IFR Navigation Systems & Procedures
Navigation aids, holding patterns, DME arcs, intercepts, and RNAV/GPS procedures
OBJECTIVE
Provide trainees with expertise in utilizing IFR navigation aids, systems, and procedures specific to the T-38 Talon, including understanding navaid types and capabilities, intercepts, tracking, DME arcs using the bearing pointer method, holding patterns with standard speeds and altitudes, and RNAV/GPS integration, to enable precise enroute and terminal navigation under Instrument Flight Rules.
CONTENT
Types of Navigation Aids (NAVAIDs)
Understanding what each navaid provides is essential for IFR navigation. Different navaids offer different capabilities—some provide bearing only, others provide distance, and some provide both.
NAVAID COMPARISON TABLE
| NAVAID | Frequency | Provides | Range | Limitations |
|---|---|---|---|---|
| VOR | 108.0-117.95 MHz | Bearing (radials) | 40-130 NM | Line-of-sight only |
| VOR/DME | 108.0-117.95 MHz | Bearing + Distance | 40-130 NM | Line-of-sight only |
| VORTAC | VHF + UHF | Bearing + Distance + TACAN | 40-130 NM | Line-of-sight only |
| TACAN | UHF (military) | Bearing + Distance | 40-130 NM | Military only, line-of-sight |
| DME | UHF paired | Distance ONLY | ~199 NM | No bearing, slant range error |
| NDB | 190-535 kHz | Bearing (via ADF) | 15-50 NM | Subject to interference |
| ILS LOC | 108.1-111.95 MHz | Lateral guidance | 18 NM | Single runway, no distance |
| ILS GS | 329.15-335.0 MHz | Vertical guidance | 10 NM | False glideslopes possible |
NAVAID DETAILS
VOR (VHF Omnidirectional Range)
Provides 360 radials (magnetic bearings FROM the station). Select a radial on the OBS, fly TO or FROM the station on that radial. Accuracy: ±1°. VOR-only stations are rare today—most are VOR/DME or VORTAC.
TACAN (Tactical Air Navigation)
Military UHF navaid providing bearing AND distance in one system. Channels 1-126 (X and Y). Civil aircraft can receive DME from TACAN but not bearing. Military aircraft use TACAN extensively—the T-38 can use TACAN for all navigation.
VORTAC
Co-located VOR and TACAN. Civil aircraft use VOR for bearing and DME for distance. Military aircraft can use TACAN for both. This is the most common type of ground-based navaid in the US.
DME (Distance Measuring Equipment)
Provides slant range distance only—no bearing. Paired with VOR or ILS frequencies. DME reads slightly high when close to the station and high above it (slant range vs ground distance). At station altitude directly overhead, DME = altitude in NM.
NDB (Non-Directional Beacon)
Low/medium frequency transmitter. Requires ADF (Automatic Direction Finder) receiver. Points TO the station. Subject to errors: night effect, shoreline effect, thunderstorm effect, terrain. Being phased out but still used for some approaches and as compass locators.
ILS (Instrument Landing System)
Localizer: Lateral guidance (left/right of centerline). Glideslope: Vertical guidance (above/below glidepath, typically 3°). Together they provide precision approach capability down to 200 ft ceiling / ½ mile visibility (CAT I).
What Does Each Navaid Give You?
Bearing Only
VOR, NDB
Distance Only
DME
Bearing + Distance
VOR/DME, VORTAC, TACAN
Lateral + Vertical
ILS
VOR/TACAN Operations
Understanding how to tune, identify, and use VOR/TACAN for navigation is fundamental to IFR flying.
TUNING AND IDENTIFICATION
Tune the frequency - Set VOR freq (108.0-117.95) or TACAN channel (1-126 X/Y)
Identify the station - Listen for Morse code ident (3-letter ID). ALWAYS identify before using!
Check flags - Ensure no OFF/NAV flag. TO/FROM should be appropriate for position.
Set course - Rotate OBS to desired radial/course
⚠️ Always Identify!
Never navigate using a VOR/TACAN without positively identifying it by Morse code. Stations undergoing maintenance transmit "TST" or no ident. An unidentified navaid could be off-air, under test, or you could be tuned to the wrong station.
