Flight Navigation Flashcards
Describe aircraft heading?
Direction of the Aircraft’s LFD relative to North Measured clockwise from North and a positive three-figure number.
Describe aircraft track?
The path of an aircraft along the ground.
Describe aircraft drift?
The angle between the aircraft heading and track. Measured in degrees to port or starboard of the aircraft’s heading.
Describe Airspeed and Groundspeed?
The airspeed of an aircraft is its speed relative to the air mass it moves through, combined with its heading to form a vector. Groundspeed is the speed relative to the ground along the track vector.
Identify the aircraft heading, track and drift angle shown on a Horizontal Situation
Heading: 310 degrees Track: 290 Drift angle: 15 degrees port.
Explain secant correction.
When flying east or west off the equator, a secant correction adjusts linear distance to angular distance due to converging longitude lines, depending on the aircraft’s latitude.
Explain the purpose of the following: Input Transducer
Converts one form of energy to another creating the initial error signal.
Explain the purpose of the following: Amplifier
Error signal is amplified to a size to drive the motor.
Explain the purpose of the following: Motor
The motor converts the amplified electrical signal into mechanical to drive the load.
Explain the purpose of the following: Load
Moves to new position dictated by the motor.
Describe what must be added to convert to a closed loop system
A negative feedback loop that opposes the initial error signal so when it reaches its desired value the error signal and the opposite error signal will be equal in amplitude in turn stopping the load from moving.
Explain the purpose of the following: Error Detector
Adds the input and output transducer signals together to provide the total error signal.
Explain the purpose of the following: Output Transducer
Provides back off signal to oppose the input signal, so that when they are equal in size but opposite in polarity. The error signal becomes zero and the system will stop in its new position.
List the disadvantages of a Closed loop system
Slower response time, Complicated, More expensive.
Examples aircraft closed loop control systems are:
Control surfaces, Engine throttle, Braking systems, Temperature control, Heated windscreen.
List the Servomechanism classification conditions
Continuous operation, Error actuated -ve feedback, Power amplification.
Explain the Operation of an E and I bar if the bar drops to the right.
If the bar moves closer to a secondary coil a greater voltage is induced in that side, this creates a difference between the outputs that is proportional to direction and amount of movement.
State the purpose of the Head Up Display (HUD).
The purpose of the HUD is to display essential flight information in line of sight of the pilot ahead of the aircraft.
Describe the term ‘field of view’ when used in Head Up Displays (HUD).
The angle, both vertical and horizontal, at which the combiner shows symbology relative to the pilot’s view of the outside world.
Explain the effect of using a HUD with a limited field of view
A low field of view reduces the cone angle of HUD information, forcing the pilot to move their head more, decreasing performance due to poor ergonomics.
Describe the term “diffractive optics” as used in a HUD
The diffractive HUD combiner uses a photosensitive emulsion film, developed with laser light and layered in glass, acting as a diffraction grating. It reflects light matching the laser’s wavelength and is transparent to other wavelengths.
List the advantages of using “Diffractive optics” on a HUD
Improved FOV, requires less light to achieve equal or better brightness than refractive, low power CRT’s can be used, Allows FLIR and Radar imagery to be displayed.
Explain the operation of a CRT
A CRT emits electrons from a cathode, forming a narrow beam that accelerates onto a fluorescent screen, creating a glowing dot. A changing field moves the dot across the screen.
Describe ‘cursive writing’?
Cursive writing describes the electron beam drawing line symbology like a pencil on paper. The beam’s glow on the fluorescent screen fades quickly, so lines are redrawn at a refresh rate to sustain the image.
Describe ‘raster scan’?
In a raster scan, the spot sweeps the entire screen in parallel horizontal lines, building the image by varying brightness in sync with the raster.
List the advantages of an Electronic HSI (EHSI) over a conventional HSI.
An EHSI’s software-driven display allows changes for different aircraft via software updates, avoiding the need for separate instruments.
