Hong Kong’s Cathay Pacific Airways said on Tuesday it had inspected its entire Airbus A350 fleet after the in-flight failure of an engine part and found 15 aircraft with components that needed replacement.

A person familiar with the matter said a leak in a fuel system appeared to have caused a brief engine fire that was quickly extinguished by the crew of the Zurich-bound A350. There were no immediate signs that Monday’s incident would trigger significant regulatory action involving the A350 fleet, the person added.

The A350-1000 returned to Hong Kong just over an hour after take-off.

Aviation Herald, an air safety publication, reported the jet had turned back after a cockpit alert warning of a fire in one of its two Rolls-Royce XWB-97 engines.

After carrying out routine checks and discharging a fire bottle, the crew dumped fuel and returned to base, it said.

The incident caused a sharp drop in the shares of British engine maker Rolls-Royce on Monday, but they bounced back on Tuesday as concerns over implications for the global fleet eased and some analysts called the sell-off overdone.

Rolls shares rose 2.4% and were among the top gainers on London’s blue-chip FTSE 100 index.

Cathay Pacific said three of the 48 Rolls-Royce-powered planes it had inspected had gone through successful repairs and all were expected to resume operation by Saturday.

It canceled at least 34 round-trip flights due to the disruption to its fleet.

Data from flight tracking service FlightRadar24 showed other major operators of the A350-1000 and the smaller, more popular A350-900, still flying their aircraft on Tuesday.

Rolls-Royce has not yet issued a directive to airlines regarding possible inspections, according to an industry source who was not authorized to speak publicly about the matter.

Such a step is typically the first sign of an official instruction from regulators, though they can act independently.

Japan Airlines (JAL), which has five A350-1000s, said it had asked Rolls-Royce for more information and had not stopped A350 flights in the meantime.

“If the engine manufacturer takes any further action, we will respond accordingly,” a JAL spokesperson said.

Cathay Pacific said it had secured spare parts for the components that needed to be replaced. Rolls-Royce said the replacement could take place while the engine remained on-wing.

The engine manufacturer said it was committed to working closely with Cathay Pacific, Airbus and investigators in Hong Kong, whose safety agency confirmed it had launched a probe.

Cathay Pacific has not specified which engine component failed, but the carrier said it was the “first of its type to suffer such failure on any A350 aircraft worldwide”.

A person familiar with the matter said the incident involved a leak in a system designed to inject fuel to the engine.

The system comprises a pipe that feeds fuel from an entry point or manifold to a nozzle that sprays fuel into the combustion chamber, the hot inner core of the engine.

Sources said partially scorched parts were being analyzed at Rolls-Royce facilities on behalf of Hong Kong investigators, but that no leaks had been found so far in other engines.

Experts say such problems are rare but, barring a deeper flaw, generally raise fewer alarms than the failure of one of the major rotating parts such as a turbine blade.

However, any widespread further inspections could be disruptive to airlines at a time when engine repair shops are already congested following increased wear on modern engines, especially those of Pratt & Whitney on smaller Airbus jets.

Airbus said it was offering “full technical support”.

‘PRECAUTIONARY MEASURE’

There are 86 A350-1000s in operation worldwide, compared with 526 A350-900s, according to Airbus data. Together, they compete with the Boeing 787 and 777 on long routes. Cathay operates a mixed Airbus and Boeing fleet.

Top A350-1000 operators include Qatar Airways with 24, British Airways which is owned by the International Airlines Group with 18, Cathay Pacific also with 18, Virgin Atlantic with 12 and Etihad Airways and JAL with five each.

Qatar Airways said its fleet of 24 A350-1000s was not affected and it continued to monitor developments.

Although the part failure occurred on one of its 18 A350-1000 jets, Cathay Pacific said it was also inspecting its 30 smaller A350-900s as a “precautionary measure”.

It said it had “identified a number of the same engine components that need to be replaced”.

Malaysia’s national carrier, which also has A350-900s in its fleet, has consulted Airbus and is operating as normal, the country’s Transport Minister Anthony Loke Siew Fook said.

Singapore Airlines said it was reviewing the engines on A350-900s but there was no impact on flights. It does not have any A350-1000s.

Cathay Pacific shares ended the day down 0.6%.