The defects caused a months-long conflict with Qatar Airways, the biggest A350 purchaser.

The European Union Aviation Safety Agency (EASA) has issued a preliminary warning that patches of the anti-lightning system may have been poorly fitted on over a dozen Airbus A350 jets after major American carrier Delta Air Lines revealed it also faced “paint issues”.

The proposed caution notification is the first time manufacturing has caught the attention of regulators after months of turbulence in the aviation industry over surface defects on the A350, which its manufacturer, Airbus, says are still safe to fly.

The European regulator said in an airworthiness ruling proposal that Expanded Copper Foil (ECF), which was used as a lightning-conductor on the A350s, may not have been properly placed on the wing covers of 13 jets.

EASA said the EFC defect, alongside an installation flaw in an adjacent fastener, would lead to fuel vapor catching fire and a “consequent loss” of the jet in the case of a heavy lightening strike.

EASA’S directive calls for checks and repairs in necessary, but did not make mention for any of the 13 jets to be grounded.

A spokesperson for the European aerospace giant said the draft directive was a “normal part of the continued airworthiness process.”

The inspection calls come as Airbus and Qatar Airways remain in a dispute over the A350 surface defects.

Qatar Airways chief says Airbus should admit to A350 defects

Qatar Airways CEO Akbar Al Baker recently confirmed that the Gulf national carrier had grounded 20 A350 jets in a long dispute mainly over cosmetic damage that had also prompted Qatar Airways to halt further deliveries in June.

Airbus has called the flaw a  “surface paint” issue while the Qatari airline describes it as problems beneath the paint, affecting the ECF and composite shell.

EASA said it did not find evidence of any airworthiness issues, while Qatar Airways says this has yet to be proven.

Al Baker has since ruled out buying freighters from Airbus, effectively closing a potential deal to rival company Boeing.

A recent investigation by Reuters found that at least five other airlines had also expressed worries over the surface defects since the A350 came into service. The investigation found that in some cases, the damage extended below paint to a layer of lightning protection.

The aerospace company had previously claimed that the issue was only found with the Qatari airline. Airbus claims that the A350 is safe for use that that the company was aware of the source of the issues.

Follow Doha News on Twitter, Instagram, Facebook and Youtube