found directly at http://battlelog.battlefield.com/bf3/news/view/2832654785919456813/
Gunship balancing in server update R31 on September 20th (all formats)
• Stationary and mobile AA cannon damage has been reduced by 30% versus the gunship.
Rationale: This fixes an issue where it was too easy for players to use stationary or mobile AA to shoot down the gunship from the other side of the map.
• Jet cannon damage has been reduced by 50% versus the gunship.
Rationale: In Conquest mode, jets have been able to single-strafe a gunship and destroy it. This re-balance will require more skill from pilots to take it down.
• The delay before moving the gunship forward to a new base in Rush mode has been increased from 15 to 30 seconds.
Rationale: Previously, the gunship was moved to the next base so quickly that it was possible to parachute from it into the base before defenders were able to prepare. This tweak will give defenders time to fall back and protect the valuable M-COM stations as intended.
• The Delay between gunship spawns has been increased from 90 to 120 seconds in Rush mode.
Rationale: After destroying the gunship in Rush mode, it reappeared too quickly to be well-balanced. With a 50% increase in spawn time for the gunship, defenders will now have more time to focus on the crates and less of a constant overhanging threat from the gunship.
• Initial delay before the gunship spawns in Rush mode has been increased from 15 to 60 seconds.
Rationale: Before this update, the gunship gunners could find the enemy before the round and instakill them when the pre-round timer ran out. Now, it will take a full minute before the gunship will spawn, giving defenders ample time to prepare.
Other changes in the server update
• Fixed a bug where a new squad leader wasn’t chosen when the current squad leader left.
• Fixed so that MK1A3 uses flechette rounds instead of frag rounds in Gun Master mode for Premium members (non-Premiums already have flechette rounds).
• Fixed a bug with Squad Rush on Sharqi Peninsula where the user was spawned outside the combat area if they deployed shortly after the first M-COM was destroyed.
So in conclusion they nerfed it in rush however they made it more tough and harder to take down, i have mixed feelings about that , while it will be nice to not get killed as soon as i get a gun seat , gonna be interesting to see how much harder its gonna be to take down