Russian investigators have reached a preliminary determination that ice buildup in the pitot tubes led to a difference in speed reading between the primary and standby air parameter modules in the Saratov Airlines Antonov An-148 that crashed on February 11 in the village of Stepanovskoye, outside Moscow, killing 65 passengers and six crewmembers. Following retrieval of both the flight data and cockpit voice recorders, Russia’s International Aviation Committee (MAK) determined a “dangerous situation” began to unfold two and a half minutes after takeoff, when the airplane had reached an altitude of about 4,265 feet at an indicator speed of 251 to 254 knots. According to MAK, a malfunction of the pitot tubes’ heating system or failure by the crew to turn on the device caused the ice buildup, thereby feeding the wrong speed reading to the aircraft’s digital flight control system.
On the same day as the catastrophe the aircraft had uneventfully performed three flights (Penza-Moscow, Moscow-Saratov, Saratov-Moscow). Crews changed as planned, according to the airline. The captain on the accident flight, which took off from Moscow Domodedovo Airport for a regularly scheduled service to Orsk, was a former military pilot with 5,099 flight hours to his credit, including 2,147 in the An-148, most of which he logged with Rossiya airline, the type’s launch customer in Russia. The copilot logged 812 flight hours in the An-148, which he collected with Angara Airline. Reportedly, the captain had warned traffic controllers about “malfunctions” and prepared for an emergency landing at Ramenskoye airport in Zhukovsky.
MAK noted that it found the flight recorder in poor condition. Mechanical damage to memory modules required their disassembly to retrieve data directly from solid-state chips. The investigators managed to successfully retrieve stored data on the previous 16 flights, including the ill-fated one.
As part of aircraft wreckage examination effort, crews removed both of the airplane’s D-436-148 turbofans powering the twinjet from the crash site for thorough investigation. Their manufacturer, Motor-Sich of Ukraine, issued a statement indicating that it assembled the engines in 2009, and that they logged 13,515 and 15,806 hours, respectively. Motor-Sich’s press service further stated that both engines operated until the point of impact. The engines underwent heavy maintenance in 2014.
UAC’s VASO plant in Voronezh, Russia, completed assembly of the aircraft in June 2010 under license agreement with type developer Antonov design bureau of Ukraine. It then went to Ilyushin-Finance Co., which leased it to Rossiya Airline. IFC then leased it to Saratov Airlines in February 2017. The latter said in a statement that the aircraft underwent a C-check in January 2018 at the airline’s home base with help of Ukrainian specialists. Saratov Airlines has grounded its remaining An-148s, temporarily replacing them with Embraer E190s and Yakovlev Yak-42Ds.