9.4 IFR Flight with GPS & Database Currency

IFR Flight with GPS & Database Currency

Quick Answer: Aviation navigation databases are updated on a strict 28-day AIRAC cycle that becomes effective at 0901 UTC on the effective date. Operating under IFR with an expired database is strictly PROHIBITED for instrument approach procedures; it is permitted for en route IFR only if all waypoints are manually cross-checked against current en route charts. All instrument approaches must be loaded by name from the current database—hand-entering coordinates is illegal. Fly-by waypoints use turn anticipation to cut inside the corner, whereas fly-over waypoints (circled star symbol) require flying directly overhead before turning.

While space-based positioning hardware provides extraordinary precision, an airborne GPS navigator is only as safe and reliable as the software and aeronautical data driving its flight planning calculations. Navigating the modern National Airspace System (NAS) under Instrument Flight Rules (IFR) requires strict adherence to database currency rules, procedure loading protocols, and waypoint navigation symbology.

---

The 28-Day AIRAC Navigation Database Cycle

Aviation navigation data changes continuously as airways are realigned, frequencies change, obstacles are erected, and approach procedures are modified. To maintain global synchronization, aeronautical databases follow the Aeronautical Information Regulation and Control (AIRAC) cycle established by ICAO and the FAA.

+-----------------------------------------------------------------------+
|                   THE 28-DAY AIRAC CYCLE LIFECYCLE                    |
|                                                                       |
|   +---------------------------------------------------------------+   |
|   | • Cycle Duration: Exactly 28 calendar days (13 cycles / year) |   |
|   | • Legal Effective Time: 0901 Coordinated Universal Time (UTC) |   |
|   | • Effective Day: Always falls on a Thursday                   |
|   +---------------------------------------------------------------+   |
|                                  │                                    |
|                                  ▼                                    |
|   +---------------------------------------------------------------+   |
|   | Navigation Database Contents:                                 |
|   | Airports, Runways, NAVAIDs, Intersections, Airways (V/Q/T),   |
|   | SIDs, STARs, IAPs (LNAV/LPV/ILS), Frequencies, Airspace Bound.|   |
|   +---------------------------------------------------------------+   |
+-----------------------------------------------------------------------+

Critical Timing Rules

• Cycle Duration: Exactly 28 days (resulting in 13 publication cycles per calendar year).
• Effective Timestamp: The database becomes legally effective at 0901 UTC on the scheduled effective date (which always occurs on a Thursday).
• Preflight Verification: During preflight avionics initialization, the pilot in command (PIC) must verify on the power-up self-test screen that the navigation database is current and covers the intended geographic area of flight.

---

Operating with an Expired Navigation Database

Under AIM 1-1-17, AC 90-100A, and 14 CFR § 91.103 (Preflight Action), strict regulatory boundaries govern flight when the airborne navigation database has passed its expiration date:

+-----------------------------------------------------------------------+
|                   EXPIRED DATABASE REGULATORY MATRIX                  |
|                                                                       |
|  Flight Operation     | Legal Status   | Mandatory Pilot Conditions   |
|  -------------------- | -------------- | ---------------------------  |
|  En Route IFR Flight  | PERMITTED*     | Manually cross-check every   |
|                       |                | fix, airway & frequency      |
|                       |                | against current charts       |
|  -------------------- | -------------- | ---------------------------  |
|  Terminal (SID/STAR)  | PROHIBITED     | Current database required    |
|  -------------------- | -------------- | ---------------------------  |
|  Instrument Approach  | STRICTLY       | NO EXCEPTIONS: Must have a   |
|  Procedures (IAP)     | PROHIBITED     | current, unexpired database  |
+-----------------------------------------------------------------------+

1. En Route IFR Operations (Permitted with Conditions)

• An aircraft may operate under IFR along en route airways using an expired navigation database only if the pilot manually cross-checks every waypoint, airway identifier, intersection coordinate, and frequency against a current, authorized paper or electronic en route chart (such as an active ForeFlight, Garmin Pilot, or FAA Sectional/En Route chart) prior to flight.

2. Terminal & Instrument Approach Procedures (Strictly Prohibited)

• Executing any published terminal procedure (SID or STAR) or Instrument Approach Procedure (IAP) using an expired navigation database is strictly illegal under FAA regulations.
• Why Approach Use is Prohibited: Approach procedures contain complex vertical angles, temperature compensation codings, obstacle clearance step-down fixes, and magnetic variation models that cannot be safely validated manually in the cockpit. Even minor unannounced frequency or fix location shifts could lead to Controlled Flight Into Terrain (CFIT).

