1.9 Use of an Air-to-Air Frequency 1.9.1 The VHF emergency frequency 121.5 is not authorized for routine use however frequency 123.45 MHz (formerly 131.8 MHz) has been designated for use as the air-to-air communication channel in the NAT and all other ICAO Regions. 1.10 Use of Satellite Communications (SATCOM) 1.10.1 Aircraft equipped with SATCOM should restrict the use of such equipment, for contacting ATC, to emergencies and non-routine messages. 1.11 Time Keeping 1.11.1 Aircraft clock errors resulting in position report time errors can lead to an erosion of actual longitudinal separation between aircraft. It is thus vitally important that prior to entry into the NAT Region, the time reference systems) to be used during the flight for calculation of waypoint Estimated Times of Arrival (ETA) and waypoint Actual Times of Arrival (ATA) shall be synchronised to Coordinated Universal Time (UTC. All ETAs and ATAs passed to ATC shall be based on a time reference that has been synchronised to UTC or equivalent. Acceptable sources of UTC include a) WWV – National Institute of Standards and Technology (NIST-Fort Collins, Colorado. WWV operates 24 hours a day on 2500, 5000, 10000, 15000, 20000 KHz (AM/SSB) and provides UTC voice every minute b) Global Positioning System (GPS) (corrected to UTC) – Available 24 hours a day to those pilots who can access the time signal over their shipboard GPS equipment c) CHU – National Research Council (NRC) – Available 24 hours/day on 3330, 7335 and 14670 KHz (SSB). In the final ten-second period of each minute, a bilingual station identification and time announcement is made. Since April 1990, the announced time is UTC d) BBC – British Broadcasting Corporation (United Kingdom. The BBC transmits on a number of domestic and worldwide frequencies and transmits the Greenwich time signal referenced to UTC) once every hour on most frequencies, although there are some exceptions ore) any other source shown to the State of Registry or State of Operator (as appropriate) to bean equivalent source of UTC.