The wonderful animated jetways of Geneva

Current situation

Since the introduction of Microsoft Flight Simulator X in 2006, jetways have largely remained the same across the Microsoft and Lockheed Martin simulators developed from it.

They are based on a robotics concept known as inverse kinematics (IK). A jetway is divided into two chains: the main handle, representing the main part, and the secondary handle, which is the rotating end. Each chain may have one or more joints with limits on movement and rotation. All together, the jetway functions like a robotic arm.

When connecting a jetway to an airplane, the simulator uses inverse kinematics to calculate how each joint should move within its allowed range to ensure the end reaches the airplane’s door.

There is also a third chain called ground lock, oriented vertically. The end of the ground lock chain tries to stay connected to the ground and restricts how much the jetway can rise and descend.

3D models of jetways are cut into parts, parts attached to joints, and that makes them move with the IK.

IK chains as explained in Microsoft Flight Simulator SDK documentation

While this setup is good enough for the simple jetways that come with Microsoft Flight Simulator, we quickly run into problems when trying to fit more detailed models into the same mold.

Stairs

Jetways usually have small stairs on the side to provide direct access between the cabin and the ground without a large detour through buildings. As the jetway rises and descends, the stairs adjust their angle accordingly. The current inverse kinematics chain configuration does not allow us to animate this and many other such details.

As a result, all airports have static stairs that remain locked in place. Sometimes they are depicted in a deployed position, suspended in the air or penetrating the ground as the jetway moves. At other airports, they are just left to the side, parallel with the jetway. Either way, it is not a good look.

Static stairs at Faro airport

Parking position

Since the inverse kinematics chains in Microsoft Flight Simulator are relatively fragile and prone to glitches, jetways are generally built at straight angles to simplify the model, and this is how they appear in the simulator too when parked. In the real world, jetways are usually retracted away just enough to leave room for airplanes to move, and left at last pitch, with the head still rotated towards the parking stand.

Typical jetways in Microsoft Flight Simulator

When we attempted to mimic natural parking positions in the simulator, we were never able to make it work without glitches at on point or another. This must be the experience of others as well, because rigid jetways standing at 90-degree angles is the norm in Microsoft Flight Simulator.

Looking for alternatives

While working on Geneva airport for JetStream Designs, we decided to abandon the recommended IK chain system in favor of developing animation-based jetways that are less constrained by the mentioned limitations.

We felt that IK chains were an over-engineered solution to the problem. Unlike robotic arms, jetways tend to be simple. They typically consist of a long section extending from the terminal that can pitch up or down and a head that rotates towards the airplane. We could animate extension, pitching, and rotation, combining them into a purely animation-driven approach without stepping beyond high school trigonometry. From previous projects, we already had animation code to run such complex actions.

The results exceeded our expectations.

Jetway at Geneva in natural parking position

We were able to create jetways that spawn in semi-random condition. Their pitch and heading vary, the ends remain rotated towards the stand, hoods slightly hanging and not fully retracted. Attachments like stairs move as they should. When you approach a parking stand, you get the feeling that someone has already been there before you.

Going the extra mile

Our novel approach improves jetway movement too. Jetways feel heavier, move more slowly, and when possible, approach airplanes in a slightly more natural manner. Wheel bogies turn smoothly and do not wobble as they did previously. We also worked around the bug that causes hoods to abruptly jump to the fully retracted position instead of slowly returning.

Some parking stands in Geneva have rare layouts with jetways that rotate a full 90 degrees to allow airplanes to taxi through parking stands without needing a pushback from a tow tractor. We were able to simulate this as well.

For that extra spark, we added audible alarms and flashing warning lights that activate when jetways are moving. Spotlights illuminate when jetways begin approaching an airplane and remain lit until retracted and parked. Metal rumble and wheel noise can also be heard as jetways move.

AI airplanes at Geneva with the new kind of animated jetways – traffic by Alpha India Group

As to tradeoffs, there are none. Performance remains unaffected. Animated jetways are easier and faster to create. They are placed the same way in Scenery Editor as other jetways. They work from the same menus and shortcuts used by regular jetways and support all the same integrations with planes and other software. They serve both user and AI airplanes. They run on PC and Xbox without requiring anything extra beyond what is included in the add-on package.

Some limitations still remain. Jetways serve only one parking stand at a time, even if several overlap. Widebody airplanes are served by only one jetway at a time, even at stands with multiple jetways.

We believe that these limitations can be overcome and will seek to do so in the future.

Geneva airport by JetStream Designs was released on 20th September 2024. It is the first airport to use our new jetways.