A method of balancing the supply of bleed air from a plurality of gas turbine engines

The method involves sensing air flow rates individually in each of air bleed lines (11a,12a,13a) from engines (11,12,13) with respective flow rate sensors (S1-S3). The air flow rates are compared to air bleed lines to derive flow matching signals (30b,31b,32b) for engines. Each flow matching signal is compared to a command signal (25) to derive a drive signal (11b,12b,13b) applied to each of control valve (V1-V3). The flow rate sensors provide air flow rate signals to a controller (20) which vary the flow rate of air bled from the engines. The command signal is derived, by comparing a demand signal (24) with sensed air pressure in a distribution line (17). The demand signal is provided to the controller indicating the demand for bleed air by an ancillary system (14).