BEIJING/PARIS (Reuters) - Development of China’s C919 single-aisle plane, already at least five years behind schedule, is going slower than expected, a dozen people familiar with the program told Reuters, as the state-owned Commercial Aircraft Corporation (COMAC) struggles with a range of technical issues that have severely restricted test flights.

FILE PHOTO: The fifth prototype of China's home-built C919 passenger plane takes off for its first test flight from Shanghai Pudong International Airport in Shanghai, China October 24, 2019. REUTERS/Stringer/File Photo

Delays are common in complex aerospace programs, but the especially slow progress is a potential embarrassment for China, which has invested heavily in its first serious attempt to break the hold of Boeing and Airbus on the global jet market.

The most recent problem came down to a mathematical error, according to four people with knowledge of the matter.

COMAC engineers miscalculated the forces that would be placed on the plane’s twin engines in flight - known in the industry as loads - and sent inaccurate data to the engine manufacturer, CFM International, four people familiar with the matter told Reuters. As a result, the engine and its housing may both have to be reinforced, the people said, most likely at COMAC’s expense – though another source denied any modification.

That and other technical and structural glitches meant that by early December, after more than two and a half years of flight testing, COMAC had completed less than a fifth of the 4,200 hours in the air that it needs for final approval by the Civil Aviation Administration of China (CAAC), two people close to the project told Reuters.

COMAC, which has been developing the C919 largely in secret since 2008, rarely discloses its targets. Company official Yang Yang told Chinese state media in September that he expected certification by the country’s regulators in two to three years, without giving any further details. The company’s previous publicly stated target was end-2020. Other COMAC officials have said they are aiming for certification and delivery in 2021.

COMAC did not respond to Reuters requests for comment for this story. CFM, a joint venture between General Electric and France’s Safran, declined comment.

COMAC has still not finalised the correct calculations and data to send to the engine manufacturer, which are key to ensuring that the engine does not fail under heavy loads, one of the sources told Reuters. Another said load calculations often evolve during development.

But given the uncertainty, there is no guarantee COMAC will meet Yang’s 2021-2022 target, people close to the program told Reuters.

Slideshow ( 2 images )

“Things do not always work out as planned, but I hope COMAC would slow down a bit and try not to rush things,” one of the sources familiar with the engine issue told Reuters. “Otherwise there will be tons of issues later on.”

TIME PRESSURE

The engine miscalculation does not reflect a lack of theoretical understanding - China has been putting people in space for almost two decades. But it does illustrate the national aerospace manufacturer’s lack of experience in designing and building commercial aircraft.

Problems have not been confined to the drawing board. COMAC found cracks in the horizontal stabilizers of some of the first few aircraft built, two sources said, although that problem has now been fixed. It also found a gearbox attached to the engine was vulnerable to cracking, which caused an engine to shut down during a test flight, three sources told Reuters, a problem that potentially affects all six C919 jets now in test flights.

Regular inspections of the gearbox to check for cracks and leaking oil have curtailed COMAC’s flight test program, they said.

The gearbox problem, discovered in 2018 and not previously reported, was due to unexpected vibrations, two sources told Reuters. Engineers on the program have found ways to minimize the risks, the sources said.

Unwanted vibration, which in the worst case can shred parts inside an engine, is a problem faced by even long-established aerospace manufacturers. U.S. engine maker Pratt & Whitney revised software due to destructive vibration on some new engines, Reuters reported in October.

However, the accumulation of problems has put COMAC significantly behind schedule, which could prove costly.

The C919 is designed to compete with the Boeing 737 MAX and Airbus 320neo families. After Boeing and Airbus struck deals to take over production of rival planes made by Embraer and Bombardier, China’s COMAC is now effectively the third option in the market for planes with more than 100 seats.

Most industry forecasters now expect the prolonged cyclical boom in demand for commercial planes to fade this year, as business confidence wanes amid geopolitical tensions, meaning a plane that debuts in 2021 or 2022 will likely miss out on orders for years to come.

COMAC is aware of the time pressure. The last three of its six test flight C919s were put into the air for their first flight before the paint job had been completed, sources told Reuters.

HIGH STAKES

Beijing made the C919 an integral part of its ‘Made in China 2025’ initiative, designed to catch up on sophisticated technologies and help the country become self-sufficient.

The effort has attracted the attention of U.S. federal prosecutors, who in 2018 charged a group of Chinese intelligence officers, hackers and company insiders with breaking into the networks of 13 aerospace manufacturers around the world, including a company whose description matches CFM, in order to steal sensitive data that might help China build a jet engine. China has denied any involvement in hacking.

Beijing may not be entirely disappointed if the C919 jet fails to compete immediately in international markets, some analysts say, as the Chinese government can direct its own airlines to buy the jet.

Chinese state-owned carriers and leasing companies account for the vast majority of the 815 provisional orders COMAC says it has received for the C919. The only overseas buyer so far is the leasing company GECAS, owned by General Electric. Few of the orders have been finalized.

“The C919’s real mission is to conquer a domestic market dominated by its two foreign competitors,” said Jean-François Dufour, chief analyst of DCA Chine-Analyse. “Ten to 15 years from now, a next-generation C919, or other models developed by COMAC, may become real competitors on the global scene.”