Thousands of flights each year in and out of New Zealand fly through radar black spots relying only on scheduled long-range radio calls to track their position.
A spokesman for Airways, which manages the country's 30 million sq km of airspace, said only 60 per cent of flights were tracked to their final destination by satellite, the rest relying on radio contact.
"It's either via radio or via what we call data link ... through the satellites," head of Auckland operations Tim Boyle said.
Individual aircraft had to opt into the data-link system, transmitting their location 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 Inmarsat [the UK satellite company] at all."
If data link updates were missed and radio contact could not be met, Airways had no way of knowing where an aircraft was, he said.
An aircraft leaving for Los Angeles would be tracked by radar out to a 321km radius where it would then enter a black spot. It would be picked up by radar around 240km from Fiji before flying through another black spot until it reached US airspace.
A spokesman from Inmarsat said there was no mandate for flights from NZ to transmit data.
Inmarsat senior vice-president of external affairs Chris McLaughlin told Radio NZ yesterday that one of the company's satellites had continued to pick up a series of hourly "pings" from MH370's Classic Aero unit, establishing that it flew for at least five hours after it had left Malaysian airspace.
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."