We often hear mentioned  Cat 1, Cat 2 or  Cat 3 but  what does it all mean ?

 The Answer is below

 

 Each runway ILS Radio Signal is given a category depending on its quality. The better the quality the higher the category. The best being Cat  3C. The worst Cat 1

Please note a  Cat 1 ILS is not Autoland approved. Only Cat 2 and 3 allow aircraft to Autoland. and then all autopilots must be working.

For a pilot to be able to make an approach  to a runway  the weather  has  to be at or above certain conditions depending on the CAT number of the ILS. 

 A table below gives these conditions

CAT 1 CAT 2 CAT 3 A CAT3 B CAT 3C
Minimum Visibility in Metres 800 M 400 M 200 M 50 M 0
Decision Height in feet 200 FT 100 FT 0 0 0

 For example if the ILS was a Cat 1 ILS and the visibility was 400 metres and the base 100ft the pilot would have to hold or divert . The CAT classification for the ILS is published in approach charts .

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