Ni-cad Battery Advantage
Holds a charge for a longer period of time
Disadvantages for a Ni-cad Battery
Thermal runaway- where the battery accepts too much charge and quickly overheats.
Power memory- tends to not become fully charged and reduces the efficiency of the battery.
Purpose of the Back-up Battery?
Power the standby attitude indicator and protect voltage sensitive equipment.
Define first stage autotransfer.
Automatic shedding of ALL normal buses during an electrical abnormality. Only the Emergency buses are being powered by the Aux Generators.
Battery Emergency Contactor is closed. Charging the battery off of the Aux Gens.
Four conditions for autotransfer.
- 1. Power Select switch in battery
- 2. At least one main gen switch in the ON position
- 3. Both main gen contactors open
- 4. 3-5 second delay
Items retained in 1st stage autotransfer.
- N- Nav 1 and 2
- A- AHRS 1 and 2
- T- T6 gauges
- T- Torque gauges
- H- Hot batt bus items
- A- Audio panels 1 and 2
- N- Nose wheel steering
- I- Inverter 2
- E- EFIS 1 and 2
- L- Left landing light
- S- Stall warning computer 1
- A- ADF 1
- S- Stick shaker 1
- S- Stick pusher 1
Important items LOST in 1st stage autotransfer.
- Normal flap operation
- Autopilot/ FD
- Engine gauges (except T6 and Torque)
- Fuel flow and quantity gauges
Define second stage autotransfer
Loss of all engine driven generators. Battery is supplying power to Emergency buses (approx 30 min.)
Some items kept in second stage autotransfer.
- C- Comm 1
- A- ADF 1
- T- Transponder 1
- S- Standby attitude indicator
- I- Inverter 2
Two major items lost in second stage autotransfer.
EFIS and AHRS
Define third stage autotransfer\
Where the electrical system drops below 19V, all contactors are open. Only the Back-up Battery is powered.
Useful instruments in third stage autotransfer
- Standby attitude indicator
- Mag compass
- Gear free fall only
What are the lights that indicate autotransfer?
6 pack + 1
- CENTRAL BUS OFF
- BATTERY OFF BUS
Inverter #1 INOP
What checklist do you call for in autotransfer?
There is no 'Autotransfer Checklist." Call for the Main Generator Failure checklist.
After completing the Main Generator Failure checklist (both main gen switches off, and electrical emergency switch in EMERG), how can you take yourself out of autotransfer?
Bring the Electrical Emergency Switch back to NORMAL. The 4 requirements for autotransfer are not met. Main gens still offline and batt emerg contactor open (aux gen not charging battery).
What is the purpose of the Electrical Emergency Switch?
Bypasses the requirements for autotransfer.
What dose the TRANSFER FAIL light indicate?
Transfer contactor failed to change position (stuck, broken). The Aux generator is not powering the system, battery being depleted.
What might you do if the TRANSFER FAIL light illuminated?
Try to force it to close with the Electrical Emergency switch to EMERG. If unsuccessful, call for the Loss of All Engine Generators checklist.
What is a Soft Transfer?
When the system losses ALL engine driven generators (main and aux) with the APU gen supplying power. Battery Contactor opens but Battery Emergency Contactor closes.
If APU gen fails, system goes strait to second stage autotransfer.
What does post-mod mean in regards to the electrical system?
Emergency Bus Contactor 2 is closed and Emergency Bus Contactor 1 is open. They work opposite of each other, to ensure that there is always power to the emergency buses.
@ 50% Nh
- 1. Start contactor opens
- 2. Ignition circuit deenergizes
- 3. HMU return solenoid closes
What do the inverters do?
Convert DC power to AC power
Inverter INOP light
The 115 VAC and the 26 VAC side have failed or the switches are OFF.
Why dose the #1 Inverter automatically switch when the 115VAC side fails?
The Transfer Controller is connected to the 115V side. No lights just transfers.
Why wont the #1 Inverter automatically transfer when the 26VAC side fails?
The 26 VAC side doesn't have a transfer controller. No checklist availible so you have to switch off Inverter 1 so #2 can takeover.
GPU AVAILABLE light
Will illuminate when the GPU is plugged in and on. May not be supplying the correct power.
