General. APU Control System. APU Door System

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1 .10 -Description and Operation General The Auxiliary Power Unit () provides electrical and pneumatic power for engine start and air conditioning, and supplies ground and in-flight electrical power. Pneumatic and electrical power may be used independently or simultaneously. The is installed in an unpressurized area of the rear pressure bulkhead, beneath engine 2 and the horizontal stabilizer. RPM, EGT, air output and electrical output are controlled by an Electronic Control Unit (ECU). controls are on the overhead panel. The external control panel is in the fairing immediately behind the left main gear well. parameters are displayed on the Systems Display (SD). Control System The control system consists of the ECU and the Electronic Fuel Control Unit (EFCU). The ECU controls starter operation, fuel scheduling, ignition, and surge bleed airflow and provides a stable, automatic start cycle. The EFCU receives control input from the ECU and controls fuel supply. The requires battery bus power for start and uses fuel from tank 2. The ECU receives primary power from the battery bus. The supplies air to operate the three air conditioning packs, before or after engine start, as required. Door System The installation has an inward-opening door for the intake duct and an outward-opening half door for the exhaust duct. An electric actuator operates the doors. The inlet and exhaust door actuation system receives electrical power from the battery bus on command from the Miscellaneous Systems Controller (MSC). If a door starts to close while the is operating, the shuts down. MD-11 [Auxiliary Power Unit] Page 1

2 Start and Shutdown The START/STOP alternate action (pushbutton) switch on the aft overhead panel commands start through the MSC, after determining running status. A DC electric starter motor, mounted on the gearbox, uses aircraft battery power for start. A battery-powered DC pump provides starting fuel flow to the from main fuel tank 2. This pump is used for start when AC power is not available. When AC power is available, the AC pump in main fuel tank 2 supplies fuel to the. Following start, the ECU controls the through the EFCU, maintaining a constant N2 rpm speed with all varying loads. The ECU also regulates the surge control valve and the load bleed valve to meet demand for pneumatic power. The EGT reaches set values with combined bleed air and power loads. The ECU commands the low pressure (N1) compressor speed to drop. A variable turbine nozzle actuator adjusts N1 speed by adjusting the position of the vanes, which are located upstream of the N1 turbine. Following shutdown, EGT is monitored continuously until the is shut down. The EGT value is displayed on the data window of the SD. Should EGT limits set by the ECU be exceeded, N1 speed is slowed to N1/EGT cutback. Shut down is automatic if there is still no control. The following automatic shutdowns, processed through the ECU, protect the against hazardous conditions and potential damage: N1 or N2 overspeed. Low oil pressure. High oil temperature. Reverse flow. Loss of EGT signal. Fire warning. Loss of N1 or N2 speed signal. High EGT. Loss of DC power. Slow start. No flame during start. Inlet door not open. Starter motor energized over 1 minute. Overcurrent. MD-11 [Auxiliary Power Unit] Page 2

3 Pneumatic System The pneumatic system supplies bleed air to the Environmental Control System (ECS) and to the main engine start system. The components of the pneumatic system are: bleed manifold. load bleed valve. surge valve. flow sensor. low-pressure bleed check valve. aircraft isolation shutoff valves. The pneumatic system shares the ducting and valving associated with the engine 2 bleed air system. When the load bleed valve is opened, low-pressure compressor discharge air flows into the engine 2 bleed line through the air load valve and the low-pressure check valve. This air is directed either to the packs or to the main engine air starters by one or both of the isolation valves. During start, load valve 2 is in the closed position and the surge valve is in the open position. After start, when no air is being routed through the ducting for use by the aircraft systems, air flows overboard through the surge control valve. Operation of the surge control valve is directed by a signal from the flow sensor. Controls and Displays indications are displayed on the SD. Alerts appear on the EAD and SD. The control panel is on the aft overhead panel. Additional controls are on the external control panel. The external control panel is in the fairing immediately behind the left main gear well. It allows fire extinguishing action by personnel on the ground. The START/STOP switch permits single switch control for manual start/stop and operation under normal ground and flight conditions. The PWR switch on the ELEC control panel also starts the, and stops the if started with this switch and not supplying bleed air. power is automatically supplied to the unpowered generator buses. With engine integrated Drive Generator (IDG) power from the respective bus, the continues to run and to power each main bus during engine shut down. If the is started with the START/STOP switch, shut down is not automatic after the load is removed. Manual shutdown with the START/STOP switch is required. MD-11 [Auxiliary Power Unit] Page 3

4 The cannot be started without battery power. During a battery start, DOOR, FUEL, and FAIL lights, if illuminated indicate malfunctions. During the start sequence, both the AVAIL light on the PWR switch and the ON light on the START/STOP switch flash. An oil quantity drop is normal during the start sequence. After start, with AC power available, the ON alert is displayed on the EAD and N1, EGT, N2, and OIL parameters are displayed on the SD. The door closes when the master switch is actuated to STOP. At this time, the indication is removed from the SD, and the ON alert disappears. A 90-second time delay provides a cushion against thermal shock to the turbine section. The continues to run after it has been commanded if air has been used. shutdown will be inhibited if the START/STOP switch is selected to STOP while the AIR switch remains selected ON. The symbol is removed from the AIR synoptic when air is no longer available. MD-11 [Auxiliary Power Unit] Page 4

