IRS Aero Flight 9601/02

IRS Aero

Industry	Aviation (Charter airline)
Headquarters	Russia
Products	Charter passenger flights

IRS Aero Flight 9601/02 was a charter service operated by an Il-18V aircraft under the airline "IRS Aero" along the route Moscow—Khatanga—Krasnoyarsk—Khatanga—Novosibirsk—Khatanga—Moscow. On November 19, 2001, during the final segment from Khatanga to Moscow, the plane abruptly entered a steep descent and impacted terrain near Kalyazin in Tver Oblast. Tragically, all 27 occupants perished, including 18 passengers and 9 crew members.

Following this catastrophe, operations involving passenger flights on the Il-18 were terminated within Russia.

Aircraft

The Il-18V bearing registration USSR-75840 (factory number 182005301, serial number 053-01) was produced by the "Banner of Labor" facility (MMZ "Znamya Truda") on September 25, 1962. Shortly thereafter, on September 29 of the same year, it was delivered to Aeroflot, initially assigned to the Vnukovo Separate Air Squadron within the Moscow Territorial UGA. On February 10, 1965, it underwent an internal conversion at Ilyushin to an Il-18RT variant equipped with an aircraft measuring station for spacecraft communication and was allocated to the aviation division of the Soviet Navy. In 1988, it was reverted to Il-18V configuration. The airline IRS Aero acquired the aircraft on February 8, 1999. It was powered by four turboprop engines AI-20 units manufactured by the Zaporozhye Machine-Building Design Bureau "Progress" named after academician A. G. Ivchenko. By the accident date, this nearly four-decade-old airframe had completed 5,582 takeoff-landing cycles and accumulated a total flight time of 11,617 hours; most components and assemblies had reached or neared their operational lifespan limits.

Crew

The personnel aboard flight LDF-9601/02 included:

• Captain (Pilot-in-Command) — Alexander Nikolaevich Sominsky.
• First Officer — Vladislav Vyacheslavovich Mikhailov.
• Navigator — Vladimir Fyodorovich Fedorishin.
• Flight Engineer — Alexey Petrovich Kozhevin.
• Flight Attendants:
  • Lyudmila Alekseyevna Solovchuk,
  • Oksana Anatolyevna Yakovleva.

Additional crew members comprised:

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

Accident

The Il-18V aircraft, bearing tail number RA-75840, was conducting a charter passenger service designated LDF-9601/02 along the route Moscow (Domodedovo Airport)—Khatanga—Krasnoyarsk—Khatanga—Novosibirsk—Khatanga—Moscow (Domodedovo) on that day. At 20:53 MSK (17:53 UTC), during the final segment from Khatanga to Moscow, the flight crew contacted radar control to report their estimated time passing the upcoming mandatory reporting point. Flight 9601/02 maintained a magnetic heading of 200° at flight level 255 (7,750 meters), traveling at a speed of 410 km/h. Onboard were 18 passengers alongside 9 crew members.

The operation was proceeding without incident until 21:17 MSK (18:17 UTC), when the autopilot was engaged and the elevator abruptly shifted into a dive position, pushing the aircraft downward. The plane pitched steeply toward the earth at an angle between 40 and 42 degrees, experiencing a brief negative g-force of 0.5 g, which limited the pilots' ability to fully manipulate the control yoke. Once normal g-force (1 g) resumed, the pilots applied a combined force estimated between 120 and 160 kilograms on the control yokes, attempting to pull them back to stabilize the aircraft, which had already accelerated beyond 580 km/h. During this effort, one pilot likely unintentionally pressed the left rudder pedal, causing the plane to bank left. At an altitude of 6,300 meters, the airliner was descending at a vertical speed of 120 m/s with a left bank angle of 19°, while its forward velocity had surpassed operational limits and reached 610 km/h. Despite their efforts, the crew could not recover from the dive. At 21:19 MSK (18:19 UTC), descending at approximately a 12° angle with a 43° left bank, flight LDF-9601/02 impacted terrain at 850 km/h and was completely destroyed. The crash site was located 15 kilometers southeast of Kalyazin in Tver Oblast, resulting in the deaths of all 27 individuals on board.

