The Australian Transport Safety Bureau (ATSB) is investigating a heavy landing of a Qantas Boeing 717-200 at Darwin airport which resulted in "substantial" damage to the aircraft.

Although at one point there were suggestions that the incident could result in the aircraft being written off - a first involving a Qantas jet - sources last week said the aircraft was believed to be repairable.

The 717 (VH-NXE) was on a scheduled QantasLink service from Cairns via Gove to Darwin on 7 February, carrying 84 passengers. On final approach to the airport, the aircraft entered an area of high sink and made a heavy landing, according to the ATSB, which is investigating the incident.

No injuries were reported and the passengers disembarked normally, says Qantas.

The aircraft was being operated by National Jet under the Qantas brand. National Jet has a contract to operate 11 717s on behalf of Qantas on regional services throughout Australia.

Qantas was last week declining to comment on the damage to the aircraft while the investigation is continuing. The airline says the investigation is being conducted with Boeing and National Jet, with the incident reported, as required, to the ATSB and Australia's Civil Aviation Safety Authority.

In its initial investigation report, the ATSB says the damage to the aircraft is substantial, with wrinkling discovered in the aft fuselage.

National Jet was unable to comment on the incident because of its contractual arrangement with Qantas.