Definition
The official, source navigation databases maintained by aviation data suppliers (such as Jeppesen or Lido) that contain the full, current set of navigation information — airports, runways, navaids, airways, fixes, instrument procedures, and airspace — from which the smaller, aircraft-specific navigation databases loaded into avionics units are derived.
Plain English
The big, complete navigation data files that data suppliers keep up to date. The smaller files loaded into your aircraft's GPS or flight management system are pulled from these.
Context Anchor
Seen in discussions of instrument navigation equipment, database updates, and storage limits in panel-mounted or portable navigation systems.
Derivation
‘Master’ here means the original, authoritative copy from which other copies are made — the same sense as a master recording in audio or a master file in computing. It is not about ranking or skill.
Why Pilots Care
The navigation data in your avionics is only as current and accurate as the master database it was built from. If a procedure changes (new waypoint, altitude, or course), it appears in the master database first, then flows down to the next aircraft database update cycle. Knowing this helps you understand why update cycles matter and why you must check effective dates.
Analogy
Think of the master databases like the full map collection at the publisher. The map in your aircraft equipment may be only the section you need for your region.
Intuition Check
Do not assume master databases are databases stored in the aircraft. Here, master means the complete source set from which the aircraft’s smaller usable database is built.
Example Sentence 1
When the FAA publishes a new approach procedure, the data supplier adds it to their master databases before issuing the next avionics update.
Example Sentence 2
Before flight the pilot verified that the master databases had not exceeded their allowed storage allocation.