Investigators have determined that the undercarriage of a Sukhoi Superjet 100 was deployed, but then retracted, before the aircraft suffered a gear-up accident at Keflavik airport.

Icelandic authority RNF has yet to explain why the aircraft failed to climb away after carrying out a missed approach at low altitude. It lost height instead and struck the runway.

The twinjet's crew had been intending to perform the missed approach, under single-engine conditions, as part of a certification programme for Category IIIa landings.

Icelandic investigation authority RNF says the aircraft was "close" to its maximum operating weight and flying in crosswinds as it performed the approach to Keflavik's runway 11 on 21 July.

The purpose of the exercise was to conduct a "low pass", it adds.

As the Superjet made its approach, and during the low pass, the landing-gear was extended, says the inquiry. The aircraft then executed a missed approach procedure and the landing-gear was retracted.

But the Superjet then descended towards the runway and made contact with the landing-gear still raised.

It skidded along runway 11 and came to a halt off the far end, resting on the pods of its PowerJet SaM146 engines.

Sukhoi says the aircraft was performing "touch-and-go procedures imitating missed approach".

"According to the previously-approved plan of trials, when the aircraft [was] climbing its landing-gear had to be retracted," it states. "The crew followed this procedure."

Video images of the aircraft being recovered - using cranes and inflatable lifting supports beneath the wings - show the landing-gear being extended without any obvious problem.

The apparent serviceability of the undercarriage is likely to turn the focus of the inquiry to the aircraft's airspeed and thrust settings.

Surveillance tracks indicate that the aircraft had performed some 40 approaches to runways 11 and 20 overnight before the accident at 05:23.

Russia's Interstate Aviation Committee is to assist the Icelandic authority in the investigation.

Source: Air Transport Intelligence news