11.5.1 Instument Systems/ Avionic Systems Flashcards
Where are the most important basic flight instruments located
The Basic T
What is not a part of the basic T but located bottom right to it
Vertical Speed Indicator (VSI)
Hat is top right of the basic T
Altimeter - Indicates altitude of aircraft above sea level
What is top left of the basic T
Airspeed indicator - Shows speed which is a reference for all aerodynamic parameters influencing aircraft lift, drag and manoeuvrability
What is top middle of the Basic T
Artificial horizon - or attitude indication is integrated in the Attitude director indicator (ADI)
Shows pitch and roll altitude in relation to the horizon
What is bottom middle of the basic T
Compass or heading indication - Integrated in the Horizontal Situation Indicator (HSI)
Shows the direction of the aircraft on the longitudinal axis in relation to magnetic north
Apart from those in the basic T what additional flight instruments are there
- Vertical Speed Indicator (VSI)
- Mach meter
- Temperature indicators
What instruments (air data instruments) use air pressure from outside the aircraft
Altimeter and air speed indicator
What two pointers do most altimeters have as a minimum
100ft and 1000ft. Larger aircraft which fly at higher altitudes also have one for 10,000ft
How does a normal altimeter calculate altitude
They measure the static pressure of the atmosphere and indicate it in feet or meters
Hat happens to pressure if altitude increases
Pressure decreases
A pneumatic altimeter is usually found in small aircraft and as a standby in large aircraft. It has a sensitive pressure gauge, what is it called
Aneroid bellows
How does a pneumatic altimeter work
- Static pressure applied around the sealed case surrounds the bellows and compresses them
- The bellows deflection moves the instrument mechanism and turns the altitude pointer which shows the altitude on a scale calibrated in ft or meters
- The altimeter indication is calibrated to the standard atmosphere shown in a graph
Altimeters accuracy decreases with altitude so what is used on large aircraft to help rectify this
Large aircraft have bellows driven by the Air Data Computer (ADC) and use only electrical components such as motors, amplifiers or digital computers
To what conditions are altimeters calibrated to
Conditions of the standard atmosphere
What is the baro setting called
QNH
What is the actual pressure of the airport called (field elevation)
QFE
What is the transition altitude
The standard setting of 1013hpa must be selected during climb at a certain altitude called transition altitude
What is done with the altimeter setting when coming in for landing
It is set to either QNH or QFE of the destination to get the correct altitude indications for landing
What variable can be an issue with altimeter settings
Temperature. When it is cold clearance over mountains must be carefully monitored as the temperature can shift pressure levels giving the altitude a slightly different reading
On an airspeed indicator what line is connected to the bellows and what line is connected to the indicator case so it surrounds the bellows
Total pressure line is connected to the inside of the bellows and the static pressure is distributed to the indicator case so that it surrounds the bellows
Airspeed indicator
Low airspeed - ?
Medium speed - ?
High speed - ?
Low speed - the total pressure is low and the bellows are compressed
Medium speed - All mechanical parts are in the present position
High speed - the total pressure is high and the bellows expand
On small aircraft what are speed limits shown as on the airspeed indicator scale
They are marked with coloured ranges and lines
What is the green band on the digital airspeed indicator
Shows the normal operating range
What does the white band on the digital airspeed indicator mean
Full flap operating range
What does the yellow band mean on the digital airspeed indicator
The caution range. This speed must only be used in smooth air with out hard manoeuvres
In a jet aircraft what shows the maximum allowed speed of the aircraft
A red and black needle.
Piston aircraft have a fixed value
What is the maximum allowed airspeed called in a jet aircraft
Maximum operating velocity (VMO)
Jet aircraft don’t have a set number as the pressure changed in the aircraft at different altitudes
Other than the warnings on the airspeed indicator what other warnings would be relevant
Over speed and stall warning indicators which are independent
What does the Vertical speed indicator (VSI) show
Shows the pilot the rate of climb or decent in feet per minute.