5 .20 Tail -Components Cone View and Exhaust Area TAIL CONE (VIEW LOOKING UP) EXHAUST AREA INLET COMPARTMENT DOOR CAG(IGDS) LB MD-11 [Auxiliary Power Unit] Page 5

6 .30 -Controls Panel and Displays 5 AGENT DISCH ENG/ FIRE TEST 1 FIRE PULL/TURN 1 2 START/ STOP ON FUEL FAIL DOOR GEN AFT OVERHEAD PANEL DB ENG/ FIRE TEST Button For description, refer to Fire Protection chapter. 2. GEN Switch - amber When pushed, resets generator control unit if electrical system is in manual mode. - Illuminates amber when generator is on speed and there is a malfunction. 3. FUEL/FAIL/DOOR Status Display - amber FUEL - Illuminates amber when fuel pressure is too low. FAIL - Illuminates amber if the fails to start. DOOR - Illuminates amber if the door does not open. DOOR also illuminates during a normal shutdown if the door does not close. Blank - Illuminates during test only (spare display). MD-11 [Auxiliary Power Unit] Page 6

7 4. START/STOP Switch - blue This switch is an alternate action pushbutton switch that starts and stops the manually. With selected, the shuts down 90 seconds after the bleed air stops. ON - Flashes blue when the is selected to START, and illuminates steady blue when the is running on speed. If the shuts down automatically due to a fire signal, ON flashes until the START/STOP switch is selected to STOP (). - Illuminates steady when the is selected to STOP. Shutdown occurs 90 seconds after the is no longer supplying bleed air. remains illuminated until the shutdown cycle is complete. If the is started with this switch, the can only be stopped manually with this same switch. 5. AGENT DISCH FIRE Handle For description refer to the Fire Protection chapter. MD-11 [Auxiliary Power Unit] Page 7

8 PWR Switch 1 GND DC TIE 3 R SERV DC 3 EMER DC TIE 2 EXT PWR ON AVAIL AC 3 ON DRIVE 2 AVAIL GEN 3 DISC ARM FAULT AC GND SERV PWR AC TIE 3 ARM ADG EMER AC DRIVE 3 DISC FAULT ON ELEC 1 /2 SYSTEM SMOKE ELEC/AIR NORM PUSH TO TURN 2/ 3 SELECT MANUAL CAB BUS 3/ 1 1. PWR Switch - green/blue Push to start the. FORWARD OVERHEAD PANEL AVAIL - Flashes green during start until N2 reaches 95 percent, then becomes steady green as the generator provides power of correct phase rotation, voltage, and frequency. If the was started from the control panel, pushing this switch supplies power to the unpowered generator buses if the green AVAIL light is illuminated. After start, power is automatically supplied to unpowered generator buses. When the IDGs are supplying the generator buses, the shuts down 90 seconds after air is no longer being used. ON - Illuminates blue when the generator is supplying power to any generator bus. If the is on and supplying electrical power, pushing this switch disconnects electrical loads. DB If the was started from the control panel, pushing this switch does not stop the. MD-11 [Auxiliary Power Unit] Page 8

9 Air Switch 1-3 ISOL ON DISAG BLEED AIR 2 BLEED AIR 3 PRESS MANF ON PRESS MANF TEMP HI USE ENG TEMP HI AIR 1 1. Air Switch - blue/amber FORWARD OVERHEAD PANEL This switch is an alternate action switch that opens and closes the load bleed valve. ON - Illuminates blue when the valve is selected open. DB USE ENG AIR - Illuminates amber when the air switch is on and cabin differential pressure is more than 1.3 psi. If air is desired for engine start, this switch must be pushed prior to pulling the ENG START switch. NOTE: When the air system is in auto mode, the 1-2 and 1-3 isolation valves are automatically controlled. MD-11 [Auxiliary Power Unit] Page 9

10 Data Window N EGT 485 N2 100 OIL CAG(IGDS) 1. N1 Readout - white/red N1 - White digits turn red and are boxed in red if limits are exceeded (displayed in percent). 2. N2 Readout - white/red N2 - White digits turn red and are boxed in red if limits are exceeded (displayed in percent). 3. OIL Readout - white/amber OIL - White digits turn amber and are boxed in amber if oil quantity (quarts) is low. 4. EGT Readout - white/red SYSTEM DISPLAY (SD) PANEL LB EGT - White digits turn red and are boxed in red if limits are exceeded (displayed in degrees centigrade). NOTE: data appears on the SD only when the secondary engine display is selected and when start cycle is initiated. MD-11 [Auxiliary Power Unit] Page 10

