The function of the exhaust system is to send the auxiliary power unit (APU) exhaust gases overboard and decrease the noise of the exhaust.

The exhaust system uses a muffler which sends the hot gases of the APU and part of the cool air of the tailcone overboard.

The APU exhaust muffler decreases the noise from the APU. The muffler also points the hot APU combustion exhaust gases and the surrounding cool tail-cone airflow overboard. The gases and airflow go directly overboard through the centerline and rear section of the tail-cone.

The bleed air ducting system interfaces with Air Inlet Ducting and Bleed Air Ducting.

The APU muffler is tubular with a circular inlet that changes its shape to oval at the outlet. The muffler has a felt metal acoustic liner that will decrease noise through a wide frequency band.

The APU muffler is found at the rear of the tail-cone. It is held at the forward end by the muffler side supports that bolt to the muffler mounts. The muffler mounts connect to the tail-cone with rivets. The APU muffler is held at the aft end by a heat resistant seal that goes into the embellisher.

A muffler drain is connected at the forward end of the APU muffler to collect unwanted fluids that go into the APU muffler. The muffler drain is rigid stainless steel tube that goes though a sealed opening in the lower tail-cone access panel to drain fluid overboard.

The APU muffler is grounded to the tail-cone by a bonding strap.

The muffler side supports attach to the muffler mounts with bolts to hold the forward end of the APU muffler. Ceramic washers and insulation blocks are installed between the muffler side supports and the muffler mounts. These insulate the tail-cone skin from the hot APU muffler.

The outer surface of the APU muffler has two high temperature insulation blankets. These blankets give protection to the tail-cone skin from excessive muffler heat. Capstans are attached to the muffler and insulation blankets. The insulation blankets are connected to the muffler by lockwire attached between the capstans. Lockwire and capstans are also used to hold the top and bottom halves of the insulation blanket together.

The heat resistant seal gives support for the outlet aft end of the APU muffler. The seal is made of a ceramic braid material which is heat resistant. The seal is installed between the APU muffler and a stainless steel embellisher at the rear of the tail-cone.

The exhaust muffler gives a continuous outlet path for the hot combustion exhaust gases from the APU while it is in operation. The exhaust muffler also gives an outlet path for the APU surge-valve airflow and the tail-cone compartment and generator cooling airflows. The Venturi effect through the exhaust muffler eductor helps the surge valve and cooling airflow to flow overboard.