A gas turbine engine comprising: a fan; a compressor section comprising a first and a second compressor; a combustor in fluid communication with the compressor section; a turbine section comprising a first and a second turbine in fluid communication with the combustor; a first spool including a first shaft that interconnects the fan, the first compressor and the first turbine; a second spool including a second shaft that interconnects the second compressor and the second turbine; and further comprising: a bleed system configured to receive bleed air from the compressor section, the bleed system comprising a first inlet duct configured to receive bleed air from an upstream location of the compressor section, a second inlet duct configured to receive bleed air from a downstream location of the compressor section a common duct into which the first inlet duct and the second inlet duct merge and a heat exchanger arranged in receiving communication with the common duct, wherein the second inlet duct includes a flow-control valve configured to selectively open and close flow from the compressor section through the second inlet duct and the first inlet duct includes a check valve, and the common duct includes a pressure-control valve; characterized in that: the first shaft is connected to the fan through a gear assembly of a fan drive gear system to drive the fan at lower speed than the first spool, the gear assembly being an epicyclic gear train; the upstream location is a high pressure compressor stage of the compressor section; and the downstream location is a diffuser stage of the compressor section. a fan; a compressor section comprising a first and a second compressor; a combustor in fluid communication with the compressor section; a turbine section comprising a first and a second turbine in fluid communication with the combustor; a first spool including a first shaft that interconnects the fan, the first compressor and the first turbine; a second spool including a second shaft that interconnects the second compressor and the second turbine; and further comprising: a bleed system configured to receive bleed air from the compressor section, the bleed system comprising a first inlet duct configured to receive bleed air from an upstream location of the compressor section, a second inlet duct configured to receive bleed air from a downstream location of the compressor section a common duct into which the first inlet duct and the second inlet duct merge and a heat exchanger arranged in receiving communication with the common duct, wherein the second inlet duct includes a flow-control valve configured to selectively open and close flow from the compressor section through the second inlet duct and the first inlet duct includes a check valve, and the common duct includes a pressure-control valve; characterized in that: the first shaft is connected to the fan through a gear assembly of a fan drive gear system to drive the fan at lower speed than the first spool, the gear assembly being an epicyclic gear train; the upstream location is a high pressure compressor stage of the compressor section; and the downstream location is a diffuser stage of the compressor section. the first shaft is connected to the fan through a gear assembly of a fan drive gear system to drive the fan at lower speed than the first spool, the gear assembly being an epicyclic gear train; the upstream location is a high pressure compressor stage of the compressor section; and the downstream location is a diffuser stage of the compressor section.