A back up Defence Force 757 aircraft has been sent on Prime Minister Chris Hipkins’ trip to China due to the aircraft’s unreliability and likely chances of breaking down.

Both planes are about 30 years old and in less than a year $33 million has been spent on repairs, on top of the $70 million already spent in the last five years.

They are both set to be replaced between 2028-2030.

Former Defence Minister Wayne Mapp told Mike Hosking he's not surprised to hear figures like that.

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