One of the last big issues from the 1979 Mt Erebus disaster may never be settled because of the apparent disappearance of the crashed DC10's cockpit voice recorder tape.
Transport Accident Investigation Commission chief executive John Britton said yesterday that modern audio and filtering equipment could produce a clearer playback
from the tape - if it could be found.
But the tape's fate is unknown, meaning it cannot be replayed to find out who said what during the aircraft's last minutes.
None of the Civil Aviation Authority (CAA), Air New Zealand or Archives NZ seems to have the tape, which recorded the last 35 minutes of conversation in the cockpit of flight TE901 before it crashed in Antarctica 25 years ago, killing all 257 passengers and crew.
Only written transcripts remain, but it has emerged that three versions exist, with crucial differences.
The version that appears in chief air accidents inspector Ron Chippindale's 1980 report on the crash, blaming the pilots, has controversial phrases such as "Bit thick here, eh Bert?"
Those do not appear on a transcript produced with American help in Washington DC.
Supporters of the pilot error theory say the "Bert" comments indicate that the aircraft was flying lost in clouds when it hit Mt Erebus.
But retired pilot Arthur Cooper, who helped to transcribe the Washington version days after the crash, said last week that the "Bert" phrase was never uttered.
He also said the Washington transcript supported royal commissioner Justice Peter Mahon's 1981 finding that a navigation computer blunder caused the crash.
The CAA has said it gave the tape back to Air New Zealand after the various inquiries into the disaster were finished.
Air New Zealand says it gave everything it held on the disaster to Archives NZ years ago.
Archives NZ outreach co-ordinator Alison Hadfield, who is responsible for an exhibition on the crash now on at the organisation's head office in Wellington, searched the records yesterday for the tape.
She found a third transcript, made in Britain apparently by Mr Chippindale, though differing from the one in his report, but she could not find the tape itself.
Archives NZ holds scores of documents and other records relating to the crash and investigations, putting many on display in the exhibition.
Mr Britton said cockpit voice recorders now had much better sound quality than in 1979, as they used digital data that produced a clear playback.
- NZPA
