Helicopter
Air Traffic Control Fully Certified
Situational Awareness; Communication Breakdown
ATC Issue All Types; Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Human Factors; Airspace Structure; Airport; Procedure
A helicopter was in the VFR traffic pattern. A [turboprop] was inbound on the GPS approach and was significantly faster than [the helicopter]. [A Cessna] was in the traffic pattern and taxiing back via on the tower frequency. [The helicopter] was sequenced ahead of a [turboprop] and [the Cessna] was told to hold short of Runway 31 for the arriving helicopter. While the helicopter was short final; the [turboprop] was overtaking the helicopter and it did not appear there would be sufficient runway separation. The local controller then asked [the helicopter] could make an approach to a taxiway; which the helicopter said they could. Local control then instructed [the helicopter] for the option on the taxiway midfield. [The helicopter] read back cleared for the option on the taxiway without saying anything about the midfield restriction. [The turboprop] was informed the helicopter would be for another intersection. [The helicopter] then overflew [the Cessna] who was on the taxiway holding short of the runway with no altitude restriction or other traffic issued. I was in the process of relieving the Controller in Charge (CIC) position while fresh on the Ground Control position and did not hear much of the calls being made at the time the incident occurred. The local control did coordinate for the use of a Taxiway; but I did not realize where the location of [the Cessna] was until [the helicopter] was already over the top of the [Cessna]. [The helicopter] should have been sequenced to follow the [turboprop]. It was unrealistic to expect the slow helicopter to stay ahead of the much faster [turboprop]. Side stepping to the taxiway would have been ok except for an aircraft already on the taxiway and no restrictions were read back by the helicopter. I would think the restriction would have needed to be cross above 500 feet to avoid overflying the [Cessna] with no restrictions.
A Tower Controller in Charge reported a helicopter was instructed to land via a taxiway and did not comply with a restriction and overflew an aircraft awaiting takeoff.