The Royal New Zealand Air Force has had to pull out of two international exercises this year because of a lack of planes, due to delays in upgrading the ageing Orion and Hercules fleets.
Currently two of the five Hercules aircraft and two of the six Orions, are out of action because they need upgrade work, which is taking longer than expected.
As a result, the RNZAF cancelled its involvement in international exercises in Canada and the United States at the start of the year.
Defence Minister Wayne Mapp says the situation is a concern, but operational matters must come first.
He says the air force operates small fleets, and in the future only one plane at a time will be taken out of service for upgrade work.
