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- Get out of the dive: SSJ-100 manufacturer has developed measures to prevent disasters of its airliners
Get out of the dive: SSJ-100 manufacturer has developed measures to prevent disasters of its airliners
Yakovlev, the manufacturer of the Superjet 100, has developed instructions on controlling the installation of angle of attack sensors for technicians and recommendations for pilots on recognizing erroneous readings to prevent accidents. It was their incorrect installation, according to preliminary IAC data, that led to the SSJ-100 crash near Kolomna on July 12, 2024. The design of the foreign Thales angle-of-attack sensors will not change, but their fasteners will be indelibly marked to prevent incorrect installation. For the new import-substituted airliners the sensor mounts are of a different design.
How to prevent SSJ-100 disasters
The developer of the Superjet 100 (SSJ-100) aircraft PJSC "Yakovlev" after the July 12 crash with a Gazprom avia plane near Kolomna has prepared a service bulletin for technicians to prevent improper installation of angle of attack (AoA) sensors, namely control over their installation. The document was familiarized with "Izvestia".
Superjet crash site, July 12, 2024.
According to the IAC's preliminary version, it was the incorrect installation of two of the four angle of attack sensors during the maintenance of the airliner at the UAC branch - Lukhovitsky Voronin Aircraft Building Plant with a deviation of about five degrees that led to the tragic finale. During climb, unreliable sensor readings led to untimely activation of the defense system that protects the aircraft from stalling. As a result, the system itself sent the SSJ-100 into the ground. The pilots had no time to recognize this failure and get out of the dive, avoiding a collision with the ground. There were no passengers on board the aircraft, but three crew members. All of them lost their lives. The airliner was produced in 2014, the board departed from the factory in Lukhovitsy after repairs and was heading to Vnukovo airport.
The angle of attack sensor is a device that has a flag vane located on the fuselage on the outside of the airplane. There are four of them on the Superjet, two on each side. They are designed to determine the so-called angle of attack - the angle between the longitudinal axis of the airplane and the velocity vector.
The bulletin, which was issued by Yakovlev, is necessary for correct fixing of ROV overlays in compartments F1 or F2 on the port and starboard sides. Indelible markings indicating the correct position of the device must be applied to the overlays and sensors.
The developer has also prepared an information letter for airlines explaining the aircraft behavior in case of two or more improperly installed ROVs. Rosaviatsia, by its directive, demanded from the aircraft operators to take these measures to prevent similar SSJ-100 crashes.
Izvestia was informed by the United Aircraft Corporation (UAC, part of Rostec State Corporation) that the bulletin provides additional clarifications to the existing procedure for installing serial sensors manufactured by Thales. At the same time, no change in their design is required, the corporation added.
Works on installation and removal of ROVs are supplemented with drawings explaining the principle of applying the control risk. Now it is required after removing the sensor to return the cover in place and fix it on the fuselage, so as not to confuse its position. When reinstalling two or more sensors, there should be mandatory control over the angle of its installation, noted in the letter "Yakovlev".
Landing gear at the site of the Superjet plane crash in Kolomensky District, July 12, 2024
Preventive measures were required for SSJ-100s already in operation with imported avionics and engines. The new import-substituted airplanes will be fitted with domestic avionics with safe ROV fasteners, UAC noted.
- The design of domestic sensors of the import-substituted SSJ-100 initially differs from the imported sensors installed on the base version of the aircraft due to a different manufacturer," the corporation said. - Their compliance with aviation norms and rules is confirmed during the ongoing certification flight tests.
In addition, on the initiative of Rosaviatsia, Yakovlev has issued a bulletin on crew actions in situations involving incorrect information from the ROV at various stages of flight, the federal agency told Izvestia. The document has been sent to the airlines and will be studied by the flight crew, it said.
"Izvestia" sent requests to carriers.
The Yakovlev letter says that equally incorrect (overestimated) data on the angle of attack from two or three incorrectly installed sensors can lead to the triggering of the aircraft's angle-of-attack limitation system. Then a symmetrical release of spoilers in flight is possible , resulting in a significant loss of wing lift. When flying at a constant angle of attack, this turns into a steady descent of the airplane, which cannot be paralyzed by a full deviation of the control stick to cabrization (flight of the airplane with altitude gain). Therefore, the crew of the SSJ-100 that crashed near Kolomna was unable to bring the airplane out of the dive, according to the preliminary report of the IAC.
According to the bulletin, pilots will be taught to recognize avionics errors and correct them in time so that the system does not send the plane into the ground.
"Izvestia" sent requests to the Ministry of Transport, IAC, "Rostec".
How automation interfered with the SSJ-100's control
- Angle-of-attack sensors are part of the system to save the plane from entering critical flight modes and stalling," Yuri Sytnik, an honored Russian pilot and aviation expert, told Izvestia. - If earlier the system only gave a warning signal, now automation intervenes in the control of the airplane even when the autopilot is turned off.
Artificial intelligence makes a decision and corrects the aircraft in space. However, if two or more sensors are not working properly, the control system can steer the airplane toward the ground, the expert notes.
According to Yuriy Sytnik, about 160 airplanes out of more than 230 SSJ-100s produced are flying today .
- " During the investigation of the airplane accident it was found that two sensors were mounted incorrectly at once," Oleg Panteleyev, executive director of AviaPort agency, told Izvestia.
According to him, if the crew had recognized the incorrect operation of the system in time, they would have been able to correct the actions of the automation and avoid a dramatic development of events.
- Therefore, it is important to control the process of ROV installation, as well as to train pilots on simulators to act in such non-standard situations," added Roman Gusarov, Editor-in-Chief of Avia.ru portal. - The application of indelible markings and strict compliance with the bulletin's instructions should be carried out at every airliner maintenance.
- The design of the angle-of-attack sensors on the Superjet 100 already contains "foolproofing". These are special guide pins that physically prevent the sensor from being put in the wrong position," Andrei Patrakov, founder of the RunAvia flight safety service , told Izvestia.
However, in the SSJ-100 airplanes in operation, the ROVs are installed through a removable pad fixed on the fuselage, and there is no "foolproof" protection on this pad. Therefore, indelible markings were required so that the position of the pad would not be confused when replacing the ROVs, the expert said.
Retraining pilots is no less important than controlling technicians. According to the IAC, a similar case with the angle of attack sensors was recorded with another SSJ-100 on May 6, 2024 during a scheduled run, but then the crew recognized the incorrect operation of the sensors in time, switched the system to a different channel (ADC3) and safely completed the flight. Unfortunately, on July 12, another crew didn't make it in time. Why no conclusions were drawn after the first accident, the IAC should answer in its final report.
According to Oleg Panteleev, carriers and training centers are now obliged to approve updated training programs for technicians with aviation authorities. It is they who should control the process of retraining pilots on simulators.
Переведено сервисом «Яндекс Переводчик»
