as long as the information is available and consulted when  appropriate. Using the chart in  Figure 3-13 , determine the maximum  gross lift that may be expected on a 60 °F day, with decisions  not to exceed 190 °F envelope temperature and 1,500 feet  pressure altitude. In this example, the established parameters  equate what many pilots consider when doing performance  planning. They decide they do not want to exceed a given  altitude or envelope temperature.) To determine the maximum  gross lift available, the nomograph should be entered at point  A, at the ambient temperature of 60 °F. Move right, to the  line indicating an envelope temperature of 190 °F (point B).  Then, move down vertically to a point equidistant between  the lines denoting altitude of 1,000 and 2,000 feet (point C).  Then, move horizontally to the left to the gross lift axis of  the chart and read the result (point D). In the illustrated  example, this computation results in a maximum gross lift  of 1,120 pounds.  As propane gets colder, it has less vapor pressure. (See chart of  propane and butane partial pressures, Appendix C). To ensure  adequate pressure in cold weather, follow the manufacturer’s  recommended method, which will be described in the flight  manual. Many manufacturers recommend the use of nitrogen,  an inert gas that may be added to the fuel tanks by means of a  regulator. This is perhaps the easiest way to pressurize tanks,  as it may be done on site, and with little or no prior planning.  It does require the use of a nitrogen tank and a two-stage  regulator. These items must be available to the pilot before  the flight. If the flight is cancelled after pressurization, and  the anticipated rise in temperature is expected to be more than  30°, the pressure will need to be bled off by using the fixed  liquid level gauge. Balloon systems using a vapor feed pilot system may not  be able to use nitrogen as it can result in an unreliable pilot  light. Those systems commonly use heat tapes or heated tank  covers in order to warm the propane. Heat tapes, similar to  those used to prevent water pipes from freezing, are reliable.  They do require frequent inspection, as normal wear and  tear may cause an electrical short, with potential danger of  damage to the fuel tanks. Among the aftermarket types of heat  tapes, the ones with an internal thermostat will cycle once a  particular temperature is reached, reducing the possibility of  overheating the tanks. Using the chart again in  Figure 3-13 , determine the maximum  altitude to which the balloon may climb, given the same  maximum gross lift figure of 1,150 pounds. In this example,  it is simply a matter of extending the lines appropriately. The  A-B line would be extended to the diagonal line indicating  a maximum temperature of 250 °F (which is the maximum  continuous operating temperature for most balloons). Then,  a perpendicular line would be drawn from that intersection  point. After that line is drawn, extend the C-D line to the  right, and the intersection of those two lines will indicate the  maximum altitude. In this example, this computation results  in a maximum altitude of 10,000 feet.  Use tank heaters and heat tapes with extra caution. Tanks must  not be heated in an area within 50 feet of an open flame, near  an appliance with a pilot light, or in a closed area without  natural ventilation. Most balloon flying is done in non-hostile terrain and benign  weather. There are, some instances in which the terrain may  be more difficult, both for the pilot and the chase crew, and the  weather may become a significant factor. With proper preflight  planning, the problems inherent in mountain flying and cold  weather flying can be resolved. While somewhat riskier than  normal flying, this type of flying can be safely conducted. Pilots, as well as crew, should be dressed appropriately  for the environment. Layered clothing that entraps warm  air is standard cold weather gear. Note that cold weather  environments commonly promote static electricity. It is  important that clothing of natural fibers be used, rather  than synthetics. A hat is important, as significant body heat  escapes from the head. Warm gloves and footwear are a must.  Remember that certain types of hypoxia, or lack of oxygen  to the brain (discussed in Chapter 9, Aeromedical Factors),  may be aggravated by exposure to continued cold. Pilots and  crew should be aware of the symptoms of hypothermia and  frostbite, guard against them, and have a plan in place to deal  with potential medical emergencies. From an equipment standpoint, the balloon requires no special  preparation, other than insuring proper pressure in the fuel  system. Pilots should be aware that seals and O-rings may  shrink somewhat or become brittle in cold weather. This may  cause a propane leak, and special caution should be taken  Some pilots prefer flying in cold weather, which offers the  advantages of more stable air and less fuel consumption to  maintain flight. This means long, gentle flights for the pilot.  There are two main disadvantages to cold weather flying:  the need to maintain adequate pressure in the balloon’s fuel  system and the difficulty of keeping the pilot, crew, and  passengers warm. Cold Weather Flying 3-10 Special Conditions