11 External Control Panel - 3 Bottle SERVICE LIGHT FIRE AGENT 1 LOW AGENT 2 LOW AGENT 3 LOW 1 DISCHARGE AGENT ARM FIRE AGENTS 2 DISCHARGE 3 DISCHARGE SERVICE INTERPHONE HORN NORMAL NORMAL NORMAL NORMAL FIRE NORMAL ON 1. ARM AGENT 2. DISCHARGE ANY FIRE AGENT SERVICE LIGHT LOOKING UP, AFT OF LEFT WHEEL WELL WARNING: Fire warning horn is very loud. Wear ear protection. NOTE: This panel is described in the Fire Protection chapter. MD-11 [Auxiliary Power Unit] Page 11

12 Maintenance Panel WINDSHLD TEST L R WINDSHLD TEST WINDSHLD TEST HORN TEST 1 TEST TEST 2 DOOR PITOT HEAT OPEN OVRD ANNUN LT TEST RIGHT OBSERVER'S STATION CAG(IGDS) 1. HORN TEST Button Maintenance use only. Tests horn. 2. Door Switch - amber Maintenance use only. When pushed, opens door. OPEN - Switch illuminates amber when door is open. LB MD-11 [Auxiliary Power Unit] Page 12

13 .40 -Alerts NOTE: The associated cue switch is shown in parenthesis (XXX) following the alert. Red Boxed Alerts (Level 3) FIRE (ENG) - fire or air manifold fail conditions in compartment. Amber Boxed Alerts (Level 2) GEN (ELEC) - generator is off (manual mode). Amber Alerts (Level 1) AUTO SHUTDOWN (ENG) - The has automatically shut down. DOOR DISAG (ENG) - The inlet/exhaust door position is not in the commanded position. FAIL (ENG) - The has automatically shut down due to a failure. A restart should not be attempted. FAULT (ENG) - There is a fault in the control circuit. operation may not be affected. FIRE AGENT LO (MAINT) - The dedicated fire bottle has low pressure. Applies only if 3rd bottle is installed. FSO NOT CLSD (FUEL) - The fuel shutoff valve did not close following normal or emergency shutdown. FUEL PRES LO (ENG) - fuel pressure is low. MAINT DOOR (ENG) - The DOOR switch on the upper maintenance panel is in the OPEN position and the inlet door is open. STARTER FAULT (MAINT) - An starting system fault exists and the should not be started. If is already running, may continue to operate. EPGS FAULT (MAINT) - A fault exists in the SMOKE switch circuit, an generator fault exists, or a generator (engine or ) auto reset has been used. GEN (ELEC) - The generator has been automatically turned off by the electrical system due to a fault or the FIRE handle has been pulled. MD-11 [Auxiliary Power Unit] Page 13

14 SEL AIR (AIR) - air switch is on and cabin is pressurized. Cyan Alerts (Level 0) AIR ON - bleed air load valve is commanded open and the is providing air. AIR/ELEC ON - is providing air and electrical power. ON - The is running, but not providing air or electrical power. POWER AVAIL - electrical power is available, but not powering any buses. POWER ON - electrical power is connected to at least one of the three buses. MD-11 [Auxiliary Power Unit] Page 14

15 .50 Components -Functional and Subsystems Schematic AGENT DISCH ENG/ FIRE TEST FIRE MISC SYSTEMS CONTROLLER START/STOP CMD FUEL DOOR FAIL START/STOP CMD ON/ STATUS IMMEDIATE SHUTDOWN PULL/TURN 1 2 START/ STOP ON GEN RESET ELECTRIC POWER CONTROL UNIT (EPCU) FUEL DOOR GEN FAIL GEN AP PWR ON AVAIL (ELECTRICAL PANEL) FUEL SUPPLY FUEL FIRE SHUT VALVES START/STOP CMD ON OPEN/CLOSE USE ENG AIR LOAD BLEED VALVE (AIR PANEL) DEUs N1, N2, EGT OIL QTY ELECTRONIC CONTROL UNIT (ECU) / AGENT ARM IMMEDIATE SHUTDOWN LOAD BLEED VALVE IGNITION UNIT (EXTERNAL PANEL) IGNITER ELECTRONIC FUEL CONTROL UNIT (EFCU) OIL LEVEL SENSOR BATTERY M STARTER MOTOR PNEUMATIC BLEED N1, N2 SPEED EGT LOW OIL PRESSURE SWITCH HIGH OIL TEMP SWITCH GENERATOR DB A MD-11 [Auxiliary Power Unit] Page 15

16 Pneumatic Supply AIR CONDITIONING PACK 2 AIR CONDITIONING PACK 1 TRIM AIR PRESSURE REG VALVE AIR CONDITIONING PACK 3 PACK 2 FLOW CONTROL VALVE PACK 1 FLOW CONTROL VALVE PACK 3 FLOW CONTROL VALVE ENGINE 1 N1 SPEED COMMAND SIGNAL ELECTRONIC CONTROL UNIT AIR CONDITIONING CONTROLLERS ENGINE 2 CHECK VALVE LOAD BLEED VALVE ISOLATION VALVES ENGINE 3 MD-11 [Auxiliary Power Unit] Page 16