What is an AIRAC cycle and why does it matter for my FMS database?

AIRAC stands for Aeronautical Information Regulation and Control, and it is a standardized worldwide system of 28-day cycles on which aeronautical data — including airways, procedures, and navaids — is updated and published. Your Flight Management System relies on a database built to a specific AIRAC cycle, and once that cycle expires, the stored procedures and routing data may no longer match the current charted information. The FAA's Instrument Flying Handbook notes that pilots must ensure FMS databases are current before using the system for IFR navigation, because discrepancies between the database and published procedures can produce unreliable guidance.

What happens if I fly with an expired FMS database?

Flying with an out-of-date FMS database means the stored instrument procedures, waypoints, and airway structures may not reflect current charted information, which can produce navigation errors and potential conflicts with terrain or traffic. From a regulatory standpoint, 14 CFR Part 91 requires that instruments and equipment be in a condition for safe operation, and using a known-expired database on an IFR flight can expose the pilot to enforcement action. Many operators mitigate this risk by cross-checking all FMS-generated routing against current paper or electronic charts and NOTAMs before and during flight.

Why do I need to check NOTAMs even if my FMS database is current?

NOTAMs provide time-critical information — such as procedure amendments, navaid outages, temporary flight restrictions, and runway closures — that may take effect between AIRAC publication dates and therefore will never appear in your FMS database regardless of how recently it was updated. The Aeronautical Information Manual instructs pilots to review all applicable NOTAMs during preflight planning to ensure the intended route and procedures are valid and safe. Relying solely on an FMS without consulting NOTAMs could lead you to fly a procedure that has been temporarily suspended or to a navaid that is out of service, undermining the reliability of your automation.

FMS Database Currency, AIRAC Cycles, and NOTAMs

Modern flight decks depend heavily on the Flight Management System (FMS) to calculate routes, manage fuel predictions, sequence arrivals, and drive autopilot guidance. But the FMS is only as trustworthy as the data it references. Two interrelated concepts govern that trustworthiness: AIRAC cycle currency — the 28-day schedule on which navigation databases are updated — and NOTAMs (Notices to Air Missions), which provide the real-time layer of information that no database cycle can anticipate. Understanding both is essential not only for the ATP knowledge test but for every flight you dispatch.

This article explains how AIRAC cycles work, what it means for an FMS database to be current or expired, the legal and operational implications of flying with an outdated database, and how NOTAMs interact with — and sometimes override — everything the FMS thinks it knows.

What Is an AIRAC Cycle?

AIRAC stands for Aeronautical Information Regulation and Control. It is an internationally standardized system, coordinated by the International Civil Aviation Organization (ICAO), that synchronizes the publication and effective dates of aeronautical information around the world. The system is built on a fixed 28-day cycle, with each cycle beginning on a specified Thursday effective date published on the AIRAC schedule. Because every country follows the same schedule, a new instrument approach procedure, a frequency change, or an airspace redesign becomes effective on the same date globally, greatly reducing the risk of conflicting information across borders.

Each 28-day period is identified by a two-part designator consisting of the year and cycle number — for example, 2401 means the first cycle of 2024. There are 13 cycles per year, consistent with the 28-day cycle length (365 days ÷ 28 ≈ 13.04 cycles per year). Navigation data vendors such as Jeppesen and Lido compile procedure data from national AIP (Aeronautical Information Publication) amendments and package it into a format loaded onto the FMS, typically via a data-transfer unit, a laptop upload system, or — on newer aircraft — over a direct datalink connection.

How the FMS Uses Its Database

The FMS navigation database is a structured electronic library containing waypoints, airways, navaids, airports, SIDs, STARs, instrument approaches, and company routes. When a crew loads a flight plan, the FMS references this library to string together legs, calculate magnetic courses, anticipate altitude constraints, and build the vertical profile the aircraft will fly. The quality of every one of those calculations depends entirely on the accuracy of the stored data.

A properly maintained FMS displays the active database cycle on its data pages, usually showing both the cycle identifier and its effective date range. During the pre-flight data check — a step in virtually every airline SOPs and referenced in the Instrument Flying Handbook — crews confirm that today's date falls within the database validity window. Most FMS units will not prevent you from flying with an expired database, but they will post an alert or advisory indicating the database is out of date.

What the FMS Cannot Know

Even a perfectly current database reflects only the aeronautical environment as it was published 28 days ago (or whenever the cycle became effective). It cannot reflect a runway closed yesterday for pavement repair, a localizer temporarily out of service, a new TFR activated two hours ago, or a taxiway displaced by construction. That gap is precisely what NOTAMs are designed to fill.

Flying With an Expired Database: Legal and Safety Considerations

The regulations governing FMS database currency are found primarily in 14 CFR Part 91 for general aviation and Part 121/135 for commercial operators, and they are nuanced. Under 14 CFR 91.103, pilots must familiarize themselves with all available information concerning the intended flight. For Part 121 and 135 operators, navigation database currency requirements used for instrument operations are addressed through the carrier's operations specifications together with FAA advisory material such as AC 90-105 and AC 20-153, which establish standards for database currency and integrity rather than 91.503, which concerns flight locating requirements and equipment for large and turbine-powered multiengine airplanes.

