STARs, VNAV & Descent Management

Standard Terminal Arrival Route (STAR)

A STAR is a published IFR procedure that provides a transition between the enroute structure and the approach environment. STARs reduce pilot/controller workload by replacing long, complex verbal clearances with a single named procedure. They define a lateral path — and often vertical constraints — from enroute fixes down to the initial approach environment (AIM 5-4-1).

Key STAR Concepts

• Transition routes connect common enroute fixes to the basic STAR. A single STAR may have multiple transitions arriving from different directions, all merging into a common arrival path.
• RNAV STARs require RNAV 1 (or RNP 1) capability. If your aircraft does not have RNAV 1 capability, you cannot accept an RNAV STAR.
• Pilot option: You can decline a STAR by filing "NO STARs" in the remarks section of your flight plan. ATC will then provide vectors or a different routing.
• Altitude and speed: STARs may include mandatory, minimum, maximum, or expected altitude constraints, as well as speed restrictions. "Descend via" clearance authorizes you to follow all published altitude and speed restrictions on the STAR.

VNAV on the G1000

The Garmin G1000's VNAV function calculates and displays a vertical descent path to arrive at a specified altitude over a specified waypoint. This is advisory VNAV — it provides guidance but does not couple to the autopilot in the same way as an ILS glideslope.

Setting Up VNAV

1. Select the target fix — the waypoint where you need to be at a specific altitude (e.g., a STAR crossing restriction)
2. Enter the crossing altitude — the altitude you must be at or above/below when crossing the fix
3. Set the vertical speed or angle — the G1000 calculates the required descent rate based on your groundspeed
4. Monitor the profile view — the MFD displays your vertical path, current position relative to the path, and distance to the target fix

VNAV Indicators

• Vertical deviation indicator (VDI): A magenta diamond on the PFD shows your position relative to the VNAV path — fly toward the diamond, just like a glideslope needle
• VNAV annunciation: "VNAV" appears in the PFD annunciator panel when active
• TOD marker: Top of Descent is displayed on the moving map and in the flight plan — this is where you should begin your descent to meet the crossing restriction
• Profile view on MFD: Shows your planned vertical path, current altitude, and the target fix with its altitude constraint

Descent Planning

Good descent planning ensures you arrive at each crossing restriction on altitude, on speed, and stabilized — not diving or floating through constraints.

The 3:1 Rule

The fundamental rule for descent planning: 3 NM of distance for every 1,000 feet of altitude to lose.

Top of Descent Calculation

To find your top of descent point:

1. Determine the altitude to lose (current altitude minus target altitude)
2. Divide by 1,000
3. Multiply by 3
4. That gives you the distance (in NM) before the fix where you should begin your descent

Example: Cruising at 9,000 ft, need to cross MUGZY at 3,000 ft. Altitude to lose: 6,000 ft. Top of descent: 6 x 3 = 18 NM before MUGZY.

Speed and Configuration

• Reduce power before descending — do not let the aircraft accelerate beyond the target speed
• ATC speed restrictions on STARs are mandatory. Common restrictions: 250 KIAS below 10,000 ft (14 CFR 91.117), plus STAR-specific constraints
• Plan ahead for configuration changes — if you need flaps or gear for speed reduction, plan when to deploy them

GPS Approach Types

RNAV (GPS) approach charts may offer multiple lines of minimums. Each line corresponds to a different level of navigation capability and provides different minimums. Understanding these is critical for knowing what you can fly and what altitude you can descend to.

LNAV — Lateral Navigation Only

LNAV provides lateral course guidance only — there is no vertical path. You fly to an MDA (just like a non-precision approach) and must see the runway environment before descending below MDA. Step-down fixes provide intermediate altitude floors during the approach.

LNAV/VNAV — Advisory Glidepath

LNAV/VNAV adds an advisory vertical glidepath to the lateral guidance. Minimums are expressed as a Decision Altitude (DA), meaning you fly the glidepath down to DA and execute a missed approach if you do not have the runway environment in sight. This glidepath can come from WAAS or from barometric VNAV (Baro-VNAV).

LPV — Localizer Performance with Vertical Guidance

LPV is the most precise GPS approach type — it provides lateral and vertical guidance comparable to a Category I ILS. Minimums are expressed as DA and are typically the lowest available on an RNAV (GPS) chart. LPV requires WAAS — Wide Area Augmentation System.

WAAS and Vertical Guidance

WAAS (Wide Area Augmentation System) is a network of ground stations and geostationary satellites that correct GPS signals for greater accuracy. WAAS enables LPV approaches and provides the vertical component for LNAV/VNAV approaches (AIM 1-1-18).

