New Delhi, Oct 06: A lot has been written on the accident rate of MiGs. In the IAF, we have four varieties of MiG-21 and two of MiG-23, MiG-25, MiG-27 and MiG- 29. The largest size is that of the MiG-21 fleet. The number of accidents we have had on Mig-21 is larger as compared to other aircraft in the fleet. Accidents were mainly due to human error and technical failure. But it is totally incorrect to say that aircraft are technically unsound. The aircraft are periodically overhauled and systems updated. Aircraft that have completed technical life are retired from service. This year we will be retiring some of the Mig-21 FL aircraft.