A total of 160 Boeing 737 planes employed by mainland airlines will go through an emergency inspection on a mechanism that controls the jet's tail flaps, China's civil aviation authority said Thursday.

The statement was made by the Civil Aviation Administration of China (CAAC) on its official website to correct an earlier report, which claimed that more than 400 Boeing 737 jets on the mainland might contain the defect.

The emergency directive, demanding airlines check the flaps on the horizontal tails of the planes, was issued on March 15 following recommendations from Boeing after a Ryanair 737-800 traveling from the Netherlands to Spain experienced "severe vibration" on a March 2 flight .

The plane managed to land safely. An inspection afterwards found "extensive damage" to the left elevator, which is a movable flap on the tail that controls the vertical pitch of the airplane.

"Severe vibration in this attach point is suspected of allowing rapid wear of the joint and resulted in failure of the attach lugs," states the United States Federal Aviation Administration's preliminary incident report. "This condition, if not corrected, could result in a loss of aircraft control and structural integrity."

The problem involves the 600, 700, 800 and 900 series of the Boeing 737 model.

A CAAC spokesman said: "Some 160 jets are concerned We will pay great attention to them and strengthen supervision, in a bid to ensure the flight safety of these jets."

The report published on the Shanghai-based National Business Daily on Wednesday, said that, by February, Chinese mainland airlines had 603 Boeing 737 planes, ranging from the 300 through the 900 series.

It estimated that some 400 Boeing 737 jets are the 600 through 900 series, including 134 Boeing 737-700 jets, 318 Boeing 737-800 jets and five Boeing 737-900 jets. They are widely used in the fleets of airlines, including Air China, China Eastern, China Southern and Hainan Airlines.

Tan Wangeng, general manager of China Southern Airlines, told China Daily on Thursday that among its 40-plus Boeing 737 planes, only two planes needed to go through the emergency inspection.

"The inspection result showed the two jets do not have the indicated problem," he said.

Other airlines confirmed they had received the directive and immediately started inspections, but declined to give the exact number of planes involved.

"We can assure the safety of our Boeing 737 planes now in operation," said Luo Zhuping, secretary to the board of directors of China Eastern Airlines. "But we have to wait for directives from the CAAC to decide how to deal with the potential security hazard in those planes."

The Shanghai-based airline has some 70 Boeing 737 jets, which are mainly used on domestic routes.

The CAAC said it has issued more than 6,500 airworthiness directives from 1986 to 2009, a measure designed to ensure flight safety.

(China Daily March 19, 2010)