Should be supplying 28VDC at 1600 amps intermittently and 1300 amps continuously.
Will external power charge the battery?
No, with the Power Select Switch in EXT PWR the battery contactor is open.
Engine start sequence
- 1. Start contactor closes
- 2. Ignition circuit is energized
- 3. HMU Return Solenoid opens
Starter/ Gen GCU: Voltage regulation
Controls the generator field to a constant output of 28.5VDC
Starter/ Gen GCU: Paralleling
Provides equal load division between two or more generators within 10%.
Only parallels the Main gens and the APU gen.
Starter/ GenGCU: Field weakening
Disables over current protection during engine start, otherwise the engine would abort every time.
Stater/ Gen GCU: Reverse current
Prohibits electrical current from flowing the wrong direction.
Starter/ Gen GCU: Overspeed protection
Prevent the starter from accelerating to fast when unloaded due to shaft shearing.
Starter/ Gen GCU: 50% Nh cancellation
Discontinues the start cycle when engine reaches 50% Nh.
Starter/ Gen GCU: Overvoltage protection
Starter/ Gen GCU: Overcurrent protection
- At 500 amps:
- 1. 3-5 second delay
- 2. Opens respective Gen contactor
- 3. Opens respective bus tie
- 4. Opens Batt contactor
Starter/ Gen GCU: Current limiting
400 amps normally, 600 amps during cross generator starts.
Starter/ Gen GCU: Overexcitation protection
Disables the generator for 5 seconds minimum when reaching 29.5VDC and not paralleling withing 15%.
Starter/ Gen GCU: Autotransfer
Automatic shedding of all normal buses during an electrical abnormality.
- 1. Power Select switch in Battery
- 2. Both main gen contactors open
- 3. At least 1 main gen switch on
- 4. 3-5 second delay
Aux Gen GCU: Voltage regulation
Aux Gen GCU: Overvoltage protection
Aux Gen GCU: Undervoltage protection
23V or less
Aux Gen GCU: Overexcitation protection
Disables generator for 5 seconds minimum when reaching 29.5V and not paralleling with 15%.
Aux Gen GCU: Anticycle protection
Aux Gen GCU: Underspeed protection
Trips generator contactor when below 70% Np
Aux Gen GCU: Overcurrent protection
At 220 amps
Aux Gen GCU: Paralleling
Provides equal load division between the two Aux gens with in 10%.
The Aux gen GCU's dont provide...
Autotransfer control or canceling of the start sequence
EEC Control Function: Slower Deceleration
EEC directs enough fuel through the torque motor to allow engine to slow down without causing a flameout.
EEC Control Function: Faster Acceleration
EEC directs enough fuel trough the torque motor to prevent a compressor stall when a lot more fuel is needed (ie: go-around).
EEC Control Function: Fixed Torque Climb
As altitude increases the P3 servo and sensor closes. To maintain the selected torque more fuel must be added after the P3 servo and sensor.
EEC Control Function: Np Fuel Governing
With the condition levers in MIN or MAX the EEC will add or reduce fuel to maintain a constant Np on the ground.
EEC Control Function: HMU De-enrichment Solenoid
Leans the HMU fuel schedule at 14000' so the the EEC can continue to add fuel.
What is the 14k switch?
It energizes or de-energizes the HMU De-enrichment solenoid at 14000' leaning the HMU fuel schedule.
What is the 10k switch?
Alerts when the 14k switch failed to de-energize during descent.
Fuel schedule too lean for lower altitudes.
What will happen when the 10k switch alerts that the 14k switch has not de-energized?
- 1. 3 chime alert
- 2. Red EEC caption on glareshield
- 3. Aural warning "Engine Control"
The EEC WILL NOT automatically revert to manual
What is 'Failed Fixed?'
If a peripheral of the EEC fails when below 14000' the EEC will not revert to manual. Instead, the torque motor freezes where it is, preventing engine spool back during takeoff.
What happens if the EEC fails above 14000'?
It will revert to manual mode, closing the torque motor, allowing only the fuel metered by the HMU to the engine.
When conducting the HMU Solenoid test and the Nh drops below 50% with the packs and bleeds off, what can you conclude?
