Abstract: A breather outlet (14) for the gearbox of a gas turbine engine comprises a mast (18) which extends from the nacelle (10) of the gas turbine engine. The mast (18) contains a breather duct (20) which interconnects the interior of the gearbox with an exhaust outlet (22). The mast (18) has an aerodynamic main portion (25) and a sub portion (27) extending rearwardly from the main portion (25). The exhaust outlet (22) is in the sub portion (27) and is arranged to direct oil and air in a downstream direction. The exhaust outlet (22) is spaced from the trailing edge (26) of the main portion (25), the sub portion (27 has guide vanes (28) in the breather duct (20) to straighten the oil and air flow and vortex generators (30) are provided on the mast to avoid oil staining of the nacelle (10).