Air contamination detection in an aircraft air system

A method of isolating a source of one or more contaminants in an air system of an aircraft having two or more gas turbine engines, the method comprising:

• providing an air contaminant detector within a flow of bleed air downstream of each of said gas turbine engines from which said bleed air is generated, including removably mounting said air contaminant detector within a wall of a bleed air duct with the detecting surface substantially flush with an inner surface of the wall of the bleed air duct that faces the flow of bleed air flowing through the bleed air duct, wherein the air contaminant detector does not extend into the flow of bleed air said air contaminant detectors having a visual indicator operable to visually indicate the presence of a predetermined fluid contaminant present in the bleed air by chemically reacting with the fluid contaminant in order to visually indicate when the fluid contaminant is present in the bleed air;
• visually inspecting said visual indicators on each of said air contaminant detectors;
• and identifying which of said gas turbine engines is the source of the contaminant detected in the air system based on which of said air contaminant detectors has the visual indicator that indicates the presence of the contaminant, wherein the air contaminant detector is a threaded bolt or plug engaged within the bleed air duct such that a tip of the threaded bolt or plug is exposed to the flow of bleed air, the tip having the detecting surface thereon.

A gas turbine engine air system comprising a gas turbine engine having a compressor and a bleed air duct in fluid flow communication with the compressor, the bleed air duct directing bleed air bled from the compressor external to the gas turbine engine for use within an aircraft, and a contamination detector mounted within a wall of the bleed air duct downstream of the compressor with a detector surface of the contamination detector substantially flush with an inner surface of the wall of the bleed air duct that faces the bleed air flowing through the bleed air duct such that the detector surface of the contamination detector is exposed to the bleed air within the bleed air duct while the contamination detector does not extend into the bleed air the detector surface including a visual indicator which senses and indicates the presence of one or more fluid contaminants within the bleed air, the contamination detector being removable from the gas turbine engine to permit visual inspection of the visual indicator, and the visual indicator of the detecting surface including a product which chemically reacts with the fluid contaminant in order to visually indicate when the fluid contaminant is present in the bleed air, wherein the contamination detector is a threaded bolt or plug engaged within the bleed air duct such that a tip of the threaded bolt or plug is exposed to the bleed air, the tip having the detector surface thereon.