RADIALS vs COURSES
Radial
Magnetic bearing FROM the station. The 090 radial extends east from the station. You are ON the 090 radial when the station is due west of you.
Course
The heading you fly. To track TO a station on the 090 radial, your course is 270°. Course = Radial ± 180° depending on TO/FROM.
Intercepts and Tracking
Intercepting and tracking radials/courses is a fundamental IFR skill. The key is understanding intercept angles and lead points.
INTERCEPT ANGLES
90°
Fastest intercept
Use when far from course
45°
Standard intercept
Good balance of speed/control
30°
Shallow intercept
Use when close to course
LEAD POINT CALCULATION
Begin your turn to course BEFORE the CDI centers. The lead point depends on:
- • Intercept angle: Larger angle = more lead needed
- • Groundspeed: Faster = more lead needed
- • Distance from station: Closer = less lead (radials converge)
RULE OF THUMB
90° intercept: Lead by 5° per 1 NM from station, or ~½ the intercept angle
45° intercept: Lead by ~20-25° (half the intercept angle)
General: Begin turn when CDI starts moving, not when centered
TRACKING (BRACKETING) TECHNIQUE
Once on course, maintain it using the bracketing method:
Note the heading required to keep CDI centered
If CDI drifts, turn toward it (e.g., 10° correction)
When CDI re-centers, turn back but not all the way—use half the correction
Continue bracketing until you find the heading that holds course (wind correction angle)
Example: Course 090°, drifting right. Turn to 080°. CDI centers. Turn to 085°. If CDI stays centered, 085° is your wind-corrected heading.
Flying DME Arcs - Bearing Pointer Method
DME arcs are curved flight paths at a constant distance from a navaid. They're commonly used on approach procedures to transition from the enroute environment to an approach course. The bearing pointer method is the most reliable way to fly arcs.
THE BEARING POINTER METHOD
The key to flying a DME arc: Keep the bearing pointer on your wingtip (90° index)
HOW IT WORKS
- • The bearing pointer points TO the station
- • If you fly with the station at your 90° (wingtip), you'll fly a circle around it
- • Clockwise arc: Keep bearing pointer on RIGHT wingtip (3 o'clock / 090° index)
- • Counter-clockwise arc: Keep bearing pointer on LEFT wingtip (9 o'clock / 270° index)
DME ARC PROCEDURE - STEP BY STEP
Approach the arc
Fly toward the navaid. Note your DME. Lead the turn to the arc by 0.5 NM.
Turn to place bearing pointer on 90° index
At arc distance (minus lead), turn 90° to place bearing pointer on wingtip.
Monitor DME and bearing pointer
Maintain constant DME. If DME increases, turn toward station. If decreases, turn away.
Make small heading corrections
Turn 10-20° toward the station each time bearing pointer moves 10° behind wingtip. This keeps you on the arc.
Lead the turn to intercept course
Lead the turn off the arc by 5° per NM (e.g., at 10 DME, lead by 5° = start turn 5° before radial).
DME ARC CORRECTIONS
DME Increasing (drifting outside arc)
Turn TOWARD the station (turn in direction of bearing pointer). Bearing pointer will move forward of wingtip briefly.
DME Decreasing (drifting inside arc)
Turn AWAY from the station. Bearing pointer will move behind wingtip briefly.
10° TURN METHOD (Alternative)
For consistent arc flying:
- • Every time the bearing pointer moves 10° behind your wingtip...
- • ...turn 10° toward the station
- • This creates a series of short straight legs that approximate the arc
- • Works well at any groundspeed—faster just means more frequent turns
Holding Patterns
Holds are racetrack patterns used for traffic management, approach sequencing, or delaying arrival. Understanding entries, timing, and speeds is essential.
