US investigators probing a fatal landing accident involving a Shorts 330 freighter have determined that the crew had a history of intentional procedural non-compliance during approach, including late turns, high descent rates and excessive manoeuvring.

The twin-engined Air Cargo Carriers aircraft was 5° nose-down and banked 22° to the left when it struck runway 5 at about 92kt while attempting to land at Charleston, Virginia, on 5 May 2017.

It departed the left side of the runway, its left wing breaking away, and the aircraft tumbled into rough ground. Neither of the two crew members, the only occupants, survived.

National Transportation Safety Board investigators reviewed 17 of the crew’s landings at the same airport – of which 10 were on runway 5 with the other seven on runway 23 – in the month before the accident.

Surveillance camera footage was only available for the seven landings on runway 23, all visual, but it showed that the approaches – from final turn to flare – lasted from 12-39s, much shorter than the 75s for approaches flown in accordance with the operator’s standard procedures.

Four of the seven approaches analysed had been flown by the captain, the other three by the first officer, who had been permanently paired by the carrier.

Information released earlier by the inquiry indicated that the first officer had previously expressed concerns – in text messages to friends – about the captain’s manner and flying abilities, including apparent discomfort and poor performance when flying in instrument conditions. She described one particular incident in a snowstorm, four months earlier, as “the biggest scare of my life”.

These text messages and follow-up interviews, the NTSB says, suggest the first officer was “not in the habit of speaking up” and that the difference in experience – the captain had nearly 4,400h flight time compared with the first officer’s 650h – probably created a steep authority gradient and a “barrier to communication”.

The crew, while 38nm west of Charleston, had been told to expect the localiser approach to runway 5 but instead requested the VOR-A circling approach, possibly because this matched the inbound flightpath while the localiser approach would have taken longer.

But the inquiry says the decision was “contrary” to the operator’s procedures because the localiser approach was available.

Radar information showed the aircraft, while following the VOR-A approach, prematurely descended to 1,600ft – below minimum altitude – before reaching the waypoint FOGAG, lying 2nm from the missed-approach point. It remained at this altitude until 0.5nm from the runway threshold, then started a descent at 2,500ft/min.

It turned steeply to the left, crossing the centerline at a bank angle of 42°, with the descent rate reducing to about 600ft/min just before impact. There were “indications of increasing pitch”, says the inquiry, suggesting the captain was pulling up as the aircraft neared the ground.

“However, it was too late to save the approach,” it states.

Investigators were unable to conclude whether the captain descended below the minimum descent altitude before exiting cloud cover in the vicinity of the airport.

But the inquiry says the descent rate was not in accordance with company guidance, which required maintaining about 500ft/min, and the crew should have executed a go-around.

“No evidence was found to indicate why the captain chose to continue the approach,” it states. “However, the captain’s recent performance history, including an unsatisfactory check ride due to poor instrument flying, indicated that his instrument flight skills were marginal.

“It is possible that the captain felt more confident in his ability to perform an unstable approach to the runway compared to conducting the circling approach to land.”

Intentional non-compliance with procedures is a “long-standing concern” of the NTSB, says the investigation authority, but Air Cargo Carriers had no formal safety and oversight programme to assess compliance with operating procedures or to monitor pilots with performance issues.