How to Build a Simulator – III – Understanding the Differences

This post is Part-3 of the “How To Build a Simulator” series. Previously published was the “How To” intro, which includes a summary of the series and a detailed schedule.

Simulators come in many different forms and can be used for many different purposes. When most hear the word “simulator” they think of a full flight sim with a full visual display, 6DOF, hydraulics, haptic feedback, and all the bells and whistles of a real aircraft. However, while simulators can be this high-tech, many are much simpler.

Technically anything that simulates an experience can be deemed a “simulator”. This includes video games, amusement rides, and VR worlds but in this post, we will be focusing on the ones used in the industry. Our focus will be on flight sims as previously mentioned as well as the three main categories of simulators.

3 Main Categories

Desktop Trainer

The Desktop Trainer (DTT) is the most basic of all the simulator groups and is the gateway to learning more advanced information. Most computer games fall under this category. The DTTs are exactly what you are picturing. It is a computer connected to a monitor with some sort of input device.

Examples include simple game controllers, semi-realistic steering wheels, flight joysticks, or yokes. These trainers are great for people who are brand new to learning how to operate the simulated vehicle and learning information before application.

Part Task Trainer

The Part Task Trainer (PTT) is much more realistic than the DTT. However, they are focused on just a few tasks. As the name suggests PTTs are used for training a particular set of tasks in repetition. PTTs are especially useful for practicing difficult maneuvers that require much experience.

A great example of a PPT is the Receiver Aerial Refueling Trainer (RAR). The RAR trains its users to fly into position allowing boom operators to refuel another aircraft mid-flight to avoid landing. This task is incredibly difficult and requires many hours of practice. One false move and the operator can send their aircraft crashing into the one they are trying to refuel.

Another great example would be the Apache Gunnery Trainer (AGT) which has the sole concentration on training gunnery tasks for the front seat e.

Hands-on Trainer

The Hands-on Trainer (HOT) is the most realistic of the three. These trainers always include a tangible part of the simulated vehicle for practicing with, other than the control input.

This allows the user to get a real understanding and feel for what they are doing. While the uses of each trainer are dependent upon the user’s objective and previous knowledge, these trainers are the best for physical maintenance practice. They can be used for pilot training, or they can include a part, like an engine or transmission, for maintenance.

The instructor can program the system to simulate a problem such as overheating. The trainee then must fix the part as if it were real. All movements made are tracked by the system. If the trainee did his job correctly, the part is fixed. If not, the part can exhibit similar consequences much like the real component.

Other simulators that can fall under the spectrum of these three categories include mission trainers (MT), combined arms tactical trainers (CATT), and flight simulators.

Flight Simulators

AVT Simulation’s customers often develop requirements based on Federal Aviation Administration (FAA) rules and guidelines. The FAA criteria described below can help differentiate simulators. 

There are two categories that fall under flight simulators, flight training devices (FTD) and full-flight simulators (FFS). Under these are cockpit procedures trainers (CPT), operational flight trainers (OFT), and weapon systems trainers (WST).

Flight Training Devices

FTDs are trainers more similar to DTTs. They are simpler in design and are much less realistic than an FFS. FTDs are ranked from 1-7 with one being the least complicated and realistic.

Level 1 Devices

Level 1 FTDs are going extinct because they are obsolete compared to the high-tech, high-fidelity sims we have nowadays. Not many are left in existence and even fewer are actually used for training purposes. These flight simulators are the precursor to modern sims.

Level 2 Simulators

These FTD are more realistic than the level 1’s but are still obsolete. Like the 1’s only a few are left in existence and are not being used for training anymore. The ones left are probably owned by flight history fanatics.

Level 3 Devices

The flight sims at level 3 like 1 and 2 are no longer manufactured. However, some previously approved ones are still in use. Level 3 is the first level to include Advanced Aviation Training Devices.

Under this category, Basic Aviation Training Devices are also included. As the names suggest the AATDs are more sophisticated than the BATDs, but either can be disapproved under the FAA’s discretion and neither were meant for practicing under visual conditions. Meaning they do not have visual systems and cannot be used for unusual altitudes training, circle-to-land maneuvers, or a circling approach.

Advanced Aviation Training Device (AATD)

The AATD can be used to log 50 hours for commercial ratings, 20 hours for instrument ratings, 25 hours for Air Transport Pilot (ATP) ratings, and 2.5 hours for private. These logged ratings help pilots to gain different flying certifications and licenses.

Basic Aviation Training Device

The BATDs are much more limited than the AATD. However, they can still be used to log 10 hours for the instrument rating and 2.5 hours for private certification.

Level 4 Devices

Level 4 is specifically for PTTs. They need accurate systems modeling and touchscreens for instrument procedures or flight management systems, but they do not require an aerodynamic model and do not have any control yoke.

Level 5 Devices

Level 5 is when the specific classes of aircraft are introduced. They represent specific models of aircraft or at least a class. Unlike the 4’s they do require systems modeling and aerodynamic programming. This allows the option of one or multiple engines. Because of the higher complexity, level 5 requires a qualification document and approval guide that must list the design criteria of the FTD.

Level 6 Devices

Level 6 is the most sophisticated of all plane-based FTD. They are much more realistic with expensive, model-specific aerodynamic data and programming, a physical cockpit, and real tangible controls.

They focus on specific aircraft rather than just the family of the aircraft like level 5, including actual functionality and spatial relations. However, again because of the complexity, level 6 requires qualification documents and approval guides. 6 has the most realistic experience in a simulated airplane as far as FTDs go.

Level 7 Devices

This is saved for helicopter training simulators.

Full Flight Simulators

The FFS are much more advanced than the FTD. They range from A-D with D as the most sophisticated. Much like the FTD, the first three levels do not exist anymore in manufacturing and training. Keep in mind, however, these levels overlap causing it hard to see subtle differences

A Simulators

These simulators are the least advance with shotty visual systems and low-grade data for ground effects. They hardly exist anymore other than the Lockheed JetStar and only a handful or so are floating around.

B Simulators

Again, these sims have scarcely survived. There are only about a dozen in the US. Like the A’s, these sims are obsolete and require 100% of users to complete re-currency training for circle-to-land privileges.

C Simulators

Level C FFS are much more common with 230 or so in the States. They have better data, visual systems, and controls. They also allow circle-to-land privileges and other visual maneuvers. Level C and B can often be confused with each other.

D Simulators

Now, this is what we were talking about in the beginning. This is what you think of when you hear the word ‘simulator’. These FFS can do anything in the simulated world their counterparts can do in the real world. They have full-type ratings for airliners and offer everything the level C’s do and more, with better data, performance tolerance, and daylight scenery. There are about 430 in the states and counting. These simulators are highly desired.

Thank you!

We greatly appreciate your interest in AVT Simulation and simulators in general. We hope this article has given you a better understanding of the differences between simulators.

Check back next week for another addition to the “How to Build a Simulator Series” focusing on the element groups and hardware of simulators.


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Initially, Applied Visual Technology Inc., AVT has been developing modeling and simulation expertise through engineering services since 1998. This is due to our founder who has accumulated over 30 years of military MS&T expertise in aviation applications. Nonetheless, everyone at AVT specializes in making old training systems new again and making new ones for less. Consequently, for 20 years AVT has served our Air Force, Army, Navy, and Marine customers by providing the highest quality of service and solutions. Following its inception, AVT’s highly specialized staff of engineers has included some of the top leaders in the simulation industry. With over 20 years of simulation experience, our dedicated team provides specialized solutions for customers with complex problems.