STANDARD HOLDING PATTERN
- • Standard hold: Right turns
- • Non-standard hold: Left turns (published as "LEFT TURNS")
- • Inbound leg: Flown toward the fix on the holding course
- • Outbound leg: Flown away from the fix, reciprocal heading
- • Abeam point: Where outbound timing begins (wings level, abeam fix)
MAXIMUM HOLDING AIRSPEEDS (FAA)
| Altitude | Max Airspeed (KIAS) | Leg Timing |
|---|---|---|
| MHA - 6,000 ft | 200 KIAS | 1 minute |
| 6,001 - 14,000 ft | 230 KIAS | 1 minute |
| 14,001 ft and above | 265 KIAS | 1.5 minutes |
Note: Some published holds have different speeds. Always check the chart. Military aircraft may use higher speeds with ATC approval.
HOLDING ENTRY METHODS
Entry depends on your heading relative to the holding course when arriving at the fix:
DIRECT ENTRY
Sector: 0° - 70° from inbound course
1. Cross the fix
2. Turn left to outbound heading
3. Fly outbound leg (1 min)
4. Turn Left to inbound course
Simplest entry - just turn outbound!
PARALLEL ENTRY
Sector: 110° - 180° from inbound course
1. Cross the fix (heading opposite)
2. Turn to parallel outbound
3. Fly parallel to inbound (1 min)
4. Turn RIGHT >180° to intercept inbound
Turn towards holding side first
QUICK ENTRY DETERMINATION
DIRECT (0° - 70°)
Approaching from the holding side, roughly aligned with inbound course
PARALLEL (110° - 180°)
Approaching from opposite the holding side, against inbound course
Note: 70° - 110° is the teardrop sector (30° offset entry) - either direct or parallel will work in this range.
DETERMINING ENTRY TYPE
Visualize (or draw) the hold at the fix with the inbound course
Draw a line at 70° from the holding course on the holding side
Your heading relative to the inbound course determines sector
WIND CORRECTION IN HOLDS
- • Inbound leg: Apply wind correction to maintain course (crab into wind)
- • Outbound leg: Apply TRIPLE the inbound correction (opposite direction)
- • Outbound timing: Adjust to achieve 1-minute inbound leg. Add time if headwind inbound, subtract if tailwind.
Example: 10° left crab needed inbound → Use 30° right crab on outbound
RNAV/GPS Navigation
RNAV (Area Navigation) allows flight on any desired path without overflying ground-based navaids. GPS is the primary means of RNAV today.
RNAV CONCEPTS
Waypoint Navigation
RNAV uses waypoints (lat/long coordinates) rather than ground stations. Fly direct between waypoints regardless of navaid locations.
Required Navigation Performance (RNP)
RNP specifies accuracy requirements. RNP 1.0 means the aircraft must stay within 1.0 NM of course 95% of the time.
RAIM (Receiver Autonomous Integrity Monitoring)
GPS self-monitoring that alerts if position accuracy is insufficient. RAIM check required before GPS approaches. T-38 EGI provides equivalent integrity.
GPS SENSITIVITY MODES
GPS CDI sensitivity changes automatically based on phase of flight:
| Mode | Full Scale | When Active |
|---|---|---|
| Enroute (ENR) | ±2.0 NM | >30 NM from airports |
| Terminal (TERM) | ±1.0 NM | Within 30 NM of airport |
| Approach (APR) | ±0.3 NM | Within 2 NM of FAF |
RNP STANDARDS
RNP 2.0
Oceanic/Remote
RNP 1.0
Enroute
RNP 0.3
Terminal/Approach
RNP 0.1
RNP AR Approach
COMPLETION STANDARDS
Trainees will demonstrate proficiency in IFR navigation through chart-based exercises, simulator practice, and oral explanations. Trainees must:
- • Identify each navaid type and explain what it provides (bearing, distance, or both)
- • Demonstrate proper VOR/TACAN tuning, identification, and interpretation
- • Calculate intercept angles and lead points for radial intercepts
- • Explain and demonstrate the bearing pointer method for flying DME arcs
- • State maximum holding speeds for each altitude range
- • Correctly determine holding entry type (direct or parallel) for any scenario
- • Explain wind correction technique for holding patterns
- • Describe GPS sensitivity modes and RNP standards
Completion: Demonstrate understanding through chart exercises, holding entry determination, and arc flying discussion