1.Diameter of helideck: at least total length of largest helicopter
- no parts of aircraft overhanging perimeter
2. Approach/takeoff routes: adjacent structures below level of helideck - no tall structutes
3. Perimeter protection (to prevent personnel from falling): handrail that can be lowered or horizontal net - no fixed handrails
4. Equipment to cope with bad weather / poor visibility: perimeter landing lights and anchor points