Executive Summary
This is a report about the internship at the Engineering Department of PIA (Pakistan International Airlines). The purpose of the internship was to introduce the telecommunication systems that are used in aircrafts. These systems include HF and VHF communication Systems, GPWS, ELTs (emergency locator transmitter), ADF (automatic direction finder), CVR (cockpit voice recorder), Weather radar, ATC (air traffic controller), LRRA (low arrange radio Altimeter), DME (distance measurement equipment), TCAS (traffic collision avoidance system), IFE (interactive flight equipment), VOR (VHF Omni Range), ILS (Information Landing System). This Internship was basically study of PIA aircrafts specially Boeing-777 and Boeing-310.
Introduction
The journey of our internship started on the very first day we were given the Security pass to enter in the engineering section. PIA has the workshops in many fields of engineering but as a telecom-engineering student we were initially sent to the RADIO overhaul section of PIA Engineering Department. RADIO overhaul workshop is place where all Communication equipment of aircraft are repaired and maintained. There were about 20 engineers working in that RADIO over haul.
Discussion
Our journey was started with HF and VHF communication Section and we were given the knowledge about the communication systems that the Aircraft uses for voice communication in the HF and VHF band. HF Communication: It is used for long distant communication. It uses sky wave propagation. The power requirement of HF transceivers is (100-200) but 120 is recommended. In PIA aircrafts 2 HF transceivers are used. At a time 1 will work because of Single HF Antenna. VHF Communication: It is used for communication up to 150 miles. t is mostly used at the time of Take-off and landing .
The power requirement of VHF transceivers is (18-28) but 22 watt is recommended. In PIA aircrafts 3 VHF transceivers are used. 3 can be Used Simultaneously Emergency locator transmitter (ELT) Emergency locator transmitter is used by aircraft to point out the flight when any emergency occur. There are two types of ELT: Automatic telecommand Portable (ATP) ATP is a transmitter placed in Airplane and is used to locate the emergency. It is activated when a heavy jerk accrue in height of flight.
When a rapid change is detected in height of flight this transmitter transmit a signal to the satellite, so that the emergency can be located. It works on the gravity so that the name G-switch is also used. Automatic survivor (AS) It is also a type of ELT but is activated when plane fall in water. It has a water detector sensor whenever the water is detected it transmits signal to satellite. ELT signal contain 3 types of information in it Plane tail number, Country code, CSN number Initially ELTs were operating on three frequencies, 121.
MHz, 406 MHz & 243 MHz but now it only operates on 406 MHz Automatic Direction Finder (ADF) An automatic direction finder (ADF) is an aircraft radio-navigation instrument which automatically and continuously displays the relative bearing from the ship or aircraft to a suitable radio station. ADF receivers are normally tuned to aviation operating in the LW band between 190 – 535 kHz. Like RDF units, most ADF receivers can also receive medium wave (AM) broadcast stations, though as mentioned, these are less reliable for navigational purposes.
The operator tunes the ADF receiver to the correct frequency and verifies the identity of the beacon by listening to the Morse code signal transmitted. On aviation ADFs, the unit automatically moves a compass-like pointer (RMI) to show the direction of the beacon. The pilot may use this pointer to home directly towards the beacon, or may also use the magnetic compass and calculate the direction from the beacon (the radial) at which their aircraft is located. Unlike the RDF, the ADF operates without direct intervention, and continuously displays the direction of the tuned beacon.
Initially, all ADF receivers, both marine and aircraft versions, contained a rotating loop or ferrite loop stick aerial driven by a motor which was controlled by the receiver. Like the RDF, a sense antenna verified the correct direction from its 180-degree opposite. More modern aviation ADFs contain a small array of fixed aerials and use electronic sensors to deduce the direction using the strength and phase of the signals from each aerial. The electronic sensors listen for the trough that occurs when the antenna is at right angles to the signal, and provide the heading to the station using a direction indicator.
In flight, the ADF’s RMI or direction indicator will always point to the broadcast station, regardless of the aircraft’s attitude or heading. Such receivers can be used to determine current position, track inbound and outbound flight path, and intercept a desired bearing. These procedures are also used to execute holding patterns and non-precision instrument approaches.
