are often pleasant on wave soaring days. Sunshine through the  canopy keeps the upper body amazingly warm for a time, but  shaded legs and feet quickly become cold. Frostbite is a very  real threat. After an hour or two at such temperatures, even  the upper body can become quite cold. Layered, loose-fitting  clothing helps insulate body heat. Either wool gloves or light,  fitted gloves with mittens over them work best for the hands.  Mittens make tasks such as turning radio knobs difficult. For  the feet, two or three pairs of socks (inner, silk; outer, wool)  with an insulated boot are recommended. In addition, the low temperatures can cause two other  symptoms: it frosts your exhaled breath on the inside of  the canopy and it causes the kidneys to excrete liquid at an  accelerated rate. The importance of understanding the need for oxygen  equipment in gliders has been heightened in recent years by a  considerable increase in the number of high-altitude soaring  flights. The exploration of mountain waves has led to numerous  flights at altitudes in excess of 30,000 feet with several record  flights in excess of 40,000 feet. In some parts of the country, it  is frequently possible to soar to a 16,000- to 18,000-foot cloud  base in thermals. In almost all parts of the United States such  altitudes are attainable in cumulonimbus clouds.  A clean piece of cloth (that will not damage the canopy) can  be used to wipe the condensation or frost from the canopy, if  needed, but the best way to clear the canopy is a little fresh  air through the side or front vent to help delay the buildup  of frost. Unfortunately, this also quickly lowers the inside  temperature, so it is best to wear clothing in layers so that  you can easily take off or put on what is needed. There is  little that can be done for the kidneys excreting liquid at an  accelerated rate. The best course of action is to plan for it  in advance by making a bathroom stop before you take off.  Remember that the body is dehydrating more rapidly because  of the cold and always be looking for signs of dehydration. At 18,000 feet, air density is only one-half that at sea level.  The purpose of breathing is to supply oxygen to the blood  and remove carbon dioxide. In each breath at 18,000 feet,  the pilot breathes in only half as much oxygen as at sea  level. This is not enough to deliver an adequate supply of  oxygen to the blood, and the situation worsens as altitude  increases. The automatic reaction is to breathe twice as fast.  This hyperventilation, or overbreathing, is almost worse than  going up without oxygen in the first place because it results  in eliminating too much carbon dioxide from the blood. The  immediate effects of hyperventilation are: Prior to launch, passengers should be briefed on the use of  safety belts, shoulder harnesses, and emergency procedures.  If ballast is used, it must be properly secured. Organize the  cockpit so items needed in flight are accessible. All other items  must be securely stowed. The necessary charts and cross- country aids should be stowed within easy reach of the pilot. The dangers of oxygen deprivation should not be taken  lightly. At around 20,000 feet MSL, pilots might have only  10 minutes of “useful consciousness.” By 30,000 feet MSL,  the time frame for “useful consciousness” decreases to 1  minute or less. For planned flights above 25,000 feet MSL, an  emergency oxygen backup or bailout bottle should be carried. If a parachute of the approved type is to be available for  emergencies, Title 14 of the Code of Federal Regulations (14  CFR) part 91 requires that a certificated and appropriately- rated parachute rigger repack it within the preceding 180  days if it is made of nylon. The packing date information is  usually found on a card contained in a small pocket on the  body of the parachute. The U.S. Air Force in cooperation with the Federal  Aviation Administration (FAA) provides a 1-day, high- altitude orientation and chamber ride for civilian pilots.  The experience is invaluable for any pilot contemplating  high-altitude soaring and is even required by many clubs  and operations as a prerequisite.  Aviation oxygen systems are designed for airborne aviation  applications. Unlike a medical-type oxygen system, an  aviation system is generally much lighter, compact, and  14 CFR part 91 also requires that the pilot in command (PIC)  use supplemental oxygen for flights more than 30 minutes  in duration above 12,500 feet and at all times during a flight  above 14,000 feet. If supplemental oxygen is used, the system  should be checked for flow, availability, and the PRICE  checklist should be used: 13-7 Aviation Oxygen Systems Oxygen System Personal Equipment Cockpit Management  •  P = Pressure •  R = Regulator •  I = Indicator •  C = Connections •  E = Emergency bail-out bottle •  Spots before the eyes •  Dizzy feeling •  Numbing of fingers and toes, followed by possible  unconsciousness