New Zealand's P3 Orion, which was recently upgraded, had satellite communications and did not require a communications relay.
However, some of the other aircraft involved did not have the same standard of communication systems, Mr McEvoy said.
While he was not aware of the Gulfstream's specific search tasks, Mr McEvoy said it was likely to be patrolling in the search area at a far higher altitude than the aircraft involved performing the search, enabling it to carry out its communication relay function.
According to the search programme for today (THUR), Mr McEvoy said seven military aeroplanes had been searching, with a wedgetail also in the air. There was no record of the G650 searching today, he said.
A spokesman from Gulfstream said the G650, described on the company's website as "the gold standard in business aviation'', cost between US$9000 (NZ$10,544) and US$10,000 to charter for an hour.
The New Zealand Defence Force is not funding the use of the G650 jet in the search.
Australia's joint agency coordination centre, which is handling all media requests regarding the Australian co-ordinated search operation for MH370 in the southern Indian ocean, did not respond to information requests before deadline.