US CAT II minimums?

[quid]

I notice on the ILS Rwy 30L CAT II to MSP that the radio altimeter is not authorized. DA(H) then is at the IM for the RVR 1200 approach. No problem there.

The 1600 RVR DH is 150'. If you are not authorized to use the RA, and there is no marker, what is used to determine the DH?

Surely not the baro altimeter. (?) I've been under the impresion that the baro "can't" be used to determine DH on a CAT II.

Rwy 16R at Sea-Tac is similar.

[m&v]

As it is the HQ of a 'major'carrier,the FAA have allowed in certain cases the use of the Barometric Altimeter in Lieu of the RA,Seattle 16 is another case.It applies when tha terrain in the Threshold area has insufficient Level area to reflect the RA signal at DH",at one time in SEA they tried to use Steel matting to provide the 'echo'

[quid]

MSP and SEA are but two of the examples where IM is used for the 1200 DH case. As you say, there is terrain leading to the aproach end that is unsuitable for RA use.

For the 1600 / 150 case, I found the answer in Appendix A of Part 91. It states that the barometric altimeter may be used "no lower" than 150 feet to determine DH. So, AT 150', use of the baro is legal.

Thanks for the reply.