Rods could be culprit in Qld plane crash

A biplane crash that killed two people on the Gold Coast could have been caused by faulty rods that join the wings to the plane, investigators say.

Pilot Alexander "Jimmy" Rae and his passenger, a 21-year-old French woman, were killed when his Tiger Moth biplane crashed into the water off South Stradbroke Island while on a joyride on December 16 last year.

Campers and resort guests saw the red and white plane spear into the water in an almost vertical position about 400 metres off the island, near the Gold Coast, before debris washed up on the beach.

The Australian Transport Safety Bureau (ATSB) said in a preliminary report released on Monday both of the plane's fuselage lateral tie rods, which join the lower wings to the fuselage, had fractured.

There were already significant, pre-existing fatigue cracking in the threaded section near the joint joining the left wing, the report said.

"The ATSB has not, at this preliminary stage of its investigation, determined whether the failure of the fuselage lateral tie rods, or another mode of wing structural failure, was the initiator of the left wing separations," it said.

The ATSB found the rods were fitted about seven years earlier and accrued about 1300 flight hours. They had about 700 hours, or 11 years of service life remaining.

A final report into the crash is due in December.