(2)
 Air Inlet Flap It is of a fiberglass fabric/Nomex core sandwich design without acoustic treatment. The flap is hinged at the forward end of the air inlet body and is operated by an attached actuator. It serves two purposes:

 -
to close the air inlet when the APU is not in operation.

 -
to form the forward portion of the upper wall when the APU is in operation.

 (3)
 Air Inlet Nose This item forms the lower wall of the air intake and is permanently installed in the air inlet body. It is of a CRES skin/aluminum core sandwich construction and is acoustically treated with feltmetal along the inlet airstream aft of the lip area.

 (4)
 Air Inlet Housing This conventional aluminum structure attached to the air inlet body serves two functions:

 -provide an attachment for the inlet flap actuator;
 -serve as maintenance platform for work within the tailcone forward of the APU compartment.

 (5)
 Air Inlet actuator This electrically operated linear actuator operates the air inlet flap. Its major components are:

 -28V DC motor with brake control (basic version),
 -
a limit switch at each end position,

 -
a flap position switch at each end position,

 -thermal overload protection device.
 The inlet airstream area up to approximately 150mm (6in) forward of the interface to the APU compartment is covered with a CRES face sheet. This serves as an extension of the APU compartment fireproof area. A fireproof gasket is used to join the air inlet assembly to the APU compartment firewall.

R **ON A/C 001-003, 051-099, 401-499,
 C. Air Duct The air duct forms the central portion of the air intake system, connecting the air inlet with the APU plenum chamber. It is located completely within the APU compartment and is installed on the access door 316AR. When subject door is opened, the air duct is dislocated from its normal installation position, thus permitting improved access to the APU. The purpose is to duct the airflow to the APU and to reduce aerodynamic noise. In case of APU compartment fire, it retains its shape.
 It consists of 2 major components, which are conventionally joined with brackets and fasteners:

 (1)
 Diffusor The purpose of the diffusor is, by means of expansion, to decelerate the airspeed and to decrease airflow turbulance. It also functions as a resonator-type muffler. The 4 walls, joined with fasteners, are of a CRES face sheet/aluminum core double sandwich design employing a CRES septum. The aerodynamic surface is acoustically treated with feltmetal. A fireproof flexible seal minimizes air losses at the junction to the air inlet and provides for a flexible interface. Drainage provisions are incorporated into the lower wall.

 (2)
 Elbow The purpose of the elbow is to redirect the airstream into the APU plenum chamber. In order to reduce aerodynamic losses, 2 guide vanes are incorporated. It also functions as a resonator-type muffler. The design of the walls and their installation is identical to those of the diffusor. The guide vanes are on the entire external surface acoustically treated, their internal design is similar to that of the outer walls. They are assembled with the elbow side walls by means of bonded-in rails. A flexible fireproof seal at the elbow/APU junction minimizes air losses while providing a flexible interface. Drainage provisions are incorporated into the lower wall.

 4. Interface_________ The air intake system has an interface with the control and monitoring system (Ref. 49-61-00).
 5. Operation/Control and Indication________________________________ (Ref. Fig. 002) The following components control the opening/closing of the air intake flap:
 -
the MASTER SW pushbutton switch,

 -
the APU main relay 4KD (APU MAIN) and

 -
the ECB.

 A.
 Opening of the Air Intake

 (1)
 The following settings are required:

 -busbar 301PP energized (carries 28V DC electrical power),
 -
circuit breaker 1KD (ECB SPLY) closed,

 -
circuit breaker 2KD (APU CTL) closed and

 -MASTER SW tch 14KD in 'ON'-position.

 (2)
 When you push the APU MASTER SW pushbutton switch in the ON position:

 -
the blue ON legend in the MASTER SW comes on,

 -
the APU main relay 4KD is energized,

 -electrical power is supplied to the ECB,
 -
the ECB transmits a 'FLAP OPEN'-command to the air intake flap actuator,

 -
the air intake flap actuator moves the flap into the
 'OPEN'-position within approximately 20s,
　
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