Low-Flying Helicopters Road Post Mounted Sign - Dia 558.1 R2/RA2 (Face Only)Where the helicopters road sign diagram 558. 1 is used, helicopters should be expected to be landing or taking off in the near vicinity. The use of this warning sign should prepare the road user for the sudden noise or appearance of a helicopter. The use of For and a distance is recommended as the positioning of the sign should be sited further back than the standard distance, otherwise, a helicopter could be virtually overhead before the driver sees