How to fix gimbal lock?

I am making a plane script and currently have no problem rotation several times over the Z axis of the plane, but if I try to rotate over the X axis it will stop at 90 or 270 degrees and all rotation axis will be locked. Any idea of a fix? Here is the script

 #pragma strict
 var myRigidbody : Rigidbody;
 var myTransform : Transform;
 var acceleration : float = 0.2;
 var maxSlope : int = 60;
 var grounded : boolean = false;
 var beingUsed : boolean = false;
 var waitForExit : int = 2;
 var player : Transform;
 var planeDoor : Transform;
 var planeCamera : GameObject;
 var maxSpeed : int = 1000;
 var flySpeed : int = 50;
 var torqueValue : int;
 var rotateSpeed : int = 20;
 var torqueRotateSpeed : float = 50;
 var flightDrag : int = 5;
 var lastRotation : Quaternion;
 var velX : float;
 var velZ : float;
 var rotorVelocity : float = 0;
 var rotateDirection : Vector3;
 var rotor : Transform;
 var currentAcceleration : float = 0;
 var maxAcceleration : int = 0;
 var takeOffSpeed : int = 10;
 var torqueUpSpeed : int = 20;
 var roll : float = 0;
 var pitch : float = 0;
 var yaw : float = 0;
 var rotateUpValue : float = 10;
 
 function Start () {
     myTransform = transform;
     myRigidbody = rigidbody;
     player = GameObject.FindWithTag("Player").transform;
     lastRotation = myTransform.rotation;
 }
 
 function FixedUpdate () {
     if (!beingUsed){
         return;
     }
 
     if (Input.GetAxis("Vertical2")){
         currentAcceleration += acceleration * myRigidbody.mass * Input.GetAxis("Vertical2");
         if (!grounded){
             currentAcceleration = Mathf.Clamp(currentAcceleration, 0, maxSpeed);
         }
         else {
             currentAcceleration = Mathf.Clamp(currentAcceleration, -4, maxSpeed);
         }
         if (Input.GetAxis( "Vertical2" ) > 0){
             rotorVelocity += Input.GetAxis( "Vertical2" ) * 0.03;
         }
         if (Input.GetAxis( "Vertical2" ) < 0){
             rotorVelocity += Input.GetAxis( "Vertical2" ) * 0.05;
         }
         audio.pitch = Mathf.Clamp(rotorVelocity, 0, 1);
     }
 
     if (Input.GetAxis("Horizontal3")){
         myTransform.Rotate(0,0, Input.GetAxis("Horizontal3") * torqueRotateSpeed * currentAcceleration);
     }
 
     myRigidbody.AddRelativeForce(0,0, currentAcceleration);
     print (rigidbody.velocity.z);
     if (Input.GetAxis("Vertical3") && myRigidbody.velocity.z > takeOffSpeed){
         myTransform.Rotate(rotateUpValue * Input.GetAxis("Vertical3"),0,0 );
     }
 
     if (rigidbody.velocity.z > maxSpeed){
         rigidbody.velocity.z = Mathf.Clamp(rigidbody.velocity.z, 0, maxSpeed);
     }
 
     if (rigidbody.velocity.z < 1 && rigidbody.velocity.z > -1){
         rigidbody.constraints = RigidbodyConstraints.FreezeRotation;
         rigidbody.drag = 0;
     }
     else {
         rigidbody.constraints = RigidbodyConstraints.FreezeRotationX;
         rigidbody.drag = flightDrag;
     }
 
     waitForExit--;
     if (Input.GetButtonDown("Use") && beingUsed && waitForExit < 0){
         planeCamera.active = false;
         beingUsed = false;
         player.gameObject.SetActiveRecursively(true);
         player.position = planeDoor.position;
         player.rotation = planeDoor.rotation;
         myTransform.tag = "Untagged";
         player.gameObject.GetComponent(GunManager).SendMessage("activateGun", player.gameObject.GetComponent(GunManager).activeGun);
     }
 }
 
 function OnCollisionStay (collision : Collision)
 {
     for (var contact : ContactPoint in collision.contacts)
     {
         if (Vector3.Angle(contact.normal, Vector3.up) < maxSlope)
             grounded = true;
     }
 }
 
 function OnCollisionExit ()
 {
     grounded = false;
 }
 
 function OnMouseOver () {
     if (Vector3.Distance(transform.position, player.position) < 18 && Input.GetButtonDown("Use") && !beingUsed){
         player.gameObject.SetActiveRecursively(false);
         myTransform.tag = "Player";
         beingUsed = true;
         planeCamera.active = true;
         waitForExit = 2;
     }
 }