The Flight Demos use the mouse as the primary flight control. This gives you more precise control over pitch and bank. To do this, the mouse controls utilize a variation of the three.js pointer lock controls module.

At the beginning of the program, add the following to the variables:

//- POINTER LOCK CONTROLS ------//----------------------------------------------
//  Adjustments
let InpMos = new THREE.Vector2(); // Mouse Inputs
//. Setup ......................................................................
let controls = new PointerLockControls(renderer.domElement,InpMos);
let blocker = document.getElementById("blocker");
let instructions = document.getElementById("instructions");
    instructions.addEventListener("click", function () {controls.lock();});
    controls.addEventListener("lock", function () {
      instructions.style.display = "none";
      blocker.style.display = "none";
    });
    controls.addEventListener("unlock", function () {
      blocker.style.display = "block";
      instructions.style.display = "";
    })
let _changeEvent = {type: 'change'};
let _lockEvent = {type: 'lock'};
let _unlockEvent = {type: 'unlock'};

Within the program, insert the following:

/*******************************************************************************
*
*   POINTER LOCK CONTROLS
*
*******************************************************************************/
//  This is a stripped-down and modified version of three.js PointerLockControls module

class PointerLockControls extends Controls {
  constructor(domElement=null,InpMos) {
    super(domElement,InpMos);
    this.domElement = domElement;
    this.InpMos = InpMos;
    this.isLocked = false;
    // event listeners
    this._onMouseMove = onMouseMove.bind(this);
    this._onPointerlockChange = onPointerlockChange.bind(this);
    this._onPointerlockError = onPointerlockError.bind(this);		
    if (this.domElement !== null) this.connect();
  }		
  connect() {
    this.domElement.ownerDocument.addEventListener('mousemove', this._onMouseMove);
    this.domElement.ownerDocument.addEventListener('pointerlockchange', this._onPointerlockChange);
    this.domElement.ownerDocument.addEventListener('pointerlockerror', this._onPointerlockError);
  }
  disconnect() {
    this.domElement.ownerDocument.removeEventListener('mousemove', this._onMouseMove);
    this.domElement.ownerDocument.removeEventListener('pointerlockchange', this._onPointerlockChange);
    this.domElement.ownerDocument.removeEventListener('pointerlockerror', this._onPointerlockError);
  }
  dispose() {
    this.disconnect();
  }	
  lock() {
    this.domElement.requestPointerLock();
  }
  unlock() {
    this.domElement.ownerDocument.exitPointerLock();
  }
}

//- Event Listeners ------------------------------------------------------------

function onMouseMove(event) {
  if (this.enabled === false || this.isLocked === false) return;
  const movementX = event.movementX || event.mozMovementX || event.webkitMovementX || 0;
  const movementY = event.movementY || event.mozMovementY || event.webkitMovementY || 0;
  this.InpMos.x = movementX; // This modifies the InpMos variable for your own use
  this.InpMos.y = movementY;
  this.dispatchEvent(_changeEvent);
}

function onPointerlockChange() {
  if (this.domElement.ownerDocument.pointerLockElement === this.domElement) {
    this.dispatchEvent(_lockEvent);
    this.isLocked = true;
  } else {
    this.dispatchEvent(_unlockEvent);
    this.isLocked = false;
  }
}

function onPointerlockError() {
  console.error('THREE.PointerLockControls: Unable to use Pointer Lock API');
}