Simulations, Flight Simulators, FTDs, and ATDs

Pilots and flight instructors often debate the value of using flight simulation to complement flight training. We casually use the phrase flight simulator when referring to non-flying gizmos that re-create, at varying levels of fidelity, the experience of being in an airplane cockpit. Simulator is a handy shortcut, but can lead to confusion about how such devices can be used during training and to maintain currency. Equally important, misunderstanding the differences among simulations, flight simulators, flight training devices (FTD) and aviation training devices (ATD) often means these tools aren’t used most appropriately or effectively.

On June 27, 2018, FAA published several important changes to 14 CFR Part 61 that expand the use of ATD, FTD, and FFS to maintain IFR currency. You can read about those changes at BruceAir here.

See also the latest version of  AC 61-136B, FAA Approval of Aviation Training Devices and Their Use for Training and Experience. More information here: New AC for ATDs.

The following discussion is based on Chapter 3, “Using PC-Based Simulations Effectively” in my last book, Scenario-Based Training with X-Plane and Microsoft Flight Simulator: Using PC-Based Flight Simulations based on FAA and Industry Training Standards (ISBN: 978-1-1181-0502-3).

For additional information about how the FAA classifies flight simulators and flight training devices, see the November/December 2017 issue of FAA Safety Briefing. That entire edition is devoted to flight simulation.

Simulators, FTDs, and Simulations

Technological leaps have blurred the lines that just a few years ago distinguished the capabilities of full-motion simulators from the features of the home cockpits that hobbyists set up in their basements and garages. Recent changes to the definitions of and the regulations governing the use of FAA-approved simulators have added to the aviation community’s confusion about these tools.

Key Categories

The FAA recognizes four general categories of flight simulation systems:

  • Full Flight Simulator (FFS)
  • Flight Training Device (FTD)
  • Advanced Aviation Training Device (AATD)
  • Basic Aviation Training Device (BATD)

The first two categories are described in 14 CFR 60: Flight Simulation Training Device Initial and Continuing Qualification and Use. ATDs are discussed in AC 61-136.

Each category of simulator and training device includes levels that describe the increasing sophistication, capability, and fidelity of the systems.

Full Flight Simulators

The term Full Flight Simulator (FFS) replaces airplane simulator, previously defined in AC 120-45A. According to the current FAA regulations, an FFS is a

…replica of a specific type, make, model, or series aircraft. It includes the equipment and computer programs necessary to represent aircraft operations in ground and flight conditions, a visual system providing an out-of-the-flight deck view, a system that provides cues at least equivalent to those of a three-degree-of-freedom motion system, and has the full range of capabilities of the systems installed in the device….(14 CFR 60, Appendix F)

The core of that definition remains “replica of a specific type, make, model, or series aircraft.” In other words, a flight simulator duplicates the performance and flying characteristics of a particular airplane, and it must re-create an airplane’s cockpit with great fidelity, including exact reproductions of the real aircraft’s physical controls, instrumentation, and switches. It must reproduce the aircraft’s flight characteristics with high fidelity. The photo below shows a typical modern full flight simulator made by CAE.


Flight Training Devices (FTDs)

The same regulations update the definition of a Flight Training Device (FTD) to:

…a replica of aircraft instruments, equipment, panels, and controls in an open flight deck area or an enclosed aircraft flight deck replica. It includes the equipment and computer programs necessary to represent aircraft (or set of aircraft) operations in ground and flight conditions having the full range of capabilities of the systems installed in the device…for a specific FTD qualification level. (14 CFR 60, Appendix F)

That description drops the requirement that an FTD must mimic a specific make or model of an aircraft. The degree to which a particular FTD must emulate an aircraft’s controls, instruments, and switches depends on the device’s certification level, but in general, an FTD doesn’t have to duplicate every switch. The photo below shows an FTD manufactured by Precision Flight Controls.

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For example, a Level 4 FTD, the least sophisticated type:

…may have an open airplane-specific flight deck area, or an enclosed airplane-specific flight deck and at least one operating system. Air/ground logic is required (no aerodynamic programming required). All displays may be flat/LCD panel representations or actual representations of displays in the aircraft. All controls, switches, and knobs may be touch sensitive activation (not capable of manual manipulation of the flight controls) or may physically replicate the aircraft in control operation. (14 CFR 60, Appendix F)

Level 5 and 6 FTDs must replicate the cockpits and flight characteristics of aircraft with increasing precision.

