NOTAM categories and time windows

A single pre-flight briefing can run to dozens of NOTAMs, and the one that matters, a closed runway or a lowered minimum, can hide among routine notices about crane lights. The defence is to sort them by category and by time window so the important ones surface first. This builds on our overview of understanding NOTAMs.

This is general educational information, not operational, legal, or regulatory advice. Rules differ by authority and change over time. Always verify against current official sources and follow your operator's approved procedures.

Scope: aerodrome, en-route, navigation warning

The broadest way NOTAMs are grouped is by scope, taken from the Q-line. The ICAO PANS-AIM (Doc 10066) format, under the parent Annex 15 (Aeronautical Information Services), marks each NOTAM as:

• Aerodrome (A): it affects a specific airfield, such as a runway, taxiway, or lighting change.
• En-route (E): it affects the airways and navigation structure between airfields.
• Navigation warning (W): it warns of an activity or hazard in the airspace, such as a temporary restricted area, military exercise, or rocket launch.

Scope is the first cut. If you are flying from one airfield to another, you care most about the aerodrome NOTAMs for your departure, destination, and alternates, the en-route NOTAMs along your track, and any navigation warnings near your route.

Subject: what the NOTAM is about

Within scope, NOTAMs sort by subject, the second and third letters of the Q-code (covered in detail in our guide to decoding NOTAM Q-codes). The practical categories pilots filter by are:

• Runways and taxiways: closures, work in progress, surface conditions, displaced thresholds.
• Navigation aids and communications: an ILS, VOR, DME, or radio frequency out of service.
• Airspace: restricted, danger, and prohibited areas, and temporary segregated airspace.
• Obstacles: new or unlit cranes, masts, and structures.
• Procedures: changes to an instrument approach, departure, or arrival.
• Lighting and services: approach lighting, fire and rescue category, fuel availability.

In the United States, regulatory and procedural changes, including temporary flight restrictions, are carried as FDC NOTAMs, while operational airfield items are distributed under the system the FAA describes in Order JO 7930.2. NOTAMs are also published in lettered series (A, B, C and so on) that group them by type and area, which is another axis a briefing service uses to organise them.

The time window: B, C and D

A NOTAM is only relevant if it is in force when you fly, and three fields set that:

• Field B) is the start of validity, as a UTC date-time group: year, month, day, hour, minute. So 2604100600 is 2026, April, the 10th, at 0600 UTC.
• Field C) is the end of validity, in the same form. It can instead read PERM for a permanent change, or carry the suffix EST for an estimated end.
• Field D) is a schedule, present only when the activity happens at specific times inside the overall window. A NOTAM valid for a fortnight might have a D) line saying it is active only 0800-1600 daily, so it is dormant the rest of the time.

From these fields, a NOTAM is active now, future (starts later), or expired (its window has passed). That status is what lets you set aside the ones that do not apply to your flight time and focus on the ones that do.

A worked example

B) 2604100600 C) 2604302200EST D) 0800-1600

Reading it: the NOTAM is valid from 0600 UTC on 10 April 2026 until an estimated 2200 UTC on 30 April, and within that window the activity is only on between 0800 and 1600 each day. Two cautions fall out of this, and the first one is the opposite of what most pilots assume. What happens if the estimate passes with nobody acting on it depends on whose system you are reading. The originator is required to cancel or replace the NOTAM before the time in C) either way: that duty is set out in the ICAO PANS-AIM (Doc 10066) format rules, under the parent Annex 15. In the United States, FAA Order JO 7930.2 says what happens if they do not: the NOTAM "will expire at the end of validity time regardless of EST". Under European processing the opposite is true. EUROCONTROL's OPADD rules keep an unactioned EST NOTAM in force and instruct the processing unit to chase the originating office for a replacement or cancellation, at least monthly, so it can sit in the database well past its estimated end. So do not memorise "an EST NOTAM always expires on time", and do not memorise the reverse either. Treat the EST time as a prompt to refresh. The trap is not that this NOTAM will still be there on 1 May. It is that the work may still be there while the notice has quietly expired, or that a replacement NOTAM has already moved the window, which is an argument for pulling a fresh bulletin close to departure rather than for trusting the one in your hand. Second, whether it affects you depends on your time over that location against the D) schedule: a flight at 1000 is inside the active hours, a flight at 1700 is not.

How to triage a briefing package

Faced with a long list, work in this order:

1. Filter by your route: your aerodromes, your track, and the altitudes you will use.
2. Filter by your time: discard NOTAMs whose window does not overlap your flight, but keep EST and PERM ones in view, because an estimated end can be moved by a replacing NOTAM.
3. Read the high-impact categories first: runway and approach changes, airspace activations, and navigation-aid outages, before obstacle and lighting notices.
4. Re-check close to departure, because new NOTAMs are issued continuously and a fresh one can change the picture.

