SABRA LANE, PRESENTER: For six months, retired Air Chief Marshal Sir Angus Houston headed up the massive co-ordinated search for the missing plane.

He's remained in contact with the families of the missing Australians.

Some of the families were in Parliament yesterday to witness a speech by the Prime Minister marking the first anniversary of the mystery.

I spoke with Sir Angus a short time ago from Canberra.

Sir Angus Houston, thank you very much for talking to 7.30.

ANGUS HOUSTON, RETIRED AIR CHIEF MARSHALL: It's a pleasure.

SABRA LANE: Sir Angus, a year is a very long time for the families of those people who are missing on board that plane. Have you talked with them this week? How are they feeling?

ANGUS HOUSTON: Well, as it happens, yesterday I attended the function at Parliament House and I was with the families from about nine o'clock in the morning through till lunchtime and I had a chance to speak to all of them. I think it's true to say that they're all in reasonable shape, although the uncertainty and the lack of closure continues to be an issue for them and of course it's very important that we continue the search to try and find the aircraft and hopefully find the aircraft so that they can reach that closure that they so much desire.

SABRA LANE: Are we any closer to knowing exactly what happened and where it is?

ANGUS HOUSTON: Well, I think that the search that's being conducted at the moment under the supervision of the ATSB is proceeding very well. At this stage, they've covered 43 per cent of the high-priority search area with the four ships that are out there and of course the search area has been very clearly defined after a very extensive analysis of all the data, a review of the data and a completely independent peer review using a completely different methodology. And the one thing that comes out of that is that the seventh arc - the seventh arc being the seventh handshake between the aircraft through the satellite to the ground station - that - that arc remains enduring. It's in the same position now as it was back 11 months ago.

SABRA LANE: Sir Angus, when you talk about the seventh arc, concisely for our viewers, could you tell us what you mean?

ANGUS HOUSTON: The seventh arc is related to the handshakes from the aircraft through the satellite to the satellite ground station. There were seven separate handshakes through the flight. The sixth one occurred more or less as expected, about one hour after the previous transmission. And then the seventh transmission was a partial transmission and it occurred eight minutes after the sixth transmission. And the experts have deducted that that's where the engines probably flamed out or lost power. That's the - that is what has been used to define the search area.

SABRA LANE: Is there a strong chance that we may never find it and may never actually know what happened?

ANGUS HOUSTON: There's always a possibility of that, but I think on the balance of probabilities at the moment, the chances of finding it are still good and we should be patient and persist with the search that's ongoing. That's the only option available to us at this time. I'm still quietly optimistic that with 57 per cent of the search area, the high-priority area still to be searched, that one day, hopefully very soon, we might wake up and hear that it's been found.

SABRA LANE: It is an expensive operation. Australia's committed $60 million to this. The Prime Minister said yesterday that he couldn't promise that the search will go on in this intensity forever. There will come a point in time where the search'll have to be curtailed, won't it? When do you think that point will come?

ANGUS HOUSTON: Well I'm not prepared to venture into that territory. Suffice it to say it's not Australia's decision. It's something that has to be done in full consultation, in full partnership with Malaysia and China, and I guess later this month there'll probably be a meeting between the three nations at the officials level, probably in preparation for a ministerial meeting some time later on in April or May. So, the decisions, the way ahead needs to be decided by the three governments that have substantial interests in the outcome of this search.

SABRA LANE: The absence of wreckage has prompted some theories, some of them quite wild. You probably would have seen some of them on the internet, from hijacking to sabotage to it being buried in Kazakhstan. Do you give any of these ideas any weight?

ANGUS HOUSTON: Look, you know, speculation about what happened that night I don't think's helpful. I think we have to be patient. The best evidence that will be available to us is if we find the aircraft and are able to recover the black boxes. If we do recover the black boxes, what we will get is very valuable data on what the aircraft was doing in terms of speed, flight level, position and was the aircraft operating as it should in normal flight and so forth?

SABRA LANE: Sir Angus, you say that we have to be patient about this. How long do you think we have to be patient?

ANGUS HOUSTON: Well, I would very quickly say that if you go back to Air France 447, the last known position from where the aircraft was eventually found was a distance of 6.5 nautical miles, or 10 kilometres, and it took the searchers one year and 10 months to find the aircraft and 3,900 metres of water. So, I think that gives you some idea of the challenge of search deep under the water with the sort of technology that is being employed on the search at the moment.

SABRA LANE: Sir Angus, thank you very much for talking to 7.30.

ANGUS HOUSTON: My pleasure, Sabra.