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IGC FILE FORMAT REFERENCE AND DEVELOPERS' GUIDE - Ian Forster-Lewis

These are notes created for my personal use to try and make the FAI documentation more useful to me as a logger developer. For a comprehensive example IGC file see this LXN-produced real IGC file.

Web links in the FIA change every time they hire a new webdev, so a copy of the FAI IGC Specification 2023 is hosted here.

This web-linked html version is for the IGC spec 2008, but it hasn't changed much. I have kept the FAI chapter/section numbers but added to some of the sections.

Contents

• Preface: ANNOTATED SAMPLE
• 1. INTRODUCTION
  
  • 1.1 Background, and IGC file production
  • 1.2 Revision control
• 2. GENERAL
  
  • 2.1 File structure
  • 2.2 Record Types
  • 2.3 Record order
  • 2.4 Units
  • 2.5 File naming
• 3. SINGLE INSTANCE DATA RECORDS
  
  • 3.1 A record - FR ID number
  • 3.2 G record - Security
  • 3.3 H record - File header
  • 3.4 I record - Extension to the fix (B) record
  • 3.5 J record - Extension to the K record
  • 3.6 C record - Task
• 4. MULTIPLE INSTANCE DATA RECORDS
  
  • 4.1 B record - Fix
  • 4.2 E record - Events
  • 4.3 F record - Satellite constellation
  • 4.4 K record - Data needed less frequently than fixes
  • 4.5 L record - Log book / comments
  • 4.6 D record - Differential GPS
• 5. DEFINITIONS
  
• 6. VALID CHARACTERS
• 7. THREE-LETTER CODES (TLC)
• 8. GNSS GEODETIC DATUMS
• 9. EXAMPLE IGC-FORMAT FILE

Preface: ANNOTATED SAMPLE

Here's a 'walk-through' of a valid IGC file, this is not in the original FAI document. 'Space' characters have been inserted for legibility, if you want to cut-and-paste this file as a starting point for your development, you could use the version of the same file in section 9 without the inserted spaces. Free text is in italics meaning you can enter pretty much anything, otherwise the exact number of characters must match the example. Each 'record' in an IGC file fits on a single line and the first few characters determine the record type. I have linked those initial chars in the sample below to the corresponding section of the specification.

1. INTRODUCTION

1.1 Background, and IGC file production. The IGC Data File Standard was initially developed by a group consisting of representatives of IGC, glider FR manufacturers and a number of independent software developers mainly concerned with flight data analysis programs. After discussion and development during 1993 and 1994 it was initially defined in December 1994 and became part of official IGC/FAI documents after approval by IGC in March 1995. It has been refined and developed afterwards, through regular amendments. It provides a common world standard data format for the verification of badge, record, and competition flights to FAI/IGC criteria. The Standard may also be used by other FAI sports and activities.

1.1.1 Production of Flight Data File. It must be possible to produce a separate and complete IGC flight data file for each flight including all record types (para 2.2 following) relevant to the flight such as header records, flight declaration, etc. Two ways of achieving this are by continuous recording of fixes between the times that the FR was switched on and off, or, for FRs that have a "standby" state on switch-on, only recording fixes after pre-set movement and pressure-change thresholds are exceeded (ceasing recording when changes are below the thresholds, but see 1.1.1.2 on short periods without external power).(AL3)

1.1.1.1 Thresholds for starting and stopping recording, also Power-on Protocol for creating new IGC files. The following thresholds before fixes are recorded have been found suitable in the past: lat/long change, 10-15 km/hr; pressure altitude change, 1 metre per second for 5 seconds. Pre-takeoff and after-landing baselines of at least 20 fixes must be provided. For the pre-takeoff baseline, a small memory circuit can be used that continuously stores the appropriate number of previous fixes and, when movement is detected, puts them into the flight data record. After landing, this can be achieved by a time delay before stopping the recording of fixes. This condition may also apply to a period in wave or ridge lift with little or no vertical or horizontal movement. Therefore, a new IGC file must not be started while external power is still connected and the recorder is still switched on, even when no movement is being detected and no fixes are being recorded. Note that this "power-on protocol" is also needed for barograph calibrations so that a new file is not produced while the calibrator is making small adjustments to the pressure at each level of the calibration. A new IGC file is produced under the "Power-off Protocol" that is described under 1.1.1.2 below.(AL5), modified by (AL9)

1.1.1.2 Loss of external power for short periods - Power-off Protocol for creating new IGC files. To allow for events such as changing or switching batteries in flight, a period of 5 minutes with no external power shall be allowed to elapse before a new Flight Data File is created on powering up again. After this period has elapsed a new IGC file must be produced, so that if several flights are made on one day, each has a complete IGC data file of its own.(AL3)

1.1.1.3 Data transfer to a PC. If the data for several flights is held in the FR memory, it must be ensured that when the data is transferred, all record types in IGC files that are subsequent to the first file are those relevant to each subsequent individual flight. If any record types are changed between flights (such as declaration, pilot name, etc.) the changes must be included in the subsequent (but not previous) flight data files.(AL3)

1.1.1.4 Recorders operating on internal power. Some recorders are designed so that all of their functions are available on internal power. For these recorders, external power is used for charging and as a backup for long flights. When operating on internal power it must be ensured that under flight conditions of little horizontal or vertical movement (such as in ridge or wave flying), the IGC file continues be able to record data and is not ended while flight continues. The IGC file shall be ended after one of the following three conditions: (1) if no horizontal or vertical movement has been detected for 10 minutes (thresholds as in 1.1.1.1 above); (2) after the recorder is switched off by deliberate action, or; (3) if the recorder is still powered after the flight, when the user establishes a connection for purposes of downloading from the recorder.(AL10)

1.2 REVISION CONTROL. The IGC flight data file format is revised through the normal amendment process for this document. See amendment procedures and list of amendment on page (i).

