Finnish investigators have revealed that pilots of a Latvian Saab 340 freighter ignored ground-proximity warnings during a highly-unstable low approach to Mariehamn airport.

At one point the RAF-Avia aircraft had a descent rate of 5,000ft/min, and was just 2s from a ground collision, after the crew lost control as they attempted to land on runway 21.

The approach required tracking an arc 10nm from the airport’s VOR/DME beacon before turning left and crossing the PEXUT fix at 1,800ft.

But while the Saab intercepted the arc it turned left prematurely, meaning it was offset by 40° to the left of the proper approach course.

Finnish investigation authority SIAF says it “could not categorically establish” the reason for the left turn, adding that analysis showed the captain’s explanation – a flight-management system fault – was “unlikely”.

But it says that simulations uncovered a “possible” chain of events, involving a navigation mode change, which might have resulted in the aircraft’s turning early to intercept the selected radial for the approach.

SIAF adds the crew might have been given the “false impression” that the aircraft was on the correct course by the presence of narrow electromagnetic lobes 42° either side of the localiser.

Despite being far from the correct approach path the aircraft continued descending below the minimum safe altitude of 1,800ft. The captain turned off the autopilot at 1,600ft and started manually flying a course perpendicular to the final approach path, continuing to descend to 1,000ft.

Although neither pilot had visual contact with the runway, the captain told the first officer that they would continue the approach.

“While it might have been possible to see the runway in the prevailing conditions, their degraded situational awareness led them to look in the wrong direction,” says the inquiry.

The first officer realised that the aircraft was intercepting the approach path at a right angle and, with the aircraft 3.1nm from the runway, advised the captain to make a left turn.

Strong flight control inputs resulted in the aircraft banking sharply to the left, with a peak bank angle of 50°. But the captain also pitched the aircraft down, by as much as 19°, and the crew momentarily lost control. The aircraft entered a sideslip, descending rapidly, triggering several alerts including eight “pull up” warnings.

At one point the aircraft was just 300ft above the ground, descending at 5,000ft/min, before the captain recovered the aircraft at a height of only 150ft. The aircraft came within 2s of striking the ground, says the inquiry, while 2.7nm from the runway threshold.

SIAF adds that the 2.06g recovery briefly exceeded the aircraft’s maximum load factor.

Even after the recovery the Saab’s captain increased the aircraft’s altitude “only a little”, the inquiry states, continuing the approach below the glideslope despite the absence of visual contact with the runway.

“The flight crew did not react to the [ground-proximity] warnings,” says SIAF. “Furthermore, according to the captain’s report, the captain did not hear the warning nor, according to the captain’s view, was the aircraft too low.”

Crew resource management was “poorly handled” and the captain “did not comply” with the carrier’s operations manual, says the inquiry. The pilots did not follow the instrument approach procedure and “ignored” the ground-proximity warning system.

Latvia’s civil aviation authority met with RAF-Avia on 15 February 2012, the day after the Mariehamn event, to discuss pilot training and compile a list of concerns, particularly given that another of the carrier’s Saab 340s had been involved in a serious incident at Helsinki six weeks earlier.

RAF-Avia accepted an action plan including the standing-down of Saab 340s, pending pilot training measures. Latvian authorities cleared the carrier to continue operations with the type on 30 April last year.