Thermal Stress

The Human

If a pilot or passenger is wearing multiple layers of clothing they may be too warm even before entering the aircraft. The easiest way to combat this would be for operators to wear appropriate layers and make sure passengers are also aware that they don't need excessive layers of clothing when flying in an enclosed cockpit (Robson, 2008).
Some operations such as military flying require multiple layers of clothing, including in warmer climates. For a video showing the layers of clothing worn by Skyraider pilots in Korea,  Anti-G suits, immersion suits, winter flying clothes, and chemical or nuclear protection garments all contribute to thermal stress.
In this instance the cruise stage of the flight may be fine as the human will not create any more heat than a normal sedentary occupation but as soon as combat is entered the pilot will be subjected to G's, be required to maintain a full lookout and workload is high (Ernsting, 1999). This will cause an increase in metabolic heat production. Low flying also produces a similar result.

The Environment

The outside environment has an impact on the amount of thermal stress felt by the pilot, ground crew and passengers.
In the case of pilot and passengers, taxiing can cause significant thermal stress because the doors are closed and the aircraft environmental controls are often inadequate on the ground, usually requiring ram air. This problem is worst in bubble type canopies.
Once at altitude the environmental systems of the aircraft work better and the outside air is cooler, however the pilot is more susceptible to sunburn. The best way to combat this is to wear a full-brimmed hat and sun block. Drinking water should also be on hand because even in a survival situation the glacial or snow waters can cause cramps (CAA, 2011). Loose fitting clothing is best for warm days (Robson, 2008).

The Aircraft

The aircraft itself is a heat source which can impact thermal stress on crews and passengers. Heat can come from avionics systems, aircraft skin at high speeds, and even from a heating system malfunction.

Effects of Heat Strain on the Pilot

The central nervous system is susceptible to impairment if it's temperature is raised which can cause problems with memory, attention, vigilance, reasoning, decision making and dexterity. Physical problems include dehydration due to excessive sweating which reduces G tolerance by about 1G (Ernsting, 1999). These issues all clearly reduce the ability of a pilot to fly safely or effectively and will affect passenger comfort.

Some Solutions to Heat Strain

According to Ernsting (1999):

• Park aircraft out of the sun in hangars before flight to minimise cockpit temperatures.
• Reflective shades.
• Air conditioned facilities for preflight briefings and planning (or waiting rooms for passengers).
• Air conditioned transport to aircraft.
• Acclimatisation.
• Adequate time between flights to recover to normal body temperature.
• Physical fitness.
• Hydration.
• Environmental control system maintaining pressure and temperature.
• Personal cooling systems (either liquid or air cooled suits).

Cold Stress

Ground crew, pilots and passengers in cold climates face the possible dangers of hypothermia, freezing (frostnip and frostbite), and non-freezing cold injuries (Ernsting, 1999). Ditching an aircraft will also expose those on board to immersion which has it's own set of challenges (CAA, 2011).

Hypothermia

Hypothermia results in degradation of mental and physical performance and occurs when the core temperature drops below 35°C. This happens through either radiation from exposed body surfaces such as your head, conduction (wind chill) or evaporation of moisture from the skin (Robson, 2008). Early symptoms include shivering (the bodies attempt at keeping warm) and slurred speech. circulation to the extremities is reduced in an attempt to keep the core temperature up and so hands and feet get cold (CAA, 2011). As the temperature decreases to 33°C the shivering stops and conciousness decreases until at 28°C spontaneous ventricular fibrillation may occur, causing death (Ernsting, 1999).
To treat hypothermia, warm the patient up. They will have slow respiration and a slow heart beat and may appear dead but doctors usually don't declare a victim dead until they have been warmed up (Ernsting, 1999). Don't rub a hypothermia victim as this will circulate cold blood to the core, making the situation worse (CAA, 2011).
Pilots flying in cold climates should ensure there is a survival kit on board in the case of an emergency landing. This should include water proof matches, a means of heating water (billy) and blankets among other things. For official recommendation on the contents of survival kits see the CAA Survival GAP book.

Freezing (Frostnip and Frostbite)

As stated by Ernsting (1999), skin freezes at -1°C and if the freezing is reversible with no damage then it is termed frostnip. If damage is caused it is frostbite. This mainly affects the ears, fingers, nose and feet but will also affect any skin which clothing is not properly insulating.
Initial symptoms include numbness then frostbitten areas will look white and waxy. Treatment is a slow warming, as rapid warming will cause more tissue damage. If there is any chance of the frostbite reoccurring before reaching medical treatment it should be left frozen.

Non-freezing cold injury

According to Ernsting (1999), these are a variety of conditions such as chillblains, which can occur when exposed to temperatures below 12°C for more than six hours. They are not well understood yet and so there is no recommended treatment. Therefore the best remedy is to avoid the problem in the first place by having all crew and passengers wear appropriate clothing for the conditions, and the provision of a properly stocked survival kit on the aircraft. GPS tracking and a 406MHz Emergency Locating Transmitter will also expedite rescue and minimise exposure to the elements thus reducing the chances of any of the cold induced conditions above (CAA, 2011).

Ditching and Immersion

Ditching an aircraft is a difficult task to pull off with many differing opinions on how to do it.. However assuming a pilot successfully ditches an aircraft and all persons on board escape uninjured, they may then have to contend with immersion in cold water until either they enter a life raft or are rescued.
Immersion causes the "cold shock response" which includes an involuntary inhalation or gasp which, if under water, will cause inhalation of water and initiate drowning (Ernsting, 1999). This will happen to even the best swimmers and hypertension, hyperventilation and tachycardia will follow. The initial gasp and hyper ventilation are evident in this video, demonstrating why the life jackets should be fitted before flight over water in single engine aircraft (Robson, 2008).

According to Ernsting (1999), after a while the hyperventilation is replaced by erratic breathing which makes it difficult to coordinate breaths while swimming and this is thought to be the main cause of drowning, even in strong swimmers close to shore or rescue.
Hypothermia rapidly sets in (heat loss is faster in cold water than cold air). Although swimming increases metabolic heat production, the convective heat loss due to moving limbs is greater than the gain so it is recommended that swimmers remain still (Ernsting, 1999).
Military pilots have access to immersion suits which can help maximise survival chances. Most aircraft operators will have access to life jackets and possibly life rafts. Crew should be trained on these and briefings held for passengers before flight on the operation of this emergency equipment (Robson, 2008).

Some Examples of Cold Stress Hazards in Aviation

As stated by Ernsting (1999):

• Hands or limbs exposed to airflow may reduce sensation making manual dexterity difficult.
• Cold can be a hazard as a psychological distractor.
• Bulky clothing to combat cold may make delicate tasks difficult.
• Contact with fuels may cause frostbite because their freezing point is below zero.

Some Solutions to Cold Stress