2. GENERAL

2.1 FILE STRUCTURE. An IGC-format file consists of lines of characters, each line giving a set of data such as for a GNSS fix. Each line starts with an upper-case letter denoting one of the Record types listed in para 2.2., and ends with CRLF (Carriage Return Line Feed). Each line is limited to 76 characters in length, excluding the CRLF which is hidden and does not appear in text form. Some Record types take up only one line, some such as task and header take up several lines. For instance, the task/declaration (C) Record includes a line for each Waypoint, and the Header (H) Record includes separate lines for GNSS FR type, pilot name, glider identification, etc. The order of Record types within an IGC file is given in para 2.3. Some Record types occur only in only one place in the file (single instance Records), others such as fixes re-occur as time progresses (multiple instance Records). Only characters listed as valid in para 6 shall be used in the file. If others such as accented characters (acutes, hatcheks, umlauts, etc) in names of airfields and turn points, are used in a manufacturer's proprietary (original) file format, such characters shall be converted to a valid character as part of the conversion to the IGC format. This is so that analysis programs designed for the IGC format do not have to recognise non-standard characters.

2.2 RECORD TYPES. The Record types are prefixed by upper case letters as follows:

IGC DATA FILE FORMAT - RECORD TYPE IDENTIFICATION LETTERS
A - FR manufacturer and identification
B - Fix
C - Task/declaration
D - Differential GPS
E - Event
F - Constellation
G - Security
H - File header
I - List of extension data included at end of each fix B record
J - List of data included in each extension (K) Record
K - Extension data
L - Logbook/comments
M, N, etc. - Spare

2.3 RECORD ORDER. The FR I/D (A) Record is always the first in the file and the last is the Security (G) Record. After the single-line A record is the multi-line Header (H) Record, followed by the I and J Records that list extension data which applies to later Record types in the file. These are followed by other Record types indicating that certain data is recorded in the file, including the task/declaration (C) Record, and the initial Satellite Constellation (F). Time-specific Records follow, placed in the file in time order using either GNSS fix-time (if the GNSS is locked on) or the FR Real Time Clock (RTC); these are B (fix), E (event), F (constellation change) & K (extension data). The logbook/comments (L) Record data may be placed anywhere after the H, I and J records and can have several lines throughout the file depending on the nature of the comments included.

IGC DATA FILE FORMAT - ORDER OF RECORD TYPES IN AN IGC FILE
A - FR manufacturer and identification (always first)
H - File header
I - Fix extension list, of data added at end of each B
record
J - Extension list of data in each K record line
C - Task/declaration (if used)
L - Logbook/comments (if used)
D - Differential GPS (if used)
F - Initial Satellite Constellation
B - Fix plus any extension data listed in I Record
B - Fix plus any extension data listed in I Record
E - Pilot Event (PEV)
B - Fix plus any extension data listed in I Record
K - Extension data as defined in J Record
B - Fix plus any extension data listed in I Record
B - Fix plus any extension data listed in I Record
F - Constellation change
B - Fix plus any extension data listed in I Record
K - Extension data as defined in J Record
B - Fix plus any extension data listed in I Record
E - Pilot Event (PEV)
B - Fix plus any extension data listed in I Record
B - Fix plus any extension data listed in I Record
B - Fix plus any extension data listed in I Record
K - Extension data as defined in J Record
L - Logbook/comments (if used)
G - Security record (always last)

2.4 UNITS.

Data in the IGC file shall use the following unit system:

Distance - Kilometres and decimal kilometres. For FAI/IGC conversions from feet and miles, see para 2.6.8
(AL6)
Speed - Kilometres per hour. For FAI/IGC conversions from nautical miles per hour (knots) and statute miles
per hour (mph), see para 2.6.8(AL6)
Date (of the first line in the B record) - UTC DDMMYY (day, month, year). See para 2.5.4(AL6)
Direction - degrees True, clockwise from 000 (North)
Latitude and Longitude - Degrees, minutes and decimal minutes with N,S,E,W designators
Altitude - Metres, separate records for GNSS and pressure altitudes.
Pressure - Hectopascals (the same as millibars) to two decimal places, for instance altimeter subscale setting, but
see * below under PPPPpp

• Time - HHMMSSsss (UTC)
  HH- Hours fixed to 2 digits with leading 0 where necessary
  MM - Minutes fixed to 2 digits with leading 0 where necessary
  SS - Seconds fixed to 2 digits with leading 0 whre necessary
  sss - number of decimal seconds are those available in the Record concerned, less fields already used for HHMMSS.(AL8)
• Distance - DDDDddd, kilometres up to 9999 with leading zeros as required and then three decimal places (that is, the last figure is metres)
• Speed - SSSsss.
  SSS - fixed to 3 digits with leading 0
  sss - number of speed decimals (the number of fields recorded are those available for speed in the Record concerned, less fields already used for SSS)
• Date - DDMMYY
  DD- number of the day in the month, fixed to 2 digits with leading 0 where necessary
  MM - number of the month in year, fixed to 2 digits with leading 0 where necessary
  YY- number of the year modulo 100, fixed to 2 digits with leading 0 where necessary
• Direction DDDddd.
  DDD - fixed to 3 digits with leading 0 where necessary
  ddd - number of direction decimals (the number of fields recorded are those available for direction in the Record concerned, less fields already used for DDD)
Lat/Long - D D M Mm m m N D D D M M m m m E
DD- Latitude degrees with leading 0 where necessary
DDD - Longitude degrees with leading 0 or 00 where necessary
MMmmmNSEW - Lat/Long minutes with leading 0 where necessary, 3 decimal places of minutes (mandatory, not optional), followed by North, South, East or West letter as appropriate