The advantages of using flat panel over CRT displays are:
Smaller
Lighter
Cheaper
More reliable
Less power
List 3 types of flat panel displays used in Avionic systems.
Light emitting diode (LED), Liquid crystal Display (LCD), Active Matrix LCD (AMLCD).
Explain the purpose of ‘soft keys’ used on MFDs.
This allows each display to show any type of information. Soft keys can assume various functions depending on the mode of the display.
Explain the term ‘Built In Test Equipment’ (BITE).
Software used that is capable of detecting failures in a system. In modern aircraft, this facility is now the technician’s main aid to fault finding.
The purpose of an Aircraft Compass.
Provides aircraft heading referenced to Magnetic North.
A compass system requires 3 desired properties.
Horizontality, Sensitivity, Aperiodicity.
Why is True North used as a Navigation Reference?
True North never moves. It is used on maps and charts.
State and explain the correction that is applied to a compass magnetic reading to give True North?
Angle of variation, and it is the angular difference measured from true north to magnetic north at any given position on the Earth’s surface.
List the 2 aircraft magnetic effects that can reduce the accuracy of a compass are?
Hard iron, Soft iron.
List the causes of Hard and Soft Iron effects?
SOFT: Earth’s magnetic field, DC current from electrical components on aircraft, weapons or cargo. HARD: Vibration caused by riveting, aircraft stationary for a long time, engine vibration, certain equipment fitted, lightning strike.
Explain the purpose of the MDU and DG
MDU: To sense the horizontal component of the Earth’s magnetic field and to update the DG with magnetic north information. DG: The Directional Gyro is simply a 2º of freedom displacement gyro using a horizontal spin axis to measure yaw displacement.
Identify the displays that are indicated on the annunciator.
MDU is monitoring gyro and they are de-synchronised.
Explain the operation of the Gyro Magnetic Compass.
The slaving loop compares MDU and DG headings with an error sensor. If they differ, a gyro precession signal drives the DG motor at 2 degrees per minute until the error signal is zero.
Briefly explain the purpose of the ‘DG Servo loop’ used in a GMC.
To drive the display pointer or compass card.
Identify the occasions when a compass swing would need to be undertaken.
When the compass system is in doubt, when the schedule requires it, after a heavy landing.
Primary function of an Inertial Navigation System.
Provide continuous latitude and longitude positional information.
Advantages of using an INS.
Self-contained, Not affected by weather or aircraft orientation, Very accurate.
The typical inputs and outputs provided by INS.
Inputs: start position, destination position, power supplies. Outputs: present position, true heading, true track, groundspeed, height, vertical velocity, attitude.
Strapdown INS has several advantages over older systems these are.
More reliable, Quicker alignment, Lower cost.
The type of accelerometer used in an INS.
Force feedback or Pendulous force balance.
Explain the operation of a Ring Laser Gyro.
They measure angular rates of rotation by sensing the difference in time taken for two beams of Laser light, travelling in opposite directions, to travel around a closed path.
A problem with early ‘Ring Laser Gyros (RLG) is lock in’ briefly explain how this is resolved.
Dithering or vibrating the ring laser cavity using a ‘dither motor’.
Explain the why a Strapdown INS requires Gravity Correction.
Gravity correction is required to counteract the effects of local gravity on all accelerometers.
List the four stages of the Strapdown INS Normal alignment sequence.
Power up and BIT, Present Position insertion, Level detection, Gyro compassing.
Explain the two methods of updating INS.
Position fixing is when the aircraft flies over a known point and updates the INS output with the latitude and longitude of a fixed position.
Position error compensation: employs a recursive software called a Kalman filter which carries out statistical analysis to predict future errors from the INS.
Describe Kalman Filtering.
The Kalman Filter carries out statistical analysis of information from the INS and other Navigation sensors and provides estimates of future INS errors.
Two types of warning given by a Ground Proximity Warning System (GPWS).
Visual and Audio.
List the PGPWS Requirements.
