On a sectional map, many large airports have “NO SVFR” printed near the airport information. SVFR refers to Special VFR, which allows a pilot to fly in lower visibility in controlled airspace. When giving flight reviews to helicopter pilots, I ask what that means. Occasionally, I am told that SVFR is not permitted at that airport. The correct answer is SVFR is not permitted for fixed-wing aircraft. FAR 91.157 states the requirements for SVFR, and appendix D, section 3 contains the verbiage that prohibits SVFR for fixed-wing only.
In fact, many of the requirements for SVFR are different for helicopters. A helicopter pilot still needs an ATC clearance and must remain clear of clouds; however they are exempted from the 1 statute mile restriction and the requirements for night time operations. Additionally, helicopters are excluded from the takeoff and landing requirements outlined in 91.157 (c). However, as with fixed-wing aircraft, the controller cannot suggest SVFR, a helicopter pilot must still request it.
In Canada the requirements for helicopters are more stringent than in the US. For example, a pilot must have at least 500 hours as pilot-in-command, have completed an approved pilot decision making course and received ground/flight instruction on issues related to reduced visibility. More details on additional requirements can be found in Canadian Aviation Regulation 602.117.