• Altitude - AAAAAaaa
  AAAAA - fixed to 5 digits with leading 0
  aaa - number of altitude decimals (the number of fields recorded are those available for altitude in the Record concerned, less fields already used for AAAAA)
• PPPPpp - Pressure in hPa (mb) with two decimal places, PPPPpp fixed to 6 digits with leading zero for settings in the 900 range). For altimeter subscale settings, 1013.25 mb (ISA Sea Level) has an PPPPpp code of 101325, and 980 mb has a code of 098000.
  * An altimeter setting (and any change to it) may be recorded, for instance where the FR feeds a cockpit display (three-letter code ATS, see para 7). However, it must not be used to change the pressure altitude recorded with each fix in the IGC file, which must remain with respect to the ISA sea level datum (1013.25 mb) at all times.
• GNSS Altitude. Where GNSS altitude is not available from GNSS position-lines such as in the case of a 2D fix (altitude drop-out), it shall be recorded in the IGC format file as zero so that the lack of valid GNSS altitude can be clearly seen during post-flight analysis.(AL3)

2.5 FILE NAMING

2.5.1 Short file name style: YMDCXXXF.IGC
Y = Year; value 0 to 9, cycling every 10 years
M = Month; value 1 to 9 then A for 10, B=11, C=12.
D = Day; value 1 to 9 then A=10, B=11, C=12, D=13, E=14, F=15, G=16, H=17, I=18, J=19, K=20, L=21, M=22, N=23, O=24, P=25, Q=26, R=27, S=28, T=29, U=30, V=31.
C = manufacturer's IGC code letter (see table below)
XXX = unique FR Serial Number (S/N); 3 alphanumeric characters
F = Flight number of the day; 1 to 9 then, if needed, A=10 through to Z=35

2.5.2 Long file name style. This uses a full set of characters in each field, a hyphen separating each field, the field order being the same as in the short file name. For instance, if the short name for a file from manufacturer X is 36HXABC2.IGC, the equivalent long file name is 2003-06-17-XXX-ABC-02.IGC. Long file names may be generated by software that is compatible with long file names, although the DOS versions of the DATA, CONV and VALI programs must continue to generate and use short file names. (AL3)

2.5.3 FR Serial Number (S/N). The three-character FR S/N must be used in the A record and be imprinted on the case of the recorder unless there is an easily-accessible electronic display which includes the S/N.

2.5.3.1 Existing FRs using serial numbers with coded systems where the XXX translates to a different five-number numerical code which is used in the A record, have "Grandfather Rights" and do not need to be changed. New FRs must use the three-alphanumeric system described above.

2.5.4. Date of flight - the date used in the file name and in the H record (DTE code) is the UTC date of the first valid fix in the flight log transferred after flight. That is, the date applicable to the time in the first line in the B (fix) record, not the date at the time of switching on, or of take-off. This is particularly important for recorders operated in time zones where they are switched on close to midnight UTC.(AL6)

2.5.5. Security of file name. The file name is not protected by the electronic security system, which only applies to data within the file itself (see chapter 2, para 2.8). File names may be changed for specific purposes such as competitions, where it may be found more convenient to change from the IGC name system in which the file is originally transferred from the FR (para 2.5), to a system using glider competition number or pilot name. No loss of data or security occurs, since all of the data in the IGC file name is repeated in the file itself in the A and H records. (AL2) Example: 16AFXYZ2.IGC = 10 June 2001, Filser FR number XYZ, Flight 2 of the day.

2.5.6 Manufacturer codes. Single- and three-character codes are tabulated below. Manufacturers applying and paying the fee for IGC-approval who are not listed should apply to the Chairman of GFAC for allocation of codes. Manufacturers using the IGC file format but not applying for IGC-approval should use the X and XXX codes, see note 2 at the end.

2.5.6.1 Name of Intermediate Format file. If a manufacturer chooses a system where data is download from the recorder in an intermediate format such as binary, the file name for the intermediate format shall be as for the IGC file but with the Manufacturer's three letter code used instead of the "IGC" after the dot. It shall then be possible to convert the intermediate format to the IGC ASCII format through the Conversion utility that is part of the manufacturer's IGC-XXX.DLL file or, for earlier systems, through the CONV-XXX.EXE program.(AL8) nbsp;

IGC DATA FILE FORMAT - CODES FOR MANUFACTURERS OF IGC-APPROVED FLIGHT RECORDERS(AL5)
Single Char. Code	Three Char. Code	Manufacturer's Name	Single Char. Code	Three Char. Code	Manufacturer's Name
A	GCS	Garrecht	S	SDI	Streamline Data Instruments
B			T	TRI	Triadis Engineering GmbH
C	CAM	Cambridge Aero Instruments	U
D	DSX	Data Swan/DSX	V
E	EWA	EW Avionics	W	WES	Westerboer
F	FIL	Filser	X	XXX	Other manufacturers, see note below
G	FLA	Flarm (Flight Alarm)	Y
H	SCH	Scheffel	Z	ZAN	Zander
I	ACT	Aircotec	0
J			1
K			2
L	LXN	LX Navigation	3
M	IMI	IMI Gliding Equipment	4
N	NTE	New Technologies s.r.l.	5
O			6
P	PES	Peschges	7
Q			8
R	PRT	Print Technik	9

Notes:

