How do you plan KDEN to KSEA in a flight simulator?

In a general-purpose flight simulator, plan KDEN to KSEA by generating an IFR route with matching navigation data, then select the SID, STAR and approach from the actual winds. A useful jet-route skeleton is KDEN–LAR–OCS–JAC–MLP–KSEA via J12 and J15, but verify every segment before loading the FMC.

A practical KDEN to KSEA IFR route

For a jet flying from Denver International to Seattle-Tacoma, this conventional high-altitude routing provides a useful starting point:

KDEN [westbound SID] LAR J12 OCS DCT JAC J15 MLP [arrival transition/STAR] KSEA

This is a planning skeleton, not a permanent cleared route. A dispatcher may add a departure transition before LAR, route the flight through different RNAV fixes, or use another Seattle arrival because of winds, traffic or navigation-data changes. If a generated route differs but connects cleanly and exists in the aircraft database, use the generated route rather than forcing this example.

The airway distance is normally around 900–1,000 nautical miles, depending on procedures and shortcuts. J12 and J15 are high-altitude airways, so this version is intended for aircraft operating at or above FL180.

How do you build the route step by step?

Build the enroute track first, then add runway-dependent procedures after checking the simulator weather.

1. Select the aircraft. A Boeing 737 or Airbus A320-family aircraft suits this sector well, but its weight and performance determine the cruise level and fuel. Do not reuse fuel figures from another aircraft type.
2. Check navigation-data compatibility. The planner, simulator and aircraft FMC should use compatible AIRAC data. A newer planner may offer fixes, airways or procedure revisions that an older FMC cannot recognise.
3. Read the weather. Check winds and pressure at KDEN, the winds aloft across Wyoming and Idaho, and the forecast at KSEA. Mountain-wave turbulence, icing and strong upper winds can materially change the plan.
4. Generate the dispatch plan. Our step-by-step SimBrief planning method explains how to enter KDEN and KSEA, choose the aircraft and review route, fuel, altitude and alternate data.
5. Inspect the route rather than accepting it blindly. Confirm that every airway starts at the preceding fix and that the track progresses north-west towards Seattle. To reproduce airline operations, use our method for finding and validating a real-world route, but make sure the route is not based on obsolete procedures.
6. Add the SID, STAR and approach. Choose transitions that join the first and last enroute fixes without a large gap, loop or reversal.
7. Load and verify the FMC. Review the LEGS or flight-plan page fix by fix, check altitude constraints and inspect the route on the navigation display. For supported MSFS aircraft, our airliner FMC setup guide covers route entry and procedure selection.

Which SID, STAR and approach should you use?

Use procedures compatible with the active runways, aircraft equipment and the route's entry or exit fix; there is no single SID and STAR that is always correct.

At KDEN, select a westbound or north-westbound departure whose transition joins LAR or the first fix in the generated plan. At KSEA, select an arrival transition from the MLP side if the planner routes you that way, then choose an approach for the runway 16 or runway 34 flow shown by the simulator ATIS.

If flying with online ATC, avoid committing to the approach too early. Load the expected arrival, but be ready to change the runway. After any change, check for duplicate fixes, new discontinuities and altered altitude or speed constraints.

How high should you fly, and how much fuel is needed?

For a typical airliner, FL340 or FL360 is a sensible planning range, but the dispatch calculation should choose the level from weight, winds and aircraft capability.

KDEN to KSEA is predominantly westbound, so an even flight level is normally appropriate under US IFR cruising-level rules. FL320 or FL380 may be better than FL340 or FL360 on a particular day; do not climb to a level the aircraft reaches only near top of descent.

There is no reliable generic fuel quantity for this route. Use the exact aircraft profile and include an alternate. KPDX may be convenient but can share Seattle's weather system, while KGEG lies east of the Cascades but adds distance; choose from forecast conditions, runway suitability and available fuel rather than proximity alone.

Why will the route not load into the FMC?

Most KDEN–KSEA loading failures come from mismatched navigation data, an incorrectly entered airway or incompatible procedure transitions.

• “NOT IN DATABASE” or “INVALID ENTRY”: compare the planner's AIRAC cycle with the aircraft database. Replace an unavailable fix only after confirming the intended track.
• The airway is rejected: enter its starting fix first, then add the airway and exit fix. J12 or J15 cannot be inserted from a waypoint that is not on that airway.
• A discontinuity appears: check whether it represents an expected radar-vector segment. Do not delete every discontinuity automatically; connect the legs only when the resulting track is valid.
• The route doubles back: look for a duplicated waypoint or a SID/STAR transition that already contains a manually entered fix.
• The simulator map and FMC disagree: some aircraft do not import all procedures from the simulator's flight planner. Enter the route through the aircraft's supported import system or programme it manually.

Can you fly KDEN to KSEA below FL180?

Do not use the J12/J15 jet route unchanged below FL180, because J routes are high-altitude airways.

A turboprop or piston plan needs suitable low-altitude airways or GPS-direct legs, legal IFR altitudes, adequate terrain clearance and realistic fuel stops. The Rockies and Cascades make the straight magenta line a poor substitute for proper planning, particularly with icing, cloud or an unpressurised aircraft.