On Saturday, January 15th, an Aeroflot Sukhoi Superjet 100-95 was operating flight SU1544 from Moscow Sheremetyevo to Penza, 625 kilometers to the southeast of Moscow, when the aircraft's autopilot spontaneously shut down. After descending to a lower altitude for the remainder of the flight, the plane landed without incident at Penza Vissarion Belinsky Airport (PEZ) at 15:19 local time.

Loss of RVSM capabilities

The plane was late taking off from Sheremetyevo. Usually, SU1544 leaves around its scheduled departure time at 09:25 (now moved to 09:00). However, on Saturday, it did not take off until 14:10, a delay of nearly five hours.

As reported by the Aviation Herald, about 15 minutes into the just above one-hour-long flight to Penza, the pilots received indications that the plane's air data system (ADS) #1 heating sensors had failed. Having worked through the relative checklists, they switched the affected ADS off. At the same time, the autothrust and autopilot both spontaneously went offline.

The cockpit crew notified Air Traffic Control that they had lost their reduced vertical separation minimum (RVSM) capabilities and descended to FL270 just after the aircraft had passed over Ryazan. They continued to Penza, where they landed about 45 minutes after the failure of the sensors and autopilot.

The aircraft is close to eight years old and has since returned to service, operating both domestic and international routes. Photo: Anna Zvereva via Flickr

Back in the air on Sunday

The aircraft suffering from the issues is registered as RA-89027 and is a 7.8-year old Sukhoi Superjet SSJ 100-95. Russia's civil aviation authority, Rosaviatsia, says that maintenance in Penza replaced the angle of attack sensor, after which the aircraft returned to service. No further details have been released about a potential cause of the malfunction.

Flight radar tracking services show the aircraft returned to Moscow on Sunday afternoon. Since then, it has operated domestic services to Orenburg and back to Penza, but also flights to Anapa and Copenhagen. RA-89027 will soon transfer to Rossiya Russian Airlines as part of the Aeroflot Group's great fleet reshuffling.

The aircraft will soon transfer to the fleet of Aeroflot subsidiary Rossiya Russian Airlines. Photo: Anna Zvereva via Wikimedia Commons

What is RSVM?

RVSM is the reduction of the standard vertical separation between aircraft flying between FL290 and FL410 from 2,000 feet to 1,000 feet. This was decided and implemented from the late 1990s onwards when air data systems and altimeters had reached a certain level of accuracy and reliability.

The new regulations significantly increased the number of aircraft that could operate between 29,000 and 41,000 feet. However, only aircraft with certified altimeters and autopilots may fly in RVSM airspace. Hence, when the Superjet's autopilot was spontaneously switched off during flight, the pilots had to descend to 27,000 feet and continue the journey at a lower altitude.

Have you ever been on a flight where the plane has had to descend to a lower altitude? How did the pilots communicate about the issue? Leave a comment below and share your experience.