Safety indices of heavy transport air lifters have been steadily declining in the past three years, the Interstate Aviation Committee (IAC) said in an annual report published on its website.

"The relative index of flight safety for all types of freightage involving heavy transport air lifters has been steadily worsening in the past three years, with the disaster figures staying almost the same," the report reads.

Last year, a total of five air incidents involving heavy aircraft with the take-off weight of more than 10 tonnes occurred in the 11 former Soviet republics who are the members of the IAC, including one air crash in which seven people perished. In 2015, a total of three incidents with cargo aircraft took place, including one air disaster that left 35 people dead.

Last year also saw the highest rate of incidents involving light and ultralight aircraft in the past five years.

"In 2016, a total of 11 air incidents took place, including seven disasters in which 12 people died. In 2015, a total of five incidents involving this category of aircraft took place, including two air disasters that left eight people dead," the report reads.