This information overload is a recognised safety issue, and authorities are modernising how NOTAMs are filtered and presented, including the FAA's NOTAM modernisation work.

SNOWTAM, ASHTAM and the special formats

Most NOTAMs use the standard ICAO format, but a few important hazards have their own structured formats, and a complete briefing has to include them. Their formats are set out in the ICAO PANS-AIM (Doc 10066), under the parent Annex 15.

• SNOWTAM. A special series of NOTAM that reports a runway contaminated by snow, ice, slush, frost, or standing water, in a fixed format. Modern SNOWTAMs carry a runway condition code (RWYCC) on a scale from 6 (a dry runway, the best condition) down to 0 (the worst, effectively unusable), one figure per third of the runway, under the international Global Reporting Format. The braking-action descriptors run from 5 (good) down through medium to 1 (poor). That code feeds directly into landing-performance assessment, so a SNOWTAM is not a notice to skim; it changes the numbers for the landing.
• ASHTAM. A special series that reports volcanic ash activity, the state of a volcano, and the ash cloud, using a colour-code system for the level of alert. Because volcanic ash is a serious hazard to engines, an ASHTAM can close large volumes of airspace and reroute traffic for days.
• Other special notices. Some authorities issue specific series for bird hazards or military activity, and the United States carries certain regulatory and procedural items, including temporary flight restrictions, as FDC NOTAMs.

A practical reading of a SNOWTAM matters most of these. Suppose it reports a runway condition code of 5/5/5 with a thin covering of wet snow. A code of 5 is "good" (a wet runway, or up to 3 mm of slush, dry, or wet snow), and that, with the depth and type of contaminant, is what you take into your landing-distance assessment, alongside the wind and your aircraft data. The point is that these special formats are where some of the most consequential information lives, so triage that surfaces aerodrome NOTAMs should be reading SNOWTAMs near the top of the list in winter, and ASHTAMs whenever a volcano is active anywhere near the route.

The same time-window discipline applies to all of them. A SNOWTAM has a validity and is superseded as conditions change, so the one that matters is the most recent, and an old SNOWTAM is as misleading as an old METAR.

FDC NOTAMs and temporary flight restrictions

In the United States, one category deserves its own mention because it carries some of the most consequential notices: the FDC NOTAM, issued by the Flight Data Center. Where ordinary NOTAMs cover the physical state of aerodromes and aids, FDC NOTAMs carry regulatory and procedural information: amendments to instrument approach procedures, changes to airways, and, importantly, temporary flight restrictions (TFRs).

A TFR closes or restricts a volume of airspace for a defined reason and period. Common ones include restrictions over major sporting events, around the movement of senior government figures, over disaster and firefighting areas, and for security or special activity. A TFR is not advisory: entering one without authorisation is a regulatory violation and can have serious consequences, so a TFR along or near your route is a high-priority item in any briefing, read carefully for its exact boundaries and times. The FAA publishes active TFRs and the NOTAMs that create them.

Other parts of the world achieve the same effect through the activation of restricted, danger, and prohibited areas and temporary segregated airspace, carried as navigation-warning NOTAMs in the scope categories described above. Whatever the local label, the principle for triage is the same: a notice that changes whether you may legally be in a piece of airspace ranks at the top of the list, well above routine aerodrome items.

Common pitfalls

• Assuming you know what an unactioned EST NOTAM does. It must be cancelled or replaced before its estimated end. If nobody acts, a US NOTAM expires there anyway, while European processing keeps it in force and chases the originator, so the behaviour is not universal. The hazard it describes may well still be there either way, so refresh rather than assume.
• Ignoring the D) schedule. A NOTAM can be valid for weeks but only active for a few hours a day.
• Reading times as local. Every NOTAM time is UTC.
• Stopping at the first read. New NOTAMs arrive constantly, so refresh close to departure.
• Treating every NOTAM as equal. A closed runway and a grass-cutting notice are both NOTAMs; category-first reading keeps them in proportion.

In Pilot EFB

Pilot EFB pulls the NOTAMs for your route and helps you work through them by aerodrome and category, and it tags each one with a time-window status so you can see at a glance whether a NOTAM is active, still to come, or finished for your flight. It organises and surfaces; it does not decide for you which NOTAMs matter or interpret what they mean, and the full raw text is always kept with keywords highlighted. NOTAMs you have already pulled stay readable with no signal, while getting the latest issued NOTAMs needs a connection. Pilot EFB is offline-first and is not a certified Electronic Flight Bag, so confirm against the official AIS source before you fly.