class AcceleratorGameController: UIViewController {

var time: Float = 0.0
var challengeController: ChallengeViewController!
var delegate : GameEnded!

override func viewDidLoad() {
    super.viewDidLoad()
    if let scene = AcceleratorGame.unarchiveFromFile("AcceleratorGame") as? AcceleratorGame {

        let skView = self.view as! SKView
        skView.showsFPS = true
        scene.viewController = self

        skView.ignoresSiblingOrder = true

        scene.scaleMode = .AspectFill
        skView.presentScene(scene)
    }
}


override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    var dest : ChallengeViewController = segue.destinationViewController as! ChallengeViewController
    dest.gameHasFinished(time) //Dont know if this does anything...
    println("Segue now!")
}

override func viewWillDisappear(animated: Bool) {
    super.viewWillDisappear(true)
    println("View will disapear")

    delegate.gameHasFinished(self.time) // ###CRASHES HERE!###
}

protocol GameEnded {
     func gameHasFinished(time: Float)
}

class ChallengeViewController : UIViewController, GameEnded {

var time : Float = 0.0

override func viewDidLoad() {
    super.viewDidLoad()
    println("ChallengeViewController geladen")
    startGame()
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "accelGane" {
        var vc = segue.destinationViewController as! AcceleratorGameController
        vc.delegate = self
    }
}
func startGame () {
    println("Start Game")

    self.showAccelGameView()
}
func gameHasFinished(time: Float) {
    println("Game has finished")
    self.time = time
}
func showAccelGameView() {

    println("Show Accel Game")
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    let vc = storyboard.instantiateViewControllerWithIdentifier("AcceleratorGameController") as! AcceleratorGameController

    self.navigationController?.pushViewController(vc, animated: true)
}

protocol GameEnded : class {
    func gameHasFinished(time: Float)
}

class AcceleratorGameController: UIViewController {

   weak var delegate : GameEnded?

   // rest of your code
}

class ChallengeViewController : UIViewController, GameEnded {

    var acceleratorGameController : AcceleratorGameController!

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
         if segue.identifier == "accelGane" {
             acceleratorGameController = segue.destinationViewController as! AcceleratorGameController
             acceleratorGameController.delegate = self
         }
    }
}