Basic and Advanced Aviation Training Devices

In 1997, the FAA published AC 61-126, Qualification and Approval of Personal Computer-Based Aviation Training Devices, which, as the title implies, discussed the use of PC-based simulations. PCATDs, as the devices were known, included software like Microsoft Flight Simulator, hardware (usually one or more consoles that incorporated a flight yoke and other controls and switches), and a display (typically an off-the-shelf computer monitor). Because the technology was new, the FAA restricted the use of PCATDs to a few basic tasks required during primary and instrument flight training.

Technological advances and the aviation community’s experience with PCATDs led the FAA to update the definition and expand the use of PC-based simulations. AC 61-136 – FAA Approval of Aviation Training Devices and Their Use for Training and Experience, first issued in 2008, retired the PCATD category and described the PC-based training devices that the FAA now approves for use in aviation training.

The core requirements for BATDs and AATDs are more general than those specified for flight simulators and FTDs. For example, according to AC 61-136B, a BATD “Provides a training platform for at least the procedural aspects of flight relating to an integrated ground and flight instrument training curriculum.”

The photo below shows a typical ATD made by Precision Flight Controls.

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The more sophisticated AATD “Provides a training platform for both procedural and operational performance tasks related to ground and flight training towards private pilot, commercial pilot, and airline transport pilot certificates, a flight instructor certificate, and instrument rating.”

The hardware specifications for BATDs and ATTDs are similar. For example, a BATD “must provide certain physical controls and may provide some virtual controls,” described as follows:

(1) Physical flight and aircraft system controls should be recognizable as to their function and how they are to be manipulated solely from their appearance. Physical flight and aircraft system controls eliminate the use of interfaces such as a keyboard, mouse, or gaming joystick to control the represented aircraft model in simulated flight.

(2) For the purposes of this AC, virtual control is any input device to control aspects of the simulation (such as setting aircraft configuration, location, and weather) and to program, pause, or freeze the device. Virtual controls should be primarily for the instructor’s use…

(4) The physical arrangement, appearance, and operation of controls, instruments, and switches…should model at least one aircraft in the family of aircraft represented as closely as practicable. Manufacturers are expected to use their best efforts to recreate the appearance, arrangement, operation, and function of realistically placed physical switches and other required controls representative of a generic aircraft instrument panel. (FAA Advisory Circular AC 61-136)

The Deeper Distinction

It’s as easy to distinguish superficially between an FFS and a BATD as it is to see the differences between a single-engine trainer and an airliner. But there’s more than technology behind the differences between types of simulation devices. They’re intended for fundamentally different uses.

Simply put, an FFS is a substitute for a specific aircraft, and in many circumstances, pilots using an FFS can receive all the training required to operate the simulated airplane and earn a type rating for that aircraft without ever leaving the ground. In fact, airline pilots who have completed training for a new type in an FFS, and who may never have been in the cockpit of the real aircraft that the simulator emulates, often make their first flights in that airplane in regular revenue service with passengers on board.

To achieve the level of fidelity necessary to meet that goal, the specifications for an FFS are extensive, detailed, and stringent. As noted earlier, they require that a simulator duplicate a specific cockpit. The FFS must also have a wide-view, high-resolution display; “flying” characteristics that closely mimic those of the real airplane throughout its normal flight envelope; a sophisticated sound system; and motion that accurately re-creates the feel of flying.

Level 4, 5, and 6, FTDs are by definition less comprehensive representations of specific aircraft or broad types of airplanes, and as such, the requirements they must meet are less stringent. They also can’t be used to complete all of the training pilots must receive. To earn type ratings or similar approvals to act as the pilot in command of an aircraft simulated by an FTD, pilots eventually must fly the real airplane—or train in an appropriate FFS.

A BATD or AATD, however, is not intended to be a replacement for a specific aircraft, or even a series of related aircraft—it’s not a simulator. In fact, as their full names imply, BATDs and AATDs are not even flight training devices.

Instead, BATDs and AATDs are Aviation Training Devices (ATDs) intended to complement aircraft—and ground-school classrooms—throughout a training program. The FAA explains the distinction this way:

Instructors have typically taught flight task procedural skills almost exclusively during in-flight training and aeronautical knowledge during ground training. However, based on the available data, the FAA has determined that instructors can successfully teach procedural understanding of certain flight tasks during ground and flight training using [BATDs and AATDs]….(FAA Advisory Circular AC 61-136)

In other words, ATD aren’t intended—primarily at least—to help pilots develop and hone stick-and-rudder skills. They’re essentially procedural and part-task trainers to help pilots understand and apply important concepts and to practice and master general procedures that apply to a variety of aircraft.


