It isnt consistent. Most times i cant lock onto helis before they are within 2 km. I even encountered a Harrier that couldnt be locked until sub-2km in front aspect. This was with the Santal.
The last few days i have had a problem with getting a lock, but not being able to fire. The lock is so poor that the seeker doesnt want to be uncaged. When i use the radar lock on the Santal, and then try to fire, it launches the missile. However, the missile just goes bananas.