Sensory Illusions in Aviation - Essay Example

SENSORY ILLUSIONS IN AVIATION Introduction Sense organs of a human being have evolved to provide critical sensory information to the brain, thereby utlise instinctual properties of humans which were necesary for basic survival in the real world. The evolution dates back to prehistoric age and many such instincts have today become liabilities in this new world. Further, the third dimension, as in the case of pilots, has further complicated the matter to an unbelieavable extent. Today, researchers are working hard to develop systems so as to save these expensive machines and invaluable lives from our "basic instincts" or sensory illusions. Aim This paper aims to bring out the relevance of sensory illusions in aviation and recommend some measures to reduce their adverse effects while in the air. Mechanism of Orientation Illusion arises from a feeling of 'something is right' when it isn't, the most common one being the Mirage of the desert. The brain's orientation, which depends on visual system and vestibular system (middle ear), is given a wrong input of the existing situation by these organs. This results in instinctual corrective action, which, if not based on facts but feelings, can lead to extremely dangerous situation in the air. Some sensory receptors throughout the body like pressure, stress, vibrations, position sense, temperature and discomfort also provide inputs to the brain prompting instinctual corrective action from the pilot. If this happens closer to the ground with inadequate understanding of the situation on the part of the pilot and inadequate time to switch over to aircraft instruments, the result could be a disaster affecting hundreds of lives direcly and thousands indirectly (Brock, 1998). Some important sensory illusions affecting the man in the air are discussed in succeeding paragraphs. Spatial disorientation can be of two kinds: False perception, where pilot does not realise the gravity of the situation and Conflicting perception in which the pilot feels a conflict between his feelings and the information provided by aircraft instruments. Former is the more critical one to understand and important to take precautions against. Visual Illusions This is inaccurate feeling or perception of position, attitude and motion relative to the centre of earth due to false visual cues. The visual system is by far most critical, and helps in determining speed and direction of flight with reference to some stationary input, like cloud or ground. These provide critical information to orient oneself on ground and also in the air. Even birds cannot fly without visual references, like, say in clouds or fog. Only bats have a developed auditory echo-location system (like Radar) so as to fly without problems at night (Antunano). Hence, it is normal for us humans to have difficulty in poor visibility conditions like in clouds o fog. Some important visual illusions affecting flight are being discussed below: Relative Motion Illusion. This happens when, for example, when the adjoining train moves, it gives us a false feeling of movement of our own train. Similar illusion in aircraft, for example in formation flying, can cause dangerous response from the pilot leading to mid-air collision. This is not an unfamiliar experience in military flying. Autokinetic Illusion. On a dark featureless night, when the pilot stares towards a stationary light like a star or other aircraft light, it appears to be moving after some time giving a false impression of it to be on a collision course with own aircraft. This again might prompt an unwarranted response from the pilot transfixed on to some harmless feature (Antunano and Mohler, 1992). To avoid this situation, pilots are trained to carry out random scanning and avoid visual fixation (Brock, 1998). Illusion due to Runway Width, Slope etc. Illusions due to sloping runways or different width/length than standard lead to a pilot assuming wrongly about his visual glide path, flare height and attempting to correct it closer to ground may lead him to entering a situation of CFIT (Controlled Flight Into Terrain). This is more dangerous if coupled with limited visibility or heavy rain scenario, where a pilot might get only a few seconds after breaking off from clouds to make an approach, thereby misjudging the perspective and hitting the ground hard. Black Hole Illusion. Black hole illusion is likely when an aircraft approaches an airfield, with no lights and dark night before the runway like say a runway on seashore, and illuminated city lights or rising terrain beyond it. This gives a false impression of being on a higher than usual glide path prompting a corrective action involving descending below the desired glide path. Flicker vertigo. Essentially a rotor aircraft phenomenon, this happens when rotating main rotor blades cast a shadow on the cockpit glass causing sensations like vertigo, nausea, vomiting and false motion. When flicker vertigo occurs while the helicopter is at the hover in a confined space and at night, a catastrophic loss of control can result - unless the pilot uses fixed cues to judge relative motion. Strobes should be turned off while at a stationary hover if possible (Brock, 1998). Depth Perception Illusion. This is especially relevant during bad weather situation, where due to limited visibility; the runway appears closer or farther than its actual position. This leads to high flares, speeds washing off faster and corresponding low touchdown speeds and chances of heavy / uncontrolled landings. Vestibular Illusions. Most sensory illusions are of vestibular category, where organs of the inner ear responsible to maintain balance in a two-dimensional world get wrong inputs from the third dimension, leading to irrational response from the pilot. The inner ear consists of otolith organs and semi-circular canals for the purpose. The problem lies in the fact that outside input is obscured and instinctive input ambiguous in the air. The only output from inner ear is problematic because it responds to rate of change, and not a sustained change. An example is when one starts a turn, ear detects rolling in. However, once the bank is achieved and held, rate becomes zero and ear gives a sensation of level flight again. After about 15 seconds, the hairs are no longer bent and brain receives input that turn has stopped. Thus, after turn, leveling out will give an impression that one is banking to the right (Kleimenhagen et al, 1993). Various illusions arising out of such conditions are enumerated below: Leans. When an airplane is banked at a small angle, the pilot feels it is in straight and level flight, and does not correct for it. This leads to change in direction/loss of altitude slowly which can go undetected for a long time. Graveyard Spin