Electrical Problem on Long Haul???

[KevinAu 441]

An interesting story was in our union magazine just recently. A 757, on a flight from Anchorage to Seattle suffered a complete electrical failure at 3AM over the Pacific Ocean. They had departed Anchorage with an MEL'd rightside IDG. An hour and twenty seven minutes into the flight, the leftside IDG also failed. The APU was running all this time and picked up the entire load immediately. Twenty minutes later, while they were in discussions with MX, the APU overheated and initiated an autoshutdown. Unfortunately, the HMG failed to kick in. Now they were left with just the peanut gauges and one cockpit lightbulb. The captain immediately turned the aircraft towards Ketchikan, about 120 miles away at their nine o'clock, from what he remembered from his last glance at the ND. Anchorage Center had lost radar contact since their transponder had stopped by that time and could offer only moral support. Ketchikan was 30 minutes away and the batteries are good for only 30 minutes. The captain decided to take a risk and restart the APU. Fortunately it started and stayed running, bringing everything back online. The aircraft proceeded to land unevenfully at Ketchikan. The passengers had no idea anything was wrong except for a few minutes of dark cabin and a much earlier landing than expected.

[marcom 139]

Are you sure it was a 757?I never knew 57' had HMG's. Only 67 have 'em as far as I know.Apart from that, pretty scary!Bat power doesn't really help you over the atlantic, as you only have one VOR and one ILS reciever avialable for navigation...As far as the APU start is concerned, according to the books, 3 starts are allowed in one hour. If it hadn't started for the 3rd try, (I don't want to continue this sentence)

[KevinAu 441]

Our 752s, 762s, and 764s are all equipped with HMGs. Our 753s are not. In the article, the hero felt that he was going a bit "outside the box" by trying to restart a failed APU and would just be risking further drain of the main battery.

[marcom 139]

Don't know for sure, but doesn't the APU use the APU battery for starting aswell as the left aft fuel pump? Also, if the main battery is dead, the backup instruments can not be supplied by the APU battery thus there is no real risk in starting the APU.

[KevinAu 441]

Yes it does. He was afraid that if there was not enough juice in the APU battery, that he would drain the main battery. Either way, I agree that the calculation of risks and benefits definitely point towards giving the APU one more try.

[Guest Ian_Riddell]

