Aircraft Avionics and Communication Systems | PDF

Aircraft Avionics And Autopilot Systems (AVIONICS-AS) Aircraft Communication System Radio Theory  Radio theory emphasizes the transmission and detection of communication signals consisting of electromagnetic waves that travel through the air in a straight line or by reflec...

Aircraft Avionics And Autopilot Systems (AVIONICS-AS) Aircraft Communication System Radio Theory  Radio theory emphasizes the transmission and detection of communication signals consisting of electromagnetic waves that travel through the air in a straight line or by reflection from the ionosphere or from a communications satellite. Wave  A progressive disturbance in a medium.  Moves outward, possesses energy.  Energy is lost due to friction. Electromagnetic Wave  Electromagnetic waves are formed when an electric field comes in contact with a magnetic field. They are hence known as ‘electromagnetic’ waves. The electric field and magnetic field of an electromagnetic wave are perpendicular (at right angles) to each other. Radio wave  Radio wave is a type of Electromagnetic Wave.  Radio wave is from the portion of the electromagnetic spectrum at lower frequencies than microwaves. They are used in standard broadcast radio and television, shortwave radio, navigation and air-traffic control, cellular telephony, and even remote-controlled toys.  The SI unit for wave frequency is the hertz (Hz), where 1 hertz equals 1 wave passing a fixed point in 1 second. A higher- frequency wave has more energy than a lower-frequency wave with the same amplitude. Radio wave Low Frequency  Long Wavelength  Low Energy  Poor Quality High Frequency  Short Wavelength  High Energy  Good Quality Factors affecting radio waves Diffraction  Occurs in low frequency radio waves, it is the bending of a radio wave. Reflection  Occurs in high frequency radio waves, it is the bouncing back of a radio wave. Refraction  Occurs in high and low frequency radio waves, it is the changing in direction of a radio wave caused by a disturbance. (E.g. Rain) Attenuation  It is a reduction of signal strength during transmission, it is the loss of energy of a radio wave, friction may cause attenuation. Radio Wave Propagation  A radio wave is transmitted via omni directional, directional or pulse & echo method. From the antenna it moves out along three paths, depending primarily upon its frequency. These paths are surface waves, sky waves, and space waves. Radio Wave Propagation Omni directional  Radio wave is propagated in all directions. Directional  Radio wave is propagated in one direction. Pulse & echo  Bouncing back of radio waves. Types of Radio Waves Ground waves / Surface waves  Follows the curvature of the Earth, this wave is restricted by gravity.  VLF, LF, and MF Sky wave  This type of radio wave is stronger than the ground waves and it can overcome gravity, but it cannot penetrate the ionosphere.  HF Space wave  This type of radio wave can overcome gravity and can penetrate the ionosphere, its limitation is line of sight.  VHF, UHF, SHF, EHF Frequency band limits Radiotelephony  Pilots, engineers and air traffic controllers communicate by using the radiotelephony phraseology that consists of a set of standardized words and phrases approved for the radiotelephony communications by ICAO in all routine aircraft situations.  The communication is made possible due to their common and work-related topics. According to the ICAO Doc 9432 Manual of Radiotelephony the following transmitting techniques will assist in ensuring that transmitted speech is clearly and satisfactorily received: 1. Before transmitting, listen out on the frequency to be used to ensure that there will be no interference with a transmission from another station. 2. Be familiar with good microphone operating techniques. 3. Use a normal conversational tone, speak clearly and distinctly. 4. Maintain an even rate of speech not exceeding 100 words per minute. When it is known that elements of the message will be written down by recipient, speak at a slightly slower rate. 5. Maintain the speaking volume at a constant level. According to the ICAO Doc 9432 Manual of Radiotelephony the following transmitting techniques will assist in ensuring that transmitted speech is clearly and satisfactorily received: 6. A slight pause before and after numbers will assist in making them easier to understand. 7. Avoid using hesitation sounds such as "er". 8. Depress the transmit switch fully before speaking and do not release it until the message is completed. This will ensure that the entire message is transmitted. 