Aviation glossary
Marginal VMC
Marginal visual meteorological conditions — weather that still meets VFR minima, but with very little margin. Demands heightened attention and an escape plan.
"Marginal VMC" is not a formally defined term but in practice means flying at the lower boundary of VFR minima — low ceilings, reduced visibility, precipitation near the route. A helicopter has the advantage over an aeroplane that it can slow down and land almost anywhere, yet the decision to continue in such conditions ("continued VFR into IMC") is one of the highest-risk decisions a pilot can make. The LION Helicopters standard is simple: when the weather deteriorates, slow down, descend to the safe minimum altitude, turn back or land safely.
Related terms
- VMCVisual Meteorological Conditions — the visibility and cloud-clearance minima that must be met for a VFR flight.
- IMCInstrument Meteorological Conditions — weather that does not meet VMC. Flight is only possible under IFR with the appropriate rating.
- Special VFRA VFR flight cleared by ATC to operate within a control zone in conditions below the standard VMC minima. The pilot is responsible for obstacle clearance.