International Civil Aviation Organization (ICAO)

Task I: Limitations Imposed on Aircraft Communication.
The International Civil Aviation Organization (ICAO) uses English as the aviation language, which enables it to enhance on the communication between pilots and air traffic controllers (ICAO). Accordingly, ICAO requires all pilots on international flights, and air traffic controllers working in international airports and routes to communicate in English effectively, as well as in their native language. Importantly, this policy helps in the elimination of communication errors and difficulty in language comprehension, which can lead to serious airspace incidences. In the UK, the Radiotelephony Manual, CAP 413 regulates the pilot – air traffic control communication.
Limitations Imposed on Aircrafts Communication by UK Radiotelephony Manual CAP 413
The operator should ensure that the receiver volume is set at an optimum level, so that there is no interference with transmission from another station. She/he should also be familiar with the microphone operating techniques and should not turn away from it while talking or vary the distance between it because varying the distance may the distort the speech (Civil Aviation Authority). Finally, the operator should avoid talking too close to the microphone, touching the microphone with the lips and holding the microphone so as not to distort the speech.
It is expected that operators use normal conversation tone, speak eloquently using the standard radiotelephony (RTF) words and phrases and distinctly at an even rate of speech not exceeding one hundred words per minute. The operator should also slow down once the elements of the message are documented and pause before and after numbers. They must maintain the speaking volume at a constant level, pause slightly before and after numbers, and avoid using hesitations, excess courtesies, and using non-operational conversations.
The transmit switch should be depressed fully before the operator starts speaking and should only be released when the message is complete to transmit the entire message. The message should not contain more than three specific phrases, comprising a clearance, instruction, or pertinent information. After every transmission, the microphone button should be released after a transmission and the microphone placed in an appropriate place so that cannot be inadvertently switched on (Civil Aviation Authority). At least ten seconds should elapse before a second call is made to eliminate unnecessary transmissions while the receiving station is getting ready to reply to the initial call.
When individual letters are required to be transmitted, words and syllables outlined in the Radiotelephony Manual, CAP 413 shall be used. Each digit shall be transmitted separately for messages containing aircraft call signs, altimeter settings, flight levels headings, wind speeds/directions, pressure settings, airspeed, transponder codes, and frequencies. All numbers used in the transmission of altitude, height, cloud height, visibility, and runway visual range information, which contain whole hundreds and whole thousands, should be transmitted by pronouncing each digit in the number of hundreds or thousands followed by the word HUNDRED or TOUSAND as appropriate. Combinations of thousands and whole hundreds should be transmitted by pronouncing each digit in the number of thousands followed by the word TOUSAND and the number of hundreds followed by the word HUNDRED (Civil Aviation Authority). For example, number 25,000, should be transmitted as Two, Five Thousand, pronounced as Too Fife Tousand.
When necessary to verify the accurate reception of numbers the person transmitting the message shall request the person receiving the message to read back the numbers. When transmitting time, only the minutes of the hour are normally required. However, the hour should be included if there is any possibility of confusion (Civil Aviation Authority). Time checks should be given to the nearest minute and preceded by the word ‘TIME.’ Co-ordinated Universal Time (UTC) should be used at all times unless specified. 2400 hours designates midnight, the end of the day, and 0000 hours the beginning of the day.
Task 2: Principles of Operation of a Typical Radio Transmitter/Receiver System
The pilot operates the transmitter while the airborne units consist of a receiver and one or more receivers. The transmitter and receiver, together form a transceiver. Today’s radios use different frequencies depending on the frequency and distance they have to transmit to. Discussed below are the principles of operation of a typical radio transmitter/ receiver system.
