Andrey Zlobin, Candidate of Technical Sciences, in the 90s, Head of the CIAM Engine Sector
The critical situation on board the Il-112V, which crashed on August 17 in Kubinka near Moscow, was provoked by an engine fire and a breakdown of the right aileron thrust destroyed by fire. This is the conclusion reached by experts from the Ministry of Industry and Trade and the Interstate Aviation Committee, the conclusion of which is provided by Kommersant.
It was found that a few minutes after takeoff in the internal cavities of the nacelle and the right wing IL-112V a powerful "kerosene" fire broke out. According to preliminary data, it happened due to loss of gas-dynamic stability of the right engine. The ensuing surge with pops and flames partially destroyed the turbine, the debris of which could interrupt the nearby fuel lines.
The first stage of the fire extinguishing system worked in automatic mode - a fire extinguishing foam composition was released into the gondola from a nearby fire extinguisher high pressure. However, the ejection was empty. After that, the pilots manually activated the second stage of the fire extinguishing system, but it also did not reach the goal, since at that time the fire had already spread to the inner cavity of the wing.
Experts note that the crew acted smoothly and quickly, without the slightest sign of panic. The pilots managed to stop the burning engine, as well as position the aircraft's rudders and select the mode of the only operating engine in such a way that, despite the raging fire and asymmetric thrust, the car went towards the airfield with an almost ideal straight course.
However, all the actions of the crew were in vain, since the plane itself "surrendered". On 45th a second after the start of the fire, the temperature in the cavity of the right wing reached 600 degrees, due to which destroyed the thrust of the aileron, which helped the pilots to provide a straight flight. IL-112V began to roll to the right and lower his nose. Experts believe that the pilots realized that the process had begun was irreversible. They could not influence the behavior of the plane, so they just kept silent ...
However, the deputy head of the Ministry of Industry and Trade, the chairman of the investigation commission, Oleg Bocharov, said that there are no final conclusions on the investigation of the Il-112V disaster so far.
"The commission for the investigation of the Il-112V disaster continues to work. There are no final conclusions about the causes of the accident," - he is quoted by the press service of the Ministry of Industry and Trade.
Bocharov also added that the information given in the media is only the assumptions of sources, and not official conclusions.
But it seems that the picture of the Il-112v disaster is starting to clear up. In any case, according to the honored pilot of Russia Yuri Sytnik, the engine seems to be actually cut off the fuel line and the kerosene fire spread to the wing of the plane. I originally also adhered to this point of view. But the main question is: why was there a problem with the engine?
I think it would be more correct to focus not only on the technical condition of the engine, but also on the flight program, which looks, as it were, to put it mildly, not entirely thought out. It would seem that if the aircraft and engines were in the testing stage, it made sense for a certain period of time to avoid dangerous modes of operation of technology. Or, more often to carry out technical control of its condition. And here is what the press reports. Having taken off in the morning from the airfield in Zhukovsky, the Il-112v landed in Kubinka. The plane was on the ground for several minutes, then it took off again. A fire broke out in just a few minutes of the flight.
To begin with, gas turbine engines have minimal clearances between a rotating rotor and a stationary outer casing (stator). These sub-millimeter clearances can decrease or increase as an airplane takes off or lands. There is such a thing as a cyclogram of engine operation. The cyclogram shows what period of time the engine operates in different modes. Time intervals of several minutes, as a rule, correspond to strong changes in parameters, for example, the transition to takeoff mode and the actual takeoff.
The operation of the engine during landing is associated with a reduced mode and also with strong changes in the parameters of the working process. That is, there are engine operating modes in which the clearances change especially noticeably, since the revolutions change greatly, parts quickly heat up or cool down. A new aircraft engine needs to run a certain number of hours in order for the rotor and stator parts to "fit" to each other and the clearances become stable.
Some engines even have special radial clearance control systems (RRZ) that maintain clearances within strict limits. If there is something wrong with the clearances, during takeoff or landing, the so-called "biting" of the rotating rotor body and the following emergency situation may occur. Similar troubles are possible both with the engine compressor, its turbine, and with the rotating seals. Frequent transients can affect bearing performance. Clearance problems can cause so-called surging (loss of gas dynamic stability), strong vibrations, overheating and destruction of engine parts. These considerations come to mind when you read about the typical time intervals of several minutes, which replaced each other several times for the Il-112v. Several minutes of landing, several minutes of parking on the ground, several minutes of re-takeoff, several minutes of flight at altitude...
Generally speaking, the sophisticated aircraft being tested must be carefully checked on the ground after each flight involving takeoff and landing. If, after the flight and successful landing in Kubinka, the plane no longer took off that day, but underwent a thorough inspection of the technical condition, perhaps the disaster would not have happened.