1. Where possible, the initial letter of a manufacturer's name will be allocated for the single-character code. Where this letter is already allocated, generally, the next letter in the manufacturer's name will be used, etc.
2. X and XXX are general designations for IGC format files from manufacturers who do not produce an IGC-approved recorder. Such recorders will not have been tested and evaluated by GFAC and may not fulfil certain aspects of the IGC Specification such as security protections, recording of pressure altitude, ENL or other variables. There is no guarantee that the file will conform exactly to the IGC format, although specimen files will be checked for compliance with the IGC format if emailed to the GFAC chairman for evaluation. Even after this procedure, no compliance guarantee can be made because the type of recorder will not have completed a full GFAC evaluation. It should be noted that although the file name will not contain the information, the details of the manufacturer and the recorder model concerned will be identifiable (if the file conforms to the IGC standard) because they will be included in the H (Header) record, see below under H Record in the line: HFFTYFRTYPE:MANUFACTURERSNAME,FRMODELNUMBER CRLF
3. The three-letter codes PFC, PLT and OOI will not be used since they could cause confusion in the L record.

2.5.7 Mandatory Records. Certain records are mandatory for any IGC file. They are summarised as follows:

3. SINGLE INSTANCE DATA RECORDS

These records only occur once in each IGC-format data file, but each record type may contain several lines prefixed with its type letter.

3.1 A RECORD - FR ID NUMBER. The A Record must be the first record in an FR Data File, and includes the three-character GNSS FR Serial Number (S/N) unique to the manufacturer of the FR that recorded the flight(AL3). Format of the A Record:

A M M M N N N T E X T S T R I N G CR LF

3.2 G RECORD - SECURITY. The G Record verifies that the data has not been altered during or following the flight. The FR manufacturer must provide a VALI program (see para 2.9.3.4 in the main body of this document) to check the integrity of the file with the security code. The security code must be generated by the FR, not by the computer extracting the flight data. Flight analysis software from sources other than the manufacturer should ignore the detailed data in this record, but can use the G record as a marker for the position of other data and records in the IGC file. All records must be included in the security mechanism, except the H records which have the O or P source, and any L records which do not have the Manufacturer ID (because some L records may be put in by the pilot).

Format of G Record:
G S S S S S S S S S S S S S S S S S S S S S S S S S S S S S CR LF
G S S S S S S S S S S S S S S S S S S S S S S S S S S S S S CR LF
etc

The G Record must not use any non-printing character, because whitespace is often removed when ASCII files are transmitted across data communication networks.

3.3 H RECORD - FILEHEADER

The H-Record is used to store data such as the date on which fixes are first recorded in the B-Record of the IGC file (that is, the day of a flight unless made in a time zone many hours from UTC), the name of the pilot, glider, the type of FR used, the type of GNSS receiver and pressure altitude sensor, amongst other things. There are several different subtypes of the H-Record which are recorded on separate lines prefixed H. All Three Letter Codes (CCC) that bear the H flag in section 7 are possible subtypes of the H-Record.

The line entries in the H-record may be created by the FR (source code F), or, for items such as pilot and glider names, by the Pilot or OO (P and O source records) after flight (see the line "Data Source" in the table below). Only H-Record data with source code F is covered by the security code and VALI check system.(AL10)

Appendix 1, Para 3.3, second paragraph. The words at the end to read The general format of the H-Record is: record identifier, source of information (S), record subtype identifer (CCC), long name of the record subtype, colon, actual information (TEXTSTRING). The long name is intended as an aid for people reading the file. For official purposes only the source of information, the record subtype (CCC) and the actual information are definitive.

GNSS Geodetic Datum. The long name, a colon and the name of the Geodetic Datum set (WGS84 = IGC number 100, see para 8) come after the IGC-assigned number for the GPS-Datum, which is located directly behind the record subtype identifer DTM.

3.3.1 Required records. The following H records are required, in the order given below:

HFDTEDDMMYY
HFFXAAAA
HFPLTPILOTINCHARGE:TEXTSTRING
HFCM2CREW2:TEXTSTRING
HFGTYGLIDERTYPE:TEXTSTRING
HFGIDGLIDERID:TEXTSTRING
HFDTMNNNGPSDATUM:TEXTSTRING
HFRFWFIRMWAREVERSION:TEXTSTRING
HFRHWHARDWAREVERSION:TEXTSTRING
HFFTYFRTYPE:MANUFACTURERSNAME,FRMODELNUMBER
HFGPS:MANUFACTURERSNAME,MODEL,CHANNELS,MAXALT(AL3)
HFPRSPRESSALTSENSOR:MANUFACTURERSNAME,MODEL,MAXALT(AL3)

plus you can have the following optional records:

HFCIDCOMPETITIONID: TEXTSTRING glider fin number
HFCCLCOMPETITIONCLASS: TEXTSTRING e.g. Standard, 15m, 18m, Open