The FAA's practical standard is this: an out-of-cycle database may be used for flight under IFR only if the operator verifies through NOTAMs and other official sources that the procedures in use have not changed since the database was compiled. This is not a blanket permission; it is a conditional allowance that places a significant verification burden on the crew. For a Part 121 carrier, using an expired database without that verification process can constitute a violation of the carrier's operations specifications.

From a safety standpoint, the hazard is concrete. Consider a new RNAV approach published mid-cycle: it will not appear in the old database. Conversely, an approach may be withdrawn mid-cycle; an expired database would still show it as valid. Altitude constraints on SIDs and STARs can change. Transition waypoints can be renamed. A crew relying on the FMS without cross-checking NOTAMs could fly an approach that no longer reflects terrain clearance as designed, or use a waypoint that has been renamed and is no longer charted on current plates.

NOTAMs: The Real-Time Bridge

NOTAMs are official notices issued by the FAA (and by national authorities worldwide) to alert pilots of conditions affecting aeronautical operations that are not reflected in permanent publications. In the United States, NOTAMs are published through the FAA's NOTAM system and are accessible through 1800wxbrief.com, ForeFlight, Jeppesen, airline dispatch systems, and the FAA's official NOTAM search tool.

NOTAMs are classified into several types. FDC NOTAMs (Flight Data Center NOTAMs) carry regulatory weight and are particularly important for instrument operations; they can temporarily change procedure altitudes, amend instrument approach minimums, or designate temporary flight restrictions. NOTAM (D) or distant NOTAMs cover navaid outages, runway closures, obstructions, and other airport-specific items. GPS NOTAMs warn of scheduled testing or interference that may degrade GPS signal integrity in a specific area — critical for any RNAV or RNP procedure. TFR NOTAMs impose temporary flight restrictions for security events, VIP movements, natural disasters, or other reasons.

For ATP-level operations, the key discipline is understanding that NOTAM review is not optional or cursory. Every FDC NOTAM affecting your departure, en route, and destination procedure must be incorporated into your planning and briefed to your crew. An approach whose minimums have been raised by FDC NOTAM requires you to use the NOTAM-amended minimums, not the charted values — even if the FMS and the chart agree with each other.

Integrating FMS Data and NOTAMs in Practice

The practical workflow for an ATP-level crew proceeds as follows. During preflight planning, the crew (or dispatch) confirms the FMS database cycle is current and covers the intended operation. A thorough NOTAM review is conducted for each airport and for the en route structure, with special attention to FDC NOTAMs, navaid outages, and GPS interference. Any NOTAM that amends a procedure the FMS will execute — say, a step-down fix altitude change on an ILS approach — must be mentally overlaid on the expected FMS behavior.

In the cockpit, crews should never assume the FMS approach trajectory or constraints are fully authoritative without confirming the underlying data is both current and unaffected by active NOTAMs. When flying an RNP AR approach — one of the most FMS-dependent procedures in modern aviation — confirming database currency and checking for any GPS outage NOTAMs along the route is part of the approach briefing discipline. Per AC 90-101A, RNP AR operations require specific operator authorization, and the procedure design relies on a current, qualified navigation database to drive the intended path rather than pilot-interpreted raw data.

Key Numbers and Rules

AIRAC cycle length: exactly 28 days, with each cycle beginning on a published Thursday effective date.
Cycles per year: 13 in most years.
Cycle identifier format: four digits — year followed by cycle number (e.g., 2407 = seventh cycle of 2024).
Expired database use under IFR: permitted only when the crew verifies via NOTAMs that affected procedures have not changed — this is an operational verification burden, not a blanket exemption.
FDC NOTAMs: carry regulatory force and can amend approach minimums, altitudes, and procedures; must be treated as amendments to the chart.
GPS NOTAMs: must be checked before any RNAV/GNSS-dependent operation; signal outages can render an approach unusable even if the database is perfectly current.
NOTAM review is required by 14 CFR 91.103 as part of the pilot's preflight information requirement for any flight, IFR or VFR — the regulation requires familiarity with all available information about the flight and does not name NOTAMs specifically, though NOTAM review is understood as necessary for compliance.

Common Test Traps

Assuming an expired database is always unusable: The FAA allows its use conditionally, but the verification requirement is significant. The test may frame this as a yes/no — the correct answer is that it may be used if procedures are verified via NOTAMs as unchanged.
Confusing AIRAC cycle length with calendar months: AIRAC cycles are 28 days, not one calendar month. 13 cycles fit in most years. This distinction matters when calculating when a database will expire.
Overlooking FDC NOTAMs when briefing approaches: Test questions may describe a scenario where the FMS and chart show the same minimums, but an FDC NOTAM has raised them. The legal minimums are always the NOTAM-amended values.
Thinking NOTAMs replace the need for a current database on RNP AR approaches: For RNP AR, a current, certified database is typically operationally required per AC 90-101A — NOTAMs supplement the database but cannot substitute for it when the procedure relies entirely on database-driven path guidance.
Missing GPS NOTAMs for RNAV operations: A current FMS database does not guarantee a usable GPS signal. Outage or interference NOTAMs must be checked independently; the database contains no mechanism to flag signal degradation on the day of flight.