Another question about the flying enemy

I want to make an enemy that can fly and I didn't find ani tutorials about it... I already made the enemy take off like helicopter, now this is my problem: after it taking off the land it need to follow me but when it not change his y axis (like it follow me in the air) but it coming to my plase.

How I make it follow me without it will change his y axis and it will not "look" at me?

That what i did so far:

var targetDistance;
 var landDistance;
 var target : Transform;
 var land : Transform;
 var inAirRange = 100.0;
 var moveSpeed = 12.0;    
 var damping = 6.0;
 private var isItAttacking = false; 

 function Update ()   
 {  
     landDistance = Vector3.Distance(land.position, transform.position);

     if (landDistance <= inAirRange)
     {
         fly ();
     }

     else
     {   
         stopFly ();   
     }   

     if(isItAttacking)  
     {  
         attack ();
     }
 }

 function fly ()
 {  
     isItAttacking = false;  
     renderer.material.color = Color.red;   
     transform.Translate(Vector3.up * moveSpeed *Time.deltaTime);
 }

 function stopFly ()
 {
     isItAttacking = true;
     renderer.material.color = Color.black;
 }

 function attack ()
 {
     targetDistance = Vector3.Distance(target.position, transform.position);
     var rotation = Quaternion.LookRotation(target.position - transform.position);
     transform.rotation = Quaternion.Slerp(transform.rotation, rotation, Time.deltaTime * damping);
     transform.Translate(Vector3.forward * moveSpeed *Time.deltaTime);
 }

Sorry for poor english.

for the following you can try

transform.position = new Vector3(  Vector3.Lerp(transform.position, target.position,Time.deltaTime).x, transform.position.y, transform.position.z);

this will only get to make the transform close to you on x axis, cuz you kept the y and z values dont copy paste it, cus its on C#, just try to make it on js