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Thousands of flights in and out of New Zealand fly through radar black-spots relying only on scheduled long-range radio calls to track their position, each year.
A spokesman for Airways, the state-owned enterprise responsible for managing New Zealand's 30 million sq km of airspace, said only 60 per cent of flights leaving the country were tracked to their final destination by satellite, the rest relying on radio contact to report their position.
"At the moment, it's either via radio or via what we call data link and that's what goes through the satellites," head of Auckland operations Tim Boyle said.
Individual aircraft had to opt into the data link system, whereby they would transmit their location data around every 15 minutes.
However, "if the aircraft chooses not to effectively enter into that contract then we don't actually get any data back from Immersat at all," Mr Boyle said.
If data link updates were missed and long range radio contact could not be met, Airways had no way of knowing where an aircraft was, he said.
An aircraft leaving New Zealand for Los Angles would be tracked by radar out to a 321km radius where it would then enter a radar black-spot, Mr Boyle said.
It would then be picked up by radar around 240km from Nadi, Fiji, before flying through another black-spot until it reached American airspace.
"There's large areas of the Oceanic region which have no radar coverage....if we're talking about surveilling an aircraft, there's lots of areas we can't surveil at the moment in the world."
A spokesman from the UK satellite company Inmarsat, which plotted the final position of MH370, revealed there was no mandate for flights from New Zealand to transmit location data.
Inmarsat senior vice president of external affairs Chris McLaughlin told Radio New Zealand yesterday that one of the company's satellites continued to pick up a series of hourly 'pings' from MH370's Classic Aero unit, establishing that it continued to fly for at least five hours after it had left Malaysian airspace.
"If you think of the Inmarsat satellite network as like a cellular phone network then the box, the Classic Aero, is the handset and then the services, like the ACARS [aircraft communications addressing and reporting system] that have been talked about and the voice and the other data are just like apps on a phone.
"Effectively the apps were turned off but the box remained on the network," he said.
Unfortunately the operator of the aircraft had not elected for it to transmit location data, Mr McLaughlin said.
"There's no, believe it or not, mandate to do so, other than over the North Atlantic route and so for many hours, planes flying from New Zealand and Australia are not necessarily reporting their position, certainly with some airlines."
An Air New Zealand spokesman declined to comment on how the airline's aircraft were tracked.
How MH370 was tracked
* The flight continued to transmit hourly 'pings', similar to a cellphone connecting with a cell tower.
* The pings were compared to data from similar aircraft and the Doppler effect was used to establish a flight line.
* While the tracking system was not precise, it could be narrowed down to a approximate area where the plane would have ran out of fuel.
* Uncertainty over weather conditions and whether the plane glided or dropped straight has influenced the size of the search area.