IRS Aero Flight 9601/02 explained

IRS Aero Flight 9601/02
Occurrence Type:	Accident
Summary:	Technical failure, maintenance errors, loss of control
Site:	15 km from Kalyazin, Tver Oblast, Russia
Aircraft Type:	Ilyushin Il-18V
Operator:	IRS Aero
Tail Number:	RA-75840
Origin:	Domodedovo International Airport, Moscow
Stopover0:	Khatanga Airport
Stopover1:	Yemelyanovo Airport, Krasnoyarsk
Stopover2:	Khatanga Airport
Stopover3:	Tolmachevo Airport, Novosibirsk
Last Stopover:	Khatanga Airport
Destination:	Domodedovo International Airport, Moscow
Passengers:	18
Crew:	9
Fatalities:	27
Survivors:	0

IRS Aero Flight 9601/02 was a charter flight operated by an Il-18V aircraft of the airline "IRS Aero" on the route Moscow—Khatanga—Krasnoyarsk—Khatanga—Novosibirsk—Khatanga—Moscow. On November 19, 2001, during the last leg of the route (Khatanga—Moscow), the aircraft suddenly went into a dive and crashed into the ground near Kalyazin (Tver Oblast). All 27 people on board were killed, including 18 passengers and 9 crew members.

After this accident, passenger operations on the Il-18 in Russia were discontinued.

Aircraft

The Il-18V (registration number USSR-75840, factory number 182005301, serial number 053-01) was manufactured by the "Banner of Labor" plant (MMZ "Znamya Truda") approximately in September 1962. On September 29 of the same year, it was delivered to the Main Directorate of Civil Air Fleet ("Aeroflot"), which initially assigned the airliner to the Vnukovo Separate Air Squadron of the Moscow Territorial UGA. On February 10, 1965, it was modified to become an Il-18RT (with an Aircraft measuring station, used for communication with space vehicles), and assigned to the aviation of the USSR Navy. In 1988, it was reconverted into an Il-18V. On February 8, 1999, it was purchased by the airline "IRS Aero". It was equipped with four turboprop engines AI-20 produced by ZMK "Progress" named after A. G. Ivchenko. By the day of the accident, the 39-year-old airliner had completed 5,582 cycles of "takeoff-landing" and had flown 11,617 hours; the service life of most units and assemblies had been almost completely exhausted.^[1]

Crew

The crew of flight LDF-9601/02 consisted of:

Captain (PIC) — Alexander Nikolaevich Sominsky.
First Officer — Vladislav Vyacheslavovich Mikhailov.
Navigator — Vladimir Fyodorovich Fedorishin.
Flight mechanic — Alexey Petrovich Kozhevin.
Stewardesses:
- Lyudmila Alekseyevna Solovchuk,
- Oksana Anatolyevna Yakovleva.

Also part of the crew were:

Senior AT Maintenance Engineer — Gennady Ivanovich Kolupaylo.
Senior AT Maintenance Engineer (A and REO) — Yuri Andreyevich Kibets.
Flight Manager — Sergey Vladimirovich Yefremov.

Accident

The Il-18V, tail number RA-75840, was operating a charter passenger flight LDF-9601/02 on the route Moscow (Domodedovo Airport)—Khatanga—Krasnoyarsk—Khatanga—Novosibirsk—Khatanga—Moscow (Domodedovo) that day. At 20:53 MSK (17:53 UTC), while the airliner was on the final leg of the route (Khatanga—Moscow), the crew contacted the radar control dispatcher and reported the estimated time of passing the next compulsory reporting point. Flight 9601/02 was flying on a magnetic heading of 200° at FL255 (7,750 meters) at a speed of 410 km/h. On board, along with 9 crew members, were 18 passengers.^[2]

The flight was proceeding normally until 21:17 MSK (18:17 UTC) when, with the autopilot engaged, the elevator suddenly transitioned to a dive position, directing the aircraft downward. The airliner pitched towards the ground at an angle of 40-42°, with a temporary negative g-force of 0.5 g, which impeded the pilots from fully exerting their physical abilities on the control yoke. When the g-force returned to normal (1 g), the pilots finally exerted a combined force on the control yokes of about 120-160 kilograms, attempting to pull them "towards themselves" to try to level the aircraft, which at this point had already exceeded a speed of 580 km/h. While attempting to pull the yokes, one of the pilots likely accidentally pressed the left pedal (controlling the rudder), causing the aircraft to bank to the left. At an altitude of 6,300 meters, the airliner was plunging towards the ground at a vertical speed of 120 m/s with a left bank of 19°, and its forward speed had already exceeded the maximum permissible and reached 610 km/h. The pilots' efforts were insufficient to pull the aircraft out of the dive, and at 21:19 MSK (18:19 UTC), at an angle of about 12° and with a left bank of 43°, flight LDF-9601/02 crashed into the ground at a speed of 850 km/h and was completely destroyed. The wreckage of the aircraft was found 15 kilometers southeast of Kalyazin (Tver Oblast), and all 27 people on board were killed.

