Airbus and Qatar Airways return to court on Friday as a contractual and safety dispute over A350 passenger jets descends into a tug-of-war over confidential documents, while the sums at stake in their unprecedented dispute top $1.5 billion. Qatar Airways is suing Airbus over damage to the painted surface and anti-lightning system on A350 jets, saying safety could be at risk from a design defect. Airbus acknowledges quality flaws but denies the design is at fault and insists the jets are safe. The two sides must provide each other with thousands of pages of documents as their row — which has already altered the shape of competition in the jet market — heads towards a rare London aerospace trial in mid-2023, barring a settlement. The case has shed a rare public spotlight on the inner workings of the global jet market, including contractual details and the industrial playbook for preparing delivery of new jets. Friday's High Court hearing is expected to hear mutual claims of foot-dragging over the release of documents including maintenance files and engineering analysis, as well as the return of millions of dollars of deposits and Airbus credits. The number of A350s grounded by Qatar because of surface damage has risen to 28 out of 53 in its fleet. Airbus said last month it had revoked all 19 remaining A350 orders from Qatar Airways, severing outstanding business with the Gulf carrier for new jets. Boeing is meanwhile being dragged into the public dispute between its arch rival and one of its own biggest clients for the first time, sources say. The dispute over the A350 widened earlier this year when Airbus revoked a separate contract for 50 smaller A321neo jets, arguing the contracts were linked by a cross-default clause. Qatar subsequently ordered the Boeing 737 MAX and this catapulted arguments over the relative merits of the jets into court, with Airbus saying the MAX was as good as the A321 in a bid to avoid being forced to build the jets for Qatar. Now the airline has been ordered to hand over a preliminary version of the MAX contract to Airbus with restrictions, but Boeing objects to elements of the rare disclosure, sources said. Boeing has declined to comment. The case's UK judge has called for a clear-the-air meeting between Airbus, the airline and Qatari and European regulators, but there are no signs so far of this happening. Under aviation rules companies usually talk to their own regulators who then discuss safety with each other, but the case has highlighted a breakdown in the usual system of goodwill. Airbus and Qatar Airways both declined to comment before Friday's hearing.