The aircraft’s position and velocity
Terrain elevation
Scan area
Set warning Height
List the navigation systems that could provide position and velocity information to a Ground Proximity Warning systems.
Inertial Navigation System, Global Positioning System.
List the factors that determine the recovery manoeuvre time in a Predictive Ground Proximity Warning system (GPWS).
The average pilot’s reaction time to a warning, A time for the aircraft to roll to wings level, The aircraft’s response to a “pull-up” stick input at a preset ‘g’ level.
List the Information contained in the “DVOF” in a GPWS.
Stored details of the location of man-made obstacles such as, radio masts, chimneys, etc.
Identify the purpose of ILS?
The ILS guides pilots along the runway centreline (localizer) and glide path (glide slope) in poor visibility, with markers indicating distance to touchdown.
Describe the Localizer signals?
The localizer signals are fed to a horizontal situation indicator or Head Up Display where they cause a deviation bar to move from side to side. (Fly Left/Right)
Describe the Glideslope signals?
The Glidepath (Glideslope) signals have a range of 10 miles, normally overlap along a glide slope angle of descent of 2½° or 3°, depending upon the surrounding terrain. (Fly up/down)
Identify the range of the Marker Beacons?
All Marker beacons operate on a carrier frequency of 75 MHz and transmit a vertical fan-shaped beam up to a height of 6,000 feet.
Explain the purpose of MLS?
The operation of MLS is similar to ILS in that signals are transmitted from the ground which enables aircraft to determine precise azimuth, elevation and range information during approach to an airfield.
Describe the Azimuth Guidance signals?
The azimuth aerial generates a narrow vertical fan-shaped beam and sweeps it to and fro across the coverage area 13 times per second. This beam has a range of 20 nautical miles.
Describe the Elevation Guidance signals?
The elevation aerial generates a narrow horizontal fan-shaped beam that sweeps up and down through the coverage area at 39 times per second. The EL beam has a range of 20 nautical miles.
Information provided by the VHF Omni-directional Ranging system (VOR).
Fly left/right indication, Morse code identifier, bearing to ground beacon with respect to magnetic north.
Explain how the VOR system measures bearing to the beacon.
By measuring the difference between 30HZ FM reference signal and the 30Hz AM variable signal.
The purpose of TACAN
The Tactical Air Navigation system is a military navigation aid which consists of ground beacons and airborne installations operating in the UHF frequency range.
State the two pieces of information provided by TACAN in the “Air to Air” mode
The beacon provides coarse bearing only along with slant range.
Explain the transponder principle used by TACAN.
The aircraft ‘transmits’ a question to the ground beacon which replies to the interrogation. The time between the transmission and reception determines the slant range.
State the frequencies used by a TACAN system
135Hz fine bearing, 15HZ course bearing.
The information provided by the identity chain
The Identity chain processes the 1350 pulse pairs into an audio signal containing the two or three letter aural Morse code which is fed to the pilot’s headset.
The purpose of DME
The purpose of Distance Measuring Equipment (DME).
What does ‘transmits’ refer to in the context of a question to the ground beacon?
‘Transmits’ a question to the ground beacon which replies to the interrogation. The time between the transmission and reception determines the slant range.
State the frequencies used by a TACAN system.
135Hz fine bearing 15HZ course bearing
What information does the identity chain provide?
The Identity chain processes the 1350 pulse pairs into an audio signal containing the two or three letter aural Morse code which is fed to the pilot’s headset.
What is the purpose of DME?
Is to provide slant range information from the the beacon. (Distance)
What equipment is DME located with?
MLS, ILS, VHF omni ranging
What is the purpose of Rad Alt?
Provide altitude with the use of radar. And is the height from the terrain not sea level. 5000ft maximum
What are the advantages of using a Radar Altimeter (Rad Alt) compared to a barometric altimeter?
Provides actual height above the ground. Provides a cross-reference capability with the pressure altimeter.
What is the main purpose of the Global Positioning System?
