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);
	
	
	
			}

		}

	}
}

Line 22, your usage of Input.GetAxis is incorrect. GetAxis returns a float, if statements must be boolean (either true or false) when considering the statement in the parenthesis.

If you read the documentation for GetAxis you will notice it turns a valie between -1…1, which may indicate left or right, or up or down, etc. You will need to change your script to evaluate the returned value vs the movement you’re targeting for the user/game character.