POWER PLANT DRAIN SYSTEM - DESCRIPTION AND OPERATION

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1. General
Various APU components, at which waste fluids (fuel and oil) may occur, incorporate provisions to collect these. In addition, the exhaust system is exposed to rain water and cleaning fluids. For safety and operational reasons, all these fluids are collected separately and drained overboard via the APU compartment drain mast.
The APU compartment itself is designed such to permit all fluids occurring to gather at the lowest point, from which they are discharged overboard via the drain mast.
All components of the drain system are fireproof.

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2. Component Location

APU Drain Lines ** ON A/C NOT FOR ALL

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| | | | DOOR | REF.

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DRAIN TANK 316 316AR/ 49-17-41

DRAIN MAST 315 49-17-42

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3. System Description

APU Drain System - Component Location ** ON A/C NOT FOR ALL

APU Drain Lines ** ON A/C NOT FOR ALL

Drain System Schematic ** ON A/C NOT FOR ALL

Drain lines are connected to:

the fuel/oil-pump drain,
the BCV actuator-seal drain,
the IGV actuator-seal drain.

These go to a collector line that goes along the underside of the APU, and then to a drain tank. The drain tank is installed on the access door 316AR and has a drain line. The drain line goes along the inside of the access door to a drain mast. Air flow across the drain mast causes a vacuum in the drain line. The suction effect produced, is sufficient to remove the contents of the drain tank at approximately 200 kts forward air speed. A vent line between the drain mast and the drain tank ventilates the drain tank and drain lines.
Drain lines, connected to:

the front bearing-seal drain,
the combustor housing drain,
the air by-pass plenum drain,
the exhaust muffler drain,

also go to the drain mast. These do not go to the drain tank, but discard the waste fluids directly overboard. The interface of the APU drain lines and the drain lines on the right access door to the drain mast, is made by spring adapter seals constructed from stainless steel. The APU compartment drainage is integrated into the installation of the drain mast at the lowest part of the APU compartment fire zone between FR80 and FR81. A leakage of any fluid from the APU will run down the inside of the access door(s) to be drained through four holes in the drain mast. The fluids discarded through the APU drain mast do not have a dangerous effect on the APU or any other components. The gearbox is vented to the APU exhaust through a vent line. All the parts used in the drainage system are fireproof.

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4. Operation

Drain System Schematic ** ON A/C NOT FOR ALL

A. APU Drain System
On the ground, cold drains (oil + fuel) are collected in the drain tank. In flight (APU in operation or not) above 200kts forward air speed, sufficiently low pressure is generated at the drain mast to permit discharging of the drain tank contents via the suction line.
Hot and/or pressurized waste fuel is drained directly overboard.
Rain and cleaning fluids are collected separately and also drained directly overboard.

B. APU Compartment Drainage
Rain or cleaning agents may reach the compartment via its ventillation louver. Oil and fuel may reach the compartment only in case of system leaks (fuel supply, hydraulic actuation or lubrication) or oil spillage during APU servicing.
If rain, cleaning fluids or fuel of sufficient quantity enter or leak within the compartment at any location, they flow to the lowest point and from there through the drain mast overboard. Only insignificant quantities of these fluids will remain in the compartment along the drainage path.

[Rev.10 from 2021] 2026.04.01 01:28:21 UTC