A method for testing an annular seal within a gas turbine engine , the method comprising: mounting a tool to a structure of the gas turbine engine , wherein a first volume is between and is formed by the tool and the structure ; applying a vacuum to the first volume through a conduit , wherein the annular seal is between the first volume and a second volume , and the conduit is connected to the first volume through the tool ; measuring a vacuum pressure within the conduit while the vacuum is applied; and comparing the measured vacuum pressure to a threshold vacuum pressure, wherein a difference between the measured vacuum pressure and the threshold vacuum pressure is indicative of leakage across the annular seal from the second volume to the first volume , characterized in that : the tool extends circumferentially about an axis , and the tool includes a base , an inner flange and an outer flange ; the base extends radially between the inner flange and the outer flange ; the inner flange is connected to an inner end of the base , the inner flange projects axially out from the base , and the inner flange is configured to axially overlap and seal against the structure ; and the outer flange is connected to an outer end of the base , the outer flange projects axially out from the base , and the outer flange is configured to axially overlap and seal against the structure . mounting a tool to a structure of the gas turbine engine , wherein a first volume is between and is formed by the tool and the structure ; applying a vacuum to the first volume through a conduit , wherein the annular seal is between the first volume and a second volume , and the conduit is connected to the first volume through the tool ; measuring a vacuum pressure within the conduit while the vacuum is applied; and comparing the measured vacuum pressure to a threshold vacuum pressure, wherein a difference between the measured vacuum pressure and the threshold vacuum pressure is indicative of leakage across the annular seal from the second volume to the first volume , characterized in that : the tool extends circumferentially about an axis , and the tool includes a base , an inner flange and an outer flange ; the base extends radially between the inner flange and the outer flange ; the inner flange is connected to an inner end of the base , the inner flange projects axially out from the base , and the inner flange is configured to axially overlap and seal against the structure ; and the outer flange is connected to an outer end of the base , the outer flange projects axially out from the base , and the outer flange is configured to axially overlap and seal against the structure . the tool extends circumferentially about an axis , and the tool includes a base , an inner flange and an outer flange ; the base extends radially between the inner flange and the outer flange ; the inner flange is connected to an inner end of the base , the inner flange projects axially out from the base , and the inner flange is configured to axially overlap and seal against the structure ; and the outer flange is connected to an outer end of the base , the outer flange projects axially out from the base , and the outer flange is configured to axially overlap and seal against the structure . <EOS>