The pressure difference on the inside and outside of the bellows acts on the instrument mechanism and moves the vertical speed pointer
What does the Mach meter indicate
The ratio of the aircrafts true airspeed to the actual speed of sound
All aircraft need this to fly safely at high altitudes
On all modern aircraft you can find temperature indications shown on Airbus ECAM, two temperatures are defined, what are they
- Static Air Temperature (SAT): this is the temperature of the undisturbed air around the aircraft, also called outside air temp (OAT)
- Total Air Temperature (TAT): it is measured directly from the TAT probe also called the Rosemont probe after the manufacturer. The probe guides the air stream around the sensing element called a thermistor
What basic T instruments need static pressure to indicate correct values
The altimeter, the airspeed indicator (AI) and the vertical speed indicator (VSI)
The indicators are connected together and are then connected to be static ports
Where are static ports located usually
In an area where smooth airflow allows an undisturbed measurement of the static pressure
What is the Static Source Error (SSE)
The difference between the measured and real static pressure
How does the aircraft static ports compensate for a side slip manoeuvre
One static port is installed on each side of the aircraft, both ports are connected together by the use of a cross porting tube which equalises the static pressure to the instruments
What is the pitot system used by
The airspeed indicator
What is inside the pitot tube to prevent water or foreign objects from entering it
A baffle
Where does the name pitot come from
The French scientist Henry pitot who first made calculations to measure airspeed
What is used to prevent ice build up on pitot tubes during flight
An electrical probe heater is used
Why must engineers be cautious when working near pitot tubes on the ground
They become very hot when the heaters are turned on
What do the pitot tubes sometimes contain
Static ports, they consist of small holes around the tube and are connected to the static system
What are pitot static tubes also called after the German invented
Prandtl
If the aircraft is being kept on the ground outside for a long amount of time, what must be done to the pitot tubes
They must be covered with a red cover with a flag.
What is the design of a pitot static system on small aircraft
- 1 airspeed indicator
- 1 altimeter
- 1 vertical speed indicator
The 3 indicators are supplied by a static pressure system with 2 static ports. The pitot pressure system supplies the airspeed indicators
Other than information from the static ports and pitot systems what else supplies data to the Mach meter, true airspeed indicator and air temperature
The Air Data Computer (ADC)
What systems does the Air Data Computer (ADC) supply information to
Other than the Mach meter, true airspeed indicator and air temperature indicator it is used for auto flight and warning systems
(ADC) Air Data Computer reliability made it possible to replace what instruments
Pneumatic instruments and their pipework
How many ADCs are usually on a large jet aircraft
One for pilot one for first officer and a redundancy, sometimes the redundancy will provide additional information if needed
What other unit can the ADC be integrated with to make the ADIRU
The Inertial Reference System
What tasks do the ADCs perform
- Measure and convert the temperature and pitot/static pressure and then calculate the necessary output signals for the indicators and aircraft systems.
- Calculate correction signals for the static source error and determine values that are not directly measurable i.e. Density
What is the altitude alert system used for
Air traffic control clear an aircraft to a certain altitude to prevent collisions with other aircraft. If the aircraft deviate from this altitude then a warning will signal
What warning would a pilot receive for an over speed
A warning from the cockpit loudspeakers and a ‘clacker’
This warning is triggered when airspeed is higher than VMO or MMO
What happens at alpha max
Airflow cannot follow the upper surface of the wing and airflow separation occurs
What warning would be given if a stall is expected
A stick shaker
What is the purpose of the flight data recorder
Records important flight data to evaluate causes of an accident
It is required by law to have a FDR on large aircraft
First generation FDR recorded what 6 parameters
- Time
- Heading
- Altitude
- Airspeed
- Vertical acceleration
- Pulse when the push to talk switch is activated
What additional data must newer data recorders also record
- Engine
- Flight Control
- System status
They can now monitor several hundred parameters
What two storage devices are used by the FDR
Magnetic tape - Which is protected against heat and shocks by insulation
Solid State Memories - Like CMOS EPROMs
They don’t need maintenance as they record the last 25 flight hours
To keep data stored during a crash the storage device must be protected against what
- High g loads up to 1000g
- High temperatures up to 1000 degrees c
How are aircraft located if they have crashed in water
The FDR has an underwater locator beacon
- Transmits an audio signal at 40khz that can be picked up by an underwater microphone
- Transmissions start when the aircraft hits water and will transmit for a minimum of 30 days
- Can withstand depths of more than 3000 meters
What triggers the FDR on/off switch
