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Hello everybody in my New program series about aviation.
Subject for today is ILS. Let’s go.
During nice weather there are no problems with landings and non-precision approach, or visual approach
Problems appear when weather is getting worse. Luckily, an ILS system comes in aid.
ILs is radio system enabling precision approach to a certain point on glide path.
The whole system consists of: two beacons, three markers (interchangeably with distance measuring equipment - DME)
and aerodrome lights (approach, edge, runway axis, runway threshold).
One of the beacons emits two different signals in horizontal plane.
Wave to the left has a frequency of 90 Hz, and wave to the right has a frequency of 150 Hz.
As a result of intersection those two waves it is possible to allocate the horizontal glide path that is exactly above the runway axis.
second beacon works just like the first one, but the signal is emitted in vertical plane.
How does it look like in practice? let’s see.
As you can see, the aeroplane is tilted horizontally and vertically, as shown by Vor-ils indicator.
Horizontal tip – GPI is responsible for the glide slope, and vertical tip – TDI – is responsible for the horizontal path.
Right now, aeroplane is above the glide slope and to the left of runway axis,
since gpi tip is below optimal position, and tdi tip is on the right of optimal position.
Sound signal is informing us about passing first (outer) marker.
In this situation, aeroplane Is below glide slope – see horizontal tip. and on the right of runway axis - see vertical tip
Again, sound signal appears and informs us about passing second (middle) marker.
Aeroplane is stabilized and ready to land. both tips are in their optimal positions.
We pass the third and last (inner) marker and land smoothly.
We cannot forget to mention that there are three categories of ILS. CAT I, CAT II, CAT III.
Each category has its own weather minima requirations for landing.
Third category has sub-categories: a, b, c each with their minima.
ILS is not the only system that allows precision approaches.
We can distinguish much less popular solutions such as: MLS, TLS, or approaches based on GPS.
That's all for today.
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