flight control to ground movement? bools not working properly

I keep getting the compiler error **cannot implicitly convert type 'float' to 'bool' I just want the game to check to see if the airBorne state is true or false so that it can use either flight controls or normal third person WASD.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class DragonControll : MonoBehaviour {
     public float airSpeed = 45f;
     public bool airBorne = false;
 
     // Use this for initialization
     void Start () {
         Debug.Log ("dragon controll script added to" + gameObject.name);
     }
     
     // Update is called once per frame
     void Update () {
         if (Input.GetKey ("space")) {
             if (airBorne == false) {
                 airBorne = true;
             }
         }
 
         if (Input.GetAxis ("left crtl")) {
             if (airBorne == true) {
                 airBorne = false;
             }
         }
         groundMove ();
             flight ();
     }
     
 
 
 
     void groundMove(){
         if (Input.GetAxis("Vertical")) {
             transform.position += transform.forward * Time.deltaTime;
         }
     }
 
     void flight ()
     {
         if (airBorne == true) {
             Vector3 moveCamTo = transform.position - transform.forward * 10 + Vector3.up * 5f;
             float bias = .96f;
             Camera.main.transform.position = Camera.main.transform.position * bias + moveCamTo * (1.0f - bias);
             Camera.main.transform.LookAt (transform.position + transform.forward * 30f);
 
             transform.position += transform.forward * Time.deltaTime * 45.0f;
 
             airSpeed -= transform.forward.y * 200f * Time.deltaTime;
 
             if (airSpeed < 35f) {
                 airSpeed = 35f;
             }
 
             transform.Rotate (Input.GetAxis ("Vertical"), 0.0f, -Input.GetAxis ("Horizontal"));
 
             float terrainHeightWhereWeAre = Terrain.activeTerrain.SampleHeight (transform.position);
             if (terrainHeightWhereWeAre > transform.position.y) {
                 transform.position = new Vector3 (transform.position.x, terrainHeightWhereWeAre, transform.position.z);
     
     
     
             }
 
         }
 
     }
 }