"Don't know for sure, but doesn't the APU use the APU battery for starting aswell as the left aft fuel pump? Also, if the main battery is dead, the backup instruments can not be supplied by the APU battery thus there is no real risk in starting the APU."Wouldn't the 757 be like the 767, guys?The 767 uses the APU Battery for cranking the APU (starter motor). This is high current stuff and will drain the battery rapidly. The Main Battery also cops a fair amount of abuse during APU start. It has to provide power to the APU Controller (computer), the DC fuel pump and the APU fuel valve during APU ops (until the APU generators kick in).... as well as all the normal emergency stuff. Here's the full list of things that the 767's Main Battery may have to cope with (although not all of these will be operating at once, there may be loadshedding... and some may not need to be used at all):BATTERY POWER DISTRIBUTION(C829 (Sec))Food Chiller Shutdown ControlL Engine Generator Control UnitR Engine Generator Control UnitAPU Control UnitLeft Engine Generator Drive DisconnRight Engine Generator Drive Disconn(Elec) Bus Power Control UnitStandby Power ControlDC Bus Tie ControlHydraulic Generator Control (HMG control)Ram Air Turbine- Auto circuitsBattery Current Monitor PowerAltn Gear Extension Motor(C897)ACARS DC PowerLeft Clock TimebaseRight Clock TimebaseL IRSR IRSC IRSEquip Cooling Ground WarningFire Extinguishing- Cargo Bottle 2Fire Extinguishing- Left Engine Bottle 1Fire Extinguishing- Right Engine Bottle 1Fire Extinguishing- APU 1Fire Extinguishing- Cargo Bottle 1Fire Extinguishing- Left Engine Bottle 2Fire Extinguishing- Right Engine Bottle 2Bus Tie EnableBattery Overheat ProtectionCenter Bus ControlFuelling ControlDefuel ValvesFuelling QtyFuelling ValvesLeft Spar Fuel Valve/ Reset BRight Spar Fuel Valve/ Reset BAPU Fuel ValveRam Air Turbine- Manual ControlParking Brake ValveStby Bus OFF Light/Batt VoltmeterBATTERY POWER DISTRIBUTION(BAT Primary)Passenger AddressInterphone- Cabin ServicesInterphone- Capt/ObserverInterphone- F/OTrim AirEquipment Cooling- OvrdPack Flow Control- RFire Detection- Cargo 1Fire Detection- Left Engine 1Fire Detection- Right Engine 2Fire Detection- APU 1Fire Detection- Left Engine 2Fire Detection- Right Engine 2Fire Detection- APU 2Fire Detection- Cargo 2Overheat Detect- Left Engine 1Overheat Detect- Left Engine 2Overheat Detect- Right Engine 1Overheat Detect- Right Engine 2Fire Switch UnlockAPU Remote Fire IndicationWheel Well Fire IndicStab Trim AlternateFuel Qty 1Fuel- DC Pump ControlFuel- DC Pump PowerForward Fuel Crossfeed ValveAft Fuel Crossfeed ValveCrossfeed IndicLeft Engine Hydraulic Pump SupplyRight Engine Hydraulic Pump SupplyHydraulic Air PumpProbe Heat Indic RAnti-Ice WindAnti-Ice R Engine AltnAir-Ground Sys 1Antiskid 2-6Antiskid 3-7Indic Lights 3Left Alternate Emergency Lights/Off Wing EscapeIndic Lights 1Indic Lights TestIndic Lights 2Right Alternate Emergency Lights/Off Wing EscapePassenger Oxygen LeftPassenger Oxygen RightPassenger Oxy ControlPassenger Oxy CenterPassenger Oxy Manual DeployBleed Isolation Altn Control RightFlush Control Lav Sys 1&2APU Altn ControlEngine Speed Sensor L2Engine Speed Sensor R2Engine Speed Sensor L1Engine Speed Sensor R1Left Engine Fuel Control Valve/Reset ARight Engine Fuel Control Valve/Reset ARight Engine Thrust Reverser Indic - AltnRight Engine Thrust Reverser Control- AltnLeft Engine Thrust Reverser InterlockRight Engine Thrust Reverser Interlock-AltnLeft Engine Start ControlRight Engine Start ControlStandby Engine IndicatorSTANDBY POWER DISTRIBUTION(115Vac)Warning Elex BLeft VOR/Marker ReceiverLeft Air Data ComputerLeft ADFLeft RDMIStandby Equipment CoolingWheel Well Fire/Duct Leak 1Standby Bus ACFlap Slat Electronics Unit 1 ContFlap Slat Electronics Unit 1 SensorStandby Instrument LightingMain Panel FloodlightsEngine Standby Ignition 1Engine Standby Ignition 2Flap/Stab Position Sensing (Center)Flight Control Electronics 2L (AC)Flight Control Electronics 1L (AC)Cabin AltimeterCabin Differential Pressure IndicCenter Multi-Mode Receiver (GPS and ILS)(28Vdc)Auto Flight WarnLeft VHF CommLeft Aural Warning SpeakerLeft Clock IndicStandby Altimeter VibratorStandby ILS IndicStandby Attitude IndicEFIS Display Switch LLeft Pack Flow ControlCabin Altitude Control- SelectForward Overboard Valve (Cabin Pressure)Cabin Altitude Control- ManualLeft FMS SwitchStandby Bus DCCat III Bus Isolation- BatterySlat Position IndicFlap/Slat Position IndicAileron Lockout (Left)Aileron Lockout (Right)Rudder TrimLeft Stick ShakerProbe Heat Indication (Left)Anti-Ice - Engine LeftLights- Emer Charger- PortableFlood Lights- Aisle StandBleed Air Isolation Valve Cont LeftEngine Thrust ReverserLeft Engine Alternate Thrust Reverser ContStab Trim Shutoff (Left)Stab Trim Shutoff (Center)Flight Control Electronics 2L- DCFlight Control Electronics 1L- DCYaw Damper LeftLeft Engine T/R SSL ControlADC Source Select Relay (Left)Sounds like your average car battery would go flat pretty soon with all this going on :-)Cheers.Ian.

[Guest]

Sounds similar to the SABENA flight over the Atlantic ages ago.Timothy