A SYDNEY-bound Qantas passenger jet had to be guided by another aircraft for almost its entire journey from Los Angeles yesterday after a malfunctioning weather radar left it at the mercy of the elements, in the first of two malfunctions experienced by the airline in 24 hours.

Qantas Flight 12, a 747-400, was three hours into its journey when the pilot reported that its complex weather radar system was providing faulty readings.

Last night the Seven Network reported that the pilot told passengers he was "flying blind".

Fortunately for the pilot and 284 passengers on board, an Air New Zealand aircraft flying from Los Angeles to Auckland had left less than an hour before and the Qantas pilot was able to "piggy-back" behind.

The Air New Zealand flight "was a short distance ahead and it provided the Qantas aircraft with information from its own radar system throughout the journey", a Qantas spokeswoman said.

"It travelled on the best weather path and the Qantas flight was able to follow behind."

The Herald understands that the two aircraft were separated by only a few thousand metres as weather updates were sent across to the Qantas plane, and that Qantas passengers could see the other jet through their windows.

"The aircraft was vertically separated according to operating procedure at all times - there was no danger to passengers," the Qantas spokeswoman said.

Rather than continuing to Sydney as planned, QF12 diverted to Auckland for repairs to the radar. It then took passengers to Sydney, arriving four hours late.

It was the first of two technical problems in the space of 24 hours.

A Qantas flight from Melbourne to Sydney was forced to turn around and return to Melbourne Airport after the pilot was alerted to a possible landing gear malfunction yesterday.

The Boeing 767 with 244 passengers on board had just taken off at 1.29pm when the landing gear fault light came on in the cockpit. The pilot immediately turned the plane around, landing safely at 2.15pm.

with AAP