View Full Version : Limits ILS CAT II

9th Oct 2010, 15:25

As everybody knows the limits for ILS CAT II are: DH 200 ft or lower but not less than 100 ft.

But, Why is published (sometimes) RA 95 ft? I donīt understand it, that means less than 100 ft.

Does anyone know the explanation for that?


9th Oct 2010, 15:31
It's because there is a 5 foot hill (relative to the touch down zone) under the radio Altimeter at that point

Coffin Corner
9th Oct 2010, 15:32
The point at which you "decide" will be 100ft above the threshold, but it may not be 100ft above the local terrain, so the RAD ALT readout of 95ft means the "local terrain" at the point which is = to 100ft above threshold is 5ft higher.


9th Oct 2010, 16:01
As stated, DH is always 'above threshold', but the picture is clouded by several ops manuals which err in this respect (including my last). Commonly they quote "Decision Height - Minimum 100 ft radio" (my bold) and then go on to offer 'Radio' DH's well below 100. 90'RA' in one case, 91'RA' in another. Obviously the manual should state "Decision Height - Minimum 100 ft ATE" and then all would be well. Previous management were sadly ill-equipped to understand the error in the text. Hopefully new team are better 'equipped':)

9th Oct 2010, 18:28

10th Oct 2010, 07:10
Do you really have control of 5' over your aircraft (other than the first and last?)