reflect (see refraction) off the ionosphere and can span the globe in a series of skips. VHF coverage, however, is normally limited to line-of-sight range. "Shanwick Radio" uses over twenty HF channels and two VHF channels. At peak times it can communicate with in excess of 1,600 aircraft during a 24-hour period. Shanwick Radio maintain HF communications with all flights within the Shanwick Oceanic Control Area and are responsible for issuing voice clearances to those flights unable to contact Air Traffic Control Officers at Prestwick Centre directly via CPDLC. Using the callsign "Shanwick Oceanic", the Prestwick Centre has two dedicated VHF frequencies specifically for the issue of oceanic clearances by Clearance Delivery Officers, (Radio operator licensed Air Traffic Services Assistants), to westbound flights entering the Shanwick OCA, and also provides an ACARS based system called Oceanic Clearance Link (OCL) for suitably equipped aircraft to obtain such clearances without the need for voice communications. Using the callsign "Shanwick Control", Air Traffic Control Officers at Prestwick are able to communicate directly, on a dedicated VHF channel, with pilots in the south east corner of the Shanwick OCA, who are routing via the fixed Tango routes, (T9 and T290). Operations transfer During October 2009, NATS transferred its Oceanic ATC operations from the former Prestwick Oceanic Area Control Centre (OACC) into the £300M Prestwick Centre. The Prestwick OACC had been located within the Scottish & Oceanic Area Control Centre (ScOACC) at NATS' Atlantic House facility, adjacent to the Prestwick Centre. The Prestwick Centre is also home to the Scottish Area Control Centre (including, since January 2010, the former Manchester Area Control Centre). Oceanic ATC operations at the Prestwick Centre are undertaken using the Nav Canada designed ATC flight data system, Gander Automated Air Traffic System+ (GAATS+). GAATS+ has been in service with NATS since November 2014. (Located close to Gander International Airport, Newfoundland, Canada, is the Nav Canada Gander ATC centre which is responsible for flights in the northwest part of the North Atlantic.) GAATS+ enables controllers to maintain accurate flight data, undertake communications with flights and electronically communicate with adjacent ATC units. Upgrades During 2005/06, upgrades to the Shanwick Radio and Shannon Aeradio equipment at Ballygirreen took place and the IAA entered into an agreement with the Flugstoðir (ISAVIA) subsidiary Gannet ATS Communications to provide additional HF communication services within the Shanwick OCA via the Gufunes Telecommunications Centre (in Reykjavík, Iceland). In June