KEY POINTS:
For the second time in a week an Air New Zealand Boeing 777 bound for San Francisco has been forced to turn back.
In the latest incident, about 300 passengers had to delay their travel plans on Sunday when their flight was forced back after a "slight vibration" in the plane's engine.
Flight crew detected the fault about 4 1/2 hours out of Auckland Airport and the pilots made the decision to turn around.
Spokesman David Jamieson said passengers' lives were not at risk but "it was better to be safe than sorry".
Engineers were working on the plane yesterday to find out the cause of the vibration and expected to know within a couple of days.
Air New Zealand accommodated the passengers at an Auckland hotel until 2.30pm yesterday when they boarded another Boeing 777.
On Monday last week a Boeing 777 hit geese shortly after takeoff. The birdstrike damaged the weather radar in the aircraft's nose, forcing the pilot to return to the airport.
The planes are the airline's newest aircraft.
