11.05.1 Instruments Flashcards
What instruments form the basic T?
- Altimeter
- Attitude Direction Indicator (ADI)
- Airspeed Indicator (ASI)
- Horizontal Situation Indicator (HSI)
What is meant by the term, International Standard Atmosphere (ISA)?
It is a model for the standardised pressure, temperature, density and viscosity of the Earth’s atmosphere
What is the static pressure at sea level in the standard atmosphere?
1013.25 hpa
What static pressure setting is used to indicate airfield elevation?
QNH
With an aneroid bellows meter, what is significant about small pressure changes at low and high flight altitudes?
At low levels there is a small indicated height change, but at high levels there are large indicated height changes
Setting an altimeter to QFE provides the pilot with what information?
The height of the aircraft at the current location with respect to the underlying ground surface
Why are altimeters set to the standard baro setting during cruise flight?
This enables all aircraft to maintain vertical separation following clearance from ATC
What two factors, external to the aircraft, can give rise to variations in indicated altitude?
- Flying through areas of differing air pressure
- Variations of air temperature
The difference between total and static pressure is known as what?
Dynamic pressure
What is the limitation of indicated airspeed (IAS)?
It’s an indication of the real speed of the aircraft at mean sea level with standard conditions
How is true airspeed (TAS) derived?
It is calculated from EAS by replacing the standard air density with the real air density. TAS increases with altitude
What are the following speed limits:
- VSO
- VS1
- VFE
- VNO
- VNE
- VSO = Stall speed in landing configuration, gear and flaps down
- VS1 = Stall speed in clean configuration, maximum weight
- VFE = Maximum allowable speed with flaps extended
- VNO = Maximum airspeed in cruise flight
- VNE = Maximum allowed airpseed
What is the difference between VNE and VMO?
- VNE is used for piston aircraft and is a fixed value
- VMO, Maximum Operating Velocity, depends on the dynamic pressure acting on the aircraft structure at low levels
What is the basic operation of a vertical speed indicator (VSI)?
- The internal bellows of the instrument is connected to the aircraft static line
- Bellows expand and contract with changes in altitude, moving a pointer accordingly
- When the vertical change stops, the pressure differential between the bellows and the inside of the instrument equalises (through metered orifice)
- Pointer then moves back to the centre position
What allows the pressure equalisation to take place in the operation of the VSI?
- Calibrated metering unit
- Capillary tube
- Capillary orifice
What is the difference between a VSI and an IVSI?
An IVSI has an internal spring-loaded piston, which responds to positive and negative gravitational forces during the initial stages of an aircraft’s changes of vertical movement. This provides instant height change indication
What is used to display the ratio of an aircrafts true air speed and the actual speed of sound?
A mach meter
What is Static Source Error (SSE)?
The difference between the measured and real static pressure
What is important about the condition of static port surfaces?
They must be kept clean and smooth to prevent disturbance of the airflow
What must be done to static ports when the aircraft is being washed or painted?
The static ports must be covered/blanked to prevent the ports getting blocked
What must be considered for the location of static ports?
Must be located in an area of smooth airflow allowing undisturbed measurement of the static air pressure
What influences SSE?
- Fuselage shape
- Airspeed
- Flap position
- Angle of attack
- Flap and gear position also have an influence
What flight condition can affect measured static pressure?
Sideslip manoeuvre
What can be done to compensate for the error in measured static pressure due to sideslip?
The installation of a second static port and cross-porting them together
How is pitot pressure measured?
It is measured by a pitot tube pointing into the airstream and directing the pressure along tubes to the instruments/pressure indicators
Where, on aircraft, are pitot tubes located?
- Selected by manufacturer so that undisturbed air pressure can be measured
- For military aircraft, at the nose
- For small aircraft below the front of the wing
- For large aircraft, generally at the front of the aircraft
why must the leading edge of the pitot tube be free from deformation and damage?
To ensure the airflow is unaffected
What prevents water and foreign objects from entering the pitot pressure line?
By fitting the tube with a baffle
How is any water or dust particles that have entered the pitot tube removed?
Through a drain hole at the lowest point of the tube
Why do pitot tubes have heaters?
To prevent the formation of ice under certain flight conditions , blocking the airflow
On large aircraft with a second pilot, what can be noted about the instruments used by both pilots?
