| CPC F16J 15/3496 (2013.01) [F15B 15/1452 (2013.01); F16J 15/3296 (2013.01); F16J 15/445 (2013.01); G01M 3/2869 (2013.01); F15B 19/005 (2013.01)] | 20 Claims |

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1. A method of monitoring a ring seal in an aircraft using a flight control computer, the ring seal being an abradable seal comprising an outer ring arrangement and an energiser for urging said outer ring arrangement against an opposing surface, wherein an outermost surface of said outer ring arrangement defines a sealing surface of said abradable seal, wherein said outer ring arrangement is configured such that after a first period of operation said outermost surface suddenly transitions from having a relatively large surface area to having a relatively small surface area, so as to cause a sudden increase in internal leakage across the seal at said transition,
wherein the method comprises using the flight control computer to:
monitor a pressure difference across said abradable seal; and
detect a sudden decrease in the pressure difference due to said sealing surface transitioning from having a relatively large surface area to having a relatively small surface area.
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