Definition
A standardized communications protocol used to transmit data between devices over a digital link, defining how data is framed, addressed, checked for errors, and acknowledged. In aviation, it underpins certain ground and airborne data communications systems, providing a reliable structure for exchanging digital messages.
Plain English
A set of rules that two devices follow when they send digital messages to each other, so the messages arrive in the right order, in the right format, and without errors.
Context Anchor
Seen in FAA acronym lists, avionics documentation, and technical discussions of aircraft data link communication systems.
Derivation
‘High level’ means the protocol works at a higher layer of organization than the raw electrical signals — it deals with structured messages rather than individual bits. ‘Data link control’ describes its job: managing the link that carries data between two points.
Why Pilots Care
A pilot usually does not operate HLDC directly, but recognizing the term helps when reading about data link equipment, aircraft electronics, or maintenance notes involving digital communication faults.
Intuition Check
“High level” does not mean high altitude here. It means a higher layer of electronic communication, where messages are organized and checked before or during transmission.
Example Sentence 1
The avionics system uses an HLDC-based protocol to exchange status messages with the ground station.
Example Sentence 2
Maintenance crews checked the HLDC protocol settings during the avionics software update.