Do Full Motion Simulators Really Have an Advantage Over Fixed Training Devices?, Aviation is a skills-based industry and towards this requirement, training goes hand in hand. Commercial airline pilots may once have been assessed wholly on their manual flying (aircraft handling) skills; nowadays pilot assessment is predominantly based on Systems and Crew Management, where management of the automated systems and maintenance of situational awareness replace many of the traditional flying skills.
Types of Simulation Devices
Flight Training Devices have no motion system at all. Flight Simulators at Levels A and B have motion systems that operate in only a limited way; that is, through 3 axes only … pitch, roll, and yaw. These devices provide motion ‘on-set’ cues only in those 3 axes. Simulators at Levels C and D provide motion ‘on-set’ cues in those same 3 axes, but also in the axes of heave (up and down), sway (left and right), and surge (forward and aft). Of course, ALL of the motion systems provide only ‘on-set’ cueing, because each of them have physical limits of movement … and the rate that the initiated motion on-set cue is removed must be taken into consideration with respect to the total distance that the motion actuator may be moved; that is, its physical dimensions. The rate that the provided motion cueing is ultimately removed – or stopped – has to be taken into consideration in the overall physical dimensioning of the actuators. But virtually countless amounts of experimentation and examination, trial and error, attempts made, repeated, modified, and re-attempted … all go into the final determination as to the size and the power that will be required to operate such systems.
Use of Flight Simulation in Training
The availability of advanced simulator technology permits replicating the cockpit’s environment at any stage of flight. Such technologies are being used extensively for training and checking of flight crew. The complexity, cost and operating environment of modern aircraft has made the use of advanced simulation necessary.
Traditionally, simulation devices come in two sub variants – Full Flight Devices (FFS) and Fixed Training Devices (FTD).
Modern Fixed Training Device Without Motion
Flight training device (FTD) means a full size replica of a specific aircraft type’s instruments, equipment, panels and controls in an open flight deck/cockpit area or an enclosed aircraft flight deck/cockpit, including the assemblage of equipment and computer software programmes necessary to represent the aircraft in ground and flight conditions to the extent of the systems installed in the device. It does not require a force cueing motion. It is in compliance with the minimum standards for a specific FTD level of qualification.
The above are broad definitions and both the FFS and FTD have several subclassifications.
Type rating and recurrent airline pilot training has changed little in past 30 years. Regulators mandate a large part of such training to be conducted on very expensive full motion simulators or an actual aircraft. Training is compliance based and some of it based on outdated legal and regulatory instruments while not covering the latest technologies and techniques.
The expense of training and the fact that it based on compliance and not scenarios can result in ineffective quality and quantity of pilot training. Type rating and recurrent training suffer most as the huge expense brings an enormous pressure on airlines to keep costs down.
FFS are extremely costly – ballpark 10 million USD per FFS – with other costs like land, buildings (at least a 3 storey structure) and infrastructure to support the device. Maintenance and operation is expensive and most airlines therefore either do not have their own simulators or use third party devices – located in different cities of even countries.
FFSs create realism by fooling sensory systems which is at variance how an actual aircraft provides sensation. A case in point – deceleration is simulated by tilting the simulator forward which creates a sense of falling out of the seat. However at this time flight instruments indicate a pitch attitude which is at variance from the expected. This causes a conflict in the pilots’ inner-ear balance and the eyes. at odds with what their eyes tell them.
Yaw or sideslip can be simulated by sustained tilting, but vertical acceleration can not be sustained. Ask any pilot (me included) – it is common to over control in a simulator than an aircraft. Because of the physical limits of an FSTD’s motion base, the ratio of inertial cues (cues from sensory organs in the inner ear that sense acceleration) to visual cues is not the same as in flight. When motion and visual cues are not congruent, pilots can become disoriented — this can even cause motion sickness in simulator training.
Over the past few years, FTD technology has advanced to a level that apart from motion, the device can replicate everything else which can be expected in a cockpit. Products are available today which provides high-fidelity reproduction of the aircraft’s cockpit and controls, have collimated (infinity-focused) visual systems that provides complete realism. Vibration and ambient noise is simulated. Seat actuation systems provide “seat-of-the-pants” sensations of turbulence, runway surface roughness or airframe vibration.
