The FAA has released a supplemental notice of proposed rulemaking (NPRM) regarding implementation on Jan. 20, 2005, of domestic reduced vertical separation minimum (DRVSM) airspace. The agency is adding a proposal to implement RVSM between FL290 and FL410 in Atlantic and Gulf of Mexico high offshore airspace and in the San Juan, Puerto Rico flight information region (FIR). The agency also intends to remove the previously proposed option that would have permitted Part 91 turboprop airplanes to operate in DRVSM airspace with a single RVSM-compliant altimeter instead of two. Comments are due April 14.