The Russian An-148 airliner, carrying out a domestic flight, crashed in the Moscow Region on February 11, 2018, killing all 71 people onboard. Investigators maintain that wrong data of flight speed, apparently due to icing, could have led to the crash. The yet unanswered crucial question is whether the pilots failed to switch on the heating unit or was it a technical issue that led to speed sensors’ malfunction.

The Saratov Airlines An-148-100B passenger plane was flying from Moscow to the city of Orsk in the Ural Mountains, Russia’s Orenburg Region, when it crashed minutes after takeoff. Radio and radar contact with the Flight 703 was lost several minutes after it took off from Domodedovo airport (DME) outside Moscow at 14:21 (local time), the Interstate Aviation Committee (IAC) performing the investigation of the crash reported.

The An-148 had apparently plummeted into a snowy field about 40 miles (64 km) southeast of the capital, near the village of Stepanovskoye in the Moscow Region’s Ramensky district. All 65 passengers and six crew members on board died in the crash. Russia’s Emergency Situations Ministry said the plane’s fuel tanks exploded on impact with ground, scattering wreckage across a wide area.

Nearly 1,500 body parts have been recovered from the crash site by February 13, 2018, and almost 5,000 pieces of debris were found since search operations started. As of February 18, 2018, the operations at the site, spanning across 50 hectares, were completed, a spokesperson for the emergency response headquarters told Sputnik. Pieces of the wreckage were transported to the Gromov Flight Reasearch Institute for examination.

Opening the Pandora’s box

On February 12, 2018, the Moscow-based IAC released an official statement saying that it had recovered onboard recorders (both FDR and CVR) from the An-148-100B RA-61704 aircraft.

After deciphering the data of the flight recorder and the preliminary analysis of the information, the Committee said a “special situation” with the An-148 plane began some 2 minutes 30 seconds after takeoff at an altitude of about 4,265 feet (1,300 meters) and speed of around 292 mph (470 km/h).

According to investigators, the flight recorders showed divergences in the data from the plane’s two airspeed sensors. These divergences reached about 18.6 mph (30 km/h), after which the one-off command for the crew appeared: “The Instrument Panel – Compare!” This command was repeated at an altitude of about 6,561 feet (2,000 meters) as the difference between the readings grew even bigger. After the second command, the crew turned off the autopilot and took manual controls.

The speed indications of the plane’s air parameter modules differed significantly from each other. One indicator showed the speed at 0 mph and the other was showing about 342 mph (550 km/h). Before the plane hit the ground, one of the sensors continued to show a speed of 0 mph while the data on the other started to fall intensively to 124 mph and lower (to 200 km/h and lower).

Reconstruction of events suggests that the pilots then performed a series of maneuvers and eventually took the plane into rapid descent with angular movement for a dive at 30 to 35 degrees before crashing. “Four-five seconds before hitting the ground, the plane developed a right-side roll of 25 degrees,” the IAC stated. 

The IAC said a factor in the crash could be the wrong data about flight speed on pilots’ displays which was likely due to iced Pitot tubes (speed indicators) since their heating systems were apparently switched off. During all previous 15 flights registered on the flight recorder, the heating of the total pressure probes was switched on before takeoff in its line-up position, the said in its IAC report.

On February 14, 2018, the Committee announced that test pilots from the Gromov Flight Research Institute will conduct an experimental flight simulating the takeoff of the An-148 in order to find out the causes of the crash, the Institute’s press office told TASS.

The flight parameters will be identical to the readings of the crashed plane, and the pilots will test various elements with the switch-off of sensors, engines and other onboard systems. The experimental flight will be conducted by pilots who have numerously tested and flown An-148 and other aircraft, the press office said. However, the Institute did not specify the date of the experimental flight.

The likeliness of human error

Investigators have been checking numerous versions for probable cause of the tragic crash. Early theories suggested a possible engine explosion as some witnesses reportedly saw an engine burning as the jet was falling. It was later determined that the destruction of the aircraft was caused by its collision with the ground.

The version of a terrorist attack was also refuted early on in the investigation as experts who conducted an express-analysis of the plane’s fragments did not find micro-particles from any explosives, Sputnik writes.

Investigators also assumed that the lack of pre-flight de-icing procedures may be the reason for the wreckage. A source, working at the Domodedovo airport, has been cited by Russian media saying that “Sometimes the crew refuses the procedure in order to save time”. The New York Post indicates a Russian RBK newspaper report in which it is claimed that the captain of the An-148 did indeed refuse de-icing procedure before takeoff.

