Understanding aviation laws and procedures can be useful in dispelling the fear that many people experience when boarding an aircraft.
Temperatures Outside the Aircraft
Temperatures fall about 2 degrees Celsius for every 1000 feet of altitude. This means that when cruising at 40,000 feet, the temperature outside is extremely cold. The air circulating in the cabin is initially superheated by the engines, then chilled by the air conditioners and enters the cabin with a moisture content of 1- 2% which is less than the driest desert in the world. For this reason it is important to drink plenty of fluids and keep skin moisturised.
Cabin Pressure and Cruising Altitude
At cruising altitude, the pressure outside the aircraft is about one third of the pressure on the ground. The cabin pressure is equivalent to an altitude of 7000 to 8000 feet which is higher than most people are used to. Altitude sickness can cause mild headaches and nausea. If the aircraft cabin depressurises, passengers are left with about 20 seconds of useful consciousness to put their oxygen mask on. This explains the emphasis on people securing their own masks before helping children and other passengers.
Oxygen Levels on Aircraft
Air normally contains about 21% of oxygen. Levels on aircraft can drop as low as 15%. These low levels can lead to a thickening of the blood which in turn leads to swollen ankles and the possibility of deep vein thrombosis. Low oxygen levels can also cause headaches and reduced mental performance.
DVT and Long Haul Flights
Deep vein thrombosis is the formation of blood clots that can travel to the lungs or brain with fatal effects. The longer a person is exposed to low oxygen levels, the more likely they are to suffer from DVT. This puts long haul flights in a more dangerous category than short flights. The recommended exercises such as ankle rotations and walking around the aircraft are designed to counteract the formation of clots and do have an effect. They are worth doing and should be started at the beginning of the flight and repeated regularly.
Causes of Turbulence
Imagine a river flowing steadily between banks. Then introduce a tributary, some rapids and a waterfall. Air streams work in a similar manner and clouds and storms are common causes of disturbance. Vertically moving air causes more turbulence than horizontally moving air. Clear air turbulence is caused by temperature and wind changes and can be frightening as it is often unexpected. Turbulence can occur at any time and that is why passengers are encouraged to keep their seat belts fastened even when the seat belt light is switched off.
Jet Lag
Jet lag is a combination of several factors:
- The distance in degrees of longitude. If traveling on the equator, two hours due east in a jet equates to an advance of one hour in time. The further north or south a journey is started, the quicker time zones are passed. Flying east or west from Scotland for an hour brings an hour’s time change.
- Body clock. This built in clock governs the function of various glands and the release of hormones. Even if the person is not sleep-deprived, it takes several days for the body to adapt to new rhythms and times.
It is said that a person needs the number of days, equivalent to the number of time zones crossed, to recover fully from jet lag. Energy drinks and tablets can mask the symptoms but the body will adjust in its own time.
Flying can be a great adventure, even with all the problems and inconveniences. Understanding what is involved can aid wise preparation and planning, resulting in a more comfortable trip.
Recommended reading: Arrive Alive by Michael Furniss, RSVP Publishing Company Limited, 2007.
 |
 |