Engine oil pressure switch or am airspeed signal
What is the purpose of a vertical gyro (VG)
Provides the attitude indication for Attitude Director Indicator (ADI)
What is the purpose of a Directional Gyro (DG)
Provides the heading reference signal for the Horizontal Situation Indicator (HSI) and Radio Magnetic Indicators (RDI)
What is a Rate Gyro used for
Used for the Rate of Turn Indication
What is a gyro
A rotating mass which keeps the direction of its axis constant as long as no force acts on it
Gyro stability relies on what 3 factors
- Mass which is eventually distributed around the spin axis
- Rotational speed (RPM)
- Distance between the axis and the centre of mass
What speeds must aircraft gyros spin at
Very high speeds up to 22,000 RPM
IMPORTANT: When a force is applied which tries to tilt the gyro axis what is the reaction of the gyro
The reaction is shifted by 90 degrees and is called GYRO PROCESSION
IMPORTANT: A gyro with which can only spin around its axis and is mounted to the aircraft with bearings has how many degrees of freedom
1 degree of freedom
IMPORTANT: A gyro with one gimbal has how many degrees of freedom
2 degrees
IMPORTANT: If the movement of the gimbal is limited by a spring what is the amount of freedom it has
Only one and a half degrees of freedom and is called a Rate Gyro
A gyro with 2 gimbals has how many degrees of freedom
3 degrees of freedom and is free in all directions
What is a gyro with a vertical axis called
A vertical gyro and is used in the Artificial Horizon
What gyro is used to provide a heading reference signal
A Directional Gyro (DG)
A gyro needs high rotational speeds to work. What causes this in small aircraft
The speed is generated by air. The air is provided by a vacuum or suction pump
On large commercial aircraft what are gyros driven by
An electric motor. They are generally more reliable and gives a stable speed in all flight situations
What does a suction regulator do to a gyro
Controls the suction to about 5 inches of mercury to prevent gyro overspeed
What type of gyro is used as the reference in all classic instruments sowing an artificial horizon
A Vertical Gyro (VG)
What are Rate gyros named after
They are named after its sensitive axis - Roll Rate Gyro
Rate gyros are used in what systems
Inertial Reference System (IRS) and auto flight systems
What is the only rate indication you find in most aircraft
The yaw rate or rate of turn indicator
It is either separate or integrated in the Attitude Director Indicator (ADI)
Why should gyros always be handled with care
To prevent causing damage to its sensitive components (bearings)
When should you never move a gyro
When it’s running at medium speed this is important between 3 and 20 minutes after power interruption and is completely stopped after 20 mins
What gyro is used as the reference for the Attitude indication in aircraft also called the artificial horizon
The Vertical gyro (VG)
How much freedom does a Directional Gyro have
3 degrees of freedom and a horizontal axis
What does a Rate gyro measure
Aircraft Rate of turn around its sensitive axis
For how long after power off is a gyro running at medium speed
3-20 mins. It is completely stopped after 20 mins
Why must there be two separate vertical gyros
The pilot and co pilot need independent attitude indications
How is the indicated heading measured
The angle between the aircrafts longitudinal axis and the North Pole
What is the angle between true north and magnetic north
Variation
What heading is all information on maps based on
Magnetic heading
What is inclination
- Earths horizontal lines declining nearer the poles
- Latitude 50 degrees already 50% decrease in horizontal component
When is an inertial stabilised system used to assist heading indications
At 70 degrees latitude or more
What is an expansion unit used for in a direct reading compass
Compensates for fluid expansion caused by temperature changes
How much does drift change the Directional Gyro direction relative to earth
Up to 15 degrees every hour
What does a flux valve do
Transfers the direction of the magnetic field into a proportional electrical signal
Where is the flux valve installed
In the wing tips away from aircrafts magnetic fields
What does EFIS consist of
4 display units
2 control panels
How is calibrated airspeed (CAS) calculated
Air pressure produced by moving aircraft
How is altitude inclination calculated
Static air pressure
What is VOR mode
VHF omni Directional radio range
Displays aircraft position relative to VOR navigation aids
When is navigation or map mode used
During cruise
What is the arc mode used for
To show weather information
What are the two types of alerts to inform flight crew about an abnormal situation
Local warning and central warning
How do push buttons work
Dark during normal operation and light up if there is a fault
What does a white light indicate on a push button
System is switched off
How is an operational limit shown as
A red band or red radial line
What are the two types of central warnings
Attention getters
Central warning displays
How many crew alerting levels does EICAS have
3
A,B,C
What does FOB stand for
Fuel on board
How much of the aircrafts mass does fuel contribute to
50%
What measures fuel temperature
A thermistor
What units does the cockpit indication show engine level of vibration
0-6
Where are the 2 vibration sensors located in the engine
Compressor section
Turbine section
What is VMS
Vibration Monitoring system