Speed indicator failure has been the most probable version since the beginning of the investigation. The retrieved data recorders suggest the pilots failed to turn on the heating unit for the pressure measurement equipment, or the Pitot probe, – used to determine airspeed – before takeoff, despite the procedure being listed on a pre-flight checklist, which in effect would cause the device to ice over.

This would mean a possible pilot error. Data from the voice recorder of the An-148 revealed that the pilots got into an argument over the speed indications as they tried to solve the problem before increasing their speed and tilting the plane towards the ground, Euronews writes.

The IAC has said it would look at whether the speed sensors could have malfunctioned, but no new reports on that have yet emerged. Meanwhile, a criminal case on charges of violations of flight safety and aircraft operation rules entailing the death of two or more people through negligence has been opened.

The possibility of technical malfunction

The An-148-100B twin-engine turbojet was developed jointly by Russia and Ukraine, but was later phased out of production due to political tensions between the two countries. The aircraft was originally developed by the Ukrainian company Antonov and, under cooperation agreement with Russia, about 40 planes were manufactured in Russia by Voronezh Aircraft Production Company using engines and other components provided by Ukraine, RFE/RL explains.

Once the production of the plane was halted in Russia in 2017, several media reports surfaced saying that some carriers, including Saratov, started experiencing a shortage of spare parts. One Russian pilot, Andrei Litvinov, was reported saying that some regional carriers in Russia were facing financial difficulties and would cut corners on servicing aircraft. “They are trying to save money on maintaining their planes to prevent going under,” Litvinov said.

Russian investigators have confirmed that the crew of the crashed airliner did not report any malfunction or send a distress signal before the crash. Meanwhile, Saratov Airlines Saratov have repeatedly stated that there had been no concerns over the technical condition of the plane. It said the jet had received proper maintenance and passed all the necessary checks before the flight. According to Saratov spokeswoman Yelena Voronova, “the plane was reliable”.

In a press release on February 12, 2018, Saratov stated it would temporarily ground An-148 planes, pending the outcome of the official investigation into the cause of the crash. The airline resumed flights less than a week later, on February 16, 2018. Saratov says it has six An-148-100 aircraft in its fleet. The An-148 with onboard number RA-61704 was received in February 2017.

As specified by the manufacturer, Antonov An-148-100B can reach the maximum height between 40,026 and 41,010 feet (12,200 and 12,500 meters); and the maximum speed of 541 mph (870 km/h). Its service range is 2,237 miles (3,600 km). The An-148 performed its first flight on December 17, 2004, and entered into operation in June 2009.

Connection with previous crashes

On March 5, 2011, failure of the speed indicator caused the An-148 crash that killed six crew members. The Antonov plane was carrying out a test flight when it went down in central Russia on the border between the Voronezh and Belgorod regions, RT reported at the time. In that incident, while the speed indicator failed showing a low speed, the pilots then increased the speed until the plane broke up in flight.

According to RFE/RL, there have been several other instances of An-148 planes experiencing major engine failures and loss of control after takeoff since 2010 in Russia, though it said the crew in each previous case was able to safely land the plane.

In regards to the latest An-148 crash, Saratov airlines spokeswoman Yelena Voronva assured the media that one of the pilots had more than 5,000 hours of flying time, 2,800 of them in an An-148, and the other pilot had 812 hours of experience, Sputnik reports.

In fact, the airline has been pretty adamant in defending its pilots, providing with full information on their education and experience. In a press release, Saratov states that “the crew members were experienced pilots” and that they had “passed all necessary trainings, programs that help to react to abnormal situations in flight”.

But the investigation into the crashed An-148 airliner has reminded many of the tragic Air France Flight 447 in 2009. Iced-over Pitot tubes were also cited as the likely reason behind the tragedy in which the airliner, flying from Rio de Janeiro, Brazil, to Paris, France, crashed into the Atlantic Ocean killing 228 people, The New York Post writes. 

Although the initial reports on the possible causes of the crash evolved around the malfunction of the plane’s Pitot tubes, the investigation concluded that the main reason for the tragedy was the pilot’s error. In his book “Computer crashes: When airplane systems fail”, Tom Dieusaert has argued that pilots are commonly blamed for tragedies like the Air France F447, without enough emphasis being put in the troubles the machine already had, particularly with its computer software.