A gas turbine engine for an aircraft comprising: an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan comprising a plurality of fan blades, wherein: the fan blades comprise a carbon fibre composite material; when operated at engine cruise conditions, a fan tip air angle θ is in the range: 64 degrees ≤ θ ≤ 67 degrees, the fan tip air angle θ being defined as: θ = tan − 1 V ThetaBladeTip Vx air where: V ThetaBladeTip = ω. D 2; ω is a fan rotational speed in radians/second; D is a diameter of the fan in metres at a leading edge thereof; Vx air is a mean axial velocity of a flow into the fan over the leading edge; a fan blade tip angle β is defined as an angle between a tangent to a leading edge of a camber line in a cross-section through a fan blade at 90% of a blade span from a root and a projection of an axial direction onto the cross-section, and the fan blade tip angle β is within 2 degrees of the fan tip air angle θ; a mass flow rate Q is defined as: Q = W T 0 P 0. A fan. where: W is a mass flow rate through the fan in Kg/s; T0 is an average stagnation temperature of the air at a fan face in Kelvin; P0 is average stagnation pressure of the air at the fan face in Pa; A fan is an area of the fan face in m 2, and at engine cruise conditions: 0.029 Kgs -1 N -1 K 1/2 ≤Q ≤ 0.036 Kgs -1 N -1 K 1/2; the rotational speed of the fan at cruise conditions is less than 2500 rpm; and engine cruise conditions correspond to a forward Mach number of 0.8; a pressure of 23000 Pa; and a temperature of -55 deg C. an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan comprising a plurality of fan blades, wherein: the fan blades comprise a carbon fibre composite material; when operated at engine cruise conditions, a fan tip air angle θ is in the range: 64 degrees ≤ θ ≤ 67 degrees, the fan tip air angle θ being defined as: θ = tan − 1 V ThetaBladeTip Vx air where: V ThetaBladeTip = ω. D 2; ω is a fan rotational speed in radians/second; D is a diameter of the fan in metres at a leading edge thereof; Vx air is a mean axial velocity of a flow into the fan over the leading edge; a fan blade tip angle β is defined as an angle between a tangent to a leading edge of a camber line in a cross-section through a fan blade at 90% of a blade span from a root and a projection of an axial direction onto the cross-section, and the fan blade tip angle β is within 2 degrees of the fan tip air angle θ; a mass flow rate Q is defined as: Q = W T 0 P 0. A fan. where: W is a mass flow rate through the fan in Kg/s; T0 is an average stagnation temperature of the air at a fan face in Kelvin; P0 is average stagnation pressure of the air at the fan face in Pa; A fan is an area of the fan face in m 2, and at engine cruise conditions: 0.029 Kgs -1 N -1 K 1/2 ≤Q ≤ 0.036 Kgs -1 N -1 K 1/2; the rotational speed of the fan at cruise conditions is less than 2500 rpm; and engine cruise conditions correspond to a forward Mach number of 0.8; a pressure of 23000 Pa; and a temperature of -55 deg C. the fan blades comprise a carbon fibre composite material; when operated at engine cruise conditions, a fan tip air angle θ is in the range: 64 degrees ≤ θ ≤ 67 degrees, the fan tip air angle θ being defined as: θ = tan − 1 V ThetaBladeTip Vx air where: V ThetaBladeTip = ω. D 2; ω is a fan rotational speed in radians/second; D is a diameter of the fan in metres at a leading edge thereof; Vx air is a mean axial velocity of a flow into the fan over the leading edge; a fan blade tip angle β is defined as an angle between a tangent to a leading edge of a camber line in a cross-section through a fan blade at 90% of a blade span from a root and a projection of an axial direction onto the cross-section, and the fan blade tip angle β is within 2 degrees of the fan tip air angle θ; a mass flow rate Q is defined as: Q = W T 0 P 0. A fan. W is a mass flow rate through the fan in Kg/s; T0 is an average stagnation temperature of the air at a fan face in Kelvin; P0 is average stagnation pressure of the air at the fan face in Pa; A fan is an area of the fan face in m 2, and at engine cruise conditions: 0.029 Kgs -1 N -1 K 1/2 ≤Q ≤ 0.036 Kgs -1 N -1 K 1/2; the rotational speed of the fan at cruise conditions is less than 2500 rpm; and engine cruise conditions correspond to a forward Mach number of 0.8; a pressure of 23000 Pa; and a temperature of -55 deg C.