HFDTEDDMMYY

HFDTE280709

HFFXAAAA

HFFXA035

HFPLTPILOTINCHARGE:TEXTSTRING

HFPLTPILOTINCHARGE: Bloggs, Bill D

HFCM2CREW2:TEXTSTRING

HFCM2CREW2: Smith-Barry John A

HFGTYGLIDERTYPE:TEXTSTRING

HFGTYGLIDERTYPE: Schleicher ASH-25

HFGIDGLIDERID:TEXTSTRING

HFGIDGLIDERID: N116 EL

HFDTMNNNGPSDATUM:TEXTSTRING

HFDTM100GPSDATUM: WGS-1984

HFRFWFIRMWAREVERSION:TEXTSTRING

HFRFWFIRMWAREVERSION:6.4

HFRHWHARDWAREVERSION:TEXTSTRING

HFRHWHARDWAREVERSION:3.0

HFFTYFRTYPE:MANUFACTURERSNAME,FRMODELNUMBER

HFFTYFRTYPE: Cambridge, FunkyLogger 77

HFGPSMANUFACTURER,MODEL,CHANNELS,MAXALT

HFGPSMarconi,SuperX,12ch,10000m

HFPRSPRESSALTSENSOR:MANUFACTURER,MODEL,MAXALT

HFPRSPRESSALTSENSOR: Sensyn,A32,11000m

HFCIDCOMPETITIONID: TEXTSTRING

HFCIDCOMPETITIONID: B21

HFCCLCOMPETITIONCLASS: TEXTSTRING

HFCCLCOMPETITIONCLASS:15m Motor Glider

And here's the field descriptions from the original FAI document.

3.3.2 Additional H records. These are optional. Additional data may be appended after the mandatory records. Two additional records (Comp ID and class) are shown below.

H S C I D C O M P E T I T I O N I D : T E X T S T R I N G CR LF
H S C C L C O M P E T I T I O N C L A S S : T E X T S T R I N G CR LF

Note - Ian Forster-Lewis: I think this is a TYPO: HSCID would not be valid format. The correct record should be HFCID. Same for HFCCL.

3.3.3 Names and identifications.

Similar names. Where there may be people with names which are similar or the same (Smith/Schmidt), full initials or other names should be used. In addition, a TLC of DOB for Date-of-Birth is available, and if used, this must be in the line following the pilot's name in the format DDMMYY (the same format as used for date of flight in the H record).

Name of Crew Member 2 (code CM2), family name first then other names or initials without punctuation but separated by spaces (for instance, SMITH B S, or SMITH BERNALD)

Sufficient characters should be made available to allow for long names and identifications. Such as, for glider registration, allow for a registration such as XXXX-AAAA (where XXXX is the designator of the Nation or National Airsport Body), requiring at least 9 characters to be available in this field. Manufacturers should provide for more rather than less characters in these fields so that flight declarations are easily made in full(AL3).

Club or organisation from which flown or operated (code CLB), with nation (for instance LASHAM UK, ELMIRA US). Where there is not space to put the Nation in full, the two-letter codes from the ISO 3166 list of National designators should be used (these are also used for Nations in Internet addresses). Some ISO 3166 two-letter National Codes are as follows(AL3):

3.4 I RECORD - EXTENSIONS TO THE FIX B record. The I record defines any extensions to the fix B record in the form of a list of the appropriate Three-Letter Codes (CCC), data for which will appear at the end of subsequent B Records. Only one I-Record line is included in each file, located after the H record and before the first B Record. The Fix Accuracy (FXA) must be included, in the form of the Estimated Position Error figure (see Glossary under EPE). This shall be followed by SIU, ENL and RPM, if these are recorded in the FR concerned. Note that although the SIU number is optional in the B record, the F Record (satellite constellation used) is mandatory, see para 4.3. The format of the I Record is as follows:(AL11)

I N N S S F F C C C S S F F C C C CR LF

The first byte of the extension data always begins at byte position 36, because that's where the basic lat/long/alt stuff of the B record ends.

The byte count starts from the beginning of the B Record, taking the first B in the line as byte one. Example:

I 01 36 40 FXA CR LF

This shows that Fix Accuracy (FXA) is recorded between bytes 36 and 40 on each B-record line. And, for a device that also records Satellites In Use (SIU) and Engine Noise Level (ENL):

I 04 3638 FXA 3940 SIU 4143 ENL 4446 RPM CR LF

This shows that on each B-record line, Fix Accuracy (FXA) is recorded between bytes 36 and 38, Satellites In Use (SIU) between bytes 39 and 40, Engine Noise Level (ENL) between bytes 41 and 43 and RPM between bytes 44 and 46. To aid clarity, some spaces have been inserted in the example line above, these should not be used in the actual B record in the IGC file.(AL11)

3.5 J RECORD - EXTENSIONS TO THE K RECORD. The K record is used for data that needs to be updated as a flight progresses but is not required as often as fix B records. The J record is a single line that defines what data will be in subsequent K-record lines. It fulfils the same function for the K Record as the I Record (3.4 above) does for the fix B record, and operates in the same way. It is placed in the file immediately after the I record line, before the first B Record. The format of the J Record is as follows:

J N N S S F F C C C S S F F C C C CR LF

Example:

J 0 1 0 8 1 2 H D T CR LF

This shows that True Heading (HDT) is recorded between bytes 8 and 12 on each K-record line.

3.6 C RECORD - TASK. (Pre-flight Declaration)

The C Record is used to specify tasks and to make preflight declarations. It is placed in the IGC file before the first fix B record and after the H, I and J records.