The HMU De-enrichment solenoid is still energized.
Where dose the torque gauge get its information?
The torque sensing unit measures the angular deviation between the torque shaft and the reference shaft teeth and sends that information to the SCU and then on to the gauge.
Information from the torque sensing unit is used for?
- 1. Toque gauge
- 2. EEC input
- 3. Autofeather
What does pre-mod mean with respect to the engine bleed air system?
The engine bleed valves fail to the closed position.
Why does the hydraulic reservoir need to be pressurized?
To prevent air bubbles in the system.
Solid aluminum spar covered with a fiberglass shell filled with low density foam.
A nickel sheath leading edge starts at the 42" station to the tip and a a rubber abrasion resistant sheath covered with a film start at the root down to the 42" station.
Governor operating ranges
- Primary- 80-101%
- Overspeed- 101- 103%
- Fuel Topping- 103-109%
How is the aux oil tank filled?
By the oil pump on the TMM.
- S- Starter gen
- C- Centrifugal breather
- O- Oil pump
- F- Fuel pump
- S- Scavenge pump
What dose the BETA valve do inflight?
Sets the primary low pitch stop (17.6o) to prevent overspeed due to low air resistance at low blade angles (hydraulic stop).
At 17.6o the BETA valve shifts and allows continuous loop of oil back to the Reverse Valve, limiting the metered oil to the servo piston. This allows supply oil to maintain a higher blade angle.
What does the BETA light inflight indicate?
Primary Low Pitch Stop has failed, the blade angle is at 12.6o.
What two conditions must be met to get the BETA light inflight?
- 1. Power lever micro switch (at FLT IDLE)
- 2. 12.6o blade angle
What happens when the Secondary Low Pitch Stop activates?
The Flight Low Pitch switch senses that the blade angle is 12.6o via the servo piston and activates the Electric Feather Solenoid. This drains the metered oil, allowing supply oil to increase blade angle.
What will happen after the Flight Low Pitch switch activates the Electric Feather Solenoid?
The Flight Low Pitch switch will no longer be satisfied and deenergize the Electric Feather Solenoid reapplying metered oil. This will pinball, causing the BETA light to flash. Propeller blade angle is moving back and forth up to the 12.6o limit.
Once power is reapplied this will disappear; the power lever microswitch is no longer satisfied and the blade angle is not 12.6o.
Reverse Valve operation
On the ground with the power levers in ground idle or reverse, the Reverse Valve opens up to the supply oil. This applies greater pressure to the servo piston on the 'metered' side moving the servo piston forward causing a blade angle decrease or go into the negative angles.
BETA valve operation on ground
On the ground the BETA valve controls blade angle. A power lever linkage adjusts the inner piston (drain) back to the Reverse Valve. If the power levers are moved forward (blade angle increase) this sets the inner piston and reduces metered oil to the servo piston, commanding a blade angle increase.
The follow up arm (connected to the servo piston) adjusts the outer piston until the drain oil equalizes with the metered oil to maintain the selected blade angle.
Flight Idle Blade Angle
Ground Idle Blade Angle
Feather Blade Angle
What is an indication that the the propeller system has pitch lock gaped?
When power lever changes change Np like a fixed pitch propeller.
What does the Electric Feathering switch do?
Activates the Aux Oil Pump (820psi) and opens the Electric Feathering Solenoid to drain metered oil.
Prop Aux Pump Test
- Aux pump buttons:
- With the power levers in reverse it sends supply oil to the POG, LSV, and through the RV. This sends supply oil to both sides of the servo piston, decreasing the blade angle.
- Electric Feather Switch:
- Supplies oil to the same places but it energizes the Electric Feathering Solenoid, draining the oil from the RV and the servo piston increasing blade angle.
What is a hydraulic fuse?
They are downstream of the anti-skid/brake valves and prevent excessive hydraulic fluid leaks should one occur downstream of the fuse.
What is the shuttle valve in the braking system?
One on each brake assembly and discriminates between normal and emergency braking.
Should a wheel start skidding (ie: left outboard), the system reduces the fluid pressure to that brake and to the corresponding brake on the other side. This allows the wheel to continue spinning and prevents asymmetrical braking.
Maximum normal brake pressure?