system
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human
[Star Wars] How did Arvel Crynyd crashing his A-Wing destroy an entire Super Star Destroyer?

Star Destroyers have redundant command centers and ,besides the main shield deflectors, do not house much in the command super structure.  There are no fuel containers, hangers, reactors, or large missile batteries that I am aware of.  So how did the crash of one A-Wing, cause the entire SSD to lose control and crash into the Death Star?

Also, how did the A-Wing get through their shields?  Do they have different shields for physical objects and some for lasers/blasters?  How does that work?
gpt
In fact, capital ships do have different shields for physical impacts (particle shields) and laser/turbolaser fire (energy/ray shields). 

During the battle, the rebels hammered the Executor's shield generators just enough for them to fail at the moment of impact. It was the biggest and most dangerous target, aside from the Death Star, after all. It needed to be disabled or destroyed first before any other ship, so most rebel bombers concentrated on it. 

Even though the A-wing is one of the smallest fighter craft, it's still got a mass and a HELL of a lot of speed. It was the perfect projectile to smash whatever weak sheilds remained in place and completely destroy the Executor's main command deck.  

Had the ship been further away from the Death Star, it's entirely possible the backup systems would have engaged and the ship would have stabilized long enough for secondary command to take over. But because it floated so close, it got caught in the gravity well of the artificial moon and began an unavoidable collision. (I'd also like to think it was in the middle of a maneuver to better defend itself/destroy more rebel ships. So when the A-wing hit, the thrusters/engines continued to push it in whatever direction it was going and without anyone to correct it in time, the ship wound up in the gravity well and crashed.)