Descend Via and RNP

FSA Learning Flight 5

Fun Fact

KDEN has been the source of several conspiracy theories—a subject the airport’s administration has embraced and even fueled. Since the opening of the airport in 1995, conspiracy theories have included: tunnels under the airport were built for secret meetings of the world’s elite, a blue horse statue is cursed, the airport is connected to the new world order and the Freemasons, and that the airport is home to aliens and lizard people.

Screenshot by Sharath M.

Flight Summary

This final Learning Flight offers several advanced navigational procedures for simulator pilots to learn and practice. First, we depart KASE using a back course, which can either be flown with the GPS or by using traditional navigation aids if you’re feeling brave. We go from this—one of the oldest navigational aids still in use today—to the ultra-modern "descend via" arrival at KDEN and finish the series with the newest approach aid: an RNAV RNP approach.

Concepts Discussed in this Flight:
  • Back courses
  • SIDS in challenging terrain
  • "Descend via" STARs
  • RNAV RNP Approaches

Airports Visited in this Flight

Aspen Airport

Aspen-Pitkin County Airport (KASE)

Elev: 7,738 ft. / 2,289 m

Addon Scenery Recommendations

Objective 1

Prepare to Fly

In preparation for Learning Flight 5, find a turbojet aircraft with good takeoff and landing performance that you’re comfortable flying. For this flight, the RNAV arrival at KDEN is only eligible to be flown by turbojet aircraft.

FSA Resource
You’ll only be able to complete this flight if you have a current navigation database. The STAR and KDEN approach are both relatively new. Visit our Navdata Guide for more information on how to ensure your simulator is up-to-date.

Thus far in the series, our flights have mostly featured smaller airports that don’t see regular commercial service. As a result, we’ve been planning our routes based on the availability of airways and navigational convenience. However, in this flight, we’re flying a route that is regularly served by SkyWest (operated as United Express). When you’re flying between airports that see regular IFR service, it can sometimes be easier to look at the routes real-world aircraft use instead of trying to come up with one on your own. The website FlightAware offers an easy way to see flight plans for aircraft around the world:

From FlightAware’s homepage, hover over "Live Flight Tracking" and then click "IFR Route Analyzer" in the drop-down menu. In the resulting page, type in the ICAO codes for the departure and arrival airports. If you do that for KASE and KDEN, you’ll see all the filed flight plans between those airports, and will notice that the route LINDZ IDENE JNETT SSKII# is used commonly by SkyWest’s CRJ-700 aircraft. That’s the route we’ll fly for this flight, using the LINDZ# to safely depart KASE.

Objective 2

Fly the LINDZ# Departure

Review both pages of the LINDZ# departure. By now, you should be familiar with picking out the key points:

  • The top altitude is 16,000 ft. MSL.
  • The departure is only applicable from Runway 33 (and requires a minimum climb gradient of 465 ft. per NM to 10,000 ft. MSL). Runway 15 departures are not approved, due to terrain.

You may also recognize this as a pilot navigation departure, which takes the aircraft directly from the runway to the enroute environment without a requirement for ATC instruction. However, unlike when we flew the ALPIN# pilot navigation SID at KJAC, this one involves a back course.

In order to understand the reasoning behind a back course approach, it’s first important to discuss how localizers work. Unlike VORs, localizers only have one radial and only transmit a signal in a single direction. Therefore, when flying an ILS approach, the needle behaves the same regardless of what course heading you have selected.

Historically, smaller airports used a localizer that transmits a signal forwards and backwards so that horizontal guidance could be given for both sides of the runway from a single installation. This allowed for cost savings. However, upgraded technology (i.e., RNAV approaches) have mostly eliminated the need to serve multiple runways with a single installation. In fact, as of summer 2020, there were only 64 back course approaches left in the United States—that’s less than 0.4% of the available approaches published by the FAA. Depending on your aircraft’s navigational equipment, flying a back course approach could mean you are dealing with a "reverse sensing" localizer: when a course deviation indicator (CDI) tells you to turn right, you actually turn left. In other words, you would turn in the opposite direction you think you need to in order to remain centered on the localizer.

Fortunately, the designers of the LINDZ# departure at KASE decided to avoid this complexity. As you can see on the chart, a note clarifies that "I-PKN back course outbound is normal sensing". In other words, when you join the "localizer" on this departure, it works just like an ILS...except it’s designed to point you away from the airport instead of toward it!