Causes

During subsequent inspections, investigators identified multiple breaches related to the technical state of the ill-fated aircraft:

1. All four AI-20 engines had exceeded their authorized storage durations.
2. Duplicate logbooks for two engines were produced by the 123 ARZ facility of the Russian Ministry of Defense with multiple irregularities — one logbook omitted repair dates and contained forged signatures from both the shop manager and senior Quality Control Department master on inserts. Another duplicate lacked creation dates; its engine release date was inconsistent with actual records; operating hours since commissioning did not align with reality; repair counts and last repair dates were absent; no documentation existed for engine preservation periods post-repair; and essential inserts listing replaced parts, engine test parameters, and installed units during repairs were missing.
3. The auxiliary power unit TG-16M No. AM 041050 logbook was absent.
4. One propeller's installation date on the aircraft was inaccurately recorded, and its installation was not entered in the aircraft’s official logbook.
5. Logbooks for the aircraft, engines, as well as unit passports within "IRS Aero" airline were completed inconsistently and with delays.
6. Monthly records documenting independent flight hours by command personnel and independent approaches and landings conducted by second pilots were not maintained.
7. Flight quality monitoring and analysis based on flight data were conducted in violation of regulatory standards; requests for comprehensive flight data decryption from flight services were not submitted; additionally, no flight quality indicators logbook was kept within flight services.
8. The scheduling for flight RA-75840 during operation LDF-9601/02 exceeded prescribed work time limits—the crew’s duty period lasted 14 hours and 45 minutes against an allowable maximum of 11 hours and 30 minutes.

Conclusions

The commission was unable to establish a definitive cause for the accident. It is most plausible that multiple factors combined to trigger the incident:

• Malfunction of the AT-2 trimming device, which led to an unexpected shift of the elevator trim tab from its neutral position to the extreme dive setting under electric control. This generated a hinge moment on the elevator, causing rotation of the control cable drum in the RM-913 rudder actuator of the autopilot's longitudinal control channel (AP-6EM-3P), resulting in the elevator deflecting into a dive while the autopilot was active.
• The protective mechanism within the AT-2 trimming system, designed to prevent spontaneous deflection of the elevator trim tab by deactivating the UTM-2 trimming actuator upon detecting threshold forces in the elevator linkage induced by trim tab movement, failed to function in this case prior to the onset of the dive.
• An uncompensated hinge moment on the elevator due to its trim tab being positioned between −4 and −4.5° at the time autopilot disengagement occurred, which caused a sudden elevator movement into a dive position and consequently a rapid descent accompanied by sharp increases in vertical and forward velocity.
• The swift transition of the aircraft into a diving attitude created a negative vertical load factor lasting up to six seconds, with vertical load factors below one persisting for twelve seconds overall. This condition hindered the pilots' ability to apply sufficient corrective force promptly to restore level flight.
• The airplane rapidly accelerated into an excessive dive speed, demanding significant physical effort from the crew to recover and stabilize flight.
• Under these circumstances, the flight crew did not utilize manual control of the elevator trim tab as recommended in the Il-18 Flight Crew Operating Manual, which might have considerably eased control column forces during recovery.

The probable root cause behind both the spontaneous dive deflection of the elevator trim tab and failure of the AT-2 system’s protective function may have been faults within components such as the RMU-5066D relay magnetic amplifier and FD-2007 phase discriminator. However, due to total destruction of the aircraft, pinpointing exact failure locations or reasons was not feasible.

Aftermath of the accident

Following this event, stringent operational limitations were enforced on "IRS Aero" airline. Concerning Il-18 aircraft specifically, it was documented that over many years of service numerous occurrences of longitudinal control system failures had been reported without ever conclusively identifying their causes. As of 2001, eighteen Il-18 planes remained active within Russian civil aviation, fourteen of which were operated by commercial carriers. In response to the crash near Kalyazin, authorities resolved to discontinue passenger flights on Il-18 models:

See also

• ČSA Flight 511
• Aeroflot Flight 630
• Aeroflot Flight 6551