AEROMEDICAL ASPECTS OF LONG DURATION FLIGHT
by
Sqn Ldr Rajesh Kumar
39 Advance Course
IAM,IAF, Bangalore

New generation Air Superiority Fighters (ASF) have changed the face of military aviation. These are multi-role fighter aircraft, with tremendous agility and massive firepower. A typical ASF has an endurance of approximately 10 hours and a range of about 8000 km, with multiple in-flight refuelling. Long haul flight operations involve night flying, crossing of multiple time zones and monotonous activities all leading to disruption of circadian rhythm, sleep loss, fatigue and dangerous decrement of performance.

ADVERSE EFFECTS OF LONG DURATION FLIGHT
Physical effects

• Fatigue: due to inability to change posture & sitting for prolonged period of time.

• Posture: cramped up posture. No opportunity to get up, stretch & walk about. This can take off the mind from actual job. The situation can lead to low arousal & the pilot will be on the descending limb of the Yerkes-Dodson curve - a highly undesirable & unacceptable situation.

• Drying of mucus membranes: due to low relative humidity. This will add to the discomfort.
• Pressure of oxygen mask on face: discomfort & distraction. Chances of contact dermatitis & interference with optimal functioning.
• Wearing of helmet: added weight causing discomfort & distraction.
• Wearing of harness: causing restriction of movements, while keeping the pilot strapped up for a long time.
• Vibration: exposure for long duration can lead to annoyance, sympathetic overactivity & performance decrement.
• Noise: prolonged exposure will interfere with optimal performance.

Psychological effects

• Psychological stress: anticipatory stress, performance anxiety etc. can lead to fatigue.
• Decision-making: presence of stress increases the tendency to err.
• Sleep-loss: can lead to decreased alertness and performance.
• Disruption of sleep-wake cycle: desynchronisation of circadian rhythm.
• Workload: the workload during cruising may be low enough to result in boredom, complacency & serious decrement in alertness. If the crew has to suddenly react to an emergency or make a critical judgement, valuable time will be lost in comprehending the emergency & making a decision.
• Altered mood state: irritability, anger, tension, anxiety and confusion may occur.
• Personality changes: loss of sense of humour, social withdrawal may occur.
• Motivation: may decline.
• Complacency: due to presence of another pilot.

Physiological effects

• Oxygen requirement: in flight refuelling prolongs the endurance of the aircraft but adequate supply of oxygen on board has to be ensured.

• Water requirement: combination of low relative humidity, breathing through mask for prolonged periods, insensible perspiration & sweating will necessitate the provision of water in flight.
• Nutrition: the aircrews on long duration sorties usually carry ready-made food items.
• Bladder problems: long hauls cause frequent urination. If pressure is not relieved, there may be stomachache, uneasiness and performance decrement.
• Physiological stress: acceleration stress, hypoxia, hyperventilation, decompression sickness, barotrauma, spatial disorientation etc. may occur due to human perception error or machine failure.
• Spatial disorientation: e.g. "leans" and "break off phenomenon" may occur. However in a multi-crew aircraft like SU-30, SD may be less of a problem, as it is very unlikely that both the pilots would get disoriented simultaneously.
• Respiratory problems: cold and blocked nose may occur.
• "Economy class syndrome": cramped sitting in a long duration flight promotes pooling of blood in the leg veins and may cause thrombosis and embolism.

Operational effects
Sustained air operations impose workload and fatigue and can lead to disruption of circadian rhythms, sleep loss, fatigue and dangerous decrement in performance. Fatigue may be caused by improper mission cycling (inadequate crew rest, extended work hours, maintenance delays) and poor nutrition, which can lead to decreased vigilance and performance, which will hamper flight safety and reduce combat effectiveness.

Countermeasures

• Sleep: good sleep, adequate crew rest, flight duty time limitations (FDTL), increased crew ratios etc. are helpful measures, but may not be possible due to operational constraints. During Operation Desert Shield, FDTL of transport aircrew were decided arbitrarily as 12 hr of uninterrupted crew rest and flying hour limit of 125-flight hr per 30 consecutive days.
• Billeting, Nutrition and Water: good accommodation / better billeting, good meals, attention to environmental lighting and heating, and post flight nutrition need equal consideration during sustained operations. A balanced in-flight meal may be taken every 2 hr by each crewmember, as it is vital for morale, energy replenishment and to prevent hypoglycaemia. Adequate water should be taken pre-flight, in-flight and post-flight. In SU-30 aircraft, there is a provision for storing in-flight meals in a closed container in the aircraft cockpit. The manuals advise in-flight meals every alternate hour, since the beginning of the flight. The flight rations consist of liquid and paste foodstuff, packed in aluminum tubes of 165 gm each. Rations include canned mashed meat or fruit, chocolate, cream or curd sweet drinks, milk, coffee canned or fresh juices. It should be remembered that while taking a meal, cabin altitude should not exceed 4.5 km to prevent severe hypoxia. The SU-30 aircraft has a limited capacity to carry drinking water; approximately 1.0 L can be carried in the container. The manuals advice to drink water in flight, not less than 100 ml every hour.
• Disposal of excreta: pilot should be provided with suitable containers (with suitable modified clothing) to facilitate disposal of urine and faeces in flight. In SU-30 aircraft a metallic cylinder with a rubber tube and funnel has been provided to collect urine.
• Physical Exercises: pilots should maintain a high degree of fitness / physical conditioning (by a judicious mix of aerobic and anaerobic exercises) in order to better withstand the rigors of long duration flight.
• Prevention of "Economy Class Syndrome": in-flight stretching exercises and avoidance smoking pre-flight and in-flight can prevent this potential hazard of long missions.
• Pharmacological countermeasures / Performance maintenance medicines: these are powerful and help to maintain high operational efficiency. Psycho stimulants have been used during combat air operations since long.

Conclusion
Induction of ASF ushers in a new epoch in long duration fighter flying. To utilize the aircraft to its optimum potential, a large number of innovations and research is required to be done. Whether it is provision of in-flight nutrition, indoctrination on CRM, training for fatigue management, exercise schedules or use of local medication for reducing dependent edema, the aviation medicine will have a large role to play.