Both sets of instruments are completely separate
The installation of an alternate static source selector is done for what reason?
In enables the captain to use the copilots static pressure system
What is used to provide pitot and static information to today’s electronic air data computers (ADC’s)?
Air data modules
Following maintenance on the pitot/static system, according to the aircraft maintenance manual, what must be undertaken?
Air data leak test
Periodically, what else must be checked for and how can it be corrected on the pitot static system?
- Water in the interconnecting pipes
- Drain out the water gathered in the drain taps
What are the three types of ADC that are used on aircraft?
- Analogue
- Digital
- Hybrid
How much deviation from a selected altitude would generate an alert to the pilot?
300ft
When would the altitude alert be inhibited?
- When a change of altitude is dialled into the autopilot control panel with the altitude knob
- When the aircraft intercepts the glide slope during an approach to landing
When would the pilot get an over speed warning?
When speed exceeds:
- VMO (Maximum operating velocity)
- MMO (Maximum allowed mach number)
What is the difference between static air temperature (SAT) and outside air temperature (OAT)?
Nothing
What is the result of ram rise?
A direct temperature reading outside the aircraft, total air temperature (TAT)
What is alpha max?
This is when an aircraft increases its angle of attack to a point where the airflow does not follow the upper surface of the wing and lift drops dramatically. Every aircraft has its own alpha max value dependent upon its flight config.
At what point during flight would the stick shaker motor start to operate?
When the comparison between an aircraft’s alpha max and actual angle of attack reach the aircraft’s critical angle of attack
What sensor is used to provide angle of attack information?
the alpha vane
What storage mediums can be used for flight data recorders?
- Magnetic tape
- Solid state memories
What is the duration of an FDR Recording?
25 hours, being constantly overwritten
To protect the recorded data, what must an FDR be able to withstand?
- High G loads of up to 3400g (was 100g)
- High temps of up to 1000 celcius
What are the operating parameters of the underwater locator beacon?
- Transmits 40khz audio signal
- Automatic operation on immersion in water for a minimum of 30 days
- Can withstand depths greater than 3000 meters
What unit combines all the required fight data parameters into a recordable format before recording by the FDR?
Flight data acquisition unit
What 3 factors affect gyro stability?
- Mass (evenly distributed around the spin axis)
- Rotational speed
- Distance between the spin axis and the centre of mass
What is precession?
A reaction force which tried to tilt the gyro axis. This reaction is shifted by 90 degrees
What type of gyro has 1.5 degrees of freedom?
A rate gyro
What is the rate of apparent drift of a horizontal gyro at the north pole?
15 degrees per hour
What is the rate of apparent topple of a vertical gyro at the north pole?
0 degrees
What is the cause of gyros eventually being affected by real drift and topple?
Incorrect handling along with wear generating unwanted precession
Why are modern gyros driven by electric motors?
Electric motors provide a more stable speed in all flight situations and are also more reliable
What type of gyro is used for horizon indication?
Vertical gyro
What is use to keep the spin axis of a vertical gyro in the correct plane?
An erection system comprising of level switches or moving mass (pendulum)
When can a gyro erection system not work correctly?
During accelerations
How are incorrect indications during accelerations avoided?
The erection system is limited to 3 degrees per minute
What flight condition must be avoided because gyro topple cannot be compensated for?
Long accelerated turns
A directional gyro is used to provide what information?
Heading
In comparison to a vertical gyro (VG), what is an important difference of the directional gyro (DG)?
The DG tends to drift
What are rate gyros primarily used for?
To detect and measure rates of change around their sensitive axis
Only one type of rate gyro can be used for indications, which one?
Yaw rate gyro
When would a rate of turn indicator display full deflection L or R?
When a full turn would take 2 minutes - a standard turn
Rate of turn indicators are only accurate in use, when?
When the gyro is operating at full speed
When a gyro is running at medium speed, what must be observed?
The gyro must not be moved, including when fitted to aircraft
What is classed as medium speed regarding gyro handling?
Between 3 and 20 minutes from power interruption
Where does the attitude direction indicator (ADI) get its attitude information from?
From the inertial reference unit or a vertical gyro
What sort of indicator is the ADI (Attitude Direction Indicator)?
Electromechanical or flat screen (LCD)
What else does the ADI display?
Flight director bars
What is DH (decision height) lamp for?
