The Aviation Science

Glide Slope 🛩️glide slope of ILS is defined as a system of vertical guidance embodied in the Instrument Landing System which indicates the vertical deviation of the aircraft from its optimum path of descent. 🛩️A glide slope station uses an antenna array sited to one side of the runway touchdown zone. The GS signal is transmitted on a carrier signal. 🛩️The centre of the glide slope signal is arranged to define a glide path of approximately 3° above horizontal (ground level). The beam is 1.4° deep (0.7° below the glide-path centre and 0.7° above). 🛩️The pilot controls the aircraft so that the glide slope indicator remains centered on the display to ensure the aircraft is following the glide path to remain above obstructions and reach the runway at the proper touchdown point (it provides vertical guidance). 🛩️Two signals are transmitted on one of 40 ILS channels. One is modulated at 90 Hz, the other at 150 Hz. These are transmitted from co-located ant...

Radio Waves 🛩️A radio wave is invisible to the human eye. It is electromagnetic in nature and part of the electronic spectrum of wave activity that includes gamma rays, x-rays, ultraviolet rays, infrared waves, and visible light rays, as well all radio waves. The atmosphere is filled with these waves. Each wave occurs at a specific frequency and has a corresponding wavelength. The relationship between frequency and wavelength is inversely proportional. A high frequency wave has a short wave length and a low frequency wave has a long wave length. 🛩️In aviation, a variety of radio waves are used for communication. Here, It is illustrated the radio spectrum that includes the range of common aviation radio frequencies and their applications. 🛩️A wide range of frequencies are used from low frequency (LF) at 100 kHz (100,000 cycles per second) to super high frequency (SHF) at nearly 10gHz (10,000,000,000 cycles per second). The Federal Communications Commission (FCC) controls ...

Types of Radio Waves 🛩️Radio waves of different frequencies have unique characteristics as they propagate through the atmosphere. VLF, LF, & MF waves have relatively long wavelengths and utilize correspondingly long antennas. 🛩️Radio waves produced at these frequencies ranging from 3kHz to 3mHz are known as ground waves or surface waves. They follow the curvature of the earth as they travel from the broadcast antenna to the receiving antenna. Ground waves are particularly useful for long distance transmissions. Automatic direction finders (ADF) & LORAN navigational aids use these frequencies. ✈️High frequency (HF) radio waves travel in a straight line & do not curve to follow the earth’s surface. This would limit transmissions from the broadcast antenna to receiving antennas only in the line-of-sight of the broadcast antenna except for a unique characteristic. HF radio waves bounce off of the ionosphere layer of the atmosphere. This refraction extends the range of...

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Inertial Navigation System 🛩️INSs contain Inertial Measurement Units (IMUs) which have angular and linear accelerometers (for changes in position). 🛩️some IMUs include a gyroscopic element (for maintaining an absolute angular reference). 🛩️Angular accelerometers measure how the vehicle is rotating in space. 🛩️Generally, there is at least one sensor for each of the three axes: pitch (nose up and down), yaw (nose left and right) and roll (clockwise or counter-clockwise from the cockpit). 🛩️Linear accelerometers measure non-gravitational accelerations of the vehicle. 🛩️Since it can move in three axes (up & down, left & right, forward & back), there is a linear accelerometer for each axis. 🛩️A computer continually calculates the vehicle's current position. 🛩️First, for each of the six degrees of freedom, it integrates over time the sensed acceleration, together with an estimate of gravity, to calculate the current velocity. Then it integrates the vel...

Automatic Direction Finder 🛩️ADF (Automatic Direction Finder) is the radio signals in the low to medium frequency band of 190 Khz. to 1750 Khz. 🛩️It has the major advantage over VOR navigation in the reception is not limited to line of sight distance. 🛩️The ADF signals follow the curvature of the earth. 🛩️The maximum of distance is depend on the power of the beacon. 🛩️The ADF can receives on both AM radio station and NDB (Non-Directional Beacon). 🛩️Commercial AM radio stations broadcast on 540 to 1620 Khz. Non-Directional Beacon operate in the frequency band of 190 to 535 Khz. ✈️ADF COMPONENTS ✈️ADF Receiver: pilot can tune the station desired and to select the mode of operation. The signal is received, amplified, and converted to audible voice or morse code transmission and powers the bearing indicator. ✈️Control Box (Digital Readout Type) : Most modern aircraft has this type of control in the cockpit. In this equipment the frequency tuned is displayed as digital...

