The airworthiness certificate for the ARJ21-700 regional jetliner issued by civil aviation authorities on Dec 30 is displayed in Beijing by Jin Zhuanglong (right), chairman of Commercial Aircraft Corp of China. The certificate means the aircraft meets the authorities' safety requirements and has permission to enter the civil aviation market. Pei Xin / Xinhua

International review

The Federal Aviation Administration, the US national aviation authority, also carried out a shadow review, to assess CAAC's capability, and randomly inspected 53 of the more than 300 CAAC experiments on the ARJ21, Shen said.

The FAA's review is ongoing, and the two authorities will sign a bilateral agreement to verify CAAC's assessment capability after the review is completed.

COMAC will also apply for airworthiness certification for the ARJ21 from the European Space Agency and, with approval from the FAA and the ESA, the Chinese manufactured aircraft will enter the international market.

COMAC deployed its outfield test team to Yanliang in 2009, together with the aircraft, and most of the ground test equipment was made there.

"I thought the work in Yanliang would last two or three years originally," said Ni Guomin, head of the team's technical support group.

The 68-year-old, who was supposed to retire years ago, was assigned to Yanliang in August 2009 to lead an 80-strong group consisting mainly of young engineers.

From the beginning, Ni and his apprentices were kept very busy as many problems were found with the plane, he said, and they had to work on weekends.

Another challenge for Ni was teaching his younger colleagues.

"We jokingly described it as 'grandpas teaching grandsons'," he said.

As the tests progressed, the young engineers became more experienced and the workload also eased.

Airplane problems became rare in 2014 and the staff could relax on weekends, Ni said.

Besides the staff of COMAC, the ARJ21's suppliers were also involved in the airworthiness examinations.

The jet was sent to the AVIC Aircraft Strength Research Institute, which is the only research center dedicated to aircraft strength in China, on Sept 28, 2007. Even now, although the aircraft has received airworthiness certification, an ARJ21 is still undergoing fatigue tests at the institute.

Takeoffs and landings are simulated on the aircraft to check its life span, which is designed to be 50,000 flying hours over 20 years.

The fatigue testing will take seven to eight years, as it simulates the aircraft's full working life, said Qiang Baoping, deputy director and chief engineer at the institute.

The aircraft also went through a three-and-a-half year static test in the institute to check its design strength.

"It was also the first time for us to work on passenger aircraft airworthiness certification," Qiang said.

The institute improved some of its equipment and test methods while working on the ARJ21 program, he said.

The ARJ21 is considered the start of China's passenger aircraft manufacturing, and all stakeholders, including the authority, manufacturers and suppliers, continue to work on the C919 and possibly the C929 - a domestically made wide-body aircraft.

The strength research institute has built a facility for the C919 in Shanghai, next to the aircraft's assembly line.

Engineer Guo and his colleagues still take care of the aircraft in Yanliang, but some may be assigned to Shanghai to work on the C919.

"The C919 will take a shorter time to get airworthiness certification, as we now have experience from the ARJ21," CAAC's Shen said.