GEFS is a free, online flight simulator based on worldwide satellite and aerial imagery.
Whether you are a licensed pilot practicing VFR, an aviation enthusiast or just looking for some fun flying a plane in beautiful landscapes, you can enjoy GEFS quickly, directly from your web browser.
Originally running on Google Earth, GEFS is now using a new, open source platform called Cesium.

Requirements:

To use this flight simulator, you will need a WebGL compatible web browser. You can test this here http://webglreport.com
If you want to play using a joystick, you will need a GamePad API compliant browser (Chrome, Firefox, Opera, etc.).

How to control the flight simulator?

Option bar

The option bar, at the bottom of the game screen, is the main way to interact with the flight simulator:

The first three menus are used to choose your aircraft, location and camera mode.

Joystick:

You can reconfigure every axis and buttons of the joystick from the "option" panel.

All other keyboard controls are the same

Mobile:

Note: this is an experimental feature. Not all mobile device may be supported.

Orientation input is only available on mobile devices

If available, yaw is set on the magnetometer axis

You can reconfigure every axis from the "option" panel.

A throttle touch pad is displayed in the viewport

Tap anywhere in the viewport to re-center the orientation inputs

Flying helicopters:

Helicopters are by definition much more difficult to fly than airplanes. The basic principle is to play with collective pitch (going up and down), cyclic pitch (going forward, backward, right and left) and anti-torque control (rotation/yaw).
By default, mouse and keyboard controls are mixing roll and yaw (aileron and rudder). This has to be disabled (in configuration panel) in order to properly fly the helicopter.
Ideally, you would have to use a joystick to be accurate enough with the helicopter but the mouse should be enough for a start.
In GEFS, the collective pitch is controlled using the same input as the throttle for airplanes: if you press '+' several times, the helicopter will lift-off, if you press '-' it will go down.
Cyclic pitch can be controlled using the arrow keys or the mouse.
When roll/yaw mixing is disabled, use the rudder keys (default are keys A & D) for the anti-torque (yaw).
The rest is just practice and finesse.

Flying Major Tom:

Major Tom is probably the easiest and most relaxing way of flying in GEFS. With just two keys you can take to the skies and look down at the earth.
The 'up' arrow key (or moving mouse or joystick up) fires the burner and when air is hot enough the balloon will take-off.
To navigate, you can try to climb to different altitudes and reach different direction and speed of wind.

Camera:

Five cameras are available. You can choose between these five modes from the option bar or by pressing "C" to cycle through all modes.

Follow: the camera follows the plane at a distance.

Cockpit: the camera gives a view from the pilot seat.

Cockpit-less: same as "cockpit" but without visible 3D model.

Chase: the camera is static but look at the plane.

Free: this is the default CesiumJS camera (uses default controls).

In "Follow" and "Cockpit" mode, you can left-click and drag your mouse to change the camera orientation.
In "Follow" mode, you can right-click and drag to set the camera's zoom factor/distance.
Use mouse wheel to increase or decrease camera field of view.
When in "Free" mode, you can position the camera to a location you like and press <Tab> to place the aircraft where the camera is.
Some aircraft will add extra cameras to the menu (cabin, wheels, wing, etc...)

Where can I fly?

Virtually everywhere!

You can pick a preset destination from the option bar.

The location selector also offer a searh input field in which you can type any destination. The aircraft will be positioned at the chosen place and at an altitude of 1000 feet.

The last (and best?) way is to use the in-game map to fly from over 30,000 runways in the world or anywhere else you may choose.

How to use the map?

Open the map using the "Nav" button in the option bar.
Three types of map are available: standard, runways and aeronautical.
In Runway mode, every coloured dot marks a runway threshold. You can click on these dots to open an info balloon in which you can see two links to "take-off from" or "fly by" the clicked runway. When choosing "take-off from", the aircraft should be positioned on the threshold and facing the runway. note: due to some imprecision in the collected data, this is not always true (especially for small airfields).
Dots are colour coded depending on the length of the runway: blue for major runways (>3,000 ft), green for airfield size runways, yellow when length is unknown.

A right-click on the map will bring a window to fly to the clicked destination from 4 pre-set altitudes.
In "Aeronautical" mode, the map shows a layer of airspace areas. This overlay has been generated using DAFIF data. While this can be useful to practice some flight patterns, these data are to be used with this game only and should not be used for real life flying.

How to block users in the chat?:

You can block a user's chat messages by clicking on it's call-sign (name) and clicking the "block" button.
If you accidentally blocked a user, you can un-block him from your profile panel (home page > profile > blocked users).

How to improve the graphics (Anti-aliasing):

CesiumJS should enable Anti-aliasing by default. If not, you can probably try to force anti-aliasing from the driver's configuration panel.
Refer to your graphic card manual to know how to access the configuration utility.
From there, you may be able to force anti-aliasing, anisotropic and texture filtering, etc...

CesiumJS performance issue:

On laptops running Windows and using dual graphic card configuration (via Nvidia Optimus), browsers seems to always be using the integrated Intel GPU.
For Google Chrome, using the --disable-gpu-driver-bug-workarounds command line flag will help forcing the browser to switch to the Nvidia GPU.
Using Opera, make sure to enable hardware acceleration in the settings panel (show advanced settings)
The configuration panel ("Simulation" tab) offers a degraded rendering to improve frame rate on low end devices.
The new dropped shadows can have a performance impact and can be disabled in the same panel.
Also read:http://alteredqualia.com/texts/optimus/https://cesiumjs.org/2014/12/01/WebGL-Profiling-Tips

How to enable Joystick control:

If your browser implements the gamePad API, simply press one of the joystick's button to activate it.

Known issues and troubleshooting:

Runways are bumpy: this is inherent to the data provided by CesiumJS. I can not do much about this.

The new Cesium based GEFS is flat (no 3D buildings): Cesium does not provide any 3D buildings yet but this is in their development plan.

The flight simulator is slow

GEFS requires a recent computer and a good graphic card in order to achieve confortable frame-rate.

Make sure GEFS only is running (close other browser tabs and background applications)

If the flight simulator does not work on your computer, please try using a different web browser.

For any other issues, please submit a bug report (see below, and remember to mention your web browser and operating system version).

Bug report:

You can report issues on this Google Group.
When reporting a bug, please be as descriptive as possible and indicate what operating system, web browser and graphic card you are using to run this game.
A "debug info" tab is available in the option panel. Please communicate this info when reporting a bug.

About:

Created 6 years ago, GEFS used to run on Google Earth via the plugin implementation. This plugin is now being retired and GEFS has moved on to a different Platform called CesiumJS (http://cesiumjs.org). While not an exact match yet, CesiumJS is open source and under very active development giving hope for an exciting evolution.
GEFS takes full advantage of CesiumJS and enables a realistic flight experience in a fantastic scenery.
While simple, the flight model is complete enough to deliver a realistic flight simulation experience. More than just a game, GEFS is a real flight simulator.

From the Piper Cub to the Airbus A380, the range of available aircraft should satisfy every aviation enthusiast.
Community members also contribute to GEFS by building new aircraft that are regularly included.
Flight simulation is a vast subject and I hope to be able to improve and enhance GEFS further.