If the flight is continued through sunset, loss of solar heating  results in a cooling of the lifting gas and a resultant loss of  gross lift. Ballast must then be used to maintain buoyancy. When the decision is made to land, all possible equipment  should be securely stowed. Occupants should don helmets  and any other protective gear. All antennas, solar panels, and  other items hanging below the basket should be retrieved  and stowed. Adequate ballast should be brought inside the  basket where it is readily available to abort or round-out a  landing.  The trail rope should be rigged and readied for deployment.  The trail rope serves three purposes. First, it slows the descent  rate. A fully deployed trail rope weighing about 40 pounds  on a 1,000 cubic meter balloon normally arrests a descent of  approximately 340 feet per minute (fpm) at 150 feet above  ground level (AGL) to a descent rate of 0 fpm at ground  contact. The descent from 150 feet will take about 45 seconds.  These numbers are only approximations and local conditions  at landing certainly cause these to vary somewhat. Secondly,  the trail rope orients the balloon so the attachment point of  the rope is on the upwind (or trailing) side of the basket. This  may be important depending on the arrangement of the basket  and/or deflation ports. Finally, as more of the rope contacts  the ground, friction slows the horizontal speed of the balloon.  The trail rope should be connected to the load ring with a  quick release mechanism to allow release should the trail rope  become permanently entangled on the ground. A final topic of interest is the effect of mixing air with the  lifting gas. It may seem that since air is heavier than the lifting  gas, the air would have a tendency to pool at the bottom of  the envelope and be expelled through the appendix as the  balloon rises into less dense air. However, this is not what  happens. The forces of molecular attractions cause the air  and lifting gas to become permanently mixed and a generally  less pure mixture occurs. When this happens, some of the  benefits of operating under the pressure ceiling are lost and  every up/down maneuver causes the loss of lifting gas along  with the expelled air. For this reason, care should be taken to close the appendix  when descending rapidly to avoid allowing air to force its way  up into the envelope through the open appendix. Maintaining  a high level of purity of the gas inside the envelope can extend  flight duration. Care must be taken to open the appendix  during rapid or prolonged ascents which bring the balloon  close to its pressure ceiling. Ascent above pressure ceiling  with a closed appendix increases internal pressure on the  envelope’s fabric and, in an extreme case, could cause the  envelope to rupture. If the gondola has rotated during flight, placing the trail rope  on the gondola’s downwind side, it does not deploy correctly  unless the pilot guides it around to the upwind side of the  gondola. Otherwise the rope deploys under the gondola and  tends to pull the leading edge of the gondola down and may  completely invert it. This is colloquially called “dog-housing”  and puts the occupants in the uncomfortable position of  being dragged along the ground trapped inside the basket.  Unlike modern hot air balloons, most gas balloon systems  do not have rigid uprights, so dog-housing is a real concern  in a high wind landing; the best antidote is to keep as much  weight as possible (including the occupants) on the upwind  (trailing) side of the basket. The landing phase is the single most critical portion of the  entire flight. The pilots may be fatigued from the long flight.  They may be in unfamiliar geography and weather conditions.  There may be time pressure to land in daylight if sunset is  approaching. A landing after dark, under a full moon and  in open territory may be performed rather routinely, but a  daylight landing is still much preferred. A night time landing  in dense woods under a new moon or with reduced visibility  can be very stressful. Five minutes on oxygen prior to landing  may help to relieve some fatigue and clear the senses. The landing decision varies with each flight and should be  discussed jointly among all the pilots. Landings should be  initiated while there is still adequate ballast available to  abort at least one approach, if necessary. The actual amount  of ballast required varies with pilot experience, weather  conditions, terrain and descent rate. For a 1,000 cubic meter  balloon in relatively easy landing conditions and under  a shallow descent, 50 pounds may suffice. Under more  adverse conditions, 250 pounds or more may be advisable.  Additional considerations for landing may include duration  of flight, fatigue level of the pilots, accomplishment of the  flight objectives, current and forecast weather, terrain, and  time of day. The trail rope also acts to stop any ascent since a rising  balloon becomes heavier as more of the rope is lifted off the  ground. This is why it is sometimes called “retrievable” or  “reusable” ballast. For this reason, the trail rope should never  be deployed until landing is completely certain. Aborting  a landing with a deployed trail rope requires ballasting  the weight of the trail rope (approximately forty pounds)  in addition to the ballast normally required to achieve the  desired ascent rate.  The anti-sail line should be pulled tight and secured to the  load ring or other strong point. The purpose of this line is  to hold the bottom of the envelope down taut to minimize  11-11 Landing, Retrieval and Packup Purity of Lifting Gas