The two companies have been fighting in court for months over the safety impact of flaking paint that exposed corrosion or gaps in a sub-layer of metallic lightning protection.

At the heart of the case is a sandwich of copper foil between the carbon fuselage and outer paint on A350 jets, designed to allow lightning strikes to wash away safely.

Reuters first reported in November 2021 that Airbus was studying a new type known as perforated copper foil (PCF), initially because it was lighter than the current expanded copper foil (ECF), but also because it would ease cracking.

Qatar told a London court on Thursday that Airbus had started implementing the change and called for more information. Airbus confirmed its partial use from late last year.

"PCF is being used on rear-section parts on aircraft delivered from the end of 2022," an Airbus spokesman said.

Wrapping up the latest preliminary hearing, Judge David Waksman described the decision to start using the new design as significant to the case.

Qatar Airways has blamed the damage on a possible design defect. Airbus argues the former design remains state of the art and is safe.

TENSE EXCHANGES

What started out as a case about damage to the painted surface of some A350s is expanding into a surgical examination of modern passenger jet technology. The A350 is a mainly carbon passenger plane competing with Boeing's (BA.N) 787 Dreamliner.

European regulators say the jets are safe but Qatar Airways says this can't be guaranteed without more detailed analysis.

Qatar Airways seeks access to raw modelling data that would allow its technical experts to simulate the impact of lightning.

But there were tense exchanges in court on Thursday after Airbus said French security services had raised concerns about sharing data models on jets, some of which are used by European governments. Airbus cited cyber attacks on such data.

Qatar Airways accused Airbus of resorting to a new tactic to block the release of data that could be valuable to its case, after the planemaker was overruled in a previous bid to use a special blocking law defending French interests.

In a rare note of compromise, lawyers for the two companies provisionally agreed arrangements to secure the data.

The dispute between two of the flagship companies of France and Qatar, which have strong diplomatic and economic ties, has risen to the attention of leaders of the two countries who spoke on the subject in recent weeks, according to diplomatic sources.

Barring a deal in ongoing settlement talks, the two sides are heading for a rare corporate trial in June.

In a recurring theme of the preliminary hearings, Airbus and Qatar Airways argued about how many emails and other records should be shared ahead of the trial.

A preparatory four-way meeting between both companies and Qatari and European regulators was abandoned last week. It is expected to be rescheduled later this month.

Airbus was also ordered on Thursday to share details of compensation deals with other airlines on the issue.

Reuters' exclusive 2021 investigation revealed that several other airlines had reported flaws in the painted surface of A350s, though only Qatar Airways has stopped flying them.