3.6.1 Lines in the C Record. The first line contains the UTC-date and UTC-time of the declaration, the local date of the intended day of flight, the task ID, the number of turn points of the task and a textstring which can be used to describe the task (500k triangle, etc). Optionally, the recorder may be configured so that a pilot can enter the intended flight date in local time, not the UTC date which will be different in countries with large time offsets from UTC (The Three-Letter Code for Time Zone Offset is TZN, see the list in para 7). The other lines contain the WGS84 lat/long coordinates and a textstring for the place or point concerned. These include the take-off airfield, start point, turn points, finish point and landing airfield. After the first line, the other lines contain the WGS84 lat/long co-ordinates of the point followed by a text string for the place or point concerned. The text describing the type of point (see example below) is mandatory so that the nature of the points can be clearly seen by viewing the IGC file.(AL6) & 11)

3.6.2 IGC terminology. "Waypoint or way point " refers to a either a start-, turn- or finish-point. The term "Turn Point" refers to a point in a measured course between the start and finish point. The points that must be specified exactly in an official IGC flight declaration are the intended start-, turn- and finish-points (Sporting Code Section 3, para 4.2). The number of turn points will be nil for a straight goal flight, one for an out-and-return, two for a triangle, three for 3-TP distance, more for some competition tasks.(AL6)

3.6.3 Takeoff and Landing. The two lines in the C-record format for takeoff airfield and landing airfield (or out-landing location if this applies), are for general information rather than being part of the official IGC Flight Declaration. They can be entered approximately or, if the co-ordinates are difficult to obtain or are not entered, the recorder shall default to 00000000N000000000E for these two lines.(AL6)

3.6.4 Number of Turn points and C-Record lines. From the above it can be seen that the number of turn points will be four less than the number of lines after line 1 (that is, those lines that contain lat/long data). These four non-turn point data lines are for takeoff airfield, exact start, exact finish, and landing airfield/location. The number of turn points is included as a sub-field in line 1 of the C-record and is placed immediately before the optional text string at the end of the line (in the form TT in the illustration below).(AL6)

3.6.5 Area Tasks. The incorporation of this facility in a Flight Recorder is optional. In some competitions, an area to be reached is specified with respect to a Waypoint in terms of distances and true bearings (radials) from the point. If a recorder has a facility to enter this in the C record, the following system shall be followed in the IGC file: At the end of the relevant Waypoint line in the C record, minimum and maximum distances follow in kilometers from the WP, followed by bearing 1 and bearing 2 in degrees true from the WP and then the word AREA after the type of point. In the case of competitions using units other than kilometres (such as statute or international nautical miles), a conversion must be made so that the IGC file continues to be in kilometres (and decimal kilometres as necessary). The area is clockwise from bearing 1 to 2. In the case of circular areas round a point the two bearings used shall be 000 to 360 and the minimum distance will be zero. Where an area referenced to a Waypoint is to be specified, after the C record line that defines the Waypoint but before CRLF at the end of the line, add:

"DDDDdddDDDDdddBBBbbbBBBbbbAREA"

The two distances Dd are first minimum distance from the WP in km and decimal kilometres, then maximum distance. The two bearings Bb are in degrees and decimal degrees true from the WP, the task area extending clockwise from bearing 1 to 2.

For instance: "C....0012000 0032000 122000 182000TURN AREA" would be an area from 12 to 32 km from the WP between the bearings 122 and 182 from the Point.(AL6)

The format of C Record is as follows, using N latitude and E longitude for the example:

C DD MM YY HH MM SS F D F M F Y IIII TT TEXT STRING CR LF
C DD MM MMM N DDD MMMMM E TAKEOFF TEXT STRING CR LF
C DD MM MMM N DDD MMMMM E START TEXT STRING CR LF
C DD MM MMM N DDD MM MMM E TURN TEXT STRING CR LF
C DD MM MMM N DDD MM MMM E TURN TEXT STRING CR LF
C DD MM MMM N DDD MM MMM E FINISH TEXT STRING CR LF
C DD MM MMM N DDD MM MMM E LANDING TEXT STRING CR LF

Spaces have been added between data fields in this example to aid clarity.

The Text String is intended to be the name and short description of the Point For an area referenced to a Turn Point:

C DD MMMMMN DDD MMMMME 0012000 0032000 122000 182000TURN AREA CR LF(AL6)

4.MULTIPLE INSTANCE DATA RECORDS

These are record types that can re-occur at different times in the course of the IGC file, unlike single instance records that occur in each file only in one place.

4.1 B RECORD - FIX. Not counting the last CRLF, this includes 35 bytes for its basic data plus those for characters that are defined in the I Record. Such as Fix Accuracy (FXA, in the form of the Estimated Position Error figure, see Glossary under EPE), Satellites In Use (SIU), Engine Noise Level (ENL for all motor gliders), RPM (additional for motor gliders with quiet engines). The required basic data is: UTC, WGS84latitude,WGS84 longitude, fix validity, Fix Accuracy, pressure altitude and GNSS-altitude. All of the information within each B-record must have a data issue time within 0.1 seconds of the time given in the B-record. Where NMEA data is used within the FR, fix data should be taken either from the GGA or GNS sentences. GGA is specific to the US GPS system. GNS is intended for all GNSS systems (GPS, GLONASS, Galileo and future systems), and should be used if it is available from the GNSS board installed. In the B Record FXA should be recorded as a three-figure group in metres and SIU as a two group number. SIU is an optional record and may be used to back up the more detailed satellite data in the mandatory F record. Leading zeros should be included as necessary. Because earlier IGC-approved GNSS FRs may not have FXA and SIU in their B-records, the position of this data in each B record line must be indicated (for instance to analysis programs) by including them in the I record which designates the positions of additional fields in the B record. FXA should be placed after the two groups for altitude, followed by optional fields such as SIU and then ENL for Motor Gliders. In each B-record line, FXA would therefore normally occupy bytes 36, 37 and 38, SIU bytes 39 and 40, ENL either 39-41 or 41-43 depending whether SIU is used. The format of the basic data is:(AL11)

B H H M M S S D D M MM MM N D D D M MM MM E V P P P P P G G G G G CR LF

To append the Fix Accuracy (FXA, mandatory), Satellites in Use (SIU), Engine Noise Level (ENL) and RPM (RPM) or any other variable to each fix, these have to be defined earlier in the I Record (so that, for instance, they will be recognised by analysis programs). For instance:

I 04 3638 FXA 3940 SIU 4143 ENL 4446 RPM CR LF

This shows that on each B record line, Fix Accuracy is recorded between bytes 36 and 38, Satellites In Use between bytes 39 and 40, Engine Noise Level between bytes 41 and 43, and engine RPM between bytes 44 and 46.

