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.
What this scenario covers
The Boeing CDU is organised around a row of hard keys — INIT REF, RTE, DIR INTC, LEGS, DEP/ARR, HOLD, PROG and N1 LIMIT among them — each of which opens a page or a family of pages. A few pages have no key of their own: IDENT and PERF INIT are reached from the INIT/REF INDEX, which INIT REF opens. Unlike a modern touchscreen, there is no discovery: you either know the key or you do not.
This scenario visits the major pages in sequence. IDENT confirms the database and model, RTE holds the route, PERF INIT the weights and performance, and LEGS the waypoint-by-waypoint detail. DIR INTC is the one key with no page of its own: it reopens LEGS with DIRECT TO and INTC LEG TO box prompts on the bottom line, the starting point for a direct-to or a course intercept.
How it applies in flight ops
Boeing's layout reflects the order of work: INIT REF and RTE at the gate, LEGS and PROG in the air, DEP/ARR at both ends. The FCOM names RTE LEGS, PROGRESS and CRZ as the primary pages in cruise.
Knowing where things are is also error-defence. When something on the display looks wrong, the fast question is "which page owns this number?" — and the quicker you can open that page, the sooner you have the answer.
Start this scenario
Opens the SimTuts 737 CDU trainer with “CDU Pages Tour” already running, so you can walk through it step-by-step on the simulated keypad.
Open trainer →Step-by-step: CDU Pages Tour
- Nothing here needs typing — this is a tour. Press the RTE page key to see where the flight plan lives.
The CDU has two different kinds of key, and telling them apart is the whole skill this tour teaches. The six keys down each side of the screen are line select keys, or LSKs — they act on whatever sits on that line. The labelled keys below the screen are page keys — they change which page you are looking at. Anything you type lands first in the scratchpad, the line along the bottom, and it only goes anywhere when you press an LSK. This tour uses page keys only, so you never need the scratchpad. RTE (Route) is where you enter origin, destination, and the route between them. On the ground the FMC's preflight flow runs IDENT, then POS INIT, then RTE; this tour skips POS INIT, which has a scenario of its own.
- Go to the PERF INIT page. PERF INIT holds the performance setup.
PERF INIT (Performance Initialisation) is where you enter zero fuel weight, fuel reserves, cost index and cruise altitude. The FMC uses them to initialise its performance calculations, and the FCOM is direct about it: this information "is required for VNAV calculations". Weight, reserves and cruise altitude are required entries before the preflight is complete.
- Go to the LEGS page. LEGS shows each waypoint of the route with predictions.
LEGS is the flight plan leg by leg: every waypoint in flight sequence, with the speed and altitude at each one — a constraint in large font, an FMC-calculated value in small. The FCOM says the RTE LEGS pages "are used to manage route restrictions and modify the route", so ATC reroutes are entered here, and in cruise it is one of the three primary FMC pages, with PROGRESS and CRZ. The ETA at each waypoint is not on LEGS: it is on the RTE DATA page.
- Press the DIR INTC key, then look at the bottom line of the page it opens.
DIR INTC has no page of its own: it opens the LEGS page you just saw, with two box prompts added on the bottom line. In the FCOM's words, "Pushing the DIR INTC key adds box prompt options to the bottom of the ACT RTE LEGS page". DIRECT TO, at 6L, is for a "direct to" clearance from ATC: a waypoint entered in those boxes "establishes a course direct to the waypoint and makes that waypoint the active waypoint". INTC LEG TO, at 6R, is for a clearance to join a course to a fix rather than fly straight at it: a waypoint entered there "allows a course to be specified to the waypoint". The FCOM's own example is radar vectors, where "intercept course modifications may be used to join the LNAV path". Nothing to enter on this tour — just know where the boxes are.
- Return to the IDENT page to complete the tour.
The CDU has more pages than the four on this tour — DEP/ARR, HOLD, N1 LIMIT, FIX and PROG among them, plus the POS INIT and TAKEOFF REF pages that complete the preflight. You now know where RTE, PERF INIT, LEGS and IDENT live, and what DIR INTC adds to LEGS. Learn these first; later scenarios build on them.
What to take away
- Most CDU functions have their own hard key; IDENT and PERF INIT sit behind INIT REF.
- IDENT verifies the navigation database; check its validity dates.
- RTE and PERF INIT are gate work; LEGS and PROG are in-flight work.
- DIR INTC adds DIRECT TO and INTC LEG TO boxes to the bottom of LEGS.
The rest of Foundations
ROUTE 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 stepsREF 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.
📍 London area navaids⏱ ~3 min📊 5 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.