9. An irritating and potentially dangerous situation in radiotelephony is a "stuck" microphone button. Operators should always ensure that the button is released after a transmission and the microphone placed in an appropriate place that will ensure that it will not inadvertently be switched on. HF and VHF Communication  VHF and HF communication systems use transceivers.  A transceivers is a self contained transmitter and receiver.  The transmitter and receiver both operate at same frequency, and the microphone button determines when there is an output from the transmitter.  In the absence of transmission the receiver is sensitive to incoming signals.  This combination of transmitters and receivers saves a lot of space and weight and are hence largely used. VHF Communication  Very High Frequency is a term used to describe the 30MHz to 300MHz portion of the radio spectrum.  This range of frequencies will provide short-range LOS (line of site) communications.  The range for VHF communications depends on equipment used, antenna height, and terrain(typically 2 to 20 miles). HF Communication  The frequency range is 3-30 MHz  This is used for long range communications because of its longer transmission range.  This is the basic band for long-range communications, mainly because its transmissions are reflected from the ionosphere.  HF transmitters have higher power outputs than VHF transmitters.  A Tuner is used to match the impedance of the transceiver to the antenna.  Use and installation of the HF communication system is same as that of the VHF communication system.  The advantage of using HF communication system over VHF communication system is that it can transmit information over long distance as the output power of the HF transmitter is higher than that of the VHF transmitter. Service Interphone System  The service interphone system provides ground crew personnel and all aircraft crewmembers with facilities that enable two-way voice communications during aircraft servicing or during normal flight operations.  Handset jacks are located throughout the aircraft, internally and externally, for use by ground crew personnel to facilitate aircraft servicing and maintenance. The service interphone switch on pilots' overhead panel P5 is used to disconnect these jacks from the system when they are not in use. Passenger Address System  The passenger address (PA) system provides means of communicating with the passengers and entertaining them with recorded music played over the speakers in the passenger compartment.  It also provides chime signals for the Passenger Call Systems, Flight Crew Call System, and Passenger Signs to attract the attention of flight attendants as well as passengers.  Announcements may be made using any of the three hand microphones or using the microphones and audio selector panels in the flight interphone system.  The passenger address system consists of a PA amplifier, loudspeakers, microphones, a tape reproducer, and interconnecting wiring. SELCAL Systems  SELCAL is a signaling method which can alert an individual aircraft that a ground station wishes to communicate with it. Two identical SELCAL (selective calling) systems are installed in the aircraft.  A four-tone alert signal from a ground station, is sent to an aircraft VHF or HF system and is detected by the SELCAL system.  The SELCAL system alerts the crewmembers by means of a light and a chime whenever a message is to be received on one of the communication systems.  The SELCAL systems are composed of a decoder, chime, and SELCAL control panel.  The chime is enclosed within the aural warning unit on the forward right side of the control stand. The SELCAL control panel is installed on the pilots' aft overhead panel. Aircraft Avionics And Autopilot Systems (AVIONICS-AS) Aircraft Communication System (Continuation) Communication  Transmitting information from one party to another.  Using different methods such as radio, METAR, ATIS, etc. Basic communication equipment  VHF Radio  Transponder  ELT VHF Radio  VHF communication systems are the most widely used for maintaining contact between ground and aircraft. This employs "Line Of Sight" transmission. Transponder  A device that receives a radio signal and sends out a signal in response. Mode A  Identification (Squawk Code) Mode C  Identification and altitude (Pressure Altitude) Mode S  Identification, altitude, data exchange. Transponder  “Squawk” assigning a transponder code  Right to left  0-7 Basic Squawk Codes  1200 – VFR  7500 – Unlawful Interference  7600 – Radio Failure/Lost Communications (NORDO)  7700 – Emergency (SOS, MAYDAY) Transponder  OFF Button  ON Button  STBY Button  ALT Button  IDENT Button Emergency Locator Transmitter (ELT)  An equipment which broadcasts distinctive signals on designated frequencies and, depending on application, may be automatically activated by impact or be manually activated.  