Abstract
Spatial Disorientation has contributed to aviation accidents since the inception of flight and remains an underlying cause today. While the root cause is often flying in a Degraded Visual Environment (DVE) wherein the pilot cannot see the horizon, it is not the only cause. Understanding why spatial disorientation occurs during flight and its effect on human body systems is important in mitigating its onset. Night Vision Devices (NVD) and Helmet Mounted Displays (HMD) were developed to help the pilot keep spatial orientation, enhance situational awareness, and reduce workload when operating in DVE. It is important to note that although NVDs and HMDs can assist in this area, if used incorrectly, they can be one of the causes of spatial disorientation onset. Given the complex nature of rotary-wing flight and the risks associated with flying in a DVE, additional studies are needed to elicit the best and most effective mitigation strategies.
Which way is up? Exploring Spatial Disorientation in Helicopters
Encyclopedia Britannica defines Spatial Disorientation as “the inability of a person to determine his true body position, motion, and altitude relative to the earth or his surroundings.” Degraded visual environment (DVE) conditions reduce the pilot’s ability to see the horizon and ultimately lose the ability to determine body position, motion, and altitude relative to the Earth. DVE typically includes but is not limited to dark conditions (night), ambient moisture, or other particulates like dust. Despite the increase in technology to combat spatial disorientation, especially for helicopter pilots under DVE conditions, it remains a significant threat in helicopter operations[1]
Understanding Spatial Disorientation
Visual and vestibular cues are needed to maintain orientation. The vestibular system, like an internal GPS, tells the body which way is up, down, left, and right, even when visual cues are reduced or absent. Combined with the visual system, the human body can detect angular and linear accelerations. The proprioceptive system is also essential, telling the mind where body parts are relative to each other to support spatial orientation. During flight, one of these systems can be misled, resulting in conflicts, illusions, and misperceptions. DVE conditions can occur at night, in low visibility, over water, in dusty or snowy conditions, or in any situation where the pilot cannot maintain visual reference with the horizon[2]. Losing visual cues contributes to Spatial Disorientation, which manifests while flying in complex conditions such as hovering, low-altitude flying, or landing in confined areas1.
The Evolution of Spatial Disorientation in Human Flight
Humans are not adapted for aerial flight based on the orientation systems within the body. Human sensory systems struggle between their capabilities and flight demands. As a result, the human vestibular system is unreliable in flight due to sensory conflicts. What is seen (visual) versus what is felt (vestibular) proves problematic when visual cues are missing or misleading2. In DVE, the optical cues that help maintain spatial orientation are absent. Helicopter pilots face specific challenges due to their operations. Most helicopter flights in the United States are medical evacuation flights (FAA, 2023). The FAA reported that 43.8% of all air ambulance hours were flown at night or in DVE. The lack of a visible horizon increases susceptibility to spatial disorientation1. The increased cognitive demands of mission-related tasks while navigating complex conditions compound the effects, contributing to spatial disorientation.
Night Vision Devices and Helmet Mounted Displays
Although designed to aid pilots flying at night, Night Vision Goggles (NVG) have reduced fields of view, altered depth perception, and the potential to worsen visual illusions, contributing to spatial disorientation[3]. More advanced systems, such as helmet-mounted displays (HMD), may not fully compensate for flight conditions, leading to an over-reliance on systems. Using such systems without proper external visual cues can also cause spatial disorientation1
Mitigation Strategies
Strategies have been developed and utilized to combat spatial disorientation in helicopters. Experimental research, enhanced training programs, workload management strategies, and improved visual cueing are tools designed and used to reduce the rates of spatial disorientation in helicopters, leading to accidents[4].
Experimental Research
Simulator-based studies recreate challenging flight conditions such as DVE to assess the pilot’s workload and performance1. The studies can then be used to drive simulator training, replicating realistic flight conditions, profiles, and illusions, which could contribute to the onset of spatial disorientation. This resource has shown promise as a training tool to teach how to survive once spatial disorientation has occurred. Other systems exist that provide an additional training element that can be used without the use of a simulator. Pictured below is a training device by AT Systems. [5]This is a stand-alone device operated through an iPad. It has its own AHRS box and can simulate a degraded visibility environment. This is a great tool that can be utilized in the aircraft to create vestibular illusions and cause spatial disorientation with a safety pilot/instructor on board. Additionally, this device can simulate low visibility in one-half-mile increments and be used with NVGs.
Other training perks are brown/white-out condition training and IFR training. Unlike the simulator, this device provides vestibular illusions similar to those in the actual aircraft. Elevating the quality of training received. NVG training to manage the unique challenges of NVG use has also been researched3
Workload Management Strategies
The workload demands of operating a helicopter in DVE are higher in most cases. As a result, the need for an optimized cockpit design to reduce the cognitive demands of the pilot during critical phases of flight is important. An optimized cockpit design improves how essential flight data is relayed and displayed to the pilot, reducing the number of head and eye movements needed, and the likelihood of spatial disorientation1 and 4. If an optimized cockpit design is not possible, then proficiency training must be considered, as experience is shown to reduce the severity of SD onset. Robust training with all crewmembers (flying and non-flying) is essential to enable the entirety of the crew to be prepared for situations where SD may arise. The FAA (2024) states that if one pilot experiences visual illusions, they should transfer the controls since pilots seldom experience visual illusions simultaneously. But what if the other front seat is occupied by a non-pilot? Awareness of the risks by non-pilot crew members can help avoid the threat from visual illusions. Verbal reports have also been shown to positively impact overcoming SD when aeronautical systems are either not there or are being challenged by the pilot’s vestibular system[6]. Systems on board are only useful if the pilots and crew routinely practice how to use and disengage them. You can have the most advanced technology onboard, but if used incorrectly, the results could be catastrophic.
Improved Visual Cueing
Spatial disorientation can occur when the pilot loses sight of the horizon, and conflicting information is provided to the brain by the vestibular, proprioceptive, and visual systems. Improved visual cueing through better visual aids is aimed at providing critical orientation cues during high workload or DVE to reduce the onset of spatial disorientation2 and 4. Spatial disorientation continues to threaten helicopter operations, especially in DVE conditions. Although technology like NVGs and HMDs help, they can also contribute to disorientation if used incorrectly. Continued research, improved spatial disorientation training, and modernized visual cueing systems are critical in mitigating the risk of spatial disorientation in rotary-wing operations.
Alicia Moen
Senior Staff Consultant, Engineering Systems Inc.
Keywords: spatial disorientation, degraded visual environment, night vision devices, helicopter operations
References
Federal Aviation Administration Aviation Safety. (2023). Helicopter Air Ambulance (HAA) Operations Data. Federal Aviation Administration. https://www.faa.fov/about/office_org/headquarters_offices/avs/offices/afx/afs/afx200/301_HAA_Data.pdf
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Kang, Y., Lazaro, M. J., & Kim, S. (2021). Crosschecking through verbal reports under spatial disorientation scenarios: Evidence from eye tracking metrics. International Journal of Industrial Ergonomics, 86. https://doi.org/10.1016/j.ergon.2021.103202
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Rainieri, G., Fraboni, F., Russo, G., Tul, M., Pingitore, A., Tessari, A., & Pietrantoni, L. (2021). Visual Scanning Techniques and Mental Workload of Helicopter Pilots During Simulated Flight. Aerospace Medicine and Human Performance, 92(1), 11–19. https://doi.org/10.3357/amhp.5681.2021