---

Autonav & Approach Loading Regulations

The FAA enforces strict standards regarding how instrument procedures are loaded into airborne navigators under AIM 1-1-17 and AC 90-105A:

+-----------------------------------------------------------------------+
|                   APPROACH LOADING REGULATORY RULES                   |
|                                                                       |
|   [✓] Approaches MUST be loaded by name from the certified database   |
|   [✓] System automatically extracts all IAFs, IF, FAF, MAP & Missed   |
|   [✗] Hand-entering individual waypoints by name is PROHIBITED        |
|   [✗] Hand-entering latitude/longitude coordinates is PROHIBITED      |
|   [✗] Deleting or inserting fixes inside the FAF is PROHIBITED        |
+-----------------------------------------------------------------------+

1. Mandatory Loading by Procedure Name

• The entire instrument approach procedure must be selected and loaded by name directly from the database (e.g., RNAV (GPS) RWY 18 via TRUMM).
• The receiver automatically extracts the complete sequence of fixes, including initial approach fixes (IAFs), intermediate fixes (IF), the final approach fix (FAF), the missed approach point (MAP), and the published missed approach holding procedure.

2. Manual Waypoint Entry is Strictly Prohibited

• Pilots are strictly prohibited from manually creating an approach by hand-typing individual fix names, inserting user-defined waypoints, or entering raw latitude/longitude coordinates.
• Technical Rationale: Hand-entered waypoints do not trigger the receiver's internal safety algorithms, including:
  • Automatic CDI sensitivity transitions (scaling from ±1.0 NM down to ±0.3 NM at 2 NM prior to FAF).
  • Autonomous approach integrity monitoring checks (RAIM/WAAS alert limits).
  • Coded vertical glidepath ($+V$ / LPV) generation.
  • Automated missed approach waypoint sequencing.

3. Loading Vectors-to-Final vs. Published IAF

• Via Initial Approach Fix (IAF): Loads full procedural routing, including procedure turns, teardrop entries, or Hold-in-Lieu-of-Procedure-Turn (HILPT) course reversals.
• Vectors-to-Final (VTF): Eliminates all feeder routes and fixes outside the Final Approach Course Fix (FACF), drawing an extended centerline vector to the final approach course. Waypoint auto-sequencing is temporarily suspended until the aircraft intercepts the final approach vector within 30° of inbound heading.

---

Fly-By vs. Fly-Over Waypoints

Modern RNAV charts utilize two distinct types of waypoints, distinguished by standard charting symbology:

+-----------------------------------------------------------------------+
|                   FLY-BY vs. FLY-OVER WAYPOINTS                       |
|                                                                       |
|   +---------------------------------+  +--------------------------+   |
|   |        FLY-BY WAYPOINT          |  |     FLY-OVER WAYPOINT    |   |
|   |                                 |  |                          |   |
|   |       ★ (Four-Point Star)       |  |  ⊛ (Star in Solid Circle)|   |
|   |                                 |  |                          |   |
|   |  • Receiver uses turn           |  |  • Aircraft MUST fly     |   |
|   |    anticipation                 |  |    directly overhead fix |   |
|   |  • Turns BEFORE reaching fix    |  |  • Turn begins AFTER     |   |
|   |  • Cuts inside corner smoothly  |  |    crossing the fix      |   |
|   |  • Prevents course overshoot    |  |  • Results in overshoot  |   |
|   |  • Used on en route airways,    |  |    and S-turn intercept  |   |
|   |    SIDs, STARs & approach IFs   |  |  • Used on MAP, Holds, PT|   |
+-----------------------------------------------------------------------+

1. Fly-By Waypoints (Standard Four-Pointed Star Symbol: ★)

• Turn Anticipation: The GPS receiver calculates aircraft groundspeed, turn angle, and bank angle to determine the exact point prior to reaching the fix to initiate the turn.
• Flight Path: The aircraft smoothly rolls into a coordinated turn before reaching the fix, cutting inside the corner so that it rolls out established on the centerline of the new outbound course leg without overshooting.
• Application: The default waypoint type used for en route airway intersections, SIDs, STARs, and approach intermediate fixes.

2. Fly-Over Waypoints (Circled Four-Pointed Star Symbol: ⊛)

• Direct Passage Required: The aircraft must fly directly overhead the waypoint before the pilot or autopilot initiates any turn.
• Flight Path: Because the turn begins only after crossing the fix, the aircraft naturally overshoots the outbound course centerline and must perform a corrective intercept turn to establish on course.
• Mandatory Applications: Used where strict terrain clearance, airspace containment, or procedural sequencing demands passing directly over the fix:
  • Missed Approach Points (MAP): (e.g., runway threshold or circled MAP fix).
  • Holding Fixes: The aircraft must cross the holding fix before turning onto the outbound holding leg.
  • Procedure Turns & Course Reversals: Guarantees entry within protected airspace.