Self contained and self powered. Transmits on distress frequencies:  121.5 MHz (civilian)  406 MHz for new ELTs  243 MHz (military) Emergency Locator Transmitter (ELT)  Automatic on impact (5G’s).  Battery should be enough to power it for at least 48 hours.  Batteries should be changed or recharged at 50 percent of the battery’s useful life. Categories of Messages Categories of Messages 1. Distress - a condition of being threatened by serious and/or immediate danger requiring immediate assistance. 2. Urgency – a condition concerning safety of an aircraft, another vehicle, or some person on board or within sight that does not require immediate assistance. 3. Communications relating to DIRECTION FINDING.  Heading  Bearing  Radial  Track vs Course Categories of Messages 4. Flight Safety Messages  Movement and control messages.  Messages originated by an aircraft operating agency or by an aircraft, of immediate concern to an aircraft in flight.  Meteorological advice of immediate concern to an aircraft in flight or about to depart (individually communicated or for broadcast).  Other messages concerning aircraft in flight or about to depart. Categories of Messages 5. Flight Regularity Messages  Messages regarding the operation or maintenance of facilities essential for the safety or regularity of aircraft operation.  Messages concerning the servicing of aircraft.  Instructions to aircraft operating agency representatives concerning changes in requirements for passengers and crew caused by unavoidable deviations from normal operating schedules. Standard Words and Phrases Standard Words and Phrases Standard Words and Phrases Call Signs for Aircrafts 1. Registration Markings  RP-C 1049 2. The telephony designator of the aircraft operating agency  Qatari 3. The telephony designator of the aircraft operating agency, followed by the flight identification  Cebu 149 Call Signs for Aeronautical Stations  Name + Call Sign Suffix  Manila Control  Clark Approach  Subic Tower  Vigan Radio Weather Reports ATIS  Automatic Terminal Information Service METAR  Meteorological Aerodrome Report TAF  Terminal Aerodrome Forecast   TAF: RPLC 221100Z 2212/2318 Weather Reports 34008KT 8000 SCT020 BKN300 TX31/2306Z TN20/2221Z TEMPO 2212/2218 36008KT 7000 -SHRA SCT020 OVC100  METAR: RPLC 221500Z 34004KT 8000 SCT020 BKN100 26/19 Q1011 NOSIG RMK A2985 VFR Procedures  Start-up  Clearances  Departure Procedures  Enroute Procedures  Arrival and Approach Procedures  NORDO Procedures Standard Call Read Back Start up and Taxi Clearance for Take-off Departure Procedures Departure Procedures Enroute Enroute Arrival and Approach Arrival and Approach Emergency Procedures (NORDO)  If the aircraft's radio fails, the recommended procedure when landing at a controlled airport. 1. Troubleshoot. 2. Observe the traffic flow. 3. Continue Blind Transmission, Squawk 7700 for 1 min then 7600 for 15 mins. 4. Enter the pattern, flash landing lights, rock the wings and look for a light gun signal from the tower to get landing clearance. 5. Land as soon as possible and safe. Light Gun Signals Aircraft Avionics And Autopilot Systems (AVIONICS-AS) Basic Aircraft Navigation System Navigation  Navigation is the method of determining position, course, and distance traveled. 1. Where you are. 2. Where you want to go. 3. The route that will take you from here to there. 4. How much fuel and time it will take to get there. Air navigation  Air navigation the science and technology of determining the position of an aircraft with respect to the surface of the earth and accurately maintaining a desired course. Visual Flight Rules  Visual Flight Rules (VFR) are the rules that govern the operation of aircraft in Visual Meteorological Conditions (VMC), the conditions in which flight is possible by visual reference.  Because of the limited communication and/or navigation equipment required for VFR flight, a VFR aircraft may be subject to limitations if and when it is permitted in controlled airspace. Pilotage  Pilotage is the use of fixed visual references on the ground by means of sight to guide oneself to a destination, sometimes with the help of a map or aeronautical chart.  Identification of present position and direction of flight by visual contact with terrain. Aeronautical Chart  An aeronautical chart is the road map for a pilot flying under VFR. The chart provides information that allows pilots to track their position and provides available information that enhances safety. Deduced Reckoning  Deduced/Dead Reckoning (DR) is a method of navigation relying on estimating one's current track, groundspeed and position based on earlier known positions. Application of laws of physics to estimate position  Estimating current position based solely on speed, direction of travel, and time since last known position (fix).  