A B C $_{Figure 7-3.}$  Example of normal flight (Line A), flying light (Line B), and flying heavy (Line C). comes only with serious practice. Unfortunately, most pilots  do not spend enough time practicing level flight. During the  practical test, given a choice of altitudes, it is easier to fly  level at a lower altitude, due to the ease of acquiring visual  references. However, the pilot must exercise care not to  violate minimum safe altitude requirements (explained later  in this chapter), and must be constantly alert for obstacles  such as power lines in the flightpath.  varies with each envelope, input action by the balloon pilot  can take from 6 to 15 seconds to be realized as a reaction by  the balloon. Planning the maneuver, anticipating the reaction  time, inputting the proper burn, and observing the reaction  must result in smooth and natural movement by the pilot.  Using evenly spaced, identical standard burns to fly level, a  pilot needs to make only two consecutive burns to have added  excess heat to make the balloon climb. For example, if the  pilot can maintain level flight with a standard burn every 35  seconds, and then makes two burns in succession instead of  one, the balloon has an extra burn and climbs. How fast the  balloon climbs depends on how much extra heat has been  added. Under nominal conditions, if the standard burn has  been made to hold the balloon at level flight and a second  burn is within a few seconds (not waiting the 35 seconds),  the average balloon starts a slow climb. Three consecutive  burns results in a faster climb. The temperature of the air inside the envelope controls  balloon altitude. A balloon that is neither ascending nor  descending is in equilibrium. To cause the balloon to ascend,  increase the temperature of the air inside the envelope. If the  temperature is increased just a little, the balloon seeks an  altitude only a little higher and/or climb at a very slow rate.  If the temperature is increased significantly, the balloon seeks  a much higher altitude and/or climbs faster. If the balloon is  allowed to cool or hot air is vented, the balloon descends. Once the desired climb rate is established, return to the level  flight routine to hold the balloon at that rate. The higher the  altitude, or the faster the rate of climb, the shorter the interval  between burns. In an average size balloon (usually a 77, 000  Even without the input action by the pilot, it must be  remembered that the air inside the envelope is dynamic.  The air mass is constantly moving within the confines of the  envelope, attempting to seek a level of equalization. While it  Ascents Ascents and Descents 7-4