To provide indication of descent to the selected decision height
What is fast/slow pointer for?
Indication of reaching or not a pre-selected landing speed
On the fast/slow pointer, what does the fill deflection up indicate?
The landing speed is 10 kts too fast
When does ADI get gyro valid signal?
When the gyro is operating at normal speed
What happens if pilot or first officer gyro fails?
The output from a 3rd vertical gyro can be switched in to replaced the failed gyro
What else can vertical gyros feed?
autopilot systems, weather radar
What safety feature is built in to the vertical reference system?
A comparison between the two attitude display systems is undertaken. If a predetermined difference is detected, a warning is indicated for corrective action
What is magnetic variation?
This is the difference between true north (TN) and magnetic north (MN)
What magnetic field lines can a compass use?
Horizontal field lines. Only occur like this at the equator
Where is compass not usable?
above 70 degrees north or south
What is used instead of compass above 70 degrees north or south?
a directional gyro based system or an inertial stabilised system
Where is a direct reading compass located?
usually at the centre post between the windscreens, away from electrical equipment and magnetic forces
What is a direct reading compass filled with and why?
A fluid to dampen movements
regarding the direct reading compass, what is deviation?
this is the difference between real magnetic north and the indicated magnetic north on the compass
How can direct reading compass deviation be corrected?
A process called compass compensation incorporating the use of small adjustable magnets within the direct reading compass
Accelerations can affect a direct reading compass, what other unit could provide stable heading information?
A directional gyro (DG)
There is an inherent problem during operation of the DG’s, what is this problem?
DG’s tend to drift and need correcting frequently
What additional unit, along with the DG, forms the core of the remote compass system?
The flux valve
What is the basic principle of operation of the flux valve?
The induction of electrical signals into 3 sensing coils by alternate switching of the detected magnetic field
How is the drift of the DG corrected in the remote compass system?
An error signal derived from the comparison of the heading displayed in the heading indicator and the detected magnetic field, is applied to a torque motor which adjusts the DG direction
What provides the pilot and indication of the difference between the indicated heading and the detected signal?
Slave annunciator
What is the advantage of using electronic instrument display systems?
- All display units are identical, so displayed information can be switched if a display unit fails
- Clear, bright coloured displays
- Fewer different parts required
In a typical cockpit display suite, the 6 main displays can be split into two groups, which are:
- Electronic flight instrument system (EFIS) - Pilot and first officer
- Engine indicating and Central Warning System - Centre Instrument panel
When does automatic display switching occur?
If an outboard display unit fails, or the centre upper display fails
If the pilot’s PFD has failed and automatic switching has taken place, how can the pilot view navigation information?
The single remaining display can be switched manually between PFD and ND information
How can the quality of a display be tested?
Select the display test picture by using the multifunction control display unit (MCDU) from the CMC (central maintenance computer) and comparing the displays driven by the same display management computer (DMC)
The flight information displayed on a PFD follows what format?
The basic T, identical to original analogue instruments
What are the two types of alert used to inform flight crew of abnormal conditions?
- Central warnings
- Local warnings
What are the different types of local warnings?
- Push Button lights
- Flags
- Display limit exceedance
What are the different types of central warnings?
- Warnings (level A for boeing, level 3 for airbus)
- Cautions (Levels B for boeing, level 2 for airbus)
- Advisories (Level C for boeing, level 1 for airbus)
What is used to give the pilots an initial indication to an abnormal condition?
Master warning and Master caution lights on the glare shield
What does the upper central display provide?
Information relating to:
- Central warning system (CWS) messages
- Permanent aircraft information
What does the upper central display provide?
Information relating to the condition of aircraft systems
The fuel system page displays what parameters?
- Valve and pump status
- Tank fuel quantity
- Total fuel
- Fuel temperature
Fuel quantity probes can also be known as what?
Tank units
What two additional sensors are used to determine the characteristics of the fuel?
- Compensators
- Densitometers
What are the three types of level sensors?
- Float switch
- Thermistor
- Single point sensor
What are the main parts to the engine vibration monitoring system?
- Cockpit indications
- Vibration sensors
- Computer - Engine Vibration Monitoring Unit (EMVU)
What are the two types of accelerometers that can be used as vibration sensors?
- Electromagnetic accelerometer
- Piezoelectric crystal acceleromter
