Eric "skyhawk" Reynolds vs. Bruce the big man Flashcards
What redundancy is built into a large aircraft electrical system?
Multiple systems
What type of electricity can be found on large aircraft?
AC and DC
Which form of electricity is more common on aircraft? Why?
AC
Alternators are lighter weight for same output
What is the general configuration of an aircraft electrical system?
What are the three types?
AC circuit powered by an alternator on each engine feeding a BUS.
Split
Parallel
Split/Parallel
Describe the split BUS system? What options are available in an engine failure?
Generator 1 will power BUS 1 in normal ops
Aircraft usually split into Left/Right side circuits on each BUS
Can be linked manually to BUS 2 in an emergency
Describe the Parallel BUS system
All generators are tied to a common BUS which powered all circuits
Describe the Split/Parallel BUS System
- Usually found of 3/4 engine aircraft
- Left hand engine generators work in parallel to supply Left BUS
- Right hand engine generators work in parallel to power Right BUS
What are the advantages of AC?
- Lighter weight for same power output
- Alternators produce more current per RPM
- Can be rectified to produce DC, or provides AC
- Can be transmitted long distances more readily
- Circuit breaker operate better under high loads at high altitudes
What is an Electrical BUS?
A common bar, off which several electrical components or systems can be powered
This allows circuits to be prioritised based on which BUS they are connected to if there is a supply breakdown
How can AC be produced from DC? In what circumstance would this be required?
An inverter can off a DC generator
A Static inverter can produce AC off a DC battery
most common in an emergency
What must happen before AC generators are connected in parallel?
Output voltage, frequency and phase rotation must be the same
When is emergency lighting required?
What are the requirements of the emergency lighting system?
- After a total power failure
- In an emergency evacuation
Needs to be armed
Automatically activated after failure of primary lighting power
What things can aircraft lighting systems illuminate?
Cargo compartments
Pilot instrument panel
Passenger cabin
External poisiton and landing lights
What does CSD stand for? What is its purpose?
Constant Speed drive
A unit that allows the Alternator to always have a constant speed, allowing it to output 400Hz electricity
Describe the CSD? how does it work?
Hydromechanical drive similar to a car gearbox
- Mechanical governors maintain constant output
- Fine adjustments made by frequency controller
- Constant speed function is similar to the function of a propeller system
- Has a fixed displacement and variable displacement hydraulic pump
- Independent oil system
What are the components of the Constant Speed Drive unit?
Input shaft Hydraulic unit (variable & fixed displacement hydraulic pumps) Differential unit Control cylinder Governor Output shaft
What system is incorporated into the CSD unit to account for a generator or gearbox malfunction? What switch will activate this system?
- GEN DISC switch in cockpit opens solenoid
- Dog clutch opens and will break drive between engine and gearbox
- Cannot be reset in flight
*Prevents having to shutdown the engine to prevent the system from malfunctioning
What is the Airbus vs Boeing terminology for the CSD?
B: Integrated drive generators (IDG)
A: Integrated constant speed drive (ICSD)
What areas does the cabin a/c and pressurisation system provide air to? why?
=Cabin and Cockpit - to heat and cool and provide pressurisation
=Cargo compartments - pet often travel in these
=Avionics and equipment bays - to prevent condensation after heat build up
What is PD? Why does it exist and how does it change as the aircraft altitude increases?
Pressure differential - exists because the cabin altitude is set to 8000ft
As altitude increases past 8000ft the pressure differential will increase
How can pressure differential be controlled?
A rate controller controls the outflow of air from the fuselage based on pilot settings and altitude
Outflow rate is maintained at a lower rate than the air conditioning inflow until desired PD is reached
What controls the vertical speed of the cabin
Rate controller - it is the same as controlling the pressure differential
What pressure differentials can be expected on a light piston, a large piston, or a jet transport aircraft?
Light piston: 3-5 psi
Large Piston: 5.5
Jet transport: 9psi (aim is for 8.9)
What controls the position of the outflow valve?
Cabin pressure controller
Manually or automatically controlled
How can a typical environmental system be controlled? What selections can be made?
Cockpit control panel:
Simple system: Off, normal or Ram air selections
Modern system: temperature control for different zones with actual temp indications also given. Can have different temperatures the cockpit and cabin
What elements are incorporated into the cockpit control panel of the environmental and pressurisation system?
- Provision for duplicated systems
- If APU has capability, its selector
- Controls & Emergency controls
- Instrumentation
- Warning lights associated with CWS
- Baro Pressure selector
- Landing altitude selector
What safety valves are part of the environmental and pressurisation system? How does each work?
