On a given path, it is possible to choose between four flight levels (FL), each associated with a mandatory flight Mach Number (M). The flight conditions, static air temperature (SAT) and headwind component (HWC) are given below: FL 370 - M = 0.80 Ts = -60°C HWC = -15 kt FL 330 - M = 0.78 Ts = -60°C HWC= - 5 kt FL 290 - M = 0.80 Ts = -55°C HWC = -15 ktFL 270 - M = 0.76 Ts = -43°C HWC = 0 The flight level allowing the highest ground speed is: