An aircraft system includes an aircraft fuselage, an auxiliary power unit and an air inlet assembly. The auxiliary power unit is within the aircraft fuselage. The auxiliary power unit may be configured as or otherwise include an engine. The air inlet assembly includes an inlet orifice, an inlet duct and a door. The inlet duct fluidly couples the inlet orifice with an airflow inlet of the engine. The door is configured to pivot about a generally horizontal pivot axis between an open position and a closed position. The door opens the inlet orifice in the open position and substantially closes the inlet orifice in the closed position.

A method and system for operating an inlet door of an auxiliary power unit are provided. A control signal comprising at least one inlet door command is output. In response to the at least one inlet door command, at least one feedback signal is received and compared to the at least one inlet door command. If the at least one received feedback signal matches the at least one expected feedback signal, operation of the auxiliary power unit is allowed. Otherwise, operation of the auxiliary power unit is inhibited.

There is provided a method and a system for controlling an inlet door of an auxiliary power unit provided on an aircraft. Input data indicative of whether the aircraft is on ground or airborne is received. If the aircraft is on ground, a first control signal comprising instructions to command the inlet door to a fully open position is output. If the aircraft is airborne, a second control signal comprising instructions to command the inlet door to a partially open position. When a current value of a rotational speed of the auxiliary power unit reaches a predetermined threshold indicative of an end of a start sequence of the auxiliary power unit, a third control signal comprising instructions to transition the inlet door from the partially open position to the fully open position is output.

A system and method for controlling a position of an inlet door of an auxiliary power unit are provided. A first control signal comprising instructions for opening the inlet door to a selected one of at least a first position and a second position is output. A possible failure in a feedback signal associated with the selected one of the at least first position and second position is detected and a second control signal comprising instructions for opening the inlet door to the other one of the at least first position and second position is then output.

A system and method for controlling an inlet door of an auxiliary power unit (APU) are provided. It is determined whether a condition to inhibit a start of the APU is present. If no condition to inhibit the start of the APU is present, a door-opening signal comprising instructions to cause the inlet door to be commanded to an open position in advance of a prospective command to start the APU is output. If the condition to inhibit the start of the APU is present, a door-closing signal comprising instructions to cause the inlet door to be commanded to a closed position is output.

A fire seal structure prevents flame from coming out of a fire-prevention region of an aircraft including a panel and a duct. The fire seal structure includes: a first member provided on the duct at a connection portion between the panel and the duct; and a second member that faces the first member around the opening and is provided on the panel. The panel defines the fire-prevention region. The duct communicates with an opening provided in the panel. The duct defines, together with the panel, the fire-prevention region. The first and the second members each contain refractory material, and the first and the second members form a labyrinth-shaped gap between the duct and the panel.

A fluid intake system including a fluid collector scoop designed to be fastened on an inside surface of a wall in order to collect the fluid flowing on the outside of the wall; and an extraction duct suitable for directing the fluid from an inlet orifice into the duct to at least one outlet orifice from the duct, is provided. The scoop is arranged so as to direct the collected fluid towards the inlet orifice of the extraction duct. In this system, at least one outlet orifice is of substantially elliptical section with a ratio of the major diameter of the ellipse over its minor diameter being greater than 1.5.

An inlet assembly for an auxiliary power unit for an aircraft, including a particle separator and a plenum having first and second inlets. A first duct configured to deliver air to an engine of the auxiliary power unit is in fluid communication with an outlet of the plenum. A second duct configured to deliver air to a compartment containing the auxiliary power unit is in fluid communication with the outlet of the plenum. The assembly is selectively configurable between a first configuration where the plenum is in fluid communication with the environment of the aircraft through the second inlet and through the particle separator, and a second configuration where the plenum is in fluid communication with the environment of the aircraft through the first inlet independently of the particle separator. An auxiliary power unit assembly and a method of feeding air to an auxiliary power unit assembly are also discussed.

An inlet assembly for an auxiliary power unit for an aircraft, including a duct configured to provide fluid communication from an environment of the aircraft to an inlet of an engine of the auxiliary power unit, and a filter received in and extending across the duct. The filter includes a first filter portion permeable to air, positioned across only part of the duct and defining a transverse edge in the duct; a second filter portion permeable to air and extending from the transverse edge to an end downstream of the transverse edge, and a collection member impermeable to water. The collection member extends between the downstream end and a duct wall. The first and second filter portions are non-parallel and the second filter portion and the collection member are non-parallel. An auxiliary power unit assembly and a method of feeding air to an internal combustion engine are also discussed.

An air intake assembly for an aircraft includes an auxiliary power unit intake that is defined by a skin of the aircraft. The auxiliary power unit intake is in fluid communication with an auxiliary power unit. The air intake assembly also includes a translatable scoop that defines a stowed condition and a fully deployed condition. The translatable scoop directs air exterior to the aircraft into the auxiliary power unit intake when in the fully deployed condition and does not direct the air exterior to the aircraft into the auxiliary power unit intake when in the stowed condition.