Calculation of basic flight parameters are necessary to safely get from point A to point B.  Airspeed indicator, clock, compass, and estimation of winds are required (wind triangle).  Basis for air navigation. Radio Navigation  Navigating or piloting the aircraft using only the instruments and the navigational systems installed such as VHF Omni directional Range (VOR) and Automatic Direction Finder (ADF). Instrument Flight Rules  Instrument flight rules (IFR) are a set of regulations that dictate how aircraft are to be operated when the pilot is unable to navigate using visual references under visual flight rules.  In order for the aircraft to be flown in instrument meteorological conditions (IMC), it must be fitted with the necessary instrumentation and certified by the regulatory authority. In addition to this, the pilot must hold an instrument rating. Automatic Direction Finder  Automatic direction finding (ADF) is an electronic aid to navigation that identifies the relative bearing of an aircraft from a radio beacon transmitting in the MF or LF bandwidth, such as a Non-Directional Beacon.  Oldest navigational system in use.  Receives radio signals from ground facilities called Non directional Beacon (NDB)  Capable also to receive Commercial Broadcasting Station which operates from 415- 1750 KHz. Non Directional Beacon (NDB)  Ground based radio transmitter that transmits radio energy in all directions.  Operates at a frequency between 190- 415 KHz LF and 510-535 KHz MF.  Limited operating range.  Strongly affected by weather  Used by Automatic Direction Finder (ADF) equipment. ADF/NDB Airborne Equipment  ADF Antenna ❑ Directional antenna ❑ Sense antenna  ADF Receiver  ADF Indicator  Definition of Terms Magnetic Heading (MH)  Direction aircraft’s nose is pointed. Relative Bearing (RB)  Degrees from the nose of the aircraft to the transmitter clockwise. Magnetic Bearing to/from (MBTO / MBFROM)  Direction to be flown to/from the station. How to find Line of Position (LOP)?  MH + RB = MBTO  MBTO +/- 180 = MBFROM = LOP Types of ADF Indicator Fixed Card ADF  Always shows 0 0°at the top.  The needle always points to Relative Bearing (RB). Movable Card ADF  Manually adjusted to show magnetic heading at top.  The needle always points to Magnetic Bearing to the station (MBTO). Very High Frequency Omni Directional Range (VOR)  VHF Omnidirectional Radio Range (VOR), is an aircraft navigation system operating in the VHF band. VORs broadcast a VHF radio composite signal including the station's Morse Code identifier, and data that allows the airborne receiving equipment to derive the magnetic bearing from the station to the aircraft. This line of position is called the "radial".  This is the most widely used means of radio navigation.  108-117.95 MHz  Accurate - with +/- 1 deg error.  Automatically compensate for wind drift. Principles of Operation  VOR station transmit radio beams, called radial , outward in every direction, based on Magnetic North.  VOR Station  VOR stations are fairly short range, the signals are line of sight between transmitter and receiver and are useful for up to 200 miles.  Each station broadcasts a VHF radio composite signal including the navigation signal, station's identifier and voice.  The navigation signal allows the airborne receiving equipment to determine a bearing from the station to the aircraft (direction from the VOR station in relation to Magnetic North). The station's identifier is typically a three-letter string in Morse code. How does the VOR station work?  Reference phase (Omni directional)  Variable phase (Directional) Classes of VOR Terminal VOR  A low-powered VOR (very high frequency omnidirectional radio- range) located at or near an airport at which a particular flight terminates and which has been specified as a NAVAID (navigational aid) in the final approach clearance.  Terminal VOR (TVOR) has a range of 25NM from 1,000 feet AGL to 12,000 feet AGL. Low Altitude VOR  Low-altitude VORs are meant to be used from 1,000 feet AGL through 18,000 feet AGL at distances of up to 40 NM from the station. High Altitude VOR  High Altitude VOR (HVOR) is a little trickier and has several different service volumes based on altitude. The first of these starts at 1,000 feet AGL up to 14,500 feet AGL with a range of 40NM.  As we increase in altitude so does range, from 14,500 feet AGL up to 18,000 feet, a range of 100NM. Then again, range will increase to 130NM from 18,000 feet up to 45,000 feet. Once we get over 45,000 feet the range will decrease back down to 100NM up to 60,000. VOR Map Depictions VOR Airborne Equipment  Antenna  VHF/NAV Receiver  Indicator Parts of the VOR 1. Omni Bearing Selector (OBS) Knob – To turn the compass card. 2. TO/FROM Indicator – Indicates if you are going TO/FROM the station. Can be changed when you turn the OBS knob. 3. Unreliable signal flag – Turns on when the VOR is broken. 