HF Communication Procedures

HF Communication in Aviation

High Frequency (HF) radio is used for long-range communication, typically between 2850 and 22000 kHz, making it vital for flights over oceans and remote regions. Unlike VHF, which is limited by line-of-sight, HF signals can reflect off the ionosphere, allowing global reach.

Standard Procedures

• Transfer of Communication: When instructed by ATC, pilots switch to a new frequency, acknowledge the transfer, and establish contact using the standard call format. If the transfer is initiated by the aircraft, the pilot requests frequency change and waits for clearance.
• Radio Checks: To confirm HF radio functionality, transmit a call including the station name, aircraft call sign, the phrase "radio check," and the frequency in use. Example: "Shanwick Radio, ABC123, radio check, 8891." The reply will indicate signal strength and readability.

Distress and Urgency

• Distress Frequencies: In emergencies, use HF frequencies such as 2182 kHz or 121.5 MHz (VHF) for distress calls. Discrete Emergency Frequencies (DEF) are reserved for these situations.
• Procedures During Distress: When a distress call is in progress, all other stations must maintain radio silence on the frequency unless they are directly involved in the emergency.

HF vs VHF

• Modulation: HF, VHF, and UHF in aviation use amplitude modulation (AM), not frequency modulation (FM).
• Frequency Separation: VHF frequencies are separated by 8.33 or 25 kHz, but this does not apply to HF, where channels are more widely spaced due to propagation characteristics.

Best Practices

• Use clear, standardized phraseology.
• Speak slowly and clearly, especially when passing critical information.
• Always listen before transmitting to avoid interference.

Understanding these HF communication procedures ensures safe, efficient, and compliant operations during long-range flights.