IN SUPPLEMENTARY CHAPTER BOEING 737 .........
note.DO NOT USE VOR/LOC AFDS mode when conducting VOR approaches if the VOR/DME statin elevation is more than 5000 ft MSL , if there is no co-located DME trasmitter available at the VOR station to be used or when the DME is invalid for any other reason.........
WHY ???
SOMEONE CAN EXPLAIN TO ME
PLEASE
THANKS