The resulting B Record becomes (with spaces for clarity in this example):

BHH MM SS DD MMMMM N DDD MMMMM E V PPPPP GGGGG AAA SS NNN RRR CR LF"

Note (Ian Forster-Lewis): This section of the document looks to be in error - this B record should contain RPM

4.2 E RECORD - EVENTS.

The E-record is used to record specific events on the IGC file that occur at irregular intervals. Such events include a pilot-initiated event (PEV code) or, for recorders fitted with proximity sensing devices, a proximity event using one of the appropriate Three-Letter Codes followed by the appropriate data as defined under the appropriate TLC in section 7. The E Record is placed before the individual fix B record for the same time that shows where and when the event occurred. Events must have a Three Letter Code (TLC) from section 7. More than one event record may be used at the same time, but Events initiated within the FR (as opposed to by the pilot) are only expected to be occasional in the time-history of the flight file and should not be used for making additional records with every fix. This may confuse the analysis programs designed for use with this file format, which often search for and highlight event records. If a FR manufacturer wishes to insert additional information with each fix, this should be through an extension to the B record, first listing the information Code (CCC) in the I record. (amended (AL9)

If a manufacturer wants to add a new type of event, a new Three Letter Code (para 7) should be requested from GFAC. The manufacturer must provide an exact definition of the event and a proposed coding. GFAC may decide that the proposal should not be treated as an event but that the information should be incorporated into the B- or K record in the normal way for these records by listing in the I and J records.

The form of the E-Record is record identifer, time, TLC, textstring. Some examples follow:

E 1 0 4 5 3 3 P E V CR LF
B 1 0 4 5 3 3 4 9 4 5 3 3 3 N 0 1 1 3 2 4 4 4 E A 0 1 3 5 7 0 1 5 0 1 CR LF

This indicates a pilot initiated event (PEV) at 10:45:33 UTC, and the associated B record shows the location 49:45.333 N 11:32.444 E, at the pressure altitude 1357 metres and GNSS altitude 1501 metres.

Some events require more than just the TLC for interpretation:

E 1 0 4 5 4 4 A T S 1 0 2 3 1 2 CR LF

The altimeter setting in a display device connected to the FR was changed to 1023.12 hPa at the time 10:45:44

E 1 0 4 5 5 5 E O N CR LF
B 1 0 4 5 5 5 4 9 4 5 3 3 3 N 0 1 1 3 2 4 4 4 E A 0 1 3 3 7 0 1 5 6 7 CR LF

The engine was turned on (EON) at 10:45:55 UTC, and the B record shows the location 49:45.333 N 11:32.444 E, at the pressure altitude 1337 metres and GNSS altitude 1567 metres.

E 1 0 4 7 3 3 C G D 1 0 3 CR LF

The geodetic datum was changed to Bessel (IGC number 103, see para 8) at 10:47:33 UTC. This would invalidate the recording for IGC purposes, for which WGS84 must be used.

4.3 F RECORD - SATELLITE CONSTELLATION.

This is a mandatory record. However, there is no requirement to update the F-record at intervals of less than 5 minutes, so that transient changes of satellites received due to changing angles of bank, flying in valleys, etc do not lead to frequent F-record lines. For the US GPS system, the satellite ID for each satellite is the PRN of the satellite in question, for other satellite systems the ID will be assigned by GFAC as the need arises. Where NMEA data is used within the FR, the ID should be taken from the GSA sentence that lists the IDs of those satellites used in the fixes which are recorded in the B record. The F Record is not recorded continuously but at the start of fixing and then only when a change in satellites used is detected.(AL4)

Format of F Record:
F HH MM SS AA BB CC DD EE FF GG CR LF

4.4 K RECORD - DATA NEEDED LESS FREQUENTLY THAN FIXES.

The K record is for data that may be needed less frequently than fix B records. The K record should have a default interval of 20 seconds. As an example, if the B record records every 5 seconds, the K-record could be set to record every 20 seconds, for instance containing true heading (HDT). The contents of the K record are listed in the J record. The following J Record specifies the information in the K Record in the next line:

J 0 8 1 2 H D T CR LF
K H H M M S S 0 0 0 9 0 CR LF

This K Record states that the true heading (TLC = HDT) is 090 (East).

4.5 L RECORD - LOG BOOK/COMMENTS. L-Records can be placed anywhere in the file after H, I and J records but before the G record. The L-Record allows multiple free format text lines to be added to the flight data records at any time in the time-sequence, although this record is not itself time-stamped. It can be initiated by a program in the FR, by pilots or official observers, and the term "comment record" may be more descriptive rather than "logbook". The FR Manufacturer three-letter ID (para 2.5) should be used in the case of data initiated by the FR, and in this case the manufacturer should state how to interpret this type of L-Record for the benefit of writers of software for the IGC format. In other cases this field (MMM below) will also be three spaces, initiated by the pilot (code PLT) or OO (OOI) as required. In the case of Free Flights where waypoints are claimed post-flight by the pilot, the PFC (Post-Flight Claim) code shall be used followed by the Waypoints in the same format as the C Record (Pre-flight declaration). It is expected that this data will be inserted by a software program (for instance, after transfer of the flight data to a PC immediately after flight, by a program outside the FR) rather than added manually, so that it is in the correct format and can be recognised by analysis programs that are designed to read Post-Flight Claim data and present the flight on screen together with the PFC waypoints. Note that L records when originated by a pilot or OO must not affect the VALI check for the rest of the file data. The format of the L Record is as follows:(AL5)

