Different types of approach.
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Different types of approach.
Folks,
Can any of you provide a lay mans explanation of the differences between a full ILS approach, and a VOR/DME approach? I know that with an ILS, an auto-land is possible, but what are the other differences? Any why and when would you use one over the other?
As a PPLer, I'll probably not have to worry about it for a while yet
, but you never know!
Can any of you provide a lay mans explanation of the differences between a full ILS approach, and a VOR/DME approach? I know that with an ILS, an auto-land is possible, but what are the other differences? Any why and when would you use one over the other?
As a PPLer, I'll probably not have to worry about it for a while yet
, but you never know!
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ILS Approach:
Precision approach that gives both centreline and glideslope information on the one instrument. Normally a 'Cat 1' installation is useable down to 200-250'. Along with the ILS you'll either have 'markers' which give an idea of how far from touchdown you are, but these are being superceded by co-located DME installations which give you a continuous distance from touch down.
Should the Glideslope portion fail you have the Localiser (LOC) approach. Again, normally with markers or a DME. Higher minima as it's not deemed 'precision' (centreline guidance only, no glidepath).
The advantage of both the above is that you don't have to set the CDI OBS indicator to the inbound heading, though it's good practice to do so.
VOR/DME approach.
Similar to the LOC or LOC/DME approach, though based, funnily enough, on a VOR as opposed to a Localiser or ILS installation. Still non precision, centreline only indications. The biggy here is that you DO have to set up the inbound track on your OBS - otherwise you end up doing an approach to the wrong radial of the VOR and therefore being away from the Final Approach Course where terrain separation is not guaranteed.
Why would you use one over the other? ILS is always preferable - but it depends whether it's available or not
Precision approach that gives both centreline and glideslope information on the one instrument. Normally a 'Cat 1' installation is useable down to 200-250'. Along with the ILS you'll either have 'markers' which give an idea of how far from touchdown you are, but these are being superceded by co-located DME installations which give you a continuous distance from touch down.
Should the Glideslope portion fail you have the Localiser (LOC) approach. Again, normally with markers or a DME. Higher minima as it's not deemed 'precision' (centreline guidance only, no glidepath).
The advantage of both the above is that you don't have to set the CDI OBS indicator to the inbound heading, though it's good practice to do so.
VOR/DME approach.
Similar to the LOC or LOC/DME approach, though based, funnily enough, on a VOR as opposed to a Localiser or ILS installation. Still non precision, centreline only indications. The biggy here is that you DO have to set up the inbound track on your OBS - otherwise you end up doing an approach to the wrong radial of the VOR and therefore being away from the Final Approach Course where terrain separation is not guaranteed.
Why would you use one over the other? ILS is always preferable - but it depends whether it's available or not
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NWSRG
Economics play a part in the process too. ILS installation, maintenance and periodic flight-testing all cost money and would have to be justified. On some Highland and Island airfields in Scotland there may be a VOR [with or without DME] that serves the en-route airway structure and because of its location, on or close to an airfield, can also be used as a let-down aid. A cheaper aid is an NDB, which is not much more than a signal transmitted from a bit of bent wire coat-hanger; your ADF will point to an NDB. A low-cost way of providing a start-up instrument approach for [say] a new airfield would be an NDB with or without a DME. You mention "autoland" .....you should be aware that the airfield would have a list of associated and complimentary requirements such as surface lighting and power supply. All these things are laid out in a range of documents, and must be complied with in order for the airfield to operate.
An ILS will serve only one landing direction, you will notice that for economic reasons some airfields have ILS on one runway only.....weather records will give guidance as to the best direction, assuming no other criteria affect the siting such as terrain.
Autoland....Further to your query...there would be no point installing an ILS and associated kit if the traffic using the airfield was not equipped to make use of it. The rules and training required for autoland, both for the aircraft and the crew, are essential elements in the economic equation.
An ILS will serve only one landing direction, you will notice that for economic reasons some airfields have ILS on one runway only.....weather records will give guidance as to the best direction, assuming no other criteria affect the siting such as terrain.
Autoland....Further to your query...there would be no point installing an ILS and associated kit if the traffic using the airfield was not equipped to make use of it. The rules and training required for autoland, both for the aircraft and the crew, are essential elements in the economic equation.
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To add alittle more information,
An ILS is considered a percision approach, you have both course guidance and glide slope guidance.
A VOR, NDB are considered non-percision approaches, you have basic course guidance but no glide slope so once the pilot crosses a specific point on the approach they descend to a pre-determined alititude.
GPS approaches are in between the two, GPS accuracy provides very accurate course guidance and is in my opinion the next best thing to an ILS.
Mike
An ILS is considered a percision approach, you have both course guidance and glide slope guidance.
A VOR, NDB are considered non-percision approaches, you have basic course guidance but no glide slope so once the pilot crosses a specific point on the approach they descend to a pre-determined alititude.
GPS approaches are in between the two, GPS accuracy provides very accurate course guidance and is in my opinion the next best thing to an ILS.
Mike