Global Positioning System is a military system that can be used to pinpoint an aircraft’s longitude, latitude, and altitude in any weather conditions, anywhere in the world, 24 hours a day.
What are the three types of information contained within the signal transmitted by a GPS satellite?
Pseudo random code, Almanac data, Ephemeris data
Describe the information in the ‘almanac data’ provided by a GPS satellite.
Each satellite continuously transmits its health status, current date, and time, essential for position determination.
List the factors that can reduce the accuracy of a GPS.
Ionosphere and troposphere delays, Signal multipath, Orbital errors, Number of satellites visible, Receiver clock errors
What is the purpose of Doppler Navigation?
It provides groundspeed, aircraft track and drift angle.
What are the disadvantages of using a ‘single beam’ Doppler system instead of a two beam system?
Pitching error, Vertical motion, Transmitter instability, Drift Error
Identify the system that stops single beam errors.
A Two beam system that uses fore and aft beams. With two beams, a nose-up pitch decreases Doppler shift in the forward beam and increases it in the rear, canceling pitch effects for accurate groundspeed.
What is the purpose of AFCS?
Overcoming stability problems caused by modern aircraft design and high-speed flight. Reducing the aircrew workload. Improving the handling or ride qualities in general or during a specific mode of operation. Carrying out automatic manoeuvres that the pilot is unable to perform either due to the accuracy required or the amount of time needed to execute a particular manoeuvre.
What is the purpose of the ‘stability augmentation system’ used in the AFCS?
To reduce pilot workload and fatigue by detecting and correcting short-term aircraft instability automatically.
Identify the components in a stability augmentation system.
Rate gyro
Amplifier and signal processor
Servo actuator
Control surface
What is the purpose of the ‘auto pilot’ used in the AFCS?
To reduce the pilot’s workload and make accurate adjustments.
State and describe the three specific modes in AFCS.
Hold, Acquire, Basic mode
List the autopilot safety devices.
Pilot’s Instinctive Cut-out, Rate and Angle Limiters, Control Limit Switches, Excess Torque Device, Monitoring Facilities
What happens when ‘Height Hold’ is selected?
Selecting ‘Height Hold’ feeds the ADC’s barometric height to a comparator via two paths: directly and through a height store. Matching inputs produce no height error.
List the disadvantages of mechanical flight control systems.
The component parts wear due to friction. The total system is large and heavy. An attack on the aircraft could also cause the linkages to break or jam. The whole system is difficult to set up and adjust.
List the advantages of using Fly By Wire (FBW) flight control systems over a mechanical system.
Weight and Space saving
No Friction or Backlash
Battle damage resistance
Optimisation
Spin Prevention
What is the purpose of the Flight Control Computer?
converts error signals into outer control loop inputs for manoeuvres.
Why is ‘air data’ information an input into a ‘fly by wire’ system?
Air Data adjusts for atmospheric and airflow effects. Higher airspeed needs smaller control deflections, while higher altitude requires larger ones due to lower air density. Air Data scheduling tailors autostabiliser performance to aircraft type, especially in transonic regions.
Explain Redundancy or Backup in FBW systems.
FBW systems use multiple computers (duplex, triplex, or quadruplex) for redundancy.
What does the psudo random code provide to the satellite?
Provided identity code of the satellite
What does the Ephemeris data provide to the satellite
Provides the location of the satellite and all other satellites.
3 segments in GPS
Control segment
User segment
Space segment
Name four other types of transducers other than an E and I bar
Control synchro
Differential synchro
Torque synchro
Resolver synchro
State the components that make up a night vision camera
Photo cathode
Photo multiplier
Phosphor screen
Identify the component of night vision goggles amplifies the electrons
Photo multiplier
Identify the best colour to use with night vision and give a reason
Green, because the human eye is sensitive to green light in low light conditions for better clarity
Night vision goggles will work in no light conditions
False
List safety measures for NVG
Never expose NVG to direct sunlight
Keep lens cap fitted when not in use
Keep away from heat sources
