How to File an IFR Flight Plan: The ICAO Form, Equipment Codes, Clearances, and Void Times
Updated: Sep 6
Filing an IFR flight plan is more than filling in boxes on an app — it's a critical step that connects your aircraft, your intentions, and the air traffic control system. A properly filed IFR flight plan helps ATC anticipate your needs, sequence traffic, and provide separation, while ensuring you meet regulatory and operational requirements. But the process has modernized in an important way: the old equipment "slant codes" (/G, /A, /U) that pilots used for decades are gone, replaced by the ICAO international flight plan format with its equipment and PBN codes. Understanding how to file today — the ICAO form, the equipment codes, and how filing becomes a clearance — is a key milestone in becoming a confident instrument pilot.
This post covers filing an IFR flight plan in practical depth: what it is and when to file, the filing methods, the ICAO flight plan form section by section (including the equipment and PBN codes that replaced the slant suffixes), filing versus activating, picking up your clearance with CRAFT, the void-time mechanics for uncontrolled fields, and the common mistakes.
Study this full length lesson (video, podcast, flashcards, and quiz) here: Full Length Lesson >
What an IFR Flight Plan Is
An IFR flight plan is a formal request to operate under Instrument Flight Rules within the National Airspace System.
Once filed and activated, it allows ATC to:
Issue an IFR clearance
Provide traffic separation
Assign altitudes and routes
Coordinate handoffs between facilities
Assist with lost communications or emergencies
The key distinction from VFR:
An IFR flight plan is REQUIRED before operating IFR
(A VFR flight plan is optional — for search and rescue)
IFR requires the plan AND a clearance
The plan is mandatory for IFR
The regulatory basis:
14 CFR 91.173: no person may operate IFR in controlled airspace without an ATC clearance
The flight plan is the basis for the clearance
Required for IFR in controlled airspace
The system's foundation
When to File
The timing, expanded.
When to file:
At least 30 minutes before departure (recommended, so it's in the system)
Before calling for your IFR clearance
Before departing VFR with intent to pick up IFR airborne
How far in advance:
Hours in advance
The day before
Even days ahead (though weather/updates may require amendment)
Flexible
The 30-minute recommendation:
Filing 30+ minutes ahead lets the flight plan propagate to the ATC system
The clearance is ready when you call
Filing too late may mean the clearance isn't in the system yet
Give it time
The proposed departure time:
File a realistic proposed departure time (Zulu)
The flight plan is held in the system around that time
If you're significantly early/late, amend it
The system uses the proposed time
Ways to File
The methods, updated.
Common filing methods:
Electronic flight planning apps (ForeFlight, Garmin Pilot, etc.) — the most common
Flight Service (1-800-WX-BRIEF, operated by Leidos) — phone filing
Online FAA/Leidos filing tools (1800wxbrief.com)
Some avionics systems (file directly from the panel)
Why electronic filing is preferred:
Reduces errors (validates the form)
Validates routes (checks for errors, suggests preferred routes)
Integrates weather and NOTAMs automatically
Faster and easier
The Leidos/Flight Service system:
Flight Service (Leidos) handles flight plan filing for the FAA
Apps file through this system (or directly to the FAA)
1-800-WX-BRIEF connects to Flight Service
The backbone of GA filing
The app advantage:
Apps pre-fill aircraft data (equipment codes saved in your profile)
Suggest ATC-preferred routes
Validate before filing
Integrate the whole preflight
The modern standard
The ICAO Flight Plan Form: What Replaced the Slant Codes
Here's the biggest modernization the basic treatment doesn't fully capture: the US moved to the ICAO international flight plan format, retiring the old equipment suffixes.
The change:
Until 2019, US domestic flight plans used the FAA domestic form with equipment "slant codes" (/G, /A, /U, /L, etc.)
These slant codes are RETIRED (as of 2019)
The US now uses the ICAO international flight plan format for all IFR (and most VFR) filing
The ICAO form uses equipment/capability CODES, not slant suffixes
Why it changed:
The old slant codes were limited (couldn't describe modern capabilities precisely)
The ICAO format describes navigation, communication, surveillance, and PBN capabilities in detail
International standardization
Better for modern equipment (WAAS, ADS-B, RNP)
The ICAO form fields (the key ones for pilots):
Item 7: Aircraft identification (registration or call sign)
Item 8: Flight rules (I for IFR) and type of flight (G for GA)
Item 9: Number, aircraft type, and wake turbulence category
Item 10: Equipment and capabilities (10a: comm/nav/approach; 10b: surveillance/transponder/ADS-B)
Item 13: Departure aerodrome and time
Item 15: Route (cruise speed, level, route)
Item 16: Destination, total EET, alternate(s)
Item 18: Other information (including the PBN code and other details)
Item 19: Supplementary (fuel, persons on board, emergency equipment — for search and rescue)
Item 10a — Equipment and capabilities:
Letter codes for equipment: e.g., G = GNSS (GPS), S = standard (VHF, VOR, ILS), R = PBN approved, W = RVSM, etc.
