How to Master APU System – ATA 49

APU General

• The APU Can Be Started On The Ground And In The Air To Its Maximum Certified Altitude. (43100 feet Altitude)
• The APU Will Start If All Pumps Not available From The Ground Till 14000 Feet
• The APU Supplies Electrical Power Only.
• The APU Is Equipped With Fire Detection And Protection, The Nose Wheel Has External Controls To Manually Shutdown The APU OR Fight An APU FIRE On The Ground.

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APU Description

• Two High-Capacity Starters/Generators (L & R), Either Of The Units Operates As A Starter, But Once The APU Is Running Both Operate As Generators. Once APU Power Is Provided It kicks Of All External Power But Does Not kick Off Engine Generator Power.

• Either Starter/Generators Are Powered By External Power OW The Engine Generator. If Both Not Available, The Right Starter/Generator will Be Used And Will Be Powered By The APU Battery.

• All Fuel pumps Can Be Configured To Feed The APU, Normally The Left AFT Fuel Pump Is The Normal Supply Source Of Fuel To The APU. The Pump Operates Automatically Regardless Of The Fuel Pump Switch Position. (The PRESS Light In the Switch Goes Out)

• If AC Power Is Not Available, A DC Pump In The Left Main Tank Will Supply Fuel to The APU Until AC power Is Available.

• The OFF Position Is Used for APU Shutdown And Resets Any Auto Fault Logic.

• The ON Position (Opens The Fuel Spar Valve, Opens the Air Inlet Door, Activates The Appropriate Fuel Pump And Powers The APU Controller)

• Below The Selector Is A Fault Light Which Illuminates Momentarily During The APU Controller Self-Test, An APU FAULT OR FIRE Is Detected, And During An APU Auto Shutdown.

• To Start, Rotate The Selector To Start And Release It Back To ON.

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APU AUTO SHUTDOWN

if The APU Fails, The APU Shuts Down Automatically And An EICAS Advisory Message APU SHUTDOWN is Displayed. (Moving The APU Selector From ON To OFF Clears The Message).

APU Battery Is Designed For Two Consecutive Stars, With A 5-minute Cooling Period.

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Attended Mode

• Either ENG Starting or Running,
• In Flight

APU Attended Mode Auto Shutdown

• APU FIRE/Inlet Over temperature

• Overspeed/Loss of Overspeed protection

• APU Controller Failure

• Speed Droop

• APU Start Failure (NO Rotation, or Acceleration)

• APU Air Inlet Door Failed Closed

Pilot Action Required

• High EGT

• High Oil Temp

• Low Oil Pressure

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Unattended Mode

On The Ground In All Other Configurations

APU Unattended Mode Auto Shutdown

• APU FIRE/Inlet Over temperature

• Overspeed/Loss of Overspeed protection

• APU Controller Failure

• Speed Droop

• APU Start Failure (NO Rotation, or Acceleration)

• APU Air Inlet Door Failed Closed

• Generator Oil filter Approaching Bypass

• High EGT/Loss of EGT Signal

• High Oil Temp

• Low Oil Pressure

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Aircraft Batteries And Functions To The APU

APU Battery

• APU Controller Commands (Ignition & Fuel)

• APU Air Inlet Door

• Right Starter Generator (If Required)

Main Battery

• APU Spar Valve

• DC Fuel Pump

• Fire Detection System

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APU Start

Starting The APU Immediately On An Unpowered Aircraft, And By Selecting the APU Battery ON, There Will Be A Delay In Start. The APU Controller Waits Until The Common Core System (CCS) Applications Are Available, This Is Because the CCS Fire Detection And Fuel Management Applications Are Necessary for Start. After Switching The APU Battery ON, Wait For The CDU To Display. Once displayed is an indication of the CCS Applications Available, Then You Can Start The APU.

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Starting Sequence

• The APU Controller Commands The Air Inlet Door To Open
• The Left AFT Fuel Pump Will Automatically Run, And The PRESS Light Switch will Go Out
• If No AC Power Available A DC Pump Automatically Runes Until AC Is Available.
• The APU Is Designed To Operate with No Pumps From Ground Till 14000 feet
• When The APU Is Up To Speed (95% Of Target Speed + 2 Seconds), The APU RUNNING Memo Is Displayed On EICAS

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APU Start Details

• After The APU Reaches The Proper Speed, The APU Controller Commands Ignition And Fuel
• At 50% RPM, The Starter Disengages And Ignition Is Turned OFF.
• When the APU Reaches 95%+2 Sec, The EICAS Memo Message APU Running Is Displayed

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Shutdown Sequence

• Normal Shutdown Of The APU Initiates a Cool-Down Period of Two Minutes Cool-Down Cycle And An APU COOLDOWN Memo Message Is Displayed. At Any Time During the Cool-Down Period, the APU May Be Returned To it’s Running Condition By Placing The APU Selector Back To ON. After the Cool-Down, The Shutdown Sequence Is Automatic, And The Memo Message Will Blank.

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Automatic Start Up Of The APU

• The APU Will Start Automatically During flight, Regardless Of The APU Selector Position if Three OR More Variable Engine/Starter Generators Fail OR Go Offline. If The Condition That Caused The Start Is No Longer Valid, It Can Be Shutdown By Positioning The Selector First To ON Then OFF.

NOTE: Even If The Condition That Caused The Automatic Shutdown Is Still Valid, The APU Can Be Shutdown Manually By Pulling The APU Fire Switch

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