The Buffer Zone – Hot Air Balloon Instruction Series

When an experienced hot air balloon pilot lifts off the ground in a balloon, he/she is immediately gathering critical information for the entire flight. Aside from the instrumentation feedback, the pilot is “feeling” the balloon burner’s responsiveness relative to the lift and performance of the balloon. 90% of this information may be accumulated by the astute balloon pilot within the first 30 seconds. The ground break and transition to level flight maneuvers usually provide enough information for a good balloon pilot to quickly adjust to the density altitude and gross weight of the hot air balloon for this particular flight. A lower hour pilot may have to run through a series of maneuvers to accomplish the same. Assuming that the balloon pilot continues to make subtle refinements to his/her burn sequence to compensate for the later morning warmer air and fuel pressure, is this adjustment enough to insure a flight safe from obstacle contact and moments of control loss? Sometimes…

The skilled balloon pilot performs the above evaluations during the course of every flight. Even the unskilled pilots do it, if subconsciously. What other factor could play a part in hot air balloon control, especially at key times while in the vicinity of obstacles? Ah, the weather of course. How does a balloon pilot adjust for the weather conditions in addition to ambient temperature and payload characteristics? It is done with the use of a “Buffer Zone”. For purposes of this discussion, the Buffer Zone is defined as the no fly zone area around an obstacle. In other words, it’s the minimum distance a balloon pilot determines that he/she can come to an obstacle without significant risk of collision based on weather conditions. Is this calculation important for every portion of the flight? You bet your life! How does a balloon pilot determine the size of this boundary layer on any given flight? It is similar to the method used to determine the performance characteristics described above. However, when Buffer Zone adjustments are made, many times they are not subtle.

The most common Buffer Zone adjustments are made when surface winds are strong and/or density altitude is high. Consider an afternoon flight with a takeoff speed of 8-10 mph. If there is a stand of trees immediately downwind, it is very unlikely that any pilot would choose to “treetop” for a while for the sake of enjoyment. In fact, if the pilot was faced with some immediate steering issues that required a low level turn, he/she would probably establish 15 feet or more as a Buffer Zone over the trees, given the conditions. What if the pilot was relatively new and there was some gusting? If 15 feet was good for an experienced pilot and no gusting, I’d say 30 feet or more might be a minimum Buffer Zone for the newbie balloon pilot. In this case, is this 30 feet figure relevant to any other part of the flight? Without question. The 30 foot Buffer Zone should be a constant throughout all of that pilot’s maneuvers as long as those particular weather conditions persist. As the evening progresses and the winds slow and cool down, the Buffer Zone may be adjusted to as little as 1 foot or even light scrapes across the trees. On the other hand, if the balloon pilot suddenly experiences a sudden downdraft from 30 feet, and manages to recover at the tree tops, it’s time to bump the Zone up to 50 feet or so with some increased vigilance. The point is that this boundary layer calculation is dynamic. It can and should change dramatically when warranted.

The Buffer Zone estimates described above are the easy ones and most intuitive. How about flying in the proximity of other hot air balloon traffic or power lines, in fickle winds. Take the case of other balloon traffic. Would the 30 foot Buffer in the conditions described above be sufficient to fly safely among other balloons? I don’t think so. Assuming you feel comfortable at keeping you balloon plus or minus 30 feet given the conditions, what if the other hot air balloon suddenly thermals closer or the pilot inadvertently burns too much. You have the added burden of trying to figure out what he or she might do in addition to your own stability. At that point, your buffer zone may adjust to 60’-100’ or more to other balloons. The good news is that once this number is established it allows you, the pilot, to relax a little and concentrate on flying.  Lets say you’ve have established a buffer zone of 20 feet because it’s still hot and breezy later in the afternoon. If 20 feet is appropriate for most fixed obstacles, what about power lines? I think 30 feet or so might work in this case. Perfect; safe Buffer Zones are determined and power lines are given an extra margin. The flight goes on and life is good. Oops, we forgot about one thing. Unless you brought a parachute, you’ve got to make a landing. A hot air balloon landing no closer than 20 or 30 feet over obstacle and power lines is possible once in a while but most of us need to grease it in a little closer to obstacles in order to hit backyards and other low impact landing areas. Do you just throw out the buffer parameters at landing? Good question. Hopefully, the wind has calmed and conditions permit safe proximities to objects at 5’ or less. This presents no problems. What if the conditions are such that a 20-30 feet buffer is still appropriate? When this occurs, it is crucial that you begin tightening your BZ as you start your initial approach. Mental concentration levels must go to 100% and the feedback must be immediate if your precision controlled approach varies any more than your anticipated minimum landing clearances require. If you experience a 10’ bump on approach, you have to include plus or minus 10’ minimum clearances from the outer dimensions of the hot air balloon to all fixed approach obstacles. The exceptions in this case are trees ( plus/minus 5’ and wires plus/minus 15’). If the initial approach is smooth and plus or minus 2 feet or so, you can grease the landing even if it’s still breezy.

The next time you fly, try to pay attention to these internal calculations. It is an intuitive exercise for experienced flyers and once these numbers are set, it allows the balloon pilot freedom to safely attend to other duties during the flight.