Ask Captain Lim

Dear Captain Lim,

I was a Flight Radio Officer for American Overseas Airlines from 1943 to 1950. During that period, I accumulated 5000 hours and 260 North Atlantic crossings. Radio officers were required, as a safety measure, to communicate on the International Maritime frequency 500 Kilocycles in case of an emergency and also to monitor that frequency twice an hour. All position reports were sent on High Frequency (HF) as were weather and operational messages.

What means are now used to "keep in touch" with ATC and company dispatch offices on Trans-Atlantic and Trans-Pacific routes?

Robert L Klein
Lauderhill, Florida, USA

Hi Robert,

Yes, technology has changed somewhat since the era of the Second World War when you started your flying with the American Overseas Airlines. Nevertheless, HF (High Frequency) communication continues to be used but its quality has improved a lot. Notwithstanding the better performance, the clarity of HF communication suffers when used at night. Hence it can be a rather irritating form of communication when traffic becomes too congested during this unfavorable period.

Today, many airliners on Oceanic flights use a new form of communication known as FANS (Future Air Navigation System) to keep in touch with the ground station. Once contact is established using CPDLC (Controller Pilot Data Link Communication), the pilot virtually stops transmitting position reports. The ground controller knows exactly where the plane is with regards to its position, speed, level, etc. When within range of any ground stations, the pilot is only required to monitor the station*s VHF (Very High Frequency) communication or the HF when it gets out of range.

To communicate with company dispatch, ACARS (Aircraft Communications Addressing and Reporting System) is being used in most modern airliners (including the Boeing 777). The ACARS makes use of satellite communications and sent or receive messages like a telex machine. Yes, we can also use the satellite phones for urgent communication but still fall back on the HF as a back up.