Terrain-warning settings on a Lockheed Martin C-130J were not adequate to detect the presence of Sweden’s Kebnekaise mountain before a Norwegian military transport fatally collided with the peak.

All five occupants were killed as the aircraft struck the snowy rock face at 280kt (518km/h), just 14s after levelling off at its cleared altitude of 7,000ft (2,130m). It had been descending towards Kiruna on a service from Evenes, as part of the Cold Response exercise, on 15 March 2012.

Owing to the high latitude, above 60°N, there was no terrain database available for the forward-looking terrain-awareness system.

Cockpit-voice recordings also revealed the crew had acknowledged that the system was operating in tactical mode. This mode offers only “heavily degraded” warnings of obstructions, says Swedish investigation authority SHK.

A downward-looking function of the ground-collision avoidance system had been set to warn at 200ft, probably in line with landing minima at Kiruna airport, rather than the 1,500ft which would have been necessary to allow an evasive manoeuvre, given the profile of the mountain ridge.

As a result the systems – which were functioning as designed – gave no warning of the impending collision.

About 8min before the accident the Royal Norwegian Air Force aircraft – carrying the callsign Haze 01 – was handed to Swedish air traffic control as it headed east at 13,000ft.

Controllers informed the pilots that, after reaching the Kiruna VOR, the aircraft would be cleared for the VAGAS 3F arrival to runway 21. The crew briefed for the approach, says SHK, but discussed heights relating to the instrument landing system at the airport.

Air traffic control cleared the aircraft to descend to 10,000ft, a height which was below the threshold of controlled airspace. The C-130, which was also outside of Swedish radar coverage, started a 2,500ft/min descent about 58nm from the VOR.

Upon contacting Kiruna tower the crew requested a visual approach and was cleared initially to descend to 7,000ft. The aircraft continued its descent, at a rate of 2,000ft/min, taking it just below the ridge height of Kebnekaise before it reached the mountain.

Haze 01 levelled off at 7,000ft, where it encountered turbulence before hitting the rock face 42nm (68km) from Kiruna. Unaware of the collision, Kiruna tower transmitted a further descent clearance to 5,000ft, but there was no response from the crew.

SHK investigators determined that the crew had not checked the minimum safe flight level for the mountainous area but was also not made aware that the initial descent clearance took the C-130 outside of controlled airspace. The inquiry says “latent weaknesses” within the RNoAF and Sweden’s air traffic service, with respect to planning and tracking the flight, were central to the accident.

Source: FlightGlobal.com