Descent Setup (DES + FORECAST)
PremiumadvancedPrepare the descent into Cleveland like a line crew: E/D altitude, target speed, forecast winds, and then take ATC's early descent with DES NOW.
What this scenario covers
The DES page carries the descent target speed and any speed restriction, and shows the end-of-descent altitude the profile is built to. The FORECAST page takes the descent winds, which materially change where the computed top of descent falls.
DES NOW is the answer to an early descent clearance: it leaves the computed path and starts down now, at a shallow rate, rejoining the path from above rather than diving to it.
How it applies in flight ops
VNAV descent planning is only as good as its inputs. Feeding realistic forecast winds is what makes the path credible; without them the aircraft plans against still air and arrives high or low depending on the day.
Being sent down early is routine in busy airspace, and it costs fuel - level flight at low altitude is expensive. DES NOW makes it a managed, shallow descent rather than a step down and a long level segment.
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: Descent Setup (DES + FORECAST)
- Set up the route: press RTE, type KORD and press 1L, then type KCLE and press 1R.
KORD → KCLE, the same Chicago–Cleveland sector as the constraints drill. The DES page is empty until a route with constraints exists - that is the point of this setup.
- Build the enroute leg and activate the route: press 6L for RTE 2, type JOT and press 1R (a DIRECT leg to join the airway), type J60 and press 2L (VIA), type DJB and press 2R (TO). Then press RTE, ACTIVATE> (6R) and the EXEC key.
J60 to DJB (the Dryer VOR/DME west of Cleveland) puts a real waypoint between origin and destination - the fix the descent will be planned around. The DIRECT to JOT (Joliet) comes first because a 737 accepts an airway only if it contains the TO waypoint of the line before it (FCOM §11.40.17), and J60 does not contain KORD. ACTIVATE and EXEC make it the active route (FCOM 11.40.18), so the constraint you enter next is a modification of the route you are flying.
- Enter the arrival constraint: press LEGS, type 240/10000B and press 2R on the DJB row, then press the EXEC key.
This LEGS constraint is where the DES page gets its E/D ALT. On the 737 the descent profile is built from the LEGS page constraints; the DES page displays and manages it, but does not own the data.
- Press the DES page key. The ECON PATH DES page appears.
E/D ALT now reads 10000 - taken from your DJB restriction. E/D ALT is display-only here: it is the altitude restriction of the end-of-descent waypoint, and the only way to change it is back on LEGS. ECON PATH is the default VNAV descent mode.
- Type .720/280 and press 2L to set TGT SPD.
A 737 descends at a Mach number until the indicated airspeed catches up, then holds the CAS - that is why the descent target is written Mach-first (.720/280), the mirror image of the climb's 280/.720.
- Type 240/10000 and press 3L to set SPD REST.
SPD REST shows the most restrictive applicable speed; dashes mean none is active. Setting 240 knots below 10,000 feet here keeps VNAV honest approaching the terminal area, slightly tighter than the standard 250.
- Press <FORECAST (6L). Confirm the transition level: type 180 and press 1L. Then enter the forecast descent wind in two parts: type FL240 and press 3L for the altitude, then type 270/40 and press 3R for the wind on the same row.
The forecast page takes wind direction and speed for up to three descent altitudes so the FMC can refine the path: here 270° at 40 knots at FL240, straight off the OFP wind summary. Each row is laid out as the FCOM draws it, the altitude on the left and the wind on the right, and the rows are "automatically ordered by altitude from highest to lowest" (FCOM 11.43.10), so they may go in in any order. TRANS LVL defaults to FL180, the US standard; entering it confirms the value in large font.
- Press <DES (6L) to return. ATC: "Descend at pilot's discretion." Press DES NOW> (6R).
You are still short of the computed top of descent. DES NOW arms an early descent: the prompt stages the change (DES NOW ARMED) and the EXEC light illuminates. Nothing happens to the aircraft until you execute.
- Execute it: press the EXEC key (this trainer also takes 6R). The title becomes ACT ECON PATH DES.
On execution the aircraft leaves cruise at about 1,000 fpm until it intercepts the computed ECON path, then follows the path down to cross DJB at or below 10,000 at 240 knots. ACT in the title means the descent phase is now active.
What to take away
- DES holds the descent speed and restriction; FORECAST holds the winds.
- Descent winds move the computed top of descent significantly.
- DES NOW starts an early descent that rejoins the path from above.
- Early descent is a fuel cost - managing it well is part of the job.
The rest of Descent & Arrival
VNAV Descent Troubleshooting: Why Isn't It Descending?
PremiumadvancedLevel at FL290 with Cleveland ahead, cleared to 10,000 - and the aeroplane will not start down. Work the classic triad on the CDU: find the floor the FMC is holding, release the constraint trapping the descent on the LEGS page, then take the late descent with DES NOW and read VNAV PATH against VNAV SPD.
📍 KORD → KCLE via J60 - VNAV will not descend⏱ ~9 min📊 9 stepsIntercept From Vectors: Rebuilding a Plan That Will Sequence
PremiumadvancedDescending into Seattle on an arrival that ends in radar vectors, the route stops sequencing and LNAV has nothing left to fly. Work the CDU half of the fix: read why a heading leg leaves a gap, put the arrival fix back on the route with its crossing restriction, then line-select it onto the active waypoint line and EXEC a plan that will sequence again.
📍 KDEN → KSEA via J20 - vectors to final⏱ ~8 min📊 8 stepsThe Approach Numbers (APPROACH REF)
PremiumintermediateAPPROACH REF for the ILS onto Heathrow 27R - a narrower page than the Airbus equivalent, and deliberately so.
📍 EGLL - approach numbers for an ILS RWY 27R⏱ ~5 min📊 4 stepsMissed Approach, Second Approach: Re-sequencing the CDU
PremiumadvancedTower has sent you around off the ILS to runway 26 at Phoenix, and approach control now expects you on the ILS to 25L. Work the CDU half of a second approach: swap the approach on the arrivals page, check the legs and link the gap, then bring APPROACH REF up to date, because the speed you selected for the first approach does not follow the new weight on its own.
📍 KDEN → KPHX, go-around off ILS 26, second approach ILS 25L⏱ ~7 min📊 8 steps
Background reading
- GuideMastering VNAV Descent: Stop Arriving Too High and Too Fast
How VNAV descent works in the PMDG 737 and Airbus A320 - PATH vs SPD, managed descent, altitude constraints, and how to recover when you're too high.
- 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.
- 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.