Such an overpowering feeling - one that the pilot is not able to easily overcome. That is the danger of spatial disorientation. Given that the phenomenon is a contributory factor in one accident a year on average, resulting in 200 to 300 casualties, Boeing and TNO have launched an initiative to develop a tool that will benefit every aircraft manufacturer, accident investigator, and pilot.
“You are on your way to your holiday destination and you have a coffee on your table,” says Jan Bos, a pilot and aviation specialist at TNO. “The aircraft makes a turn and descends into the clouds. Because the coffee stays on the table and you no longer have any visual reference in relation to the earth, you have the feeling that the aircraft is flying horizontally. But in reality, it is flying at an angle. That is the simplest way to describe a situation in which the aircraft is in a different position in relation to the earth to what you think.”
Spatial disorientation has been a topic of research at TNO for more than 25 years now. Researcher Eric Groen explains, “We focus mostly on the effects of movements that people experience in transport situations. Using the mathematical model that we have developed over the years, we can calculate how people perceive movements of this type - or wrongly perceive them. The best-known consequence of incorrectly perceiving a movement is that of passengers being affected by seasickness, carsickness or airsickness. However, if a pilot wrongly perceives the motion or position of his aircraft, this could lead to incorrect actions and, ultimately, Loss of Control In-flight (LOC-I) or, worse, Controlled Flight Into Terrain (CFIT), a major cause of serious aircraft accidents.”
“The movements of an aircraft are sometimes so subtle that they fall outside the spectrum of natural head movements to which the organ of balance is attuned”
Beyond the spectrum
The organ of balance is well capable of accurately passing on movements made by the head, such as nodding or shaking, to the brain. But the movements made by an aircraft largely pass by our sensory perceptions. Groen continues, “These movements fall outside the spectrum of natural head movements to which the organ of balance is attuned. They can even fall below the radar of human perception, remaining unnoticed. One example is when an aircraft very subtly makes a coordinated turn from left to right, without the pilot actually noticing it. Or it could be that he does notice it, but interprets it incorrectly. That is why the brain erroneously interprets continuous linear acceleration, which goes hand in hand with greater pressure on the back, as if the nose of the aircraft is lifting upwards.”
“When a pilot concentrates and regularly checks his instruments, there is no reason for concern,” Groen continues. “The six basic flight instruments (basic six) or the Primary Flight Display (PFD) and the other instruments give a clear display of the condition of the aircraft. But in situations that involve a heavy workload or where there are distractions, the pilot’s attention may be drawn away from the instruments, with his sensory illusions possibly forming a serious threat. Good communications between the pilot and co-pilot is a safety net, but investigations into every major incideMist nt have revealed poor communications as a factor.”
“The Spatial Disorientation investigation Tool (SDiT) automatically recognizes the danger of spatial disorientation”
Spatial Disorientation investigation Tool
In a joint project with Boeing, TNO modified the mathematical motion perception model in a way that enables accident investigators to analyse recordings (in flight data recorders, or ‘black boxes’) of aircraft movements prior to and during aviation accidents. The Spatial Disorientation investigation Tool (SDiT) automatically recognizes the danger of spatial disorientation. Groen explains, “The tool compares the calculated perception of the organ of balance with the actual movements of the aircraft. If there are differences, it may be that disorientation was a factor, providing the pilot had no reliable information about his surroundings.” The tool is currently used by international aviation authorities like the EASA and FAA for analysing different phases of flights, which serve as the basis for new rules issued by these bodies.
The three most important symptoms of disorientation
SDiT recognizes the three most important symptoms of disorientation resulting from the limited spectrum of the organ of balance: the somatogravic illusion, where the nose of the aircraft seems to be rising during a continuous linear acceleration; the somatogyral illusion, where an aircraft seems to be flying horizontally while flying in a bend; and a minimal level of perception in which the pilot experiences no motion whatsoever. Bos says, “Pilots obviously know about the phenomenon in theory, but there is too little practical training in this area. The illusions are so convincing that they need to be made aware of the circumstances in which they could become disoriented. With SDiT, we can demonstrate that very clearly.”
Exactly what the industry needs
Boeing is very pleased with the tool. Aviation expert and accident investigator Dr Randy Mumaw, who commissioned TNO: “We really appreciated the in-depth presentations on the TNO modeling and the development of the illusion ‘decision aid’. It is clear that TNO understood the set of illusions/accidents we are experiencing in the commercial jet transport world. I think the tool is well-positioned to identify the relevant set of illusions from the data we can provide. The tool’s functionality is exactly what the industry has needed.”
“In future, we would like SDiT to operate online in aircrafts”
“In future, we would like SDiT to operate online in aircraft,” says Bos. “As soon as there is any risk of disorientation, the pilot will feel where the horizon is by means of a vibration in his tactile vest, for example. Another possibility we are keen on is making the tool suitable for helicopters in situations with reduced visibility. We are currently working on the AEOLUS joint innovation programme with Boeing and other parties in order to expand the model to visual illusions. Flying schools, airlines, simulator builders and other interested readers who would like to use SDiT or find out more about it are very welcome to get in touch with me.”