What is the difference between ILS CAT 3b and ILS CAT 2 ????

Answer 1

Here are the FAA regulations specifying ILS categories:

ILS CATEGORIES- 1. ILS Category I. An ILS approach procedure which provides for approach to a height above touchdown of not less than 200 feet and with runway visual range of not less than 1,800 feet.- 2. ILS Category II. An ILS approach procedure which provides for approach to a height above touchdown of not less than 100 feet and with runway visual range of not less than 1,200 feet.- 3. ILS Category III:

a. IIIA.-An ILS approach procedure which provides for approach without a decision height minimum and with runway visual range of not less than 700 feet.

b. IIIB.-An ILS approach procedure which provides for approach without a decision height minimum and with runway visual range of not less than 150 feet.

c. IIIC.-An ILS approach procedure which provides for approach without a decision height minimum and without runway visual range minimum.

Answer 2

The main difference is in the Decision Height (DH) and the Runway Visual Range (RVR)

Cat II - DH 100 ft and RVR 1200 ft
Cat IIIb - No DH or DH below 50 ft and RVR less then 700 ft but not less than 150 ft

On both Cats there is special authorization and equipment requred.