This paper studies the properties of preserving extreme points in Banach spaces and obtains the following theorem: Let X be a Banach space, A is a non-empty convex set of X , then x is a preserving extreme point if and only if x is a WMLUR point of A .

Ground-holding policies (GHP) in air traffic control aim at trading oft" unavoidable airborne delays for ground delays in order to prevent uncontrollable situations where a number of airplanes is placed in a "holding pattern" over busy destination airports.