REF NAV DATA: Navaid Lookup
PremiumintermediateBefore an approach, real crews verify the navaids they are about to use. REF NAV DATA is where you look them up.
What this scenario covers
REF NAV DATA returns the database record for a navaid, waypoint, airport or runway: identifier, frequency, position and class. It is a lookup page — nothing you do here changes the flight plan.
The scenario looks up two VORs you would expect on a Heathrow ILS 09L approach: one for the initial fix and one for the intermediate. Confirming their frequencies against the plate is a normal part of the briefing.
How it applies in flight ops
The check exists because the navigation database and the chart in your hand can disagree — a database out of cycle, a navaid decommissioned, or a frequency change published between updates. The chart is the authority.
It is also a fast way to sanity-check a suspicious waypoint. If the FMC has taken a name you did not expect, looking it up tells you whether it is the fix you meant or a same-named one on the other side of the world.
Fly this one with Premium
The CDU checks every entry as you make it, and tells you when an entry was accepted but wrong.
Step-by-step: REF NAV DATA: Navaid Lookup
- Open the REF NAV DATA page. From IDENT, press INIT REF then LSK 1R for NAV DATA.
REF NAV DATA is information-only. Unlike the Airbus MCDU RAD NAV page, the Boeing CDU does NOT tune the VHF NAV radios — that happens on the cockpit pedestal panel above the throttles. The CDU's job is letting the crew verify frequencies and positions before they need them in the cockpit.
- Look up DVR (Dover VOR). Type DVR and press 1L.
DVR is the Dover VOR/DME on the Kent coast, frequency 114.95 MHz. Heathrow departures bound for Brussels leave by way of it: the UK Standard Route Document routes them DET, then L6 to DVR and L9 to KONAN, the exit into Belgian airspace.
- Now look up BIG (Biggin VOR). Type BIG and press 1L.
BIG is the Biggin VOR/DME south-east of London, frequency 115.10 MHz. It is one of Heathrow's four terminal holding fixes, with Lambourne (LAM), Bovingdon (BNN) and Ockham (OCK), where arrivals hold as their STAR chart details. Verifying its frequency on REF NAV DATA gives you a sanity check before pulling out the chart — if the database disagrees with the chart, something is wrong (stale AIRAC, chart misprint, etc.).
- Look up a navaid that is not in the database to see how the page reacts. Type ZZZZ and press 1L.
The CDU's navaid database only contains navaids in the current AIRAC cycle's coverage area. Idents not present return NOT IN DATABASE — useful confirmation that you typed the right code, or that an obscure navaid is too far from your current FMC region of operation. Always cross-check the AIRAC cycle on IDENT if a known navaid is missing.
- Look up DVR one more time to end on a known good value. Type DVR and press 1L.
What to take away
- REF NAV DATA is read-only — a database lookup, not an entry page.
- Verify approach navaid frequencies against the chart, every time.
- The chart wins when the database disagrees.
- Same-named waypoints exist; the lookup is how you catch one.
The rest of Foundations
CDU Pages Tour
beginnerA tour of the 737 CDU with nothing to type: where each page lives, so that later scenarios can say "go to LEGS" and mean something.
⏱ ~3 min📊 5 stepsROUTE Page Basics
beginnerRTE and PERF INIT — the two pages every 737 flight is built on. Program a JFK to Heathrow route from empty.
📍 KJFK → EGLL⏱ ~5 min📊 11 stepsPOS INIT: Aligning the IRS
PremiumbeginnerBefore the FMC will do anything useful, the inertial reference system has to know where it is. POS INIT is where you tell it.
📍 POS INIT · EGLL⏱ ~3 min📊 4 stepsThe EXEC Light: Boeing's Commit Step
PremiumbeginnerThe single biggest difference between the Boeing CDU and the Airbus MCDU: on the 737, nothing you type takes effect until you press EXEC.
📍 DIRECT LFPG⏱ ~2 min📊 3 steps
Background reading
- GuideThe Boeing 737 CDU / FMC Explained: Every Page
What is the 737 CDU and FMC? A plain-English guide to every Boeing 737 CDU page plus the EXEC/MOD workflow. Practice free in our CDU trainer.
- GuidePMDG 737 FMC Tutorial: Program Your First Flight Plan Step by Step
Program the PMDG 737 FMC from scratch: IDENT, POS INIT, ROUTE, PERF INIT, takeoff speeds, and VNAV setup. Every CDU page explained with the exact inputs.
- Guide737 FMC Constraints — 250B/, 10000A, and Every LEGS-Page Format That Actually Works
Every 737 CDU constraint format that works: A and B suffixes, speed/altitude pairs, the trailing slash rule, windows, DELETE, and why entries get rejected.