Comac has begun modifying the landing gear of its ARJ21 regional jet, a move that could lead to the aircraft's certification being pushed back once again.

Liebherr-Aerospace, which supplies the landing gear, says that "improvements" made to the aircraft after years of flight tests have affected its landing gear system.

These need to be "adapted to the updated aircraft's operational features", says a Liebherr spokeswoman. The flight tests, which began in 2008, have also identified "potential interface issues" between the landing gear and the rest of the aircraft, she adds.

"The resolution of these potential interface issues has been integrated into the batch of current modifications," she says.

Liebherr would not give more details about the modifications, and it is not clear if the interface issues are largely physical or electronic in nature.

It is not often that modifications are made to an aircraft's landing gear this late into a programme.

Comac has four ARJ21 test aircraft, which have accumulated over 2,800 flight hours since 2008.

At Airshow China in Zhuhai last year, Comac said it hopes to receive certification from the Civil Aviation Administration of China (CAAC) for the ARJ21 in the first half of 2013, and to deliver the aircraft to launch customer Chengdu Airlines by 2014.

The delivery of the ARJ21 - a project that began some 11 years ago, was initially scheduled for 2007. The deadline was pushed back several times as engineers encountered problems in the development as well as certification process.

The US Federal Aviation Administration is conducting a shadow certification process alongside the CAAC's certification.

Source: Air Transport Intelligence news