This letter is to inform airmen of a means to identify the Cape Area within Boston Terminal Approach Control (A90 TRACON) Airspace that maybe impacted and result in an interruption of Air Traffic services.The attached chart and associated textual description depict A90 TRACON Cape Area boundaries for use in the event of an A90 Cape Area service interruption. An accompanying NOTAM will be issued in the event of a disruption of Air Traffic service advising this area is being affected. This information should only be used in the event of an interruption of Air Traffic services and airmen are advised to use existing preferential routing to avoid the affected airspace where it is available.