VISN search opens up many possibilities in the area of heuristic search. It can be advantageous for several reasons. Most immediately, for some problems searching a large neighborhood can be more effective than searching smaller neighborhoods. In some cases there simply is no small neighborhood that can be used for a neighborhood search. The VLSN search for airline fleet scheduling described in this article is one such case-no existing natural small neighborhood could lead to improved solutions. VISN search adds flexibility and power to existing search techniques, especially when used in conjunction with those techniques. The VLSN search can also take advantage of subproblems that may be easier to solve. Human schedulers sometimes use computer algorithms as part of an iterative process to find improved solutions. In this case, the human is doing the scheduling, and the computer is offering suggested changes to the current solution. Neighborhood search is required to keep the solution stable from iteration to iteration, with no solution differing markedly from its predecessor. mathematical Finally, from the viewpoint of applied mathematics, VLSN search has intrinsic interest: it opens up a domain of interesting problems for which answers are needed.