and Spiral. This happens when an intentional spin or spiral is entered into and held for some time, say to the left. The brain perceives equilibrium after some duration has elapsed, and corrective action leads to a perception of entering a spin or spiral in opposite direction to the right. This leads to false perception of entering an inadvertent spin to the right, prompting another false corrective response from the pilot to the left again, seriously aggravating the situation. Many aircraft have gone into ground due to this phenomenon, hence the name (US Army Aviation Study Guide). Coriolis Illusion. This is the most dangerous form of vestibular illusion. A climbing or descending turn coupled with movement of head in opposite direction moves the middle ear fluid from actual canal to other two canals. Combined effect of the action being that the pilot perceives the aircraft motion to be in opposite direction to that of actual (US Army Aviation Study Guide). This illusion in low visibility conditions can assume dangerous propositions due to non-availability of external reference of horizon and false perceptions. Unless the pilot understands this phenomenon and switches over to instruments immediately, it can adversely affect safety of the aircraft at low altitudes. Occulogravic/Elevator/Occuloagravic Illusions. A forward, upward or downward acceleration of aircraft causes the inertial reaction of a feeling of nose-high attitude or downward/upward fixation and eye tracking with likely reflex action, which might be dangerous. Again, the pilot should consciously maintain control of the aircraft directly with reference to the instruments and not his feelings. Head-up or Head-down Illusion. A sudden upward or downward movement of head causes a false feeling of nose-up or nose-down attitude leading to instinctive push or pull of control column. This is more prevalent at night when as such there is scarcity of references. This situation at low speeds or closer to ground can lead to a dangerous situation, especially when the aircraft is breaking off from an instrument approach for a landing in particularly bad weather and poor visibility conditions. Rotor Wash. This happens in rotary wing aircraft where dust or water thrown about due to rotor wash gives a sensation of forward, rearward or sideways movement. This leads to unnecessary or incorrect inputs by pilots aggravating the situation further. Well-detached points of reference if maintained properly can alleviate this situation. The list is endless, and many accidents occurring without apparent reasons today may in future be attributed to newly discovered disorientation patterns. While professional syllabi covering known sensory illusions are mandatorily covered during flying/ground training, some basic actions by individual pilots can go a long way in ensuring that our aircraft can have equal number of safe take-offs and landings. Some important ones are being elaborated below: Always trust your instruments. They have been usually found to be working perfectly in most CFIT accidents across the world. Following these instruments would have averted the crash in most circumstances. Avoid fixation, aural or visual. In a dynamic environment such as the air, where things are moving fast, fixation onto one aspect has resulted in a crucial lapse on the part of the aircrew in others, leading to disasters. Similarly, sensory fixation is also dangerous and should be avoided through gradual scanning of instruments, outside and inside references, and improving general situational awareness. Avoid fatigue, stress, smoking, alcohols and drugs. When in doubt, do transfer aircraft flying control to the other pilot. Both pilots do not suffer from spatial disorientation at the same time. Simulate disorientation emergencies in simulator sessions. They give very good indications of the likely scenario and offer valuable suggestions to overcome or tackle sensory illusions. Ensure adequate instrument flying practice during good weather period. Early and conscious transition to instruments would avoid one from getting into irreversible situations in the first place. Take further precautions during high risk flights like at night or during bad weather periods. Reduce unnecessary maneuvers or head movements, which cause disorientation. Share such experiences with colleagues and get their feedbacks too. Conclusion. Limitations of human sensory system are frequently challenged by the third dimension. Unfortunately, most of the time, the response of the pilots is correct as per his evolution process of two dimensions but not applicable in aviation. A major cause of continuous automation in aviation has been introduced to overcome limitations of human factors in aviation accidents. Most accidents due to spatial disorientation have taken place due to lack of situational awareness of the pilots. The situation becomes truly grave when an already compromised 'facts Vs feelings' situation is encountered in marginal weather conditions. This results in an additional build-up of anxiety, and even perceived/actual risk situation, thus a further adverse effect on the performance of these pilots. Consequently, training of human perceptions, sensory illusions and other such human factors affecting him or her in flight are mandatory as per most aviation authorities, and are being implemented elsewhere. While this may take time, it is imperative upon operators and pilots themselves to make sure they understand the dynamics of human limitations, and not allow a situation to develop into a dificult one by initiating a corrective action at the very outset. One day we might actually accomplish the final dream of - Number of Take-offs = Number of Landings BIBLIOGRAPHY 1. Melchor J Antunano and Stanley R Mohler. 1992. Inflight Spatial Disorientation. Human Factors and Aviation Medicine, Flight Safety Foundation Retrieved from http://www.flightsafety.org/hf/hf_jan-feb92.pdf. 2. Dr. Jeff Brock. 1998. Fatal Illusions. Vol 20. Retrieved 12/12/2007 from http://www.amsanz.org.nz/avmedia/20/am20fill.htm 3. Verdon Kleimenhagen, Ron Keones, and James Szajkovics of FAA and Ken Patz of MN/DOT Office of Aeronautics. 1993. FAA Aviation News/January February 1993. 178 Seconds to Live: Spatial Disorientation can be a Killer. Retrieved 12/12/2007 from www.aviation.uiuc.edu/institute/research/arl/technical-reports/178SecondstoLive.html 4. US Army Aviation Study Guide retrieved 12/12/07 on http://www.usarmyaviation.com/Documents/Th-67/P2studyguide2.doc 5. Dougal Watson. 1992. Dark night takeoffs and the "false climb" illusion. Retrieved 12/12/2007 from http://aeromedical.org. 6. Melchor J Antunano. Medical facts for Pilots. Publication 400-00/1. Retrieved from http://www.faa.gov/pilots/safety/pilotsafetybrochures/media /SpatialD_Seeing.pdf Read More