LNAV+V vs. LNAV/VNAV

These look similar but are fundamentally different:

• LNAV+V: An LNAV approach (lateral only, MDA minimums) where the WAAS receiver adds an advisory glide path indicator. The "+V" is pilot convenience only — it does not change the approach type or the minimums. You still fly to MDA, not DA.
• LNAV/VNAV: A published approach with both lateral and vertical guidance designed into the procedure. The glidepath is part of the approach design. Minimums are DA. This is a different line of minimums on the approach chart.

Step-Down Fixes

Step-down fixes are intermediate fixes along an approach that define mandatory altitude constraints. They exist to provide terrain and obstacle clearance between the FAF and the missed approach point.

Altitude Constraint Notation

Step-down fixes serve a critical traffic separation purpose. In busy terminal environments, ATC depends on aircraft meeting altitude constraints at specific fixes to maintain vertical separation. Missing a crossing restriction can compromise the safety of other traffic in the arrival sequence.

False Glideslopes

ILS glideslope transmitters produce the primary glideslope signal at approximately 3 degrees, but they also produce false glideslope lobes at steeper angles — typically at 6 degrees and 9 degrees. These false signals appear as valid glideslope indications but lead to dangerously steep descent paths.

Protection Against False Glideslopes

1. Always intercept the glideslope from below — fly at or below the published Glide Slope Intercept Altitude (GSIA) until the glideslope needle centers from above
2. Verify your descent rate. A 3-degree glideslope at 90 knots requires approximately 480 FPM. If your descent rate is dramatically higher (1,000+ FPM), you may be on a false lobe.
3. Cross-check altitude at the FAF. The approach plate publishes the expected altitude at the FAF for the glideslope. If you are significantly higher, you intercepted a false glideslope.

Setup

Start at KAVP (Wilkes-Barre/Scranton). Reposition to 10,000 feet, approximately 20 miles from MUGZY on the LVZ STAR inbound to Morristown (KMMU). This positions you for a realistic arrival scenario — descending through a STAR with crossing restrictions, transitioning to an approach at MMU.

Phase 1: VNAV Descent to Crossing Restriction

Meet MUGZY Crossing Restriction

1. Review the STAR chart: Identify the crossing restriction at MUGZY — note whether it is "at or above," "at or below," or "at" (mandatory)
2. Program VNAV: On the G1000, enter the crossing altitude for MUGZY. The system will calculate your top of descent and required vertical speed.
3. Monitor the profile page: Switch the MFD to the VNAV profile view. Verify the TOD point and the planned descent path.
4. Begin descent at TOD: When the VNAV annunciator indicates top of descent, reduce power and begin descent to match the VNAV path.
5. Track the VDI: Keep the magenta diamond centered on the PFD. Adjust vertical speed as needed — wind will shift the required descent rate.

Monitoring During Descent

• Altitude: Cross-check between the VNAV path and the altimeter. Do not bust the crossing altitude.
• Speed: Monitor airspeed trends. If speed is building, reduce power before it becomes a problem. Remember 250 KIAS below 10,000.
• Lateral deviation: Stay on the STAR lateral path. The CDI should remain centered in GPS mode.

Phase 2: GPS Approach Comparison

Fly three approaches to KMMU to experience the difference between GPS approach types firsthand. After each approach, execute the missed approach and re-sequence for the next attempt.

Approach 1: LPV

1. Load the RNAV (GPS) approach and verify the GPS annunciates "LPV"
2. Note the DA on the LPV minimums line — this will be the lowest
3. Fly the approach using the coupled glidepath. The CDI provides both lateral and vertical guidance — fly it like an ILS.
4. At DA, execute a missed approach

Approach 2: LNAV/VNAV

1. On the second attempt, configure the GPS for LNAV/VNAV if the approach supports it
2. Note the DA on the LNAV/VNAV line — higher than LPV
3. The glidepath is advisory (if Baro-VNAV) or WAAS-derived. Fly the diamond down to DA.
4. At DA, execute a missed approach

Approach 3: LNAV Only

1. On the third attempt, fly LNAV only — lateral guidance with no vertical path
2. Note the MDA on the LNAV line — highest of the three
3. Use step-down fix altitudes to manage your descent. Do not descend below each step-down altitude until passing the fix.
4. At the MAP (missed approach point), if the runway is not in sight, execute a missed approach

Phase 3: ATC Amendments

During the STAR and approach segments, your instructor will issue simulated ATC amendments to test your ability to handle real-world disruptions:

• Speed restriction: "N12345, reduce speed to 170 knots." — Comply, adjust power and pitch, and re-evaluate your descent profile.
• Altitude change: "N12345, descend and maintain 4,000." — This overrides STAR altitudes below 4,000. Reprogram VNAV or adjust manually.
• Reroute: "N12345, proceed direct MUGZY, cross MUGZY at 6,000." — Enter direct-to, set new crossing altitude, recalculate descent.
• Hold for sequencing: "N12345, hold at MUGZY as published, expect further clearance in 10 minutes." — Enter the hold, manage fuel awareness.

