Birth of a NOTAM

NOTAM (Notice To Airmen) starts life as messages on the Aeronautical Fixed System (AFS). They are received centrally from originators within your country and from foreign NOTAM offices. Staff check and edit the NOTAM if necessary and they are then placed in the transmit queue for transmission to all NOTAM recipients. These include ATC offices, some airlines, briefing services etc.

There is no central world-wide NOTAM database, databases are built up individually by users from the incoming message stream.

ICAO NOTAM format
The format of NOTAM is defined in Annex 15 to the International Convention on Civil Aviation. An explanation of the format can be found here. Here is a typical NOTAM and its decode.

A1484/02 NOTAMN
Q) EGTT/QMRXX/IV/NBO/A/000/999/5129N00028W005
A) EGLL
B) 0208231540
C) 0210310500 EST
E) RWY 09R/27L DUE WIP NO CENTRELINE, TDZ OR SALS LIGHTING AVBL

Notam Decoder
A1484/02 - one letter to indicate the Series, a 4-digit NOTAM number followed by a stroke and two digits to indicate the year.

NOTAMN - Suffix N Indicates this is a new NOTAM. Other options are R for NOTAM replacing another or C for one cancelling another.

Q) EGTT/QMRXX/IV/NBO/A/000/999/5129N00028W005

This is the "Q" or qualifier line, it always starts Q) and contains the following fields, each separated by a stroke.

FIR (here EGTT, London FIR)

NOTAM Code, a 5 letter code starting with Q, defined in Annexe 15. Here QMR indicates that it concerns a Runway. XX indicates that remaining detail is in Plain Language. In this particular case the text shows that certain runway lighting is unavailable. Strictly speaking under ICAO rules this should have appeared as separate NOTAM for each type of lighting. QLCAS is the code for centreline lighting u/s QLZAS is the code for Touch Down Zone lighting u/s and QLAAS is the code for Approach Lighting u/s (note in all cases AS indicates unserviceable). The use of QMRXX here is a sensible compromise that reduces the number of NOTAM from three to one. A full list of codes is included in ICAO document 8126 (Aeronautical Information Services Manual).

IV - Indicates that this is significant for IFR and VFR traffic

NBO - indicates for immediate attention of aircraft operators, for inclusion in PIB's and Operationally significant for IFR flights

A - Indicates scope, here Aerodrome, others are E (en-route) or W (nav warning)

000/999 - lower and upper limits expressed as a flight level. In this case it has been left as the default as it is not applicable.

5129N00028W005 - Indicates the geographical centre and radius of influence, always this number of digits. In this case the radius is 5 n.m.

A) EGLL - ICAO indicator of the aerodrome or FIR (London Heathrow) can include more than one FIR

B) 0208231540 - Date/time group (UTC) when this NOTAM becomes effective

C) 0210310500 EST - Date/time group (UTC) when the NOTAM ceases to be effective. Note "EST" means "estimated" (NOT Eastern Standard Time!). All NOTAM with EST remain in force until cancelled or replaced.

E) RWY 09R/27L DUE WIP NO CENTRELINE, TDZ OR SALS LIGHTING AVBL - text of the notam using ICAO abbreviations.

Decode of this is "Runway 09/27 due to work in progress no centreline, touchdown zone or simple approach lighting system available"

Here's the whole thing again
A1484/02 NOTAMN
Q) EGTT/QMRXX/IV/NBO/A/000/999/5129N00028W005
A) EGLL
B) 0208231540
C) 0210310500 EST
E) RWY 09R/27L DUE WIP NO CENTRELINE, TDZ OR SALS LIGHTING AVBL

and here's the same thing as it appears in the PIB produced by ANAIS
AGA : FROM 02/08/23 15:40 TO 02/10/31 05:00 EST A1484/02
E)RWY 09R/27L DUE WIP NO CENTRELINE, TDZ OR SALS LIGHTING AVBL

You can see that the Q line is omitted entirely, A) has been stripped out because it appears as the header to the section and B) and C) have been reformatted and placed in the first line. AGA has been derived from the Q Code "QMR" (see Annex 15)

INTERNATIONAL NOTAM (Q) CODES
This appendix is to be used to interpret the contents of coded international NOTAM's.