Finally a simulation, flight or otherwise, is just a representation—these days typically a virtual representation—of something. That something can be a physical object or a process.

The key to using PC-based simulations effectively, then, is understanding that like BATDs and AATDs, they are tools to help pilots grasp general principals and practice basic procedures through hands-on experience.

Where X-Plane and Microsoft Flight Simulator Fit In

You may have noticed the discussion of BATD and AATD hasn’t mentioned X-Plane or FSX. The reason is straightforward—neither product by itself meets the FAA standards for a “training device,” which by definition must include software and hardware, such as flight controls and cockpit switches.

Physical flight and aircraft system controls [of an ATD] should be recognizable as to their function and how they are to be manipulated solely from their appearance. Physical flight and aircraft system controls eliminate the use of interfaces such as a keyboard, mouse, or gaming joystick to control the represented aircraft model in simulated flight. (FAA Advisory Circular AC 61-136)

The only significant physical difference between X-Plane or FSX configured as described in Chapter 1, “What You Need to Use this Book,” and a BATD is the use of a “gaming” joystick for primary flight control and a mouse to operate the virtual switches and other controls depicted on the cockpit display. The FAA requirements for a BATD restrict the use of a mouse and keyboard as follows:

Except for setup and/or fault mode entry, neither the keyboard nor the mouse may be used to set or position any feature of the BATD in the represented aircraft for the maneuvers or flight training to be accomplished…The pilot must operate the additional equipment needed in order to accomplish a training procedure…in the same manner in which it would be operated in the represented aircraft. For example, [by using] landing gear, wing flaps, cowl flaps, carburetor heat control, and mixture, propeller, and throttle controls. (FAA Advisory Circular AC 61-136)

The latest flight yokes, throttle quadrants, and other accessories developed for hobbyists, however, meet the FAA requirement that they be “recognizable as to their function and how they are to be manipulated solely from their appearance.”  Many BATDs use such off-the-shelf cockpit controls.

Flight Dynamics

No issue generates more heated debated among users of PC-based simulations—including pilots and flight instructors—than the perceived realism of the “flight” characteristics (also known as the “flight models,” or, more formally, the “flight dynamics”) of different simulations.

Because BATDs and AATDs are aviation training devices, not flight simulators, the FAA lays out only general standards for the flight models that drive them. Note that throughout the following descriptions, there is no requirement that a flight model replicate the characteristics of a specific airplane:

(1) Flight dynamics of the ATD should be comparable to the way the represented training aircraft performs and handles. However, there is no requirement for an ATD to have control loading to exactly replicate any particular aircraft…

(2) Aircraft performance parameters (such as maximum speed, cruise speed, stall speed, maximum climb rate, hovering/sideward/forward/rearward flight) should be comparable to the aircraft or family of aircraft being represented.

(3) Aircraft vertical lift component must change as a function of bank, comparable to the way the aircraft or family of aircraft being represented performs and handles.

(4) Changes in flap setting, slat setting, gear position, collective control or cyclic control must be accompanied by changes in flight dynamics, comparable to the way the aircraft or family of aircraft represented performs and handles.

(5) The presence and intensity of wind and turbulence must be reflected in the handling and performance qualities of the simulated aircraft and should be comparable to the way the aircraft or family of aircraft represented performs and handles. (FAA Advisory Circular AC 61-136, Appendix 2)

Put in more familiar terms, the virtual airplane inside an ATD must bank left when you move the yoke to the left. The nose must pitch up when you pull back on the flight controls. Changing power should make the aircraft speed up or slow down (or affect its rate of climb or descent). The rates at which the airplane rolls, pitches, and yaws should be “comparable” to the way a given airplane or family of similar aircraft responds to a pilot’s actions.

For the purposes of this book, then, there’s no meaningful distinction between the “blade element theory” at the core of X-Plane and the classic “6-degree-of-freedom” model employed in FSX. (If you’re interested in the technical details of each approach, see the links to more information at this book’s website.) Both simulations, in fact, exceed the general requirements for the flight model at the heart of an ATD. The choice of which PC-based simulation to use depends largely on personal perception of how the virtual aircraft respond and on other considerations, as described in Chapter 5, “Choosing a PC-Based Simulation: X-Plane or FSX?”

Additional Information