Airbus SE suffered a one-two punch on its popular A320 airliner after revealing a quality issue on some fuselage panels — just days after a software glitch on about 6,000 jets required emergency upgrades.

“Airbus is taking a conservative approach and is inspecting all aircraft potentially impacted — knowing that only a portion of them will need further action to be taken,” the company said in a statement, responding to an earlier report by Reuters identifying the issue. 

The European manufacturer appeared to have averted a major headache the morning of December 1, when it said only a tiny portion of the aircraft needing the software fix still required attention. But the disclosure of quality lapses on a key section of the aircraft spooked investors anew, driving the stock down the most since April.

The company said that the source of the latest issue has been identified and contained, and that newly produced panels conform to all requirements. Still, it’s unclear how the additional inspections may affect Airbus’s tight delivery schedule of aircraft for the year and how many planes are affected. 

Airbus delivered about 70 aircraft in November, according to people familiar with the figures, leaving the company with about 165 units it must hand over to customers in December, which would mark a record. 

The planemaker has a target of 820 aircraft deliveries for the year, a feat that looks just about achievable if everything falls into place perfectly. According to RBC Capital Markets analyst Ken Herbert, Airbus has averaged about 109 deliveries in December, with the record achieved in 2019, when it handed over 138 aircraft.

Airbus shares fell as much as 11% in Paris trading, marking the worst intraday drop since April 7. The company has long grappled with parts shortages, from engines to kitchen units to toilets, that have held back output.

The A320 is, by far, the company’s most popular product. On November 28, Airbus called for an urgent software revision on more than half its active A320 family fleet after an incident uncovered possible corruption of flight controls because of solar radiation. 

Given that Airbus has not issued a stock-market release changing its guidance on deliveries, the panel issue looks to be controllable, JPMorgan analysts David H Perry and Lucy Fitzgerald wrote in a note. The batch of flawed panels is for the front of the aircraft, fitted behind the cockpit alongside the two front doors, the analysts wrote, citing Airbus.

Aircraft deliveries are closely watched metrics because they give investors clues about the health of a manufacturer’s supply chain and production processes. Airbus has been forced to revise the annual target in the past, but the company came within its goal last year.