Most of the 41 passengers who perished in the Russian Sukhoi Superjet (SSJ100) which crashed on landing at Moscow’s Sheremetyevo airport in May earlier this year, died as a result of fire heat and poisoning by fire by-products, a controversial report alleges.
The revelations have come in an exclusive interview in the major Russian newspaper Kommersant Daily, given by the Gen. Lt. of Justice, Zigmund Lozhis, who is head of the main forensics directorate of Russia’s Committee of Investigations (SKR). He was responding to questions about the SSJ100 incident that occurred on May 5, 2019 at Sheremetyevo airport when 41 people died in the aircraft’s burning embers following an emergency landing.
The Russian regional aircraft, registered as RA-89098 and operating flight SU1492, had returned to the Moscow airport following a lightning strike during take-off which shut down its fly-by-wire flight controls and its radio communications systems.
According to Lozhis, most of the people died not from the impact of the aircraft hitting the ground, but from the fire heat and poisoning brought about by fire by-product gases. According to his preliminary data, hazardous combustion products were emitted not only by burning fuel, but also by the aircraft’s plastic passenger cabin cover materials.
SKR has specifically questioned the fire-protection characteristics of the plastics used in passenger cabin panels. Answering the question on whether the passengers were using oxygen masks, Zigmund Lozhis commented: “Everything happened very quickly, most of the people died in their seats with fastened seatbelts. They had no chance to react to the accident.”
Talking to Kommersant FM, a Moscow-based business radio station, Boris Rybak, head of Infomost Consulting pointed out: “The design [of commercial aircraft] is a highly regulated process – and airworthiness requirements are absolutely stringent. Certification standards demand in particular that, in emergency situations, including external fires, the airframe should be capable of protecting the passengers for minimum periods of time – sufficient, at least, for the evacuation of passengers and crew. If this did not happen, then something went wrong, either at the design/manufacturing stages or during the aircraft certification processes. That would mean that such an aircraft does not correspond to airworthiness requirements.
“Establishing root causes of accidents is the ultimate goal of any aircraft accident investigation, because the process helps to prevent similar accidents in the future. The fact that half of the passengers failed to even make an attempt to leave the aircraft means that there was a weak link somewhere. Besides the cabin interior, there are other structural and interior elements that would be crucial for passenger cabin fire protection,” he added.
“Some experts question the protection qualities of the composite passenger cabin floor panels (which are covered with synthetic fabric carpets) and are located directly above the main landing gear wells. There is evidence that the [crashed jet] floor burned through in a few seconds instead of protecting the cabin for at least 240 seconds [a minimum figure required by airworthiness standards].”
Dmitry Kalenichenko, the director of public relations at Sukhoi Civil Aircraft Co (SCAC), pointed out in an official comment that the SSJ100’s passenger cabin interior was originally designed and manufactured by US specialist Collins Aerospace. The testing of interior materials and structures were therefore conducted at accredited laboratories in the USA and Europe according to approved methodologies, and with the participation of experts from Interstate aviation committee (IAC) Aviation Register and EASA.
“Test results were also signed off by representatives of respective national aviation authorities and were included into the set of documents, confirming that the aircraft type corresponds to an approved certification basis. The SSJ-100, its systems and components, including the fuselage, wing, landing gear etc, all passed the required number of certification tests – both on the ground and in the air – thereby demonstrating compliance with airworthiness and environmental standards and requirements,” he stated.
It wasn’t long after the tragic accident in Sheremetyevo that many government and industry officials were quick to point to matters connected with EASA certification as the ultimate argument supporting their opinion that the aircraft had in fact performed flawlessly – and that this tragic accident was possibly therefore exclusively the result of mistakes made by the captain.
Yet EASA has remained tightlipped, proffering no comments about the certification process regarding the landing gear and passenger cabin fire protection – even after the release of those preliminary results of the IAC investigation which have sparked intense industry discussion. It is unknown if EASA even took part in the investigation of this accident.
Following the certification process, the Interstate Aviation Committee (IAC) issued the SSJ-100 with a Russian type certificate in 2011. EASA had issued the SSJ100’s European type certificate in February 2012 and since then more than 150 SSJ100 aircraft have been delivered to airlines and air operators, with almost one third of them operated by Aeroflot.
In the last 20 years, a lot of criticism has been directed at the organisational structure of civil aviation authorities in Russia, where the Interstate Aviation Committee (IAC) had been responsible for both the certification of aircraft and the investigation of accidents.
In this specific case it created a major problem because the Superjet is the first really new Russian passenger aircraft that has been certified by the IAC. Therefore the Sheremetyevo accident raised several technical questions, the first of which regarded the design of the aircraft’s main landing gear and its structural integration with the airframe. On the fitting of the main landing gear there are structural elements that ensure that, in the case of overload, the landing gear detaches safely.
“However, during the fatal Sheremetyevo accident, the nose landing gear had remained relatively intact and upright, even though it had suffered a maximum 5.8g-load at the third bounce, while both of the main landing gear mechanisms had collapsed. The main landing gear’s brace struts were detached as designed but at the same time the integrity of the fuel tank was broken by the hydraulic actuator which was attached to the rear spar web and had not been equipped with any safety features,” Rybak added.
“In other words, during this accident, the main landing gear did not separate as it should have, in turn tearing up the wing’s rear spar web which resulted in a massive fuel leak and subsequent catastrophic fire,” Rybak told Aviation Insider.
“All airworthiness standards – the USA’s FAA, Europe’s EASA, or Russia’s FAR –all unconditionally require that this must not happen, regardless of vertical speed, g-load or the number of bounces, if any.”
Bearing in mind these controversial allegations, Interstate Aviation Committee has very little or no motivation at all to question the certification of the landing gear design or the passenger cabin fire protection.
The crash investigation remains under the close radar of the Russian and international aviation communities – with the likely common expectation that all blame will eventually be placed exclusively on the shoulders of the aircraft’s captain.
(c) Russian Aviation Insider