This news item just out in New Zealand media:
France's BEA air accident investigation agency, in its final report, said the pilots were not competent to fly at such a low level and that ground crew had incorrectly washed the airliner, causing water to enter key detectors.
Once in flight, the water froze in the probes, which measure the plane's angle of flight and ought to have emitted a warning if the jet was stalling.
The pilots - who should not have been flying so slowly - lost control of the plane and crashed into the sea, the BEA report concluded.
While the pilots were permitted to conduct the unusual test flight, they lacked the technical competence to do so and "the decision to undertake the test at a low altitude" and at low speed contributed to the crash.
Pilots at fault in Air New Zealand crash - report | Stuff.co.nz
Canīt find the BEA report on their website yet, though.