4. Course Deviation Indicator (CDI) needle – Tells the pilot if the aircraft is deviated to the right or left or when moving sideways. 5. Deviation dots – Tells the pilot how many degrees the aircraft is deviated. Outer dot is 10 deg / 2 deg per dot. 6. Course index and Reciprocal course index – Tells the pilot the radial or Line of Position (LOP) TO/FROM the station. Steps how to use the VOR “Going away FROM the station” 1. Twist OBS until ‘FR’ appear. 2. Continue twisting OBS until CDI centers. 3. Once CDI is centered, your RADIAL or LINE OF POSITION reads under Course Index. Steps how to use the VOR “Going TO the station” 1. Twist OBS until ‘TO’ appears. 2. Continue twisting OBS until CDI centers. 3. Once CDI is center, your RADIAL or LINE OF POSITION reads under Reciprocal Course Index. Things to remember before using the VOR  Tune in to the correct frequency.  Identify through Morse code.  Test the VOR Testing the VOR Accuracy 1. VOR ground checkpoints - pre determined area in the airport with a known radial. +/ 4ᵒ allowable error. 2. VOR airborne checkpoints - a known landmark associated with a published radial. +/ 6ᵒ allowable error. 3. VOT (VOR Testing Facility) - broadcasts signal for radial 360 regardless of position. Testing the VOR Sensitivity  Twist OBS 10ᵒ left and right from the selected radial and there must be a full deflection of the CDI needle Testing the VOR. Ambiguity  Twist OBS 90ᵒ left and right from the selected radial and OFF flag must appear. VOR Limitations  Line of Sight – e.g. Terrain  Cone of Confusion – Happens when near the VOR station, CDI needle becomes erratic, Off position or no signal symbol is on.  Zone of Ambiguity – Center of TO and FROM.  Reverse Sensing – Pilot error Distance Measuring Equipment  Distance Measuring Equipment (DME) is defined as a navigation beacon, usually coupled with a VOR beacon, to enable aircraft to measure their position relative to that beacon.  Aircraft send out a signal which is sent back after a fixed delay by the DME ground equipment. An aircraft can compute its distance to the beacon from the delay of the signal perceived by the aircraft's DME equipment using the speed of light.  Combination of ground and airborne equipment which gives a continuous slant range distance-from-station readout by measuring time-lapse of a signal transmitted by the aircraft to the station and responded back.  DMEs can also provide groundspeed and time-to-station readouts by differentiation. VOR vs DME  VOR provides the ability to capture and track any radial, but it only provides direction. More information is needed in order to determine actual location. Can use information from 2 VORs and see where the radials intersect on a map to determine location.  VOR is passive, no input required from the plane.  Another way is to incorporate an additional device called a ‘DME’, Distance Measuring Equipment, required for operation above FL240, Ultra-high frequency  DME is active, requires transmitter and receiver at each end (Plane and DME).  Plane must send a signal to DME for it to activate. Marker Beacons  Marker beacons are vertically broadcast radio signals that indicate distance from runway and Outer Marker are more sensitive (narrower broadcast vertical cone) closer to the runway. Outer Marker Middle Marker Inner Marker Marker Beacons Outer Marker  The outer marker, which normally identifies the final approach fix (FAF), is situated on the same course/track as the localizer and the runway center-line, four to seven nautical miles before the runway threshold.  It is typically located about 1 NM (1.85 km) inside the point where the glideslope intercepts the intermediate altitude and transmits a 400 Hz tone signal.  The valid signal area is a 2,400 ft (730 m) × 4,200 ft (1,280 m) ellipse as measured 1,000 ft (300 m) above the antenna. When the aircraft passes over the outer marker antenna, its marker beacon receiver detects the signal. Marker Beacons Middle Marker  A middle marker works on the same principle as an outer marker. It is normally positioned 0.5 to 0.8 nautical miles (1 km) before the runway threshold.  When the aircraft is above the middle marker, the receiver's amber middle marker light starts blinking, and a repeating pattern of audible Morse code-like dot-dashes at a frequency of 1,300 Hz in the headset.  This alerts the pilot that the CAT I missed approach point (typically 200 feet (60 m) above the ground level on the glideslope). Marker Beacons Inner Marker  A inner marker located at the beginning (threshold) of the runway on some ILS approach systems (usually Category II and III) having decision heights of less than 200 feet (60 m) AGL.  