Of all the memorabilia in a man's closet, a military G1 flight jacket is likely the most revered. Its symbolic representation of the heroic aviators in the twentieth and twenty-first centuries carries the emotional weight of much of U.S. history. Although the heavy leather jackets are nearly indestructible, the knitted cuffs and waistband are not, and they are not repairable when they become shabby, stretched, and ragged. However, they can be replaced, and the replacement parts are available, but they will likely require professional installation.
Purchase replacement cuffs and waistband from a reputable dealer or one of the few Internet sources available. A very reputable leather repair shop or tailor may also have sources for purchasing the replacements. Be sure to match the colour of the original cuffs and waistband when ordering; the knitted pieces are adjustable for size.
Read the directions accompanying the replacement parts. Most will suggest relying only on a professional to attempt the sewing, and most professionals, unless they are experienced at working on flight jackets, may not be able to guarantee their work. It is likely that the sewing will not perfectly match the original installation, though variations may be very slight. Prices for installation will vary widely depending on location and who does the work.
Send the flight jacket to the original manufacturer, if possible. The next best alternative is to find a leather manufacturer who makes flight jackets for any branch of the military. These professionals will install a new waistband and cuffs so that they will appear to be part of the original jacket. Sending the jacket to a manufacturer will be the most expensive way to restore the jacket.