• A NOTAM code group contains five letters. The first letter is always the letter "Q'' to indicate a code abbreviation for use in the composition of NOTAM's.
• The second and third letters identify the subject being reported. (See Second and Third Letter Decode Tables).
• The fourth and fifth letters identify the status of operation of the subject being reported. (See Fourth and Fifth Letter Decode Tables).

Area Forecasts For Operations At or Below 10,000 Feet

The Area Forecast system is designed primarily to meet the needs of pilots of general aviation. There is an emphasis on plain language and brevity in a simple, easy to read format. The system provides for the routine issue of forecasts for designated areas (see map below) and the prompt issue of amendments when prescribed criteria are satisfied.

More detail of the area forecast boundaries with place locations is contained in Airservices Australia's Planning Chart Australia (PCA).

There may be variations in commencement of validity between different regions, and between those times when daylight saving is or is not operating. However the following principles apply:

• the standard validity period is twelve hours but this may vary from state to state.
• an area forecast covering daylight hours will be available as soon as practicable in the morning.
• area forecasts are not prepared for those times when air traffic volume is so low as not to justify routine issues. In these cases a route forecast will service any individual flights.
• area forecasts will generally be available a minimum of one hour before commencement of validity.

Message Structure

Message Identifier

The forecast is identified as AREA FORECAST unless the forecast is an amendment in which case it will be denoted AMEND AREA FORECAST. In the case of amended area forecasts, all individual sections that are amended will be annotated with AMD preceding the section heading.

Validity Period

The validity period is written DDHHMM TO DDHHMM, where DD is the day of the month and HHMM is the time in hours and minutes UTC.

Area Number

The relevant forecast area is specified by an area forecast district number. These are given in more detail on the current Airservices Australia's Planning Chart Australia. Note that Areas 24, 87 and 88 are only designated for the purpose of Area QNH. Any flights in these areas can be provided with a route forecast.

Overview

The overview will highlight any conditions which may inhibit safe operations for pilots flying under visual flight rules, and will make reference, where necessary, to any spatial and temporal variations. It will assist the pilot in making the following types of decisions:

• Are the meteorological conditions Visual Meteorological Conditions (VMC), marginal, Instrument Flight Rules (IFR) or too poor for flying?
• Is it better to plan for a coastal or inland track?
• If bad weather is encountered, what is the contingency plan? Return? Change altitude? Change heading? Land immediately?

Subdivisions

Area forecasts may be divided into spatial, temporal or weather-related subdivisions. Spation subdivisions are given using PCA (Planning Chart Australia) or lat/lon coordinates

Winds and Temperatures

Upper level winds are given for 2000 (or 3000 in elevated regions), 5000, 7000, 10 000, 14 000 and 18 500 feet. The expected mean wind direction is given in three figures to the nearest ten degrees True, followed by a solidus (/), followed by the mean wind speed in two figures to the nearest five knots, 290/40. CALM and VRB05 (wind direction variable at 5 knots) are used when appropriate.

A REMARKS section may be included below the WIND section to provide further information on winds.

Upper level temperatures are given for 10 000, 14 000 and 18 500 feet. These are given in whole degrees Celsius, following the forecast of the upper wind for the level concerned. e.g. 290/40 PS08, 300/50 ZERO, 360/10 MS10. The abbreviation PS is used for positive temperatures, and MS (minus) is used for negative temperatures.

Cloud

The inclusion of cloud is restricted to:

• any CB or TCU.
• any cloud with a base at or below 5000 feet above the highest terrain in the area covered by the forecast.
• any cloud layer of more than 4/8 (broken or overcast) amount with base at or below 20 000 feet above MSL.
• any cloud associated with any forecast precipitation, moderate or severe icing and moderate or severe turbulence.