Triggers a flashing white light on the same marker beacon receiver used for the outer and middle markers; also a series of audio tone 'dots' at a frequency of 3,000 Hz in the headset. Aircraft Avionics And Autopilot Systems (AVIONICS-AS) Advance Aircraft Navigation System Instrument Landing System  The Instrument Landing System is a precision runway approach aid employing two radio beams to provide pilots with vertical and horizontal guidance during the landing approach.  The localizer (LOC) provides horizontal guidance, while the glideslope (GS) defines the correct vertical descent profile.  Marker beacons and high intensity runways lights may also be provided as aids to the use of an ILS. Principles of operation  An instrument landing system operates as a ground-based instrument approach system that provides precision lateral and vertical guidance to an aircraft approaching and landing on a runway.  It uses a combination of radio signals and in many cases, high-intensity lighting arrays to enable a safe landing during instrument meteorological conditions (IMC), such as low ceilings or reduced visibility due to fog, rain, or blowing snow. Beam Systems  Previous blind landing radio aids typically took the form of beam systems. It normally consists of a radio transmitter that was connected to a motorized switch to produce a pattern of Morse code dots and dashes.  The resulting signal is sent into the air that consists of dots sent to one side of the runway and dashes to the other. The beams were wide enough so they overlapped in the center.  The pilots would hear dots or dashes if they were to the side of the runway, or if they were properly aligned, the two mixed together to produce a steady tone, the equisignal. ILS Components  Localizer  Glideslope  Marker Beacon  Approach Light System Localizer  A localizer (LOC) is an antenna array normally located beyond the departure end of the runway and generally consists of several pairs of directional antennas.  The Localizer generates and radiates signals to provide final approach azimuth navigation information to landing aircraft. The antenna sends a VHF carrier signal with 90-Hz and 150-Hz sideband signals that the aircraft instruments determine as left and right of the centerline.  The aircraft interprets the signal and displays them on the cockpit indicator guiding the pilot until the runway is in sight. Glideslope  The Glide Slope sends a UHF carrier signal with the same two 90-Hz and 150-Hz sideband frequencies that aircraft instruments determine as above or below the desired glide path.  The GS aerials are usually located so that the glide- slope provides a runway threshold crossing height of about 50 ft. This is approximately 3° above horizontal (ground level) to remain above obstructions and reach the runway at the proper touchdown point which gives the aircraft a descent rate of approximately 500 feet per minute.  The glide slope is normally positioned 1000 feet after the approach end of the runway Marker Beacon  These are vertically broadcast radio signals that indicate distance from runway and are more sensitive (narrower broadcast vertical cone) closer to the runway. Approach Light System (ALS)  ALS provide the basic means to transition from instrument flight to visual flight for landing. ALS are a configuration of signal lights starting at the landing threshold and extending into the approach area a distance of 2400-3000 feet for precision instrument runways and 1400-1500 feet for non- precision instrument runways.  Some systems include sequenced flashing lights which appear to the pilot as a ball of light traveling towards the runway at high speed. Visual Approach Slope Indicator (VASI)  The VASI is a system of lights so arranged to provide visual descent guidance information during the approach to a runway. These lights are visible from 3-5 miles during the day and up to 20 miles or more at night.  The visual glide path of the VASI provides safe obstruction clearance within plus or minus 10 degrees of the extended runway centerline and to 4 NM from the runway threshold.  The basic principle of the VASI is that of color differentiation between red and white. Each light unit projects a beam of light having a white segment in the upper part of the beam and red segment in the lower part of the beam. Precision Approach Path Indicator (PAPI)  The precision approach path indicator (PAPI) uses light units similar to the VASI but are installed in a single row of either two or four light units. These lights are visible from about 5 miles during the day and up to 20 miles at night.  