You list the codes for your aircraft's capabilities
Replaces the old single slant code
Describes what you can actually do
Item 10b — Surveillance:
Transponder and ADS-B codes: e.g., C = Mode C, S = Mode S, B1/B2 = ADS-B Out, U1/U2 = UAT ADS-B, etc.
Describes your surveillance equipment
Includes ADS-B capability
Part of the modern form
Item 18 — PBN code:
If you put R in Item 10a (PBN approved), you specify the PBN capabilities in Item 18 (the PBN/ code)
Codes like B2, C2, D2, O2 describe RNAV and RNP capabilities
Details your area-navigation approvals
Required if claiming PBN
The practical reality for pilots:
Your app stores your aircraft's ICAO equipment codes (set once in the profile)
You don't manually type them each time (usually)
But you should understand what they mean
Get them RIGHT (they determine your routes and approaches)
Why the codes matter:
They determine which routes you can fly (RNAV routes need the right codes)
Which approaches you're authorized (GPS approaches need GNSS capability filed)
How ATC sequences and separates you
Incorrect codes = amended clearances, delays, denied RNAV routes
Filling Out the Key Sections
Section-by-section guidance, updated for the ICAO form.
Aircraft Identification (Item 7):
Your registration number (e.g., N123AB) or call sign
Must match your transponder configuration and radio call sign
Consistent identification
The tail number for GA
Flight Rules and Type (Item 8):
I for IFR
G for General Aviation (type of flight)
Tells ATC how to handle the flight
Standard for GA IFR
Aircraft Type and Wake Category (Item 9):
Aircraft type designator (C172, PA28, SR22, etc.)
Wake turbulence category (L for light, M for medium, etc.)
Identifies the aircraft
For separation
Equipment (Item 10):
The ICAO equipment/capability codes (10a and 10b)
As discussed above
Critical for routing and approaches
Set in your app profile
Departure and Time (Item 13):
ICAO airport identifier (KXXX)
Proposed departure time (Zulu)
Helps ATC anticipate traffic
Realistic timing
Route and Altitude (Item 15):
Cruise speed, requested altitude (level), and the route
Altitude: meets IFR hemispherical rules, clears terrain (MEAs), matches performance
Route: departure procedure (SID) if applicable, airways/RNAV fixes, STAR/approach transition if appropriate
Use ATC-preferred routes
Destination, EET, Alternate (Item 16):
Destination ICAO identifier
Total estimated enroute time (EET)
Alternate airport(s) if required
For traffic planning and SAR timing
Other Info (Item 18):
The PBN code (if applicable)
Other relevant information (equipment notes, etc.)
Remarks
Supplementary details
Supplementary — Fuel, Souls (Item 19):
Total usable fuel (in time — hours and minutes)
Persons on board
Emergency equipment
Used for SAR (not transmitted to ATC normally, held by Flight Service)
Choosing a Route
Routing guidance, expanded.
Your route should be:
Legal (airways, valid fixes)
Efficient (reasonable, direct where possible)
Realistic (what ATC will actually clear)
Typical routing components:
Departure procedure (SID) if applicable
Airways (Victor/T-routes) or RNAV fixes
STAR (arrival) or approach transition if appropriate
Connected logically
Preferred routes:
Many city pairs have ATC-preferred routes
Filing the preferred route increases clearance acceptance
Apps suggest them
Avoid getting a full-route amendment
The tower-en-route option:
For shorter flights between certain airports, "tower en route control" (TEC) routes exist
Stay in approach control airspace (no center)
Specific TEC routes are published
An option for regional IFR flights
Avoid:
Overly creative or unrealistic routes
Ignoring preferred routes into busy airports
Routes your equipment can't support (RNAV without the codes)
Getting a full reroute at clearance
The "expect" reality:
ATC may clear you via a different route than filed
The preferred route increases acceptance
Be ready to copy an amended route
Flexibility
Filing vs. Activating
The critical distinction, reinforced.
Filing:
Submits your flight plan to the system
Does NOT authorize IFR flight
The plan is on file (proposed)
Step one
Activating:
Occurs when ATC issues and you ACCEPT an IFR clearance
The clearance activates your IFR flight
You're now cleared into the system
Step two
The key point:
You are NOT IFR until you receive AND accept your clearance
Filing alone doesn't make you IFR
The clearance is what authorizes IFR operation
Filing ≠ cleared
How activation happens:
On the ground: get the clearance before departure (at a towered field or via clearance delivery/RCO)
In the air: pick up the clearance airborne (if departing VFR)
Either way, the clearance activates it
Two common methods
Picking Up Your IFR Clearance
The clearance process, expanded with CRAFT decoded.