Non Directional Beacon 🛩️A Non-Directional Beacon is a ground-based, low frequency radio transmitter used as an instrument approach for airports and offshore platforms. 🛩️The NDB transmits an omni-directional signal that is received by the Automatic Direction Finder, a standard instrument onboard aircraft. 🛩️The pilot uses the ADF to determine the direction to the NDB relative to the aircraft. 🛩️To navigate using the ADF, the pilot enters the frequency of the NDB and the compass card (or arrow) on the ADF will indicate the heading to the station. 🛩️The signal is transmitted on an uninterrupted 24/7 basis. 🛩️An audible Morse Code call sign of one or more letters or numbers is used to identify the NDB being received. 🛩️NDB’s used for aviation are standardized by ICAO, Annex 10 which specifies that NDB be operated on a frequency between 190 to 1800 kHz. 🛩️In North America, the frequency range is typically from 190 to 625 kHz, for offshore operation...

Runway Designation 🛩️Since aircraft are affected by the wind during takeoffs and landings, runways are laid out according to the local prevailing winds. 🛩️Runways are numbered (designated) to the nearest 10° in relation to magnetic north based on approach direction. ✈️Example: 084° is marked 08 ✈️Example: 085° is marked 08 or 09 ✈️Example: 086° is marked 09 🛩️This number becomes the runway's name, and is how it is referenced by Air Traffic Control (ATC)and other pilots. 🛩️The opposite end of the runway is then marked with the reciprocal heading. 🛩️Reciprocal heading is determined by adding or subtracting 180° from the runway heading. 🛩️You must therefore add 180 to any runway 180 or below, and subtract 180 to anything 180 or above. ✈️Example: (using runway 26) 260° - 180° = 080° ✈️Example: (using runway 08) 080° + 180° = 260° 🛩️If your answer comes out to be greater than 360, or negative, then you added when you should have subtrac...

Instrument Landing System 🛩️An Instrument Landing System (ILS) enables pilots to conduct an instrument approach to landing if they are unable to establish visual contact with the runway. 🛩️It is defined by the International Telecommunication Union as a service provided by a station. 🛩️The ILS works using two components, a localizer and a glideslope. 🛩️The frequencies for the localizer are between 108.1-111.95 MHz and the glide slope between 329.15-335.0 MHz. 🛩️These frequencies are the carrier waves that the modulation takes place. 🛩️A pilot is only concerned with the localizer frequency as the navigation equipment knows the paired glideslope frequency for any given localizer frequency. 🛩️The localizer antenna broadcasts two lobes down the length of the runway for a few miles (typically 18 nm). 🛩️The glideslope antenna sits around the 1000 ft touchdown zone markers on the runway, offset a little bit from the runway. 🛩️It broadc...

PAPI & VASI 🛩️ The visual approach slope indicator (VASI) is a system of lights on the side of an airport runway threshold that provides visual descent guidance information during approach. 🛩️These lights may be visible from up to 8 kilometres (5.0 mi) during the day and up to 32 kilometres (20 mi) or more at night. 🛩️Basic visual approach slope indicators consist of one set of lights set up some 7 metres (23 ft) from the start of the runway. 🛩️Each light is designed so that it appears as either white or red, depending on the angle at which it is viewed. 🛩️When the pilot is approaching the lights at the proper angle, meaning the pilot is on the glide slope, the first set of lights appears white and the second set appears red. 🛩️When both sets appear white, the aircraft is too high, and when both appear red it is too low. 🛩️This used to be the most common type of visual approach slope indicator s...

Precision Approach Path Indicator 🛩️ A precision approach path indicator (PAPI) is a visual aid that provides guidance information to help a pilot acquire and maintain the correct approach (in the vertical plane) to an airport or an aerodrome. 🛩️It is generally located on the left-hand side of the runway approximately 300 meters beyond the landing threshold of the runway. 🛩️The ratio of white to red lights seen is dependent on the angle of approach to the runway. 🛩️Above the designated glide slope a pilot will observe more white lights than red. 🛩️At approaches below the ideal angle more red lights than white will be seen. 🛩️For the optimum approach angle the ratio of white to red lights will remain equal throughout, for most aircraft, the exceptions being the Boeing 747 and now retired Concorde. 🛩️With the 747, because the cockpit is approximately 20 feet behind the nose and much higher than other aircraft, the fl...