Lesson Notes By Weeks and Term v4 - SHS 1
Fundamentals of Avionics
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Fundamentals of Avionics
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Subject: Aviation And Aerospace Engineering
Class: SHS 1
Term: 2nd Term
Week: 4
Grade code: 1.2.1.LI.3
Strand code: 2
Sub-strand code: 1
Content standard code: 1.2.1.CS.2
Indicator code: 1.2.1.LI.3
Theme: Avionics
Subtheme: Fundamentals of Avionics
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This lesson introduces the fundamental concept of surveillance systems in aviation. We often see surveillance in our daily lives, like the CCTV cameras at the Accra Mall, in banks, or even at Kotoka International Airport (KIA). These systems help us monitor what is happening to ensure safety and security. In aviation, surveillance is even more critical. It is how Air Traffic Controllers (ATCs) "see" aircraft in the sky, even when they are hundreds of kilometres away, hidden by clouds, or flying at night. Understanding these systems is the first step to appreciating how Ghana manages its airspace safely, guiding thousands of flights and passengers to their destinations without incident.
A. What is Surveillance in Aviation?
In simple terms, surveillance is the process of monitoring something from a distance. In aviation, it specifically means knowing the position, and often the identity and altitude, of aircraft in the airspace.
Think of a busy junction in Accra like the Kwame Nkrumah Circle interchange. Without traffic lights or a police warden directing traffic, there would be chaos and accidents. Air Traffic Controllers are like the police wardens of the sky, and surveillance systems are their eyes. These systems allow them to build a mental picture, or a real picture on a screen, of where every aircraft is, where it's going, and how fast. B. The Two Main Types of Surveillance
Aviation surveillance is divided into two major categories based on whether the aircraft being watched needs to help. Non-Cooperative Surveillance: This system works without any help from the aircraft it is tracking. The aircraft can be completely passive. Analogy: Imagine you are in a large, dark cave. If you shout "HELLO!", you will hear an echo bouncing back from the walls. From the direction and the time it takes for the echo to return, you know *something* is there and how far away it is. You don't know *what* it is, just that it's there. The main example is Primary Surveillance Radar (PSR). Cooperative Surveillance: This system requires the aircraft to have special equipment (a transponder) that actively participates in the surveillance process. Analogy: Imagine you are in the same dark cave, but this time when you shout "WHO IS THERE?", a voice replies, "IT IS AMA, I AM 50 METRES AWAY AND I AM STANDING ON A BOX!" This system gives you much more information because the other person cooperated. Examples include Secondary Surveillance Radar (SSR) and Automatic Dependent Surveillance-Broadcast (ADS-B). C. Key Aviation Surveillance Systems Explained Primary Surveillance Radar (PSR) What it is: The most basic form of radar. It is a non-cooperative system. How it works (Step-by-Step): A large rotating antenna on the ground sends out a powerful pulse of radio energy (a "ping") into the sky. This energy travels outwards at the speed of light. If the energy hits an object, like an aircraft, a small fraction of that energy is reflected back towards the antenna (an "echo"). The radar system measures two things: Time: The time it took for the echo to return. Since radio waves travel at a constant speed, this time is used to calculate the distance (range) to the aircraft. Direction: The direction the antenna was pointing when it received the echo. This gives the bearing (direction) of the aircraft. Function: To detect the presence, range, and bearing of any object in the sky, whether it is a cooperating aircraft, a flock of birds, or even an unauthorised drone. Its main advantage is that it sees everything that reflects radio waves. Limitation: It cannot identify the aircraft or know its altitude. It just shows a "blip" on the controller's screen. Secondary Surveillance Radar (SSR) What it is: A more advanced, cooperative system that works alongside PSR. How it works (Step-by-Step): The SSR ground station sends out a coded radio signal called an "interrogation." An aircraft equipped with a device called a transponder receives this interrogation. The transponder automatically sends back a coded "reply." This reply contains much more information than a simple echo. It includes: Identity: A unique 4-digit code (called a "squawk code") assigned by Air Traffic Control. Altitude: The aircraft's pressure altitude, read from its own instruments. Function: To provide Air Traffic Controllers with the precise identity and altitude of cooperating aircraft. This turns the anonymous "blip" from the PSR into a tagged, identified target on their screen, making it much easier to manage traffic. For example, a flight from Kumasi to Accra might be assigned the squawk code "2103". Automatic Dependent Surveillance-Broadcast (ADS-B) What it is: The modern, satellite-based standard for air traffic surveillance. It is a cooperative system. Let's break down the name: Automatic: The system works all the time without needing to be interrogated by a ground station. Dependent: It *depends* on the aircraft's own navigation systems (like GPS) to know its precise position. Surveillance: Its purpose is to provide surveillance information. Broadcast: The aircraft continuously broadcasts its information, like a radio station, for anyone with the right receiver to hear. How it works (Step-by-Step): The aircraft uses its GPS receiver to determine its exact position (latitude, longitude, altitude), speed, and direction. This information, along with its identity, is packaged into a digital message. About twice per second, the aircraft's ADS-B transmitter broadcasts this message. The signal is received by ground stations and by other nearby aircraft that are also equipped with ADS-B receivers. Function: To provide highly accurate, real-time position and velocity data to both air traffic controllers and other pilots. It is more accurate than radar and allows for more efficient routing of aircraft, saving fuel and time. This is the technology being implemented globally to upgrade air traffic management. Traffic Collision Avoidance System (TCAS) What it is: An onboard safety system designed to prevent mid-air collisions. It is independent of ground control. How it works: TCAS works by interrogating the transponders of other nearby aircraft, just like SSR. It uses the replies to build a 3D map of the traffic in the immediate vicinity. If it calculates that another aircraft is on a potential collision course, it issues alerts to the pilots. Levels of Alert: Traffic Advisory (TA): An audible alert ("Traffic, Traffic") tells the pilots to visually search for the other aircraft. Resolution Advisory (RA): If the risk becomes critical, TCAS gives the pilots a direct, life-saving command, such as "Climb, Climb!" or "Descend, Descend Now!". The TCAS systems in both aircraft coordinate so that one is told to climb while the other is told to descend. Function: To act as the last line of defence against mid-air collisions. Pilots are trained to follow a TCAS RA command immediately, even if it contradicts an instruction from air traffic control.