The goal is flexibility. Real-world arrivals rarely go exactly as filed. The pilot who plans for the STAR but adapts smoothly to amendments is the one who stays ahead of the airplane.

ATC Audio

Listen to the following ATC communications for this lesson. Practice reading back each clearance accurately before listening to the correct readback.

Key Takeaways

1. STARs bridge enroute and approach. They reduce workload by replacing complex verbal clearances with a single published procedure. Transition routes connect enroute fixes to the basic STAR. You can decline with "NO STARs" in your flight plan remarks.
2. VNAV is your descent planning tool. On the G1000, program crossing altitudes and target fixes. The VDI diamond shows your position relative to the planned path. Monitor TOD, vertical speed, and the profile view on the MFD.
3. Three GPS approach types, three levels of guidance. LNAV = lateral only (MDA). LNAV/VNAV = lateral + advisory vertical (DA). LPV = precision-like lateral and vertical (DA, lowest minimums). The approach your GPS annunciates determines which minimums line you use.
4. Step-down fixes are mandatory altitude floors. On LNAV approaches, do not descend below a step-down altitude until passing the fix. Overline = at or below. Underline = at or above. Both = mandatory.
5. The 3:1 rule makes descent math simple. Three nautical miles for every 1,000 feet of altitude to lose. At 120 knots groundspeed, that works out to roughly 500 FPM. Start your descent at the calculated TOD to arrive on altitude without rushing.
6. Crossing restrictions are not optional. "Descend via" means comply with all published lateral and vertical restrictions on the STAR. Missing a crossing restriction can compromise separation with other traffic in the arrival sequence.
7. WAAS enables lower minimums. WAAS provides the vertical guidance for LPV and LNAV/VNAV approaches. Do not confuse LNAV+V (advisory, MDA minimums) with LNAV/VNAV (published glidepath, DA minimums). The "+V" convenience does not change your minimums.

Oral Exam Self-Test

1. What is a STAR, and what purpose does it serve in the IFR system?
2. How do transition routes relate to the basic STAR? Can a single STAR have multiple transitions?
3. What does "descend via" authorize you to do? How does it differ from "descend and maintain"?
4. Explain the 3:1 descent rule. How far from a fix should you begin descent if you need to lose 5,000 feet?
5. What are the three GPS approach types on an RNAV (GPS) chart? For each, state whether minimums are MDA or DA and what equipment is required.
6. What is the difference between LNAV+V and LNAV/VNAV? Which minimums line applies to each?
7. How do step-down fix altitude constraints appear on an approach chart? What do the overline and underline notations mean?
8. What is a false glideslope? At what angles do false lobes typically occur, and how do you avoid capturing one?
9. What is GSIA and why is it important for glideslope intercept?
10. On a G1000, what does the VNAV vertical deviation indicator (VDI) look like and how do you interpret it?
11. Can you decline a STAR? If so, how?
12. What is the mandatory speed restriction below 10,000 feet MSL, and where is it found in the regulations?

Pilot Preparation for Lesson 8

Lesson 8 covers lost communications, IFR diversions, and 14 CFR 91.185 — what to do when you lose radio contact with ATC while operating under IFR.

Reading

1. 14 CFR 91.185: IFR operations — two-way radio communications failure. Read the regulation in full — it is short but dense.
2. AIM 6-4-1: Two-way radio communications failure procedures
3. Instrument Flying Handbook: Lost communications chapter
4. Everything Explained: Lost communications section

Key Topics to Preview

• The AVE-F MEA rule for altitude selection during lost comms
• Route: continue on the route ATC last assigned, then the route filed, then as expected
• When to begin an approach at the destination
• Transponder code 7600
• Diversion decision-making — weather, fuel, alternates
• How ATC handles a NORDO aircraft

Resources

• Instrument Rating Files — STAR charts, VNAV descent planning worksheets, GPS approach comparison
• Instrument Flying Handbook (FAA-H-8083-15B)
• Instrument Procedures Handbook (FAA-H-8083-16B)
• 14 CFR 91.185 — Lost Communications