Cockpit Voice Recorder (CVR)
A cockpit voice recorder (CVR), often referred to as a “black box, is a flight recorder used to record the audio environment in the flight deck of an aircraft for the purpose of investigation of accidents and incidents. This is typically achieved by recording the signals of the microphones and earphones of the pilots’ headsets and of an area microphone in the roof of the cockpit. Where an aircraft is required to carry a CVR and utilizes digital communications the CVR is required to record such communications with air traffic control unless this is recorded elsewhere. As of 2005 it is an FAA requirement that the recording duration is a minimum of thirty minutes, but the NTSB has long recommended that it should be at least two hours. A standard CVR is capable of recording 4 channels of audio data for a period of 2 hours.
The original requirement was for a CVR to record for 30 minutes, but this has been found to be insufficient in many cases, significant parts of the audio data needed for a subsequent investigation having occurred more than 30 minutes before the end of the recording. The earliest CVRs used analog wire recording, later replaced by analog magnetic tape. Some of the tape units used two reels, with the tape automatically reversing at each end. Other units used a single reel, with the tape spliced into a continuous loop, much as in an 8-track cartridge.
The tape would circulate and old audio information would be overwritten every 30 minutes. Recovery of sound from magnetic tape often proves difficult if the recorder is recovered from water and its housing has been breached. Thus, the latest designs employ solid-state memory and use digital recording techniques, making them much more resistant to shock, vibration and moisture. With the reduced power requirements of solid-state recorders, it is now practical to incorporate a battery in the units, so that recording can continue until flight termination, even if the aircraft electrical system fails.
Low Range Radio
Altimeter Low range radio altimeter (LRRA) or simply RA measures altitude above the terrain presently beneath an aircraft or spacecraft. This type of altimeter provides the distance between the plane and the ground directly below it, as opposed to a barometric altimeter which provides the distance above a pre-determined datum, usually sea level Radar altimeters are frequently used by commercial aircraft for approach and landing, especially in low-visibility conditions (see instrument flight rules) and also automatic landing, allowing the autopilot to know when to begin the flare maneuver.
In civil aviation applications, radio altimeters generally only give readings up to 2,500 feet (760 m) above ground level (AGL). Today, almost all airliners are equipped with at least one and usually several radar altimeters, as they are essential to auto landing capabilities (determining height through other methods such as GPS (Global Positioning System) is not permissible under current legislation). Even older airliners from the 1960s, such as Concorde and the British Aircraft Corporation BAC 1-11 were so equipped and today even smaller airliners in the sub-50 seat lass are supplied with them (such as the ATR 42 and BAe Jet stream series).
Radio altimeters are an essential part in ground proximity warning systems (GPWS), warning the pilot if the aircraft is flying too low or descending too quickly. However, radar altimeters cannot see terrain directly ahead of the aircraft, only that directly below it; such functionality requires either knowledge of position and the terrain at that position or forward looking terrain radar which uses technology similar to a radio altimeter.
Weather RADAR
A weather radar, or weather surveillance radar (WSR), is a type of radar used to locate precipitation, calculate its motion, estimate its type (rain, snow, hail, etc. ), and forecast its future position and intensity. Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to intensity of the precipitation. Both types of data can be analyzed to determine the structure of storms and their potential to cause severe weather.
Weather radars send directional pulses of microwave radiation, on the order of a microsecond long, using a cavity magnetron or klystron tube connected by a waveguide to a parabolic antenna. The wavelengths of 1 to 10 cm are approximately ten times the diameter of the droplets or ice particles of interest, because Rayleigh scattering occurs at these frequencies. This means that part of the energy of each pulse will bounce off these small particles, back in the direction of the radar station.
Air Traffic Control (ATC)
Air traffic control (ATC) is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other support for pilots when able. In some countries, ATC may also play a security or defense role (as in the United States), or be run entirely by the military (as in Brazil).
Preventing collisions is referred to as separation, which is a term used to prevent aircraft from coming too close to each other by use of lateral, vertical and longitudinal separation minima; many aircraft now have collision avoidance systems installed to act as a backup to ATC observation and instructions. In addition to its primary function, the ATC can provide additional services such as providing information to pilots, weather and navigation information and NOTAMs (Notices to Airmen).
In many countries, ATC services are provided throughout the majority of airspace, and its services are available to all users. When controllers are responsible for separating some or all aircraft, such airspace is called “controlled airspace” in contrast to “uncontrolled airspace” where aircraft may fly without the use of the air traffic control system. Depending on the type of flight and the class of airspace, ATC may issue instructions that pilots are required to follow, or merely flight information (in some countries known as advisories) to assist pilots operating in the airspace.