- Outflow valve (pressure control valve in normal ops)
- Pressure relief valve (operates automatically)
- Negative pressure valve (automatically stops cabin alt being higher than aircraft alt)
- Emergency depressurisation valve (operated by WoW switch or activated through cockpit controls)
- Emergency cabin altitude control
What is the location of:
- Negative pressure valve
- pressure relief valve
- emergency depressurisation valve
- emergency cabin altitude control
- emergency depressurisation control
- Cabin pressure control valve
- Negative pressure valve: Rear of aircraft
- Pressure relief valve: Rear of aircraft
- Emergency depressurisation valve: fuselage behind cockpit
- emergency cabin altitude control: cockpit
- emergency depressurisation control :cockpit
- Cabin pressure control valve: Central fuselage in middle of wing
Describe how the vapour cycle air conditioning works
- Continuous cycle
- Refrigerant absorbs latent heat from cabin air
- Refrigerant temp does not change but changes state from liquid to gas
- Refrigerant is now in gaseous form and flows to a heat exchanger outside the aircraft.
- Refrigerant releases latent heat and becomes a liquid again
- Process repeats
What is the most common refrigerant used in air conditioning systems? Why?
Di-chloro-di-fluro-methane (called Refrigerant 12, R12, Freon 12)
- Stable at high and low temps
- Does not react with materials in system
- Colourless
- Practically odourless
What are the 2 oxygen delivery systems in use on aircraft and what are the advantages of each?
Continuous flow system:
- Simplest
- Automatically actuated
- Immediate and continuous flow of O2
Pressure Demand system:
- Delivers oxygen in response to user breathing suction
- Prolongs O2 supply
- Diluter demand regulator dilutes O2 with suitable amount of atmospheric air
- Dilution ratio adjustable in case of smoke/contaminants
What are the limitations of the Pressure demand O2 system?
-Dilution with atmospheric air limited to 34,000ft or below
What are the advantages of chemical Oxygen systems compared to gaseous oxygen?
- Requires less space
- Less equipment
- Less maintenance
What are the disadvantages of chemical oxygen systems compared to gaseous systems?
- Higher fire hazard
- Not tamperproof
- Won’t turn off
What fire protection systems are usually included on large transport aircraft?
Fire detection
Overheat detection
Smoke detection
Fire extinguishing system
How does an automatically fired fire extinguishing system work? Where are they normally located?
Some cargo compartments and toilets
- Fire bottle fitted with eutectic head (also called squib)
- Squib melts at 70-75˚C
- Melted squib allows extinguishing agent to exit the bottle
- Bottle discharges into a line which is sprayed into the compartment
What are the 4 types of extinguishing agent? How does each one work?
Water: cools fire, excludes Oxygen
Carbon Dioxide: Displaces Oxygen in atmosphere
Dry Chemical: Smothers fire/excludes oxygen
Halogenated Hydrocarbons (freon): Chemically interferes with combustion
What is a halogenated hydrocarbon (freons)?
Low toxicity airborne fire extinguishing agent
Freon type is a successor to CO2 extinguishers
What are the advantages of Halogenated hydrocarbons as an extinguishing agent?
- Low concentration is effective (allows people to still breath, 2% concentration vs 40% in CO2)
- Can be used in occupied pax compartments
- Effective on all 3 types of fires
- No residue remains after use
Describe the thermal loop switch? What type of electricity is provided?
- 28V DC applied to both paths of thermal loop switch
- If fire occurs, wires will expand
- Contact between loops will close the circuit to ground
- Thermal loop switches arranged in parallel
What happens to the fire detection circuit at other points if a fire is only detected by one of the thermal loop switches?
The rest of the circuit will still provide fire protection surveillance at the remaining points
How does the thermal loop test switch work?
- Test switch tests the entire loop
- Shows operator if an open circuit is present in the power input lead of the loop
What will a short circuit in the thermal loop switch do?
-Cause a false fire warning indication
What happens to the fire detection system indicator (aka fire alarm) at night?
Dimming relay provides low voltage to the light
What is the principle of operation of the pneumatic fire detection system?
- Gas in tube expands when heated
- When trigger temp is reached gas pressure overcomes check valve and flows to right side of diaphram
- This forces diaphragm contacts to the left onto the alarm contacts
- Alarm circuit is closed`
What is the advantage of the pneumatic fire detection system if the fire is no longer sensed?
- Gas will return to a low pressure
- Diaphragm will force gas back into tube
- System is effectively reset, ready for another operation
What is the principle of operation of the flame detector system?
- Infrared detectors receive directed or reflected rays from flame
- Detectors located in engine nacelle
- When IR rays detected signal is sent to an amplifier
- Amplifier powers an alarm in the cockpit
Self resetting to standby state
What is the principle of operation of the smoke detection system?
- Photoelectric cells have alight directed at them
- If sufficient smoke present, reference beam is interrupted and alarm is triggered
Self resetting to standby state
Is a photoelectric sensor commonly used on gas turbine engines? Why/Why not?
