By Tim Hepher, Allison Lampert and David Shepardson

FARNBOROUGH, England (Reuters) - The world's largest air show fizzled out on Thursday with a solid new Saudi jetliner order unable to dispel the gloom over recent problems in producing planes fast enough to meet demand.

Britain's Farnborough Airshow opened earlier this week amid alarm signals from airlines over falling yields or average fares. But delegates said they remained above historic levels and although quiet, the show confirmed demand for wide-body jets.

Airbus and Boeing posted about 40 firm orders - a fraction of recent years - and were roughly level depending on whether Qatar Airways' decision to come forward as the previously unnamed buyer for an existing Boeing order was counted.

Including preliminary new orders, Airbus pulled ahead after announcing a deal on Thursday for 90 planes including 15 A330neos from Saudi carrier Flynas. Reuters reported talks with Flynas on the model ahead of the show.