To fly the LINDZ# departure, start by setting up the airplane. Tune your navigation radio to the localizer frequency (108.50) and set the course to 303° (although tracking the localizer won’t technically be affected by your course setting, having it set correctly aids in situational awareness). You’ll need to be able to intercept this localizer when you get airborne.

Take off from Runway 33 and make a right turn to a heading of 343°. When IMC, it’s standard practice to fly the runway track until at least 400 ft. AGL before making any turns, so most IFR pilots will maintain the centerline until 400 ft. AGL, then turn right to 343°. Climb to 9,100 ft. MSL and then turn left to heading 273°. Fly that 273° heading until you intercept the localizer and are tracking it outbound. Because the back course is "normal sensing", the localizer works just like an ILS: if the needle tells you to turn left, you are right of course and need to turn left to re-join. You’ll track the localizer until reaching LINDZ, which you can identify:

  • With your GPS or FMS.
  • By the intersection of the localizer and the DBL R-244.
  • By 13 DME from the DBL VOR.

Reaching LINDZ, you can switch to GPS navigation and track directly to IDENE and then follow the remainder of the flight plan. For terrain, you’ll want to reach LINDZ at 14,000 ft. MSL or higher, and then leave IDENE above 16,400 ft. MSL. A good cruising altitude for this route is the one SkyWest’s pilots use: FL230.

If you’re flying an advanced aircraft with updated navigation data, chances are this entire departure is built into your FMS with GPS waypoints. You may be able to load the departure and fly it entirely using the FMS/GPS and in fact it’s legal to fly it without even having the localizer tuned. However, it’s certainly a good practice to have the localizer tuned even when you don’t plan to use it, especially when you’re flying in actual IMC.

Objective 3

Prepare for the SSKII# Arrival

Once you've safely departed KASE, it's time to look at the SSKII# arrival into KDEN. You’ll notice the arrival is broken across multiple pages (3, if you’re using FAA charts). You’ll need to look at each of the pages to get the complete picture of how the arrival works. This profiled RNAV arrival is a little different than the relatively simple BEARR# arrival at KSLC.

Open the first page of the SSKII# arrival at KDEN:

This first page of the arrival shows the transition routes: BOWLL, BUMMP, HAQHY, WUNZE, and the one we’re flying: JNETT. These transition routes take us to the SSKII waypoint. Then, the second and third pages of the STAR show and describe the runway transitions: the different "branches" of the procedure that pilots follow based on the assigned landing runway.

For example, if Denver Approach assigns you "Runway 25", your route would be: SSKII BGDEE TLRID ZATUT LOOOP JIBAT. However, if you are given "Runway 16R", you would instead fly SSKII BGDEE TLRID EPPIC RDDVL CLFFF. This might mean you have to re-program your aircraft as you approach the airport.

Look at the Arrival Route Description for aircraft Landing Runway 16R. It explains the waypoints to fly and then says "cross at 11000 and at 210K, then on track 353°. Expect RADAR vectors to final approach course". As you can see, after crossing CLFFF, the correct procedure is to continue on a track of 353° and await vectors from ATC. Turning from CLFFF toward the runway or the approach is incorrect. Depending on your aircraft, this may mean you need to switch from "NAV" to "HDG" mode when you cross CLFFF. If the airplane tries to do anything other than continue straight ahead after CLFFF, intervene to ensure you continue flying north (unless ATC has given alternate instructions).

Pilot Tip

As navigation procedures like STARs and approaches become more airplane-dependent, there is a risk to pilots becoming over-reliant on automation. To help keep pilots sharp, many North American airlines actively encourage pilots to "hand fly" departures, arrivals, and approaches when conditions warrant.

Remember, you are still flying the airplane, even when the autopilot is on. If the aircraft’s automation starts doing something incorrect, like descending below a charted waypoint or turning when it shouldn’t, saying "the autopilot did it" won’t be good enough when the FAA calls! However you elect to fly this flight, remember that it is your responsibility to ensure the aircraft does what it is supposed to.

In addition to the lateral navigation varying based on the assigned runway, this STAR also includes a vertical profile: coded speed and altitude restrictions at each waypoint. Using Page 2, let’s look at how these restrictions are depicted:

Speed and altitude restrictions can take the form of an "at" restriction (bars above and below the restriction, like at CLFFF), an "at or above" restriction (one bar below the restriction, like at SSKII), or an "at or below" restriction (one bar above the restriction, like at JNETT in the image below). It’s important not to confuse these speed and altitude restrictions with the MEA. Remember, MEAs are advisory only; they are not descent instructions!