Modern FTDs use the same simulation software as the full-flight simulators, based on manufacturer-supplied data packages, and with high-fidelity aerodynamic, ground and engine performance and control forces.
Coming to the subject line of this blog. It may not be completely true that a full-motion FFS is better than a state of the art fixed base device. I argue that scenario based training in a modern FTD with induced failures such as wind shear, ground proximity and systems failure as compared to legacy training in an old school FFS will actually result in a higher level of effective training.
There have been numerous scientific studies performed over the last sixty years or so to test this theory, and the result have been surprising. Using all sorts of simulators from light aircraft to turbo-props to jet fighters, scientists have tested how motion simulation affects the control strategies that pilots learn (i.e. how they move the controls) and how well the training translates into the real aircraft.
The studies followed a similar pattern; train half of the test group in a fixed-base simulator (i.e. with no motion) and half in a motion simulator. Then test both groups’ performance in a full-motion simulator or a real aircraft (there is of course a limit to what we can test in an aircraft; stalling airliners for the sake of academic research is not wise!)
Here is a summary of some of the more interesting results:
One of the biggest advantages of motion is that it reduces the pilot’s reaction time to a disturbance. Even with full instrumentation and visual scenery, the pilot will respond first to the initial motion of, say an engine failure. This will then draw their attention to the instruments for analysis and corrective action. But does training with motion translate to quicker reaction times in the aircraft? If we train with motion off, do we produce pilots who take longer to react when motion is present? The answer, quite simply, is No. Training without motion does not make any appreciable difference to a pilot’s response times after motion is introduced.
Control on the ground
If an engine fails at high speed during the take-off roll, the pilot must react quickly to control the aircraft laterally whilst either continuing the take-off or stopping. In this instance, the motion cueing is the primary means of control, and a full-motion simulator cannot be replaced with seat-based or fixed motion for fully effective training.
Other motion cues
What about a maneuver like stalling, where the pre-stall buffet is a vital clue to inform the pilot of the state of the aircraft? Surely in this case we need a motion simulator? Here the answer must be yes; the buffet cannot be replicated and learned as a cue without motion. But there is no need to have an expensive and complex six-legged platform to simulate this vibration. Seat-based motion cueing, where the pilot’s seat vibrates or moves over a very limited range, is just as effective.
One of the first lessons a pilot must learn in order to gain an instrument rating is to ignore many of the physiological sensations felt during flight in cloud. The inner ear is sensitive to acceleration but not to steady state motion. As we saw with the fake elevator there is a minimum threshold below which your vestibular system will not register acceleration. In cloud therefore it is very easy to become disorientated; your inner ear says that you are rolling to the left while your instruments read straight and level flight.
Studies have shown that even full-motion simulators cannot effectively produce this spatial disorientation, so this training must be done on a real aircraft.
Vection is the illusion of self-motion in the absence of physical motion. High-quality visuals, a realistic cockpit and good audio can be enough to fool the brain into thinking there is actual motion. Often pilots in a full-motion simulator won’t even notice when the motion platform is switched off. In one study with low-hours pilots the simulator was programmed to randomly reverse the direction of roll motion. None of the pilots in the study noticed anything out of the ordinary when they rolled the aircraft to the right and the motion platform rolled left!
Most studies conclude that there is no significant difference in the rate of learning or the overall performance outcome between motion and no motion simulators. Some studies actually showed slightly faster learning without motion, perhaps as the trainee is more able to concentrate on seeing and doing a new task without the added distraction of moving around.
It will not be practical for airlines to sustain frequent positioning of aircrew all over the world for flight simulator training any longer. Such travel will incur a huge financial burden and would also not be a wise considering the pandemic and social distancing requirements.
To be fair most regulators are aware of advances in simulation capability and are prepared to take advantage of the latest training tools. A FFS now does not have an edge over a modern FTD. Interest is being generated in using modern FTDs as alternatives to more expensive Level D “zero flight time” FFS for recurrent training. Shifting to motion less simulators with scenario and competency based training rather than just limiting to what is the minimum accepted compliance based training requirements is the need of the hour.
The world has evolved rapidly in the COVID19 environment. A paradigm shift in aviation training is needed and we have to start thinking and planning now to be better prepared for the uncertain future.