “airplane controls was transferred to the right seat passenger, at an altitude of about 4,500 ft msl.” At 10:13, the plane was at just under 1,900 feet and that all three said they could see the ground. “Although a positive transfer of airplane control was not recorded, subsequent communication between the pilot and right seat passenger was consistent with the pilot having resumed control of the airplane at that time.” At just after 10:13, the pilot turned the plane right towards the west and requested that the landing gear be extended. “Subsequent discussions were consistent with the landing gear being configured, however, the gear indicator lights were not illuminated.”

• Jack Dutton noted just before 10:14 on the common traffic advisory frequency that they were “having some issues here.” Biffle references power to an alternator — the Cessna Citation 550 does not have an alternator. After a brief audio quality issue with the cockpit voice recorder, Dennis Dutton is heard saying there was a “problem” but did not specify what the problem was “or what actions were taken to correct it.”

• The GPS data resumed recording just after 10:14 and Dennis Dutton “made comments which indicated he had acquired the runway visually” around 10:15. Data from the GPS “showed that the airplane’s airspeed and altitude continued to decrease from the time the airplane was aligned on final approach to the runway until 10:15:18” when the airplane’s altitude had dipped below 1,000 feet and under 99 KTS.

• The plane hit a light station approximately 1,400 feet from the runway threshold and “a group of damaged trees located about 235 feet” from that light station “were sheared about 12 feet above ground level. “The first indication of fire was blackened branches and grass near the west side of the trees.”

• “A ground impression was observed about 350 feet from the [light station], near the airport perimeter fence, and extended through the [runway lights]. The debris path continued along a westerly heading through the runway overrun to where the main wreckage came to rest on the runway blast area about 400 feet short of the runway 28 threshold.” “Heavy charring” was seen from a second set of lights “and continued along the remaining length of the debris field to the wreckage.”

• The engines remained attached to the plane after it came to a stop and both thrust reversers were in the stowed position. Investigators found “no evidence of unconfined engine failure with either engine. Examination of the cockpit throttle quadrant found both thrust levers to be in the full forward position and both reverse throttle levers in the down position, consistent with being stowed.”

Biffle competed for 16 full or part-time seasons in NASCAR’s Cup Series from 2002 through 2022. He raced full-time in the Cup Series from 2003 through 2016 and scored 19 wins and 92 top-five finishes over 515 career starts.

His best season came in 2005, when he finished second to Tony Stewart in the points standings. Biffle’s six wins were the most of anyone in the Cup Series that season and his average finish of 11.9 was second only to Stewart.

Biffle is one of just two drivers to have won both a championship in the third-tier NASCAR Truck Series and the second-tier NASCAR Xfinity Series.