The golden rule of IFR flying is that you can never leave an altitude until given instruction to do so by ATC. Even if a STAR has an "at or below" restriction, you cannot descend to meet that instruction until you receive clearance. Although speed restrictions published on a STAR are always required, the altitudes are only activated by the phrase "descend via". Unless you are given a "descend via" clearance, the published altitude restrictions can be disregarded. If you are approaching your calculated top of descent and have not been given further instruction, it is your responsibility to advise ATC and request descent.

Here are a few key points about the use of "descend via" instructions:

  1. You are not cleared for the vertical profile until issued a "descend via" clearance.

  2. You cannot climb to a higher altitude when issued a "descend via" clearance.

  3. If you were issued a speed to maintain and are later issued a "descend via" clearance, all published speeds become mandatory unless the controller specifically assigns a speed after the "descend via" clearance is issued.

  4. If you are vectored off the arrival, you will be given an altitude to maintain. When you are "re-cleared" on the arrival, a clearance to join the arrival only gives you lateral clearance. You will be issued a new "descend via" clearance to rejoin the vertical profile.

  5. Any other altitude instructions (e.g., "descend and maintain FL240", "cross SSKII at and maintain FL210") override the published altitudes on the arrival. Published altitudes only become applicable again if a new "descend via" clearance is received.

  6. When meeting restrictions, descend to (or close to) the target altitude, then slow just prior to the restriction. Slowing down too early can negatively impact aircraft behind you.

Air Traffic Control (Click to Expand) (Click to Collapse)
Ground School Seminar: RNAV
For a full walk-through of how to fly RNAV arrivals, including FMS programming screenshots, check out Boston Virtual ARTCC’s RNAV Procedures Ground School. This 50-minute video goes step-by-step through the world of RNAV, and includes a sample flight from KJFK to KBOS.

Objective 4

Fly the SSKII# Arrival

Now that you have the background on RNAV arrivals, let’s look at how we would fly the SSKII# arrival for Runway 16R. Based on the wind, you may elect to fly the arrival and approach to a different runway. The same concepts will be applicable to any runway.

Air Traffic Control (Click to Expand) (Click to Collapse)

Let’s start at 1 in the picture above: we’ve reached our cruising altitude of FL230. We’ll check the weather at KDEN and confirm that Runway 16R is appropriate for landing. We’ll select the 16R runway on the SSKII# arrival and also select the RNAV Z RWY 16R approach, which we’ll discuss in the next objective. Now is a good time to confirm the waypoints and their corresponding speed/altitude restrictions are depicted along your FMS/GPS route. You’ll also want to review the planned taxi route from Runway 16R to your expected gate and/or parking location.

The arrival starts at 2 when we cross JNETT. Since we are at FL230, the "at or below" FL260 is not applicable to us, even if we were given "descend via".

Just before HAMIC 3, you hear "descend via the SSKII# arrival, landing south". You are now authorized to descend to 11,000 ft. MSL (the altitude restriction at CLFFF), while respecting the intermediate altitudes. In most aircraft, you would set 11,000 ft. in your altitude selector and engage any form of VNAV you have. However, it’s also just as possible to fly the arrival by stepping down at each waypoint or calculating your own descent. From HAMIC, you need to:

  • 4Cross SSKII at FL200 or above. Based on the profile of the STAR, you can likely still be at FL230 when you cross SSKII.
  • 5Descend to cross BGDEE between FL210 and 17,000 ft. MSL, at 250 knots.
  • 6Continue the descent to cross TLRID between 17,000 ft. MSL and 15,000 ft. MSL, still at 250 knots.
  • 7Follow the arrival to the left, crossing EPPIC between 15,000 ft. MSL and 13,000 ft. MSL, at 240 knots.
  • 8Level off at CLFFF at 11,000 ft. MSL and 210 knots.
  • 9After CLFFF, continue flying the 353° track, at 210 knots, until further ATC instruction is received.

Objective 5

Fly an RNP Approach

Required Navigation Performance (RNP) is a type of RNAV approach that requires special onboard navigation performance monitoring and alerting capability to ensure the aircraft remains within a certain distance of the procedure. You can think about RNP approaches as a type of "extra accurate" RNAV approach that also incorporates additional flexibility with the introduction of curved (or "RF") legs. RNP approaches are the only ones that can include a curved track; other RNAV approaches require straight-line tracks between waypoints.