No
- Cannot detect hot air leaks
- Hot air leaks are a common malfunction, which can cause fire if directed at fuel or oil lines
What high temperature states can the fire and smoke detection system differentiate between?
Overheat
Hot air leak
Actual fire
What pressure does the engine fire extinguishing bottle operate at?
500-600 PSI
What is the principle of operation of the fire extinguishing bottle
- Relief valve is a fusible disc which will rupture in an overheat
- To discharge electrical current applied to contactor which detonates an explosive cartridge
- Shatters disc located in bottle outlet
- extinguishing agent flows into the engine
Describe how fire extinguishers can be cross-fed?
- Distribution system allows for number 1 bottle to be used in number 1 engine, as well as number 2 bottle in number 1 engine
- Same is also true in reverse
What things affects the effectiveness of primary flight controls?
- Aerodynamic force (by the amount of deflection, and speed of airflow)
- The moment are from the CoG
What can happen when controls are used at high speeds, in structures that are inherently flexible?
The resulting force may can the wing to twist about its torsional axis
How are large aircraft control surfaces designed to prevent torsional rotation when flying at high speeds? how does this system work? What is the additional benefit of this?
Flight controls are split
- At low speeds they are operated in tandem
- At high speeds lockout system automatically actuated when ADC signal is received.
- Added benefit of providing redundancy
Describe the split control systems for the roll primary controls?
Ailerons are split
-At high speeds only inboard sections may be used, or flaperons/elevons may be used
What features may be designed for primary and secondary controls on a large aircraft? Swept wings/modern flexible aircraft?
- Controls split into multiple sections
- Flying tailplanes
- All moving wing tips
- All moving tailplanes
Describe the lift augmentation system on large aircraft? What does it consist of and when is it used?
- Used during takeoff and landing to reduce speeds
- Form part of the aerofoil at high speeds
- Slats, slots, leading and trailing and leading edge flaps, fowler flaps
What issues can arise with power boosted controls in the high subsonic and transonic range?
Control buffeting from shockwaves
Vibrations fed back into the control system
Systems in place to prevent this from reaching pilot, however this means pilots have no control feel
How do pilot controls actually actuate flight controls in heavy aircraft? How do they get control ‘feel’?
- Actuate control valves
- Control valves direct hydraulic fluid to control surface actuators
- Known as the Power Control Unit (PCU)
Control feel is built into the system to give stick force proportional to flight loads on the control surfaces
What is the type of halogenated hydrocarbon that is used in aircraft extinguishers?
Halogen 1301 (Halon 1301)
Bromo-trifluro-methane
What is the purpose of position transducers in the Fly-by-wire system? Describe the path of electrical signals to actuate the controls?
Position transducer convert flight crew command input to electrical signals
- Signals go to actuator control electronics
- There signals converted to digital format
- Digital signals sent to primary flight computers
What functions does the primary flight computers provide in the fly-by-wire system?
- Pilot input can be analysed
- If pilot input outside the operating envelope signals can be modified to stay within the correct envelope
- Can be operated through IFS system to give auto flight control
- Feed flight control position data to flight data recorder
What aircraft components are employed during an auto landing?
- Autopilot(s)
- Auto-thrust
- Radio altimeter
- Nose wheel steering
-Auto-brake (not integral part)
What cautions should be noted when flying an auto land on CAT 1, or CAT2/3 when not in poor vis configurations?
- Some CAT1 systems not suitable when below minimal due to offset ground stations
- When carrying out Auto-land tests/currency in good weather ATC may not be protecting Critical areas
What happens at 1500ft AGL of an ILS/GLS approach when in Approach mode is active?
- Self test mode
- Electrical system automatically reconfigures to isolate various electrical inputs (to enhance robustness)
- Once completed auto land status message will be displayed
In what cases will the pilots have to activate reverse thrust?
All cases
What is a fail operational auto land system capable of doing? what does it require?
- Has 2 autopilots engaged
- Has no decision height
- Failure of one AP will still allow the approach to be continued
What is a fail passive auto land system capable of doing? What does it require?
- associate with at least a single autopilot approach
- AP failure will not cause anything drastic, but PF should immediately take control and carry out Missed approach unless sufficient visual reference
- Lowest allowable DA is normally 50ft AGL
What is the gain program in the final stages of an auto land? What situation must the aircraft be in for it to happen? (Ap modes/actual position on the approach)
- Part of the approach mode of AFDS
- As aircraft approaches DA, localiser becomes more sensitive requiring less control input
- Expands localiser display to assist pilot in judging appropriate an appropriate control input to maintain localiser course
Where does air get taken from in a piston engine air conditioning system?
Leading edge air scoop
Engine superchargers
What occurs at 300, 200 and 100ft AGL during an auto land?
300ft: glideslope sensitivity reduced
200ft: longitudinal axis is aligned with ILS ‘runway’
100ft: AoA protection is inhibited to allow the flare
