By SCOTT MacLEOD transport reporter
A United States airliner nearly hit an Air New Zealand jumbo jet with 395 people on board after a computer told the US pilot to make an impossible manoeuvre.
The two planes mirrored each other's moves as they closed head-on at 1700 km/h - missing each other by an estimated 1.2km to 3.8km.
Details in a US National Transportation Safety Board preliminary fact sheet also suggest that poor communication between air traffic controllers was to blame.
The incident happened on December 1, 700km southwest of Los Angeles, when the two planes approached each other 11km above the Pacific Ocean.
The report said the Air NZ Boeing 747-400's collision avoidance system saw the Aviation Partners Boeing 737 when it was 64km away, directly in front, and at the same altitude.
Soon afterwards, the system warned the Air NZ pilot of a possible impact within 25 seconds and told him to go into a dive - but the other plane did the same thing.
The Air NZ pilot then turned left, but saw the other plane again turn towards him, so he twisted right and went into a steeper dive. The pilot said the US plane shot past 130m below him and 1200m to the side.
A jumbo jet pilot told the Herald yesterday that on-board computers were meant to "talk" to systems on other airliners, giving their pilots the right instructions to avoid collisions.
"The fact that both aircraft mirrored each other's manoeuvres is disquieting," he said.
The report confirmed that the computer on the American plane told its pilot to climb at the same time as the Air NZ plane dived. But the US plane was already at its maximum altitude, so its pilot instead opted to dive and turn right. He put the near-miss at between 3.2km and 4.8km.
The report also said that US Navy air traffic controllers failed to coordinate the US plane's flight path with the Oakland Oceanic Control Centre, which was controlling the Air NZ flight.
A spokesman for the Civil Aviation Authority, Martyn Gosling, described the incident as "a serious event" in which Air NZ "couldn't have done much more."
Alastair Carthew of Air NZ said the report showed that his airline's Traffic Alert and Collision Avoidance System worked as it was supposed to, and that the plane's crew took "appropriate" action.
Mr Carthew said he did not know whether the 378 passengers would have noticed the manoeuvres.
Aviation Partners vice-president (sales and marketing) Dick Friel seemed to know little about the incident. He thought his plane was a Gulfstream 2, and denied an assertion that it was engaged in a test flight at the time of the near miss.
The report said the Navy cleared the Aviation Partners plane and its two crew for a winglet test flight off the California coast.
When the 737 went out of radar range, the Navy failed to coordinate the flight with air traffic control.
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