They all have a power supply circuit that converts the input electronic signal such as audio, video or scan into the required output.  An electronic oscillator generates a carrier signal; this is a radio signal generated by the radio signal through a process called modulation. The carrier wave carries data through ‘space.’ Information is added to the carrier signal by a modulator circuit. This process is done by varying the aspect of the carrier wave, which is then magnified by a radio frequency (RF) amplifier, which increases the range of radio waves (Miles). The signal is then applied to the antenna, which radiates radio waves to the receiver (Miles). There are two main types of antennas, omnidirectional (radiate in all directions) and directional (directed to particular direction). An aircraft may require many antennae, but this depends on the type of transmitter fitted on the aircraft.
A tuned radio frequency receiver intercepts the electronic waves from the transmitter, demodulates them and responds specifically to the intended signals. For superheterodyne receivers, the signals are transformed into video signals. Information is also collated and transmitted in short burst transmission via a data link. This information can be from the aircraft flight management computer, weather broadcasts, monitoring devices, airborne radar pictures, messaging service. For aircrafts crossing the Atlantic and Pacific oceans, the controller-pilot datalink communications are used for communication purposes (Miles). The aircraft’s location, speed, and altitude are sent to the air traffic controllers using the aircraft’s flight management computer. Data link messages can be encrypted to achieve security.
Lastly, there is an emergency locator transmitter, which is carried in crew life jackets. It is used to locate survivors in cases of crashes. In summary, the transmitter communicates with the receiver by generation carrier signal; this is only possible when the receiver is tuned to detect transmitters signal.
Task 3: Performance Specifications of an Aircraft Receiver
2.4GHz Transmitter RC Airplane Transmitter
Source: Carpenter
The above is a traditional multi-channel RC airplane transmitter. The transmitter has trims and switches, two control sticks, rotating dials and sliding levers on the face and top of the transmitter body (Carpenter). The dials are strategically placed within easy fingertip reach. The switches, dials, and levers are used for any channels over and above the primary controls, like the landing gear and flaps (Carpenter). The control sticks move up and down, right and left to control at least two functions.
To fine tune and iron out unwanted tendencies that planes may have while in the air, transmitter trims move the respective control surface by a very small amount. Minor trim changes are usually made during every flight for one reason or the other. When any input is made by the pilot, be it moving a stick, flicking a switch or rotating a dial, a radio signal is sent out via the transmitter’s antenna and is picked up by the receiver, located inside the model (Carpenter). That signal passes from the receiver directly to the servos, which makes the plane to have an even movement of its control surface, throttle, and other flight features (Carpenter).
The transmitter has amplifiers and modulators and oscillators. The amplifiers increase the strength of the signal so that the EM waves travel a useful distance from the antennae while the modulator combines the AF and RF signals so that information can be transmitted. The output of the modulator, modulated RF, is demodulated to produce an AF output. A proper combination of AF and RF should have proper relative strength for maximum efficiency. The oscillator produces frequencies needed by both the transmitter and the receiver. A simple modulator is made up of; a capacitor that gives the desired frequency, and the inductor is parallel.
The antenna transforms EM waves into an electrical signal on a receive antenna. The antenna is used for either receiving, transmitting or both, depending on the radio system used. Its length must be one-half the wavelength of the signal being transmitted or received. The 2.4GHz transmitter has a short antenna, about 150cm long, this is because it has a much shorter wavelength and therefore requires a shorter antenna (Carpenter).
Aircraft radios supply an output for the pilot and voice transmitters require an audio input from the microphone, the speaker transforms electrical waves into sound waves. Computerized transmitters will have an LCD screen to display relevant information to the pilot. The 2.4GHz transmitter is not computerized and is one of the most basic transmitters.

Works Cited

Carpenter, Pete. R/C/ Airplane World. Radio Control Gear Explained. (N.d). Accessed 20th February 2017,
ICAO. ICAO Promotes Aviation Safety by Endorsing English Language Testing. 2011. Accessed 20th February 2017,
Miles, Malcolm. Avionics and Aircraft Systems. 2016. Accessed 20th February 2017,
Civil Aviation Authority. Radiotelephony Manual CAP 413. 2015. Accessed 20th February 2017,