Interpretation of Alternate Minima
Was flying into Dusseldorf DUS/EDDL the other day using Dortmund DTM/EDLW as the alternate. All navaids at DUS were OK so the ILS Cat l min applied for planning, and it was OK. However at DTM the Glideslope was out leaving the best approach navaid as the LLZ/DME approach. As it was the alternate, the 'step down' approach was the VOR/DME approach and the weather was well above that minima too. On closer inspection the Minima for the VOR/DME was the same as the LLZ/DME so in effect, no stepdown. As the principle of the 'stepdown' usually raises the minima making the best letdown become visual above the minima and in the event of a failure of that best letdown aid the second best letdown should get you visual AT the minima, or, if the weather does deteriorate you have a margin before it reaches the lowest minima assuming the best aid remains serviceable, what happens when both minima are, as in this example, the same values. Seems to me that you no longer have a safety margin on that airport considering that you'll only be using it as a last resort anyway, leaving you in the unenviable worst case scenario position of possibly having to bust the minima.
Any thoughts ?