Cloud amount is given using the following abbreviations:

FEW - Few (1 to 2 oktas)

SCT - Scattered (3 to 4 oktas)

BKN - Broken (5 to 7 oktas)

OVC - Overcast (8 oktas)

...except for cumulonimbus and towering cumulus, for which amount is described as:

ISOL - Isolated

OCNL - Occasional (well separated)

FRQ - Frequent (little or no separation)

EMBD - Embedded (in layers of other cloud)

Cloud type is given using the following abbreviations:

CU - Cumulus

SC - Stratocumulus

CB - Cumulonimbus

TCU - Towering cumulus

ST - Stratus

AS - Altostratus

AC - Altocumulus

NS - Nimbostratus

If subdivisions are used and one or more subdivisions have no cloud associated with it, the format used is NIL CLOUD.

When CU and SC, or AC and AS, occur together at similar heights, they are combined, i.e. CU/SC or AC/AS.

Cloud base and tops are given in feet above MSL (mean sea level).

Weather

Weather information relating to the layer below 21 000 feet above MSL is given following the word 'WEATHER'. If subdivisions are used and one or more subdivisions have no weather associated with it the format is, WEATHER A: NIL.

Visibility

Horizontal visibility is given in metres to the nearest 100 metres up to and including 5000 metres, and in whole kilometres above that value. Forecast visibilities of 50 metres or less are given as 'ZERO'. The forecast value is followed by the units used e.g. '8KM' or '1000M'. Significant variations of visibility are included. If the visibility is forecast to be above 10 kilometres throughout the area, the words 'UNRESTRICTED' or 'GOOD' are used. Vertical variations of horizontal visibility, which might prevent flight under VMC conditions, are significant. For example, information is supplied on the depth of layers affected by drizzle, haze and dust storms, and the levels of haze layers under inversions. Visibility variations with these phenomena is given.

Freezing Level

Freezing level is the height, in feet, above MSL of zero degrees Celsius. Reference is made to any variations in height greater than 1000 feet, and to the occurrence of more than one freezing level.

Icing

The icing section gives information on the expected occurrence of moderate or severe icing in cloud (including convective cloud), or precipitation, in the layer below 20 000 feet above MSL.

The height above MSL of the bottom and top of the layer is given as, for example, MOD IN RA 5000/8000.

When the layer of icing is expected to extend above 20 000 feet, descriptions such as MOD ABOVE 14000 are used.

Turbulence

This section provides information on moderate or severe turbulence including turbulence associated with convective cloud.

The height above MSL of the bottom and top of any layer(s) is given as, for example, MOD IN CLOUD 12000/16000

When the turbulence is expected to extend to ground level, descriptions such as BELOW 8000 are used.

When the turbulence is expected to be confined to clouds, descriptions such as MOD IN CLOUD BELOW 8000 are used.

When the turbulence is expected to extend above 20 000 feet, descriptions such as SEV ABOVE 15000 are used.

Critical Locations

These are locations such as gaps in mountain ranges which are frequently used by general aviation aircraft.

Currently, critical location forecasts are appended to Area Forecasts for Bowral and Mt Victoria (NSW) on AREA 21; Mt Victoria and Murrurundi (NSW) on AREA 20; and Kilmore Gap (Vic) on AREA 30.

Critical location forecasts are written in a mixture of plain language and TAF format making reference as necessary to cloud, visibility and weather.

CAVOK is used to indicate visibility greater than 10 KM, cloud ceiling above 5000 FT above ground level and nil significant weather.

Remarks

This section will include any relevant information not included elsewhere in the forecast.

Abbreviations and Codes Used in Area Forecasts

AC - Altocumulus

AC/AS - Altocumulus and Altostratus with bases at the same level

AS - Altostