The cause of the crash of the Il-112V prototype
A five minute read on the unofficial analysis of the fatal crash of the Il-112V prototype.
The Russian newspaper Kommersant has published an analysis by the Ministry of Industry and Trade (Minpromtorg) and the Interstate Aviation Committee (IAC) describing the root cause of the catastrophy with the experimental Ilyushin Il-112V.
The aircraft crashed during a preparation flight on 17 August 2021, five days before the start of the Army-2021 forum, between the village of Nikolskoye and the Odintsovo urban district of the Moscow region.
According to this analysis, the critical situation on board was caused by a starboard engine fire which caused structural collapse of the right aileron. This failure sent the aircraft into an uncontrolled side roll at low altitude and the aircraft crashed into the ground almost inverted. There was nothing that the test pilots of PJSC Ilyushin, Hero of Russia Nikolai Kuimov and Dmitry Komarov, as well as test flight engineer Nikolai Khludeev, could do in this situation to save the aircraft and themselves.
Experts from the Minpromtorg and the IAC established that the development of the disaster started with the loss of gas-dynamic stability of the starboard TV7-117ST engine a few minutes after takeoff. The engine surge following the loss of stability was accompanied by flame bursts and the combination probably led to a partial destruction of the turbine, with the debris, in turn, having damaged the adjacent fuel lines. This led to a powerful kerosene-fueled fire in the internal cavities of the engine nacelle and the right wing of the Il-112V.
The people who first noticed the fire were the dispatchers of the Kubinka airfield from where the aircraft took off and they immediately informed the crew about the problem via radio comms. The crew confirmed that they had a warning panel light already lit up and that the first stage of the fire extinguishing system working in the automatic mode has already engaged. This resulted the flame retardant foam having been released into the nacelle from the adjacent high-pressure fire extinguisher cylinder.
The crew reacted to the alarm promptly. Having realized that the first foam attack was not successful, the pilots subsequently manually activated the second stage of the fire extinguishing system, alas to no avail.
As explained by sources close to the investigation team, both fire extinguishing systems on the Il-112V were primarily focused on the engines, therefore the foam formed from carbon dioxide enriched by inert gases mainly filled the engine nacelle. Unfortunately, by that time the fire had already spread into the inner wing cavity. Even worse, the manufacturer has only mounted two fire extinguishing systems for each engine of the Il-112V, therefore there was nothing else left to suppress the fire with. The existence of mere two foam bursts has proven to be a design fault, in comparison, the fire extinguishing system for civil Ilyushin aircraft can provide six.
The pilots were left with no other choice than to return to the airfield of departure and request for an immediate emergency landing. Based on the cockpit recordings, the experienced crew acted smoothly and precisely. The commander, without the slightest sign of panic, ordered the second pilot 'Emergency Situation', he also calmly summed up on the execution of the procedures, reporting that the burning engine was safely stopped and that the blades of the starboard engine propeller were set on feathering. The crew also correctly positioned the rudders of the aircraft and selected a single engine operating mode, so despite the raging fire and asymmetric thrust, the crippled aircraft took an almost ideal straight course to the Kubinka runway, which was less than two kilometers away. The experts unite in their opinion that the crew, now struggling for survival, were perfectly able to successfully land the struggling hauler that way.
Unfortunately, this is where the aircraft has failed them once again. In the 45th second after the start of the fire, the temperature in the cavity of the right wing reached 600 degrees which resulted in a structural collapse of the aileron support strut. A temperature of 650 degrees is critical for the material (D16 duraluminium) from which the strut and most other parts of the aircraft’s wing were made of, but already at 600 degrees the hinges holding the right aileron in the lowered position, started to creep and lose elasticity.
After the collapse of the strut, the aileron, which enabled the pilots to balance out the asymmetry and ensure the straight flight of the aircraft, returned back to the neutral position and the machine began to roll to the right while losing altitude. Based on the released footage, at the beginning the roll occured slowly but the crew already must have known that the process was irreversible. The pilots could not influence the behavior of the aircraft anymore and, apparently, as experienced as they were, they did not consider it necessary to comment on the critical situation. There was no recorded communication on the intercom in the last seconds of the flight and the crew seem to have died in complete silence. The investigators of the accident have stated that it was impossible for the pilots to get the plane out of the roll in such conditions and that only by coincidence the aircraft did not crash in the Patriot Park, over which the demonstration flight of the Il-112V should have occured.
So, the true reason for the tragedy was obviosuly poor preparedness of the prototype for test flights and the possible haste with its commissioning. The crashed example No. 0001, assembled by the PJSC VASO (Voronezh Aircraft Manufacturing Company), was the only flight example of the Il-112V type, with an additional airframe serving as a static testbed. During its short lifespan, the first prototype only managed to take 23 flights, with most of them only lasting for a few minutes. On top of that, the aircraft was grounded for two years (between March 2019 and March 2021) due to numerous technical flaws which needed to be eliminated while most complaints were related to the TV7-117ST engines, manufactured by JSC UEC-Klimov.
In the light of this situation, the decision to demonstrate the experimental prototype on the MAKS 2021 held in July 2021, and then on the Army-2021 Forum, held from 22 to 28 August starts to look dubious, at best.
As experts believe, the unnecessary haste created the conditions for a disaster, but whether this opinion will become the official conclusion of the commission of the Minpromtorg is not yet clear. In the meantime, Russian president Vladimir Putin posthumously awarded the crew with the Order of Courage, a state decoration of the Russian Federation to recognise 'selfless act of courage, valour and dedication shown in testing and mastering new aviation technology.'
Photo by Alexander Shipilenko via RussianPlanet.net