The Paper reporter Shao Bingyan
On July 7, some netizens posted a video of the flight of Air China flight CA1921 on the Internet.
According to the video, during the flight of the plane, one screw was missing from the area looking out of the window, and one was obviously loose.
In the evening of the same day, Air China issued a Weibo response saying that in response to the loose screws on the inner side fairing of the left wing of Air China flight CA1921 reported on the Internet, Air China attached great importance to it and immediately checked the relevant parts of the aircraft to check the loose screws. Maintenance was carried out and the relevant fleet was investigated.
Air China will adhere to "safety first" to ensure aviation safety.
Thank you for your concern and attention to Air China.
According to the Air Travel APP, the aircraft type flying Air China CA1921 is a Boeing 737-800.
According to a number of industry insiders who told reporters that on the evening of July 7, many airlines have begun to strengthen the inspection of aircraft.
"Screws" for fixing the cover
Qiao Shanxun, a member of the Chinese Aeronautical Society and Secretary-General of the Expert Committee of the Henan Aviation Industry Association, told The Paper that combined with the Boeing manual, it was found that the area where the screws were loose in the video was the trailing edge flap slide fairing of the passenger aircraft, which is commonly called a boat-shaped fairing. The cover wraps the flap actuating structural components such as the flap rails like a shell.
The place where the screw is loose is the tail vertebra of the boat-shaped fairing, which can be missing in Boeing's list of shape defects.
Qin Ming (pseudonym), a senior maintenance engineer from a former airline company, told The Paper that the screws in the video belong to "screws", which are only used to fix the cover without too much force.
The back of the screw is equipped with a pallet nut, which has the function of preventing loosening.
Generally, screws and bolts are used to distinguish fasteners. Screws are installed in places where they are not under stress, and are often used on aircraft covers.
The bolts are installed on the stressed structure.
Zhang Lei (pseudonym), a flight engineer, told The Paper that the main reason for the loosening of the screws was due to flight vibration.
"Removing one screw is usually not a problem. The doubt in this incident is whether the remaining screws are loose."
Regarding the impact of screw loosening and falling, Qin Ming said that the most serious degree is that the conical fairing falls off and hits other parts of the aircraft, which will affect flight safety, but the final result is not easy to assess.
Qiao Shanxun introduced that the flap slide rail fairing, the fasteners play the role of fixing the fairing, this place vibrates violently and frequently, and looseness is normal.
It is not a big problem to remove or install this piece, and it may affect the aerodynamic performance of the aircraft.
Several maintenance engineers and industry experts told The Paper that the lost screws were not sure whether they were dropped in flight.
"There are very few cases where the screws fall off during the flight, and in general, there are many cases where they cannot be screwed down."
Expert: Comprehensive inspection should be accelerated to reduce secondary disasters
Qiao Shanxun said that the loosening of the screws will not directly lead to a disaster, but this is also an abnormal situation and can be completely avoided. The airline needs to speed up the tightening of the aircraft fairing area and fasteners. comprehensive inspection.
In addition, this phenomenon may cause secondary disasters, such as vibration during the take-off of the aircraft, causing parts to fall off the runway, affecting other aircraft.
"It is dangerous for fasteners such as screws and bolts or the fairing to loosen during flight. If it falls at the airport, it may be inhaled by the engine of the aircraft behind." Zhang Lei said that from the airport, similar situations occur every year. Fasteners are always picked up.
Qiao Shanxun also said that the loosening of the fastener will not have much direct impact on the operation of the Boeing 737 airliner.
However, if it falls on the runway during takeoff, it becomes foreign object debris (FOD, foreign object debris), which may be inhaled by the aircraft behind, thereby damaging the engine, cutting aircraft tires, getting stuck in aircraft parts, causing failure, jetting or injury during propeller propulsion.
Regarding the frequency of checking the looseness of fasteners such as screws, Qin Ming said that the general maintenance will check the appearance of the aircraft during the short stop of the flight, including checking whether the screws are falling off and loose, and will strive to complete the release of the aircraft within 30 minutes. The unit and operation control leave a certain preparation time.
"After the plane landed and stopped, the crew began to check around the plane while disembarking passengers and unloading goods. However, the position of the loose screws in the video has already exceeded the height of ordinary people, and it is basically impossible to check during this period. Although the plane is circled, it is not With the help of height tools, such as the upper surface of the flat tail and the top of the fuselage, it cannot be inspected." Qin Ming said that the real chance of approaching this area is to remove the fairing during the regular inspection, lubricate the flap screw, and then Put the fairing back on.
Qin Ming also told the surging news reporter that the safety guarantee system process for large transport aircraft is very complete, and it is enough to "take medicine according to the order".
Trusting in science, management and technology, the general public need not worry too much.
Qiao Shanxun also said that the public does not need to be too anxious, and the safety redundancy of the current aircraft is quite high.
But at the same time, the aircraft is also relatively fragile. It is necessary to remind all maintenance personnel that inspection and maintenance need to be carried out in strict accordance with the rules and regulations.