Method of manufacturing a gas turbine engine having a fan track liner with an abradable layer

A method of trueing blades of a gas turbine engine, the gas turbine engine comprising an array of blades arranged around a hub and a casing member positioned circumferentially around the blades, the casing member having an abradable layer, the method comprising:

• providing an arrangement for interacting with the fan blades to adjust the length of the fan blades during initial running of the engine;
• running the engine for a pre-determined time so that the arrangement interacts with one or more of the fan blades and adjusts the length thereof, wherein the arrangement is substantially removed during rotation of the fan blades;
• and
• providing an abrasive layer on a radially inward surface of the casing member and running the engine so as to abrade one or more of the blades and shorten the length thereof, wherein the abrasive layer comprises abrasive particles.

A fan casing for fitment around an array of radially extending fan blades of a gas turbine engine, the fan casing comprising:

• an annular casing element;
• and
• an annular fan track liner positioned radially inward of the annular casing element,
• wherein the fan track liner comprises an abradable layer and an abrasive layer, the abrasive layer being positioned radially inward of the abradable layer and proximal, in use, to the fan blades,
• wherein the abrasive layer is a sacrificial abrasive layer,
• wherein the abrasive layer is arranged so as to be substantially removed after engine pass-off and/or after running the engine at maximum speed for a predetermined number of rotation, and
• wherein the abrasive layer comprises abrasive particles.