In all cases, however, the pilot in command has final responsibility for the safety of the flight, and may deviate from ATC instructions in an Emergency. Distance Measurement Equipment DME Distance measuring equipment (DME) is a transponder-based radio navigation technology that measures distance by timing the propagation delay of VHF or UHF radio signals. Aircraft use DME to determine their distance from a land-based transponder by sending and receiving pulse pairs – two pulses of fixed duration and separation. The ground stations are typically co-located with VORs.
A typical DME ground transponder system for en-route or terminal navigation will have a 1 kW peak pulse output on the assigned UHF channel. A low-power DME can also be co-located with an ILS GLIDE SLOPE where it provides an accurate distance function, similar to that otherwise provided by ILS Marker Beacons.
Traffic Collision Avoidance System (TCAS)
A traffic collision avoidance system or traffic alert and collision avoidance system (both abbreviated as TCAS) is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft.
It monitors the airspace around an aircraft for other aircraft equipped with a corresponding active transponder, independent of air traffic control, and warns pilots of the presence of other transponder-equipped aircraft which may present a threat of mid-air collision (MAC). It is a type of airborne collision avoidance system mandated by the International Civil Aviation Organization to be fitted to all aircraft with a maximum take-off mass (MTOM) of over 5700 kg (12,586 lbs) or authorized to carry more than 19 passengers.
Official definition from PANS-ATM (Nov 2007): ACAS / TCAS is an aircraft system based on secondary surveillance radar (SSR) transponder signals which operates independently of ground-based equipment to provide advice to the pilot on potential conflicting aircraft that are equipped with SSR transponders. In modern glass cockpit aircraft, the TCAS display may be integrated in the Navigation Display (ND); in older glass cockpit aircraft and those with mechanical instrumentation, such an integrated TCAS display may replace the mechanical Vertical Speed Indicator (which indicates the rate with which the aircraft is descending or climbing).
In-Flight Entertainment (IFE)
In-Flight entertainment (IFE) refers to the entertainment available to aircraft passengers during a flight. At first, IFE consisted of looking out the window. (Zeppelin sightseeing flights were available in Europe before the First World War. ) In 1936, the airship Hindenburg offered passengers a piano, lounge, dining room, smoking room, and bar during the 2-1/2 day flight between Europe and America. ) After the Second World War, IFE was delivered in the form of food and drink services, along with an occasional projector movie during lengthy flights.
In 1985 the first personal audio player was offered to passengers, along with noise cancelling headphones in 1989. During the 1990s the demand for better IFE was a major factor in the design of aircraft cabins. Before then, the most a passenger could expect was a movie projected on a screen at the front of a cabin, which could be heard via a headphone socket at seat. The largest manufacturers of IFE systems are Panasonic Avionics Corporation, Thales Group, Rockwell Collins and Live TV.
Design issues for IFE include system safety, cost efficiency, software reliability, hardware maintenance, and user compatibility VHF Omni Range (VOR) VOR, short for VHF Omni directional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station’s identifier, voice (if equipped), and navigation signal. The identifier Morse code, the voice signal is usually station name, in-flight recorded advisories, or live flight service broadcasts.
The navigation signal allows the airborne receiving equipment to determine a magnetic bearing from the station to the aircraft (direction from the VOR station in relation to the Earth’s magnetic North at the time of installation). VOR stations in areas of magnetic compass unreliability are oriented with respect to True North. This line of position is called the “radial” from the VOR. The “intersection” of two radials from different VOR stations on a chart provides an approximate position of the aircraft.
Information Landing System (ILS)
An Optical Landing System (OLS) is used to give glide path information to pilots in the terminal phase of landing on an aircraft carrier from the beginning of aircraft landing on ships in the 1920s to the introduction of OLSs, pilots relied solely on their visual perception of the landing area and the aid of the Landing Signal Officer (LSO in the US Navy, or “batsman” in the Commonwealth navies). LSOs used colored flags, cloth paddles and lighted wands.
Conclusion
It was a great experience for me as internee at PIA. I got a lot of practical exposure. We basically study about PIA aircrafts (777 and 310). 310 were old and 777 were new. 310 consists of old technology and they mostly consists of analog systems while the 777 were consists of digital systems and new technology. We visited both models completely and studied about their technology thoroughly. The Systems we learn were CVR, LRRA, Weather radar, ATC, DME, TCAS, IFE, VOR, and ILS.