Where to get your clearance:
Clearance Delivery (at busier towered fields)
Ground Control (at some towered fields)
A Remote Communications Outlet (RCO) or clearance delivery phone (at non-towered fields)
ATC airborne (if departing VFR and picking up IFR)
The CRAFT format (for copying clearances):
C — Clearance limit: where you're cleared to (usually the destination)
R — Route: the route (as filed, or amended)
A — Altitude: the altitude (and any "expect" altitude)
F — Frequency: the departure frequency (for after takeoff)
T — Transponder: the squawk code
Decoding CRAFT:
Clearance limit: "Cleared to KXYZ airport" (your destination)
Route: "as filed" (they accepted your route) or an amended route to copy
Altitude: "Climb and maintain 3,000, expect 8,000 ten minutes after departure" (initial and expected)
Frequency: "Departure frequency 124.3" (contact after takeoff)
Transponder: "Squawk 4271" (set this code)
The "expect" altitude:
Clearances often give an initial altitude and an "expect" higher altitude
The "expect" altitude is for lost communications (climb to it at the expected time if you lose comms)
Part of the clearance
Note it
Reading back the clearance:
Read back the clearance to confirm (especially the route, altitude, and squawk)
Ensures you copied it correctly
ATC confirms or corrects
Standard procedure
The "hold for release" possibility:
At non-towered fields, you may get the clearance but be told "hold for release"
You can't depart IFR until released (ATC coordinates the traffic)
Wait for the release
Common at uncontrolled fields
Void Times at Uncontrolled Fields
A crucial mechanic the basic treatment doesn't cover: departing IFR from a non-towered airport.
The clearance void time:
At a non-towered field, your IFR clearance comes with a CLEARANCE VOID TIME
You must depart before the void time
If you don't depart by then, the clearance is void (canceled)
ATC holds the airspace only until the void time
Why void times exist:
At an uncontrolled field, ATC can't see you depart
They reserve the airspace for a window (until the void time)
If you don't go, they release the airspace to other traffic
A time limit on your departure
How it works:
"Clearance void if not off by [time]" (e.g., void if not off by 1415Z)
Depart before that time
If you can't, the clearance is void (call for a new one)
Depart within the window
The "if not off by" and reporting:
You may also be asked to report your departure time (or airborne) to ATC
"If not off by [time], advise [facility] not later than [time] of intentions"
Report as instructed
ATC needs to know if you didn't depart
The release:
You may get a "release" with a void time
"Released for departure, clearance void if not off by [time]"
Depart within the window
Then contact departure/center airborne
Why this matters:
Departing a non-towered field IFR requires understanding void times
Don't blow the void time (call for a new clearance if you can't make it)
Report as required
A key uncontrolled-field procedure
Cancelling IFR
The other end of the flight, worth including.
Cancelling IFR:
You can cancel IFR when you no longer need it (in VMC, clear of clouds)
"Cancel IFR" to ATC (or Flight Service)
Frees you from the IFR clearance (and frees the airspace)
Common when arriving VMC
At a non-towered destination:
Landing IFR at a non-towered field ties up the airspace until you cancel
Cancel in the air (if VMC) or on the ground (by phone/radio) after landing
IMPORTANT: if you don't cancel, ATC may initiate search and rescue (they think you're still flying)
Cancel promptly
The cancellation methods:
Airborne: "Cancel IFR" to ATC (if in VMC)
On the ground: call Flight Service or ATC to cancel
At a towered field: landing cancels it automatically (the tower knows)
Cancel to close the loop
Why cancelling matters:
Frees the airspace for other IFR traffic
Prevents an unnecessary SAR response
Good practice
Don't forget
Common IFR Filing Mistakes
The errors, expanded.
Incorrect equipment codes:
The #1 mistake
Wrong ICAO codes = denied RNAV routes, amended clearances, delays
Set them correctly in your profile
Verify they match your actual equipment
Unrealistic routing:
Filing creative routes ATC won't accept
Use preferred routes
Get a full reroute if you don't
File realistic routes
Filing an invalid alternate:
An alternate that doesn't meet alternate minimums (or is NA)
Verify alternate minimums
Check it's usable
A planning error
Forgetting to update the departure time:
Filing for a time you miss significantly
Amend if early/late
The system uses the proposed time
Keep it current
Filing without checking NOTAMs:
Missing NOTAMs affecting the route/approach/alternate
Check NOTAMs as part of filing
Part of preflight (91.103)
Don't skip
Assuming ATC will "fix" everything:
ATC handles a lot, but a bad flight plan creates workload
File it right
Reduce the back-and-forth
Your responsibility
Blowing a void time (non-towered):
Not departing before the clearance void time
Understand void times
Depart in the window or call for a new clearance
An uncontrolled-field error
Forgetting to cancel IFR (non-towered arrival):
Not cancelling after landing at a non-towered field
Can trigger a SAR response
Cancel promptly
Close the loop
Best Practices
Expanded advice.
