ALCOHOL AND FLYING DON'T GO HAND IN HAND
by
Surg Lt Cdr S Swamy
39 Advance Course
IAM,IAF, Bangalore

Flying an aircraft is a complex task. It requires the analysis of a variety of sensory information, its cognition, and responding by the psychomotor tasks in response to the perceived situation.

The basic faculties required for flying are intact and unimpaired senses of vision and hearing, adequate intelligence and judgment and motor skills which include adequate muscle power, dexterity, and coordination to manipulate aircraft controls, co-ordination of speech for communication, and agility to enter and egress from an aircraft. Further all this faculties have to be potentiated by training.

The stresses of flying such as the hypoxia at higher altitude, higher accelerations during aircraft manoeuvring, and visual-vestibular illusions, high noise levels, constant communication with ATC makes the flying task all the more stressful. Even quite low levels of alcohol can act to impair the human faculties required to fly in a safe and effective manner.

The effect of alcohol most pertinent to aviation is its impairment of a variety of central nervous system functions. Other systems affected are the gastro-intestinal tract, the liver and pancreas, muscles, the blood, the heart, endocrine organs, the immune system, the respiratory system, fluid and electrolyte balance and metabolism.

Association With Fatal Aircraft Accidents
During the last four decades, a high incidence of the presence of alcohol in the blood of pilots involved in fatal general aviation accidents has been demonstrated. In the United States the percentage of pilots with elevated blood alcohol levels involved in fatal general aviation accidents during the early 1960s was approximately 43%. In 1070's,this proportion had fallen to 15% In the recent times, it is between 10% - 30% level. Military or professional commercial aviation accidents show different relations possibly due to the effect of decomposition on measured blood alcohol levels. Despite these technical discrepancies in some studies, the balance of the data does suggest a strong correlation. The considerable amount of data available supports the postulate that alcohol has a causative role in many of these accidents. The statistical correlation between elevated blood alcohol levels and fatal civil general aviation accidents has prompted attempts at identifying pilot impairment during flight, simulated flight, and a variety of flight related tasks.

Impairment of Flight
Performance impairments due to the ingestion of alcohol depend, in part, on the blood alcohol levels produced and on the ability requirements of the task .One in-flight study of pilots with blood alcohol levels of 0%, 0.04%, 0.08%, and 0.12% has suggested that even quite low blood concentrations of alcohol cause significant performance decrements in flight. This study stated that blood alcohol concentrations of 0.04% are associated with substantial and highly significant increases in the number and potential seriousness of procedural errors committed by both inexperienced and highly experienced pilots". Aircraft flight simulators studies also have found a relationship between the blood alcohol level and the number of aviation procedural errors.

Impairment Of Higher Cortical Functions
Acute ingestion of alcohol causes impairment of functioning of the higher cortical faculties responsible for planning, judgement, cognition, calculation, attention, vigilance, sequencing, and memory which are all essential for safe and successful piloting of an aircraft. In addition, impairment of psychological functions such as perception, discrimination, association, and voluntary response also occur.

Blood alcohol levels as low as 0.027% causes a decrease in visual tracking performance during whole body motion and also in stationary individuals. Reaction time tasks (monitoring and decision components) are also impaired by alcohol levels of 0.09%. Psychomotor and spatial orientation capabilities of pilots are impaired by 0.1% blood alcohol levels. Complex task performance and reaction times have been shown to be impaired by blood alcohol levels in excess of 0.04% and 0.08% respectively Alcohol disrupts the laying down of memory with a likely subsequent reduction in aviation safety.

All of these functions play an important role in the safe piloting of aircraft. Impairment of any of these functions will be detrimental to flight safety.

The Effects Of Alcohol On Visual And Visual-Vestibular Function
Vision is the prime sensory modality used during aviation and is required for spatial orientation and navigation during both 'visual' and 'meteorological' flight conditions as well as the monitoring and adjustment of aircraft performance. 70% of spatial orientation cues come from the sense of vision. Any impairment of the sense of vision, therefore, has the potential of adversely influencing flight performance and flying safety.

The ability of movement of the eyes while pursuing a target, and reaction times is reduced by ingestion of alcohol in concentrations in excess of 0.04%. Blood alcohol levels of 0.05% and above have been shown to slow the ability of the eyes to accommodate or adjust their focus. Double vision and dilatation of the pupils, resulting in blurred vision, can also result from alcohol intoxication.

During the angular accelerations of flight there occur reflex rapid, oscillatory eye movements called nystagmus, which tend to impair the view of objects within the aircraft. This can result in blurring of vision of instruments and a subsequent impairment of performance. Usually a pilot is able to suppress this nystagmus by deliberately fixating on an instrument. Flying in low illumination with alcohol ingestion (with blood levels as low as 0.02%) impairs the ability to suppress this nystagmus.