Presently, RNP approaches require special aircrew and aircraft certification, which restricts them primarily to airlines or commercial operations. However, this may change in the future—and even a GPS with WAAS (which most modern general aviation aircraft have) can support RNP approaches. And, for the purpose of flight simulation, certifications are free!

The image below shows one of the benefits of RNP approaches. For years, the "Stadium Visual RWY 29" approach was the only option for northeast arrivals at Newark (KEWR). Requiring visual weather, this approach has aircraft navigate via a series of visual landmarks to approach the airport. However, the procedure is not authorized at night or in instrument conditions. It also requires pilots to correctly identify these visual landmarks. By comparison, the RNP approach to Runway 29 can be flown in almost any weather conditions, at night, and doesn’t require visual references: pilots can easily navigate to the runway following the same precise track every time:

This benefits passengers (safer), pilots (easier), operators (more fuel efficient), and even the noise-sensitive residents living close to the airport.

Another example of the benefits of RNP is shown at the airport where we started the Learning Flights series. The RNAV RNP Y RWY 19 approach at KJAC allows pilots to fly a curved track along the valley, allowing a more direct approach than the other options:

At KDEN, we can also take advantage of the benefits of RNP on the approach to Runway 16R. Instead of having to issue vectors, ATC can simply clear an aircraft for the approach from CLFFF, which you’ll notice has the same altitude and speed restrictions as on the SSKII# arrival. Following the curved track and profiled descent, the aircraft can make a minimum-power approach to the runway, offering fuel savings and noise benefits:

In practice, flying this approach is just like any other RNAV approach. Assuming you receive clearance prior to CLFFF (or are flying without ATC), you cross CLFFF at 11,000 ft. MSL and at 210 knots or less. From there, you follow the curved track (using LNAV) and descend along the vertical profile (VNAV) to join the final approach course at JETSN.

As you fly the approach, if you think to yourself that Runway 16R looks pretty’re right! At 16,000 ft. long, Runway 16R/34L at KDEN is the longest commercial runway in North America. That’s not by accident. On hot days in the summer, aircraft need the extra length to depart this airport, which is located above 5,300 ft. MSL. In fact, even with 16,000 ft. of runway, some fully-loaded aircraft still can't take off safely on hot days!

Air Traffic Control (Click to Expand) (Click to Collapse)

Objective 6

Land and Taxi to Parking

Once you’ve landed on Runway 16R (or another runway as required by ATC or weather), taxi to your parking spot of choice. If you’re planning to park at Signature (the FBO located off taxiway "L1" on the southeast corner of the airport), you have a long taxi ahead of you. That’s because KDEN is the largest airport in North America by land area. At over 52 square miles, it’s actually the second-largest airport in the world, second to King Fahd International Airport in Saudi Arabia.

If you’re flying an airliner, getting to the gates will be a little shorter. High-speed taxiway "D5" makes for a nice exit. In addition to showing routes, another benefit of FlightAware is that gate assignments are also available. If you’re flying a SkyWest CRJ (United Express), you’d be parking at the "B" gates, on the southeast corner of the "middle" terminal (off taxiline "BS").

FSA Resource
If you’re using Jeppesen charts (for example, from Navigraph), you’ll be able to access a more detailed view of the parking areas near the gates. Unlike other countries, the FAA does not publish detailed ramp or apron charts. For more information, visit our Charts resource.

Go Flying

Flight 5 takes you from a conventional navigation departure at KASE to an ultra-modern RNAV STAR and RNP approach at KDEN. Start by departing KASE on the LINDZ# departure and then navigate along the SSKII# arrival to an RNP approach at KDEN to finish the Learning Flights series!

  1. Load your aircraft at KASE and set the weather.
  2. Fly the LINDZ# departure.
  3. Navigate enroute via LINDZ IDENE JNETT.
  4. At JNETT, join the SSKII# arrival at KDEN.
  5. Fly an RNP approach; we recommend the RNAV Z RWY 16R.
  6. Taxi to an appropriate parking spot at KDEN.

You’ve now completed FSA’s Learning Flights series—congratulations! This program covers, very quickly, some very complex but highly applicable topics for flight simulation pilots. Especially if you plan to take your flying online, or if you want to add some realism to your virtual flying, it’s our hope that these flights have offered a good starting point for you.

We hope you’ve found these flights to be fun, educational, and offering interesting and challenging flying. We welcome your feedback! If you have any comments, suggestions, or ideas for our next series, please Contact Us. It’s our hope to build on this series in the future by offering educational flights based on procedures in other countries and looking at new topics.