Investigation

Causes

During the checks, the commission discovered several violations regarding the technical condition of the crashed aircraft:

All four AI-20 engines had expired storage periods.
The duplicate logbooks for two engines were created at the 123 ARZ of the Russian Ministry of Defense with violations and deviations from the established requirements — specifically, one logbook did not specify the date of repair, and the signatures of the shop manager and the senior master of the Quality Control Department on the inserts to the duplicate logbook were falsified. The duplicate of another logbook lacked the date of its creation, the date of the engine release did not match the actual date, the operating time from the start of operation did not match the actual time, the number of repairs and the date of the last repair were not indicated, there was no record of the engine conservation periods after repair, and the inserts with a list of parts replaced during the repair, control test parameters of the engine, and a list of units installed during the repair were not attached.
The logbook for the APU TG-16M No. AM 041050 was missing.
The installation date of one of the propellers on the aircraft did not match reality, and its installation on the aircraft was not entered in the aircraft logbook.
The logbooks of the aircraft, engines, passports of units and products in the "IRS Aero" airline were filled out irregularly and untimely.
Records of monthly independent flight hours of the command flight personnel and the performance of independent approaches and landings by the second pilots were not kept.
The monitoring and analysis of flight quality performance based on flight data were carried out with violations of the regulations, and requests from the flight service for comprehensive decryption of flight data were not submitted. The flight quality indicators logbook was not maintained in the flight service.
The schedule for flight RA-75840 during the execution of flight LDF-9601/02 was developed by the airline's management with an exceedance of working time norms, as the working time of the crew lasted 14 hours 45 minutes with a norm of 11 hours 30 minutes.

Conclusions

The commission could not precisely determine the cause of the accident. It is most likely that a combination of several factors led to the accident:

Failure of the AT-2 trimming machine, which caused the spontaneous deflection of the elevator trim tab from the neutral position to the extreme dive position with electric control, resulting in the creation of a hinge moment on the elevator, leading to the rotation of the control cable drum of the RM-913 rudder machine of the longitudinal control channel of the autopilot AP-6EM-3P and the deflection of the elevator to the dive position with the autopilot engaged.
The AT-2 trimming machine's protection system against spontaneous deflection of the elevator trim tab, which, upon the appearance of certain (threshold) forces in the elevator control linkage generated by the deflecting trim tab, should have disabled the UTM-2 trimming actuator before the elevator began to dive, but in this case, it did not work.
The presence of an uncompensated hinge moment on the elevator due to its trim tab being in the −4...-4.5° position at the moment the autopilot was disengaged, which caused a sharp movement of the elevator to the dive position, in turn leading to a rapid descent with a fast increase in vertical and forward speeds.
Due to the rapid transition of the aircraft into a dive, a negative vertical load factor arose, lasting up to 6 seconds, and a vertical load factor of less than 1 persisted for a total of 12 seconds, which resulted in the pilots being unable to timely exert sufficient effort to recover the aircraft to level flight.
The aircraft quickly entered a dive and accelerated to an excessive speed, which required excessive effort from the pilots to pull it out into level flight.
In the given situation, the crew did not resort to the manual control of the elevator trim tab indicated in the Il-18 RLE, which could have significantly reduced the control yoke effort during recovery to level flight.

The most likely cause of the spontaneous deflection of the elevator trim tab to dive and the failure of the AT-2 system to protect against a dangerous level of spontaneous trim tab deflection could have been malfunctions in the relay magnetic amplifier RMU-5066D and the phase discriminator FD-2007. However, due to the complete destruction of the aircraft, it was impossible to definitively determine where and why the failure occurred.

Aftermath of the accident

After the accident, severe restrictions were imposed on the "IRS Aero" airline. Regarding Il-18 aircraft, it was noted that during their many years of operation, there had been numerous instances of longitudinal control failures, and in no case could the exact cause be determined. As of 2001, 18 Il-18 airliners were still in operation in civil aviation in Russia, with 14 of them in commercial airlines. After the crash near Kalyazin, it was decided to cease commercial passenger operations on Il-18 aircraft:

Notes and References

Web site: Ilyushin Il-18V Tail Number: RA-75840. Russianplanes.net. 2013-04-26. https://www.webcitation.org/6GIXPpcoP?url=https://russianplanes.net/reginfo/34245. 2013-05-01.
Web site: Il-18V Crash of IRS Aviation in Tver Region. airdisaster.ru. 2013-04-26. https://web.archive.org/web/20130520025713/http://www.airdisaster.ru/database.php?id=27. 2013-05-20.