A crack in the engine has grounded Nasa's high-tech aeroplane due to fly out of New Zealand to study the skies of the Southern Hemisphere.

The Stratospheric Observatory for Infrared Astronomy (Sofia), a highly modified Boeing jetliner and huge internal telescope, arrived in Christchurch this month.

For the next two months, the world's largest flying observatory and its crew of scientists, astronomers, mechanics and technicians were scheduled to make up to two dozen 10-hour night scientific flights out of the US National Science Foundation's Antarctic Programme facility at Christchurch International Airport.

But the plane has been grounded, and the mission's scientific productivity affected, after a crack was found in the thrust casing of one of Sofia's Pratt & Whitney JT9D-7J engines during a routine pre-flight visual inspection last Wednesday.


"The crack was beyond acceptable limits set by the engine manufacturer. For safety reasons, Sofia will remain on the ground until the engine is replaced," Nasa said.

Sofia has had engine changes in the past and has spare engines, Nasa says.

Flights should resume on about June 28.

"This engine change will impact the observatory's scientific productivity during the deployment," Nasa said.

After the engine repair is complete, Sofia will finish its new schedule of science flights on the originally scheduled end date July 20 and will return to Nasa's Armstrong Flight Research Centre in Palmdale, California, on July 26.

The Boeing 747SP, built in the late 70s as a Pan Am passenger plane, has had hundreds of seats removed and instead has been fitted with a giant gyro-stabilised highly sensitive 2.7m-diameter telescope and Nasa-style control centre.

Once the plane reaches an altitude of 10.6km, a specially fitted door opens for the telescope to peek out.

It makes observations that are impossible for even the largest and highest of ground-based telescopes as the plane flies from 12-14km, which puts it above 99 per cent of the Earth's infrared-blocking water vapour layer.

The aircraft also carries heavier, more powerful instruments than space-based observatories, which can also be changed and upgraded for different missions.

The observatory's position, along with its suite of seven highly specialised instruments, make it ideally suited for studying a range of astronomical objects and phenomena, including the life cycle of stars, formation of new solar systems, black holes at the centre of galaxies, nebulae and interstellar dust, complex molecules and the planets, comets and asteroids in our solar system.