Another condition, called Positional Alcohol Nystagmus (PAN), also results from alcohol ingestion and also threatens flight safety. Positional Alcohol Nystagmus results in rapid, oscillatory eye movements when the head is placed in specific positions in the absence of angular acceleration. This condition may result in impairment of vision as well as spatial disorientation and has been measured 34 hours after alcohol ingestion, long after there is no measurable alcohol in the blood. Positional Alcoholic Nystagmus has also been reported 48 hours after alcohol intake during long duration radial acceleration. Positional Alcohol Nystagmus has been proposed as the cause of some aviation accidents where there are no detectable blood alcohol levels.

Alcohol has little direct effect on visual acuity and the information concerning its effects on colour vision is conflicting.

Spatial Orientation
The importance of spatial orientation during flight cannot be over stressed. Orientation is maintained primarily by vision but the vestibular apparatus (balancing organ) and the somatic sensory organs (from muscles and joints) also contribute. The loss of spatial orientation, called spatial disorientation, can lead to loss of control of the aircraft and an accident will result unless control is regained.

The function of the vestibular apparatus, and its interaction with the eyes in maintaining correct posture and balance is impaired by alcohol levels greater than 0.04% . High doses of alcohol retard the suppression of post-rotatory nystagmus, an important consideration in turning aircraft. Positional Alcoholic Nystagmus, mentioned above, may play a role in spatial disorientation. Impairment of the visual system and the intimately related vestibular system, by alcohol would cause some degree of pilot incapacitation, and could lead to spatial disorientation and an aircraft accident. Alcohol could adversely affect flight safety in this manner.

Impairment Of Motor Skills
Coordinated motor actions are required during routine flying operations. Flying operation require slight to moderate muscle action. Fine dextrous movements are also required in the operation of aircraft radio communication and navigation equipment.

While alcohol has little effect on muscular strength it impairs the coordination of motor functions. Basic motor coordination tasks such as hand steadiness and a variety of sensorimotor tracking/pointing tasks are all impaired by alcohol. Impaired coordination during sensorimotor actions could lead to reduced pilot performance and a reduction in flight safety.

Alcohol Effects In Conjunction With Altitude Hypoxia
The hypoxia produced by aviation altitude exposure will subtly or potently impair pilot performance. The degree of hypoxic impairment varies with the altitude exposure. The issue of whether alcohol and altitude act to impair performance in a purely additive manner or whether there is a synergistic effect is also of concern in the practice of aviation medicine. Traditionally, it was considered that alcohol and altitude hypoxia had a synergistic effect on performance impairment . While alcohol and altitude hypoxia both impair pilot performance it has not been conclusively shown that their interaction is additive or synergistic in nature.

Alcohol Induced Hypoglycaemia
Hypoglycaemia is the state of a lower than normal blood sugar level. When the blood sugar level is lower than normal, performance may be impaired due to insufficient sugar for the central nervous system to function. Low blood sugar is not compatible with the safe piloting of an aircraft.

Alcohol ingestion results in a lowering of the blood sugar levels.Performance impairment due to alcohol induced hypoglycaemia is likely to contribute to a reduction in flying safety.

Tolerance To Positive Radial Acceleration
Ingestion of alcohol reduces the G tolerance. A 'moderate' dose will reduce the threshold by 0.1 - 0.4 G and will intensify the severity of the symptoms produced by a given level of acceleration.

Interference With Speech Based Communication
Speech based communication is an essential component of most types of flight. Any impairment in a pilot's ability to speak or understand the spoken word may have a direct effect on aviation safety.

Alcohol ingestion causes alterations of speech including 'thick, slurred speech', 'difficulty in speech', 'repetitive speech', 'low, raspy speech', and 'slow, mumbled, and incoherent' speech. Memory for words, fluency in their use, and quality of word associations are also impaired by alcohol. Pilot radio communication has been shown to be impaired by alcohol. This impairment was found to be greater in older pilots than younger pilots.

Alcohol, in impairing various aspects of speech, will interfere with the efficiency of aircraft radio communication and intercommunication. This has the potential for reducing operational safety.

Risk Taking Behaviour
The euphoria induced by alcohol as well as the impairment of judgement may cause a pilot to undertake manoeuvres that he would not undertake while sober. Attempting such manoeuvres while psychomotor performance is impaired may lead to an aircraft accident.

Hangover Effects
Post Alcohol Impairment has been defined as 'performance impairment after alcohol is no longer detectable'. This condition is the equivalent of the lay term of 'hangover'.

Post Alcohol Impairment has been observed 14 hours after alcohol ingestion (to 0.08% and 0.1% blood alcohol concentration) in simulated flight tests.

Conclusion
Flying is a complex task requiring continuous and coordinated sensory, cognitive, and motor functioning by the pilot. Alcohol impairs most aspects of the flying task. Some flight related skills are adversely affected by blood alcohol levels as low as 0.025% while aircraft flight and simulator flight is clearly impaired by levels of 0.04%. Higher blood alcohol levels result in correspondingly more profound impairment of flying skills and reduction in flying safety.

"ANY CONCENTRATION OF ALCOHOL IN THE PILOT IS UNACCEPTABLE AND CAN CONTRIBUTE TO AIRCRAFT ACCIDENTS".

(Adapted)