Shares in Airbus (AIR.PA) suffered their worst drubbing in more than six years on Wednesday after the planemaker predicted flat profits in 2016, a year in which investors had expected it to start feeling the benefit of new and recently upgraded models.

The world's second-largest planemaker after Boeing (BA.N) was also forced to call off a ceremony to mark the first delivery of its new A350 jetliner to Qatar Airways on Saturday, after the Gulf airline said it was delaying the handover indefinitely.

Analysts said the rebuff from the airline, which is famously picky about accepting new aircraft and is widely believed to use such tactics to obtain last-minute concessions, was overshadowed by concerns over the model it replaces, the A330.

Airbus, which has already announced plans to cut A330 production by 10 percent to nine aircraft a month, said it would have to cut production again in 2016 to an unspecified level.

That signals it is struggling to find buyers for the current model ahead of a mid-term upgrade called A330neo in 2017, as well as a sharp output ramp-up for the all-new A350.

"The most critical years are 2016 and 2017," Chief Executive Tom Enders told analysts at an annual investor conference.

Partly as a result, Airbus said core operating income would return to growth in 2017, whereas some analysts had expected double-digit improvements as early as 2016.

That gap helped push the Airbus share price down 10.4 percent to close at 43.175 euros, the lowest level since mid-October and the biggest one-day percentage fall since July 2008.

Aerospace industry analyst Rob Stallard said the transition between current models and new ones, which also affects the smaller A320 family, was proving a bigger drag on profits than expected.

For now he and other analysts advised against reading too much into the postponed first A350 delivery, which Airbus has targeted by year-end and which it still predicts will happen "very soon".

Meanwhile Airbus remained in sober mood on the poor-selling A380, the world's largest airliner.

Last year Reuters reported that it had begun weighing up three strategic options, on whether to cut production, invest in an upgrade or stop trying to sell more A380s and merely produce what it had already sold.

Enders said Airbus would take a decision "purely on economic terms" in the near to mid-term. Finance Director Harald Wilhelm said the project would break even in 2015 and stay in balance through 2018, whether it decided to improve or discontinue it.

Airbus is still trying to find a new customer before end-year. Industry sources said it is in talks to try to shift a handful of planes no longer destined for Japan's troubled Skymark Airlines to larger Japanese carrier ANA (9202.T). Airbus said it would not comment on specific discussions.

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