The visual glide path of the PAPI typically provides safe obstruction clearance within plus or minus 10 degrees of the extended runway centerline and to 3.4 NM from the runway threshold. ILS Indicator Limitations of ILS  Localizer systems are sensitive to obstructions in the signal broadcast area, such as large buildings or hangars.  Glide slope systems are also limited by the terrain in front of the glide slope antennas. If terrain is sloping or uneven, reflections can create an uneven glidepath, causing unwanted needle deflections.  ILS critical areas and ILS sensitive areas are established to avoid hazardous reflections that would affect the radiated signal. The location of these critical areas can prevent aircraft from using certain taxiways leading to delays in takeoffs, increased hold times, and increased separation between aircraft. Categories of ILS Approach Where: RVR – Runway Visual Range Microwave landing system (MLS)  Microwave Landing System (MLS) is an all- weather, precision radio guidance system intended to be installed at large airports to assist aircraft in landing, including blind landings.  MLS was intended to replace or supplement the instrument landing systems (ILS). MLS has a number of operational advantages over ILS, including a wider selection of channels to avoid interference with nearby installations, excellent performance in all weather, a small "footprint" at the airports, and wide vertical and horizontal "capture" angles that allowed approaches from wider areas around the airport. Inertial Navigation System (INS)  Referred to a self-contained navigation system utilizing a gyro-stabilized platform for dead- reckoning, and with a pilot interface allowing a limited number of waypoints to be entered and basic navigation information to be displayed.  Inertial Navigation is a form of “Dead- Reckoning” that relies on accelerometers and gyroscopes to detect acceleration and velocity respectively along 3 perpendicular axes. An approximate 2 or 3 dimensional position can be constantly determined in relation to a known starting point, velocity and orientation. Inertial Reference Unit (IRU)  It refers to a computer that integrates Inertial Reference System (IRS) outputs and provides inertial reference outputs for use by other navigation and flight control systems, including the Flight Management System (FMS).  An IRU is like a modern, automated, dead- reckoning device.  IRU works on basis of latitude/longitude, so it is independent of magnetic North; it is considered as true location.  Use accelerometers and gyros to track changes in acceleration and direction. Global Navigation Satellite System (GNSS)  Global navigation satellite system (GNSS) is a general term describing any satellite constellation that provides positioning, navigation, and timing (PNT) services on a global or regional basis.  GPS is the most well known type of GNSS. Global Positioning System (GPS)  The Global Positioning System (GPS) is a U.S.-owned utility that provides users with positioning, navigation, and timing (PNT) services. This system consists of three segments: the space segment, the control segment, and the user segment.  GPS is a satellite based radio navigation system which utilizes precise range measurements from GPS satellites to determine precise position anywhere in the world. Global Positioning System (GPS)  Twenty four (24) satellites operated by USAF provide 24 hour, all weather, global coverage.  Satellites are equipped with atomic clocks.  Minimum of four (4) satellite signals enable receivers to triangulate position and time.  System is passive, it allows for unlimited number of users. Performance Based Navigation (PBN)  Performance Based Navigation (PBN) is comprised of Area Navigation (RNAV) and Required Navigation Performance (RNP) and describes an aircraft's capability to navigate using performance standards.  Performance-based Navigation (PBN), in simple terms, redefines the aircraft's required navigation capability from sensor (equipment) based to performance based. The foundation for Performance Based Navigation is area navigation or RNAV.  PBN defines performance requirements for aircraft navigating on an Air traffic service route (ATS) route, on a terminal or on an approach procedure. Area Navigation (RNAV)  Area navigation (RNAV) is a method of navigation that permits aircraft operation on any desired flight path within the coverage of ground or space based navigation aids, or within the limits of the capability of self- contained aids, or a combination of these. Required Navigation Performance (RNP)  Required Navigation Performance (RNP) is a family of navigation specifications under Performance Based Navigation (PBN) which permit the operation of aircraft along a precise flight path with a high level of accuracy and the ability to determine aircraft position with both accuracy and integrity.