Elapsed Time Indicator Installation 500
49-72-11 Figure 401 Nov 15/67
Page 402
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
4. Restore Airplane to Normal Configuration
A. Position lower shroud against upper shroud and close shroud latches.
CAUTION: MAINTAIN A MINIMUM CLEARANCE OF 0.18 INCH BETWEEN ENGINE PLUMBING, FIRE DETECTOR, CLAMPS AND INSIDE SURFACE OF LOWER SHROUD.
EXERCISE EXTREME CARE NOT TO DAMAGE SHROUD DRAIN LINES WHEN HANDLING SHROUD.
B. Disengage APU compartment access door support rods and stow rods. Close and latch access door.
C. Close the circuit breaker on M280 module-APU accessory unit on E3-3 electronic shelf.
D. Position BATTERY SWITCH to ON and remove placards.
500
Nov 15/70 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 49-72-11 Page 403
APU EXHAUST SYSTEM - DESCRIPTION AND OPERATION
1. General
A. The APU exhaust system conducts the APU engine exhaust gases overboard and reduces the noise level of the high velocity gas flow. The system consists of an exhaust duct and an aft fairing. The duct and fairing are located in the tail section of the airplane (Fig. 1).
2. Exhaust Duct
A. The exhaust duct consists of a heat shield and a muffler (Fig. 1). The muffler is fitted inside the heat shield in such a way that a cylindrical air space exists between the muffler and the heat shield. A felt metal liner is installed on the inside surface of the muffler for reducing the sound level of the APU exhaust. Two fire detection elements are attached to the exhaust duct assembly. One circles the forward end of the muffler and the second running laterally, is attached at top and bottom of the heat shield. For information regarding the fire protection of the APU, refer to AMM 26-15-0/001. At the forward end, the heat shield is supported by the engine shroud, and has a drip pan attached to protect the heat shield against hydraulic leakage. A bonding jumper, located at forward, lower left side of heat shield, provides a positive electrical ground to airplane structure. The muffler does not come in contact with the exhaust port of the APU turbine section, there is a gap between the exhaust port and the muffler. At the aft end, exhaust duct is supported by the aft fairing.
B. ON AIRPLANES WITH THE DUCT ALIGNMENT ASSEMBLY; A duct alignment assembly is installed on the heat shield to align the exhaust duct with the exhaust port of the APU turbine section.
3. Aft Fairing (Fig. 1)
A. The aft fairing supports the aft end of the exhaust duct. It consists of a machined casting that fairs with the airplane tail cone, and two short cylindrical ducts: an outer duct that mates with the heat shield and an inner duct that mates with the muffler. The casting is provided with the holes for exhaust duct cooling air intake. The aft fairing in attached to the airplane tail cone skin and to the exhaust duct heat shield with bolts.
4. Operation (Fig. 2)
A. When the APU is operating, high velocity exhaust gases flow overboard through the exhaust duct. The exhaust duct is air cooled by aspiration. The gas flow in the muffler develops negative pressure at the gap between the exhaust port of the APU turbine section and the forward end of the muffler. This draws the ambient cooling air through the air holes in the aft fairing. The cooling air passes between the inside surface of the heat shield and the outside surface of the muffler into the opening aft of the exhaust port, where it mixes with the engine exhaust gases and is exhausted overboard.
575
Oct 20/93 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 49-81-0 Page 1
C81918 C81857
APU Exhaust System Component Location 524
49-81-0 Figure 1 Oct 20/93
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
500 APU Exhaust System Schematic
Oct 20/93 Figure 2 49-81-0
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
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