Abstract: A method for detecting fault in a resolver generating a sine voltage and a cosine voltage. The method includes obtaining a sum of a square of the sine voltage and a square of the cosine voltage. The sum is filtered through a first filter having a first time constant to generate a first filter output. The sum is also filtered through a second filter having a second time constant to generate a second filter output. The first filter output and second filter output are compared to detect a fault in the resolver.

Abstract: The invention relates to a control system which controls the diameter of a turbine shroud which surrounds a turbine in a gas turbine aircraft engine. The invention seeks to minimize the clearance between the turbine rotor and the shroud. Air is bled from the compressor in the engine and ducted to the shroud in order to heat or cool the shroud in order to, respectively, either expand or shrink the shroud to a proper diameter. The air temperature which is required is computed based on compressor speed and other engine parameters, but not upon directly measured rotor temperature, despite the fact that rotor temperature has a significant influence upon rotor diameter, and thus upon shroud diameter needed. Air at two different temperatures is bled from two different compressor stages in the engine and mixed together in a ratio which is determined according to flight conditions, in order to provide air of the required temperature for the shroud, and then ducted to the shroud in order to modify shroud size.