2002 Khankala Mi-26 crash
On 19 August 2002, a group of Chechen fighters armed with a man-portable air-defense system brought down a Russian Mil Mi-26 helicopter in a minefield, which resulted in the death of 127 Russian soldiers in the greatest loss of life in the history of helicopter aviation. It is also the deadliest aviation disaster ever suffered by the Russian Armed Forces.
Source: Wikipedia — 2002 Khankala Mi-26 crash (CC BY-SA 4.0)