US Patent 12000341 Method for starting an auxiliary power unit

Methods for starting an aircraft auxiliary power unit (APU) in different operating conditions are provided. A method includes performing a first start attempt on the APU when the APU is subjected to an operating condition and determining that the first start attempt was unsuccessful. The first start attempt includes delivering fuel to a combustion chamber of a combustion engine of the APU. After terminating the first start attempt, the method includes determining whether or not a change in the operating condition to which the APU is subjected is below a threshold. When the change in the operating condition is below the threshold, the method includes performing a second start attempt on the APU. The second start attempt includes delivering fuel to the combustion chamber of the combustion engine at a fuel flow rate greater than the fuel flow rate of the first start attempt.