A disclosed example non-transitory machine readable storage medium includes instructions to cause programmable circuitry to at least determine, based on output from at least one sensor, (i) a first parameter corresponding to a first position in a casing of a gas turbine engine, the first position at or downstream of a volume at which flows from respective ones of bleed offtakes are combined, and (ii) a second parameter corresponding to a second position in a casing of a gas turbine engine, the second position upstream from the first position, determine a status of at least one of the bleed offtakes or the at least one sensor based on the first and second parameters, and provide or indicate the status in response to the status indicating improper operation of at least one of the bleed offtakes or the at least one sensor.