File early, then amend if needed
Use preferred routes whenever possible
Double-check your ICAO equipment codes (set once, verify they're right)
Brief your clearance before calling ATC (anticipate the route/altitude)
Understand void times for non-towered departures
Remember to cancel IFR at non-towered destinations
Treat filing as part of your IFR risk management
Use CRAFT to copy clearances
Final Thoughts
Filing an IFR flight plan is not just a formality — it's your entry point into the IFR system. When done correctly, it sets the tone for a smooth clearance, predictable routing, and lower cockpit workload. The process has modernized: the old slant codes are gone, replaced by the ICAO format's equipment and PBN codes, which describe your aircraft's capabilities precisely and determine your routes and approaches.
A thoughtful, accurate flight plan helps ATC help you, reduces surprises, and enhances safety. Understand the ICAO form and its equipment codes, use preferred routes, copy your clearance with CRAFT, and know the void-time and cancellation procedures for non-towered fields. Mastering this process is a key milestone in becoming a confident, proficient instrument pilot.
On the Written Test and Checkride
IFR flight plan filing appears on tests and checkride orals (instrument especially). The most commonly tested topics:
Filing vs. activating (you're not IFR until cleared)
The equipment/capability codes (ICAO format)
The CRAFT clearance format
Void times at non-towered fields
Cancelling IFR (and the SAR implication)
Required flight plan information
Quick Reference
IFR Flight Plan:
Formal request to operate IFR
REQUIRED before IFR flight (91.173)
Enables clearance, separation, altitudes, handoffs, SAR
When to File:
30+ minutes before departure (recommended)
Before calling for the clearance
Realistic proposed time (Zulu)
Filing Methods:
Apps (ForeFlight, Garmin Pilot) — most common
Flight Service (1-800-WX-BRIEF / Leidos)
Online (1800wxbrief.com)
Some avionics
The ICAO Form (slant codes RETIRED 2019):
Item 7: Aircraft ID
Item 8: Flight rules (I) and type (G)
Item 9: Type + wake category
Item 10: Equipment (10a comm/nav, 10b surveillance/ADS-B)
Item 13: Departure + time
Item 15: Route (speed, level, route)
Item 16: Destination, EET, alternate
Item 18: Other info (PBN code)
Item 19: Fuel, souls (SAR)
Key Equipment Codes (Item 10):
G = GNSS (GPS)
S = standard (VHF, VOR, ILS)
R = PBN approved (specify in Item 18)
Item 10b: C (Mode C), S (Mode S), B1/B2 (ADS-B Out)
Filing vs. Activating:
Filing: submits the plan (NOT authorized to fly IFR)
Activating: ATC issues + you accept the clearance
You're NOT IFR until cleared
Getting Your Clearance:
Clearance Delivery, Ground, RCO, or airborne
Copy with CRAFT
CRAFT:
C — Clearance limit (destination)
R — Route (as filed or amended)
A — Altitude (initial + "expect")
F — Frequency (departure)
T — Transponder (squawk)
Void Times (non-towered):
Clearance comes with a VOID TIME
Depart before it (or the clearance is void)
Report if you don't depart
"Hold for release" = wait to depart
Cancelling IFR:
Cancel when VMC/no longer needed
Non-towered arrival: cancel promptly (or risk SAR)
Towered: landing cancels automatically
Common Mistakes:
Incorrect equipment codes (#1)
Unrealistic routing
Invalid alternate
Not updating departure time
Skipping NOTAMs
Blowing a void time
Forgetting to cancel (non-towered)
Key Principle:
An IFR flight plan is required before IFR flight, but filing doesn't make you IFR — you're not IFR until ATC issues and you accept a clearance (copied via CRAFT). File on the ICAO form (the old slant codes are retired), with accurate equipment and PBN codes that determine your routes and approaches. At non-towered fields, understand void times (depart before the clearance voids) and remember to cancel IFR on arrival to avoid triggering search and rescue.
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Author: Nathan Hodell
CFI, CFII, MEI, ATP, Creator and CEO
Nathan is an aviation enthusiast with thousands of hours of flying and dual instruction over the past 15+ years. Through his aviation career he has been able to earn his ATP, fly as an airline pilot, own/operate flight schools, and create and host wifiCFI.