L MMM T E X T S T R I N G CR LF
L PLT T E X T S T R I N G CR LF
L PFC TEXT AS C RECORD CR LF

The L records which have the FR Manufacturer's ID MMM must be included in the digital signature (security system) for the file. Other L records (eg those put in by the pilot (PLT) or an OO (OOI)) will not be covered by the digital signature for the file, see para 3.2. Examples of pilot inputs:

LPLT This flight was my second 1000km attempt
LPLT from Eagle Field

4.6 D RECORD - DIFFERENTIAL GPS.

This indicates that differential GPS is being used and can be a multiple-instance record if, during the flight, more than one differential beacon is used. It is placed in the IGC file before the first fix B record after the H, I, J and C records. The format of the D Record is as follows. (AL8)

D Q S S S S CR LF

These parameters correspond to the NMEA GGA GPS quality indication. The absence of a D Record indicates that differential GPS was not used. Any use of DGPS is subject to GFAC approval, and it must be shown that the use of GPS preserves the integrity of basic lat/long and other flight data.

5. DEFINITIONS

6. VALID CHARACTERS

These consist of all printable ASCII characters from Hex 20 to Hex 7E, except those tabulated below as reserved. A text string is a sequence of valid characters. The following table shows the character first and then the hexadecimal code, and the second table presents the same information in hex order:

7. THREE-LETTER CODES (TLC)

These are shown as CCC in the formats earlier in this appendix. Their meanings are listed below together with the Records in the IGC file in which they can be used. If a manufacturer wants to add a new type of event, a new TLC should be requested from GFAC. The manufacturer should provide an exact definition of the event and a proposed coding.

8. GNSS GEODETIC DATUMS

The Sporting Code for gliding states that the WGS 84 Geodetic Datum (serial 100 below) shall be used for all lat/long co-ordinates that are recorded and transferred from the FR after flight. Other Geodetic Datums have been numbered by IGC as follows.

Note from Ian Forster-Lewis: I skipped this section - just use WGS84 IGC code 100.

9. EXAMPLE IGC-FORMAT FILE

For a complex real-world example see this LXN-produced IGC file from a real flight in 2022

9.1 The IGC file format starts with the A Record and is followed by the H (header) and other records. The record letter is always at the start of the appropriate line in the file when it is viewed in text format. For more details of formats for individual records, see the relevant paragraphs earlier in this Appendix.

9.2 In this example, spaces have been used between subject fields to make the layout and sequence clearer to a reader. In a real IGC-format file there should be no spaces in any record except within a text string as a word separator.

9.3 CRLF = line terminator, not flight data.

9.4 In a real file there would be many more B records at the preset fix intervals for cruise and fast fix rates.

9.5 In the example below, some notes appear in brackets. These are not part of the file format itself. Also, for clarity, some spaces are used in B record lines between different variables that are recorded, but no spaces should be used in the IGC file itself.

AXXXABC FLIGHT:1
HFFXA035
HFDTE160701
HFPLTPILOTINCHARGE: Bloggs Bill D
HFCM2CREW2: Smith-Barry John A
HFGTYGLIDERTYPE: Schleicher ASH-25
HFGIDGLIDERID: ABCD-1234
HFDTM100GPSDATUM: WGS-1984
HFRFWFIRMWAREVERSION:6.4
HFRHWHARDWAREVERSION:3.0
HFFTYFRTYPE: Manufacturer, Model
HFGPSMarconiCanada: Superstar,12ch, max10000m
HFPRSPRESSALTSENSOR: Sensyn, XYZ1111, max11000m CR LF
HFCIDCOMPETITIONID: XYZ-78910
HFCCLCOMPETITIONCLASS:15m Motor Glider
I033638FXA3940SIU4143ENL (note: I corrected a TYPO from the original document that had RPM on this record)
J010812HDTCRLF
C150701213841160701000102 500K Tri
C5111359N00101899W Lasham Clubhouse
C5110179N00102644W Lasham Start S, Start
C5209092N00255227W Sarnesfield, TP1
C5230147N00017612W Norman Cross, TP2
C5110179N00102644W Lasham Start S, Finish
C5111359N00101899W Lasham Clubhouse
F160240040609123624221821
B1602405407121N00249342WA002800042120509950
D20331
E160245PEV
B1602455107126N00149300WA002880042919509020
B1602505107134N00149283WA002900043221009015
B1602555107140N00149221WA002900043020009012
F1603000609123624221821
B1603005107150N00149202WA002910043225608009
E160305PEVCRLF
B1603055107180N00149185WA002910043521008015
B1603105107212N00149174WA002930043519608024
K16024800090 (AL7)
B1602485107220N00149150WA 00494 00436 190 08 018
B1602525107330N00149127WA 00496 00439 195 08 015
LXXXRURITANIAN STANDARD NATIONALS DAY 1
LXXXFLIGHT TIME: 4:14:25, TASK SPEED:58.48KTS
GREJNGJERJKNJKRE31895478537H43982FJN9248F942389T433T
GJNJK2489IERGNV3089IVJE9GO398535J3894N358954983O0934
GSKTO5427FGTNUT5621WKTC6714FT8957FGMKJ134527FGTR6751
GK2489IERGNV3089IVJE39GO398535J3894N358954983FTGY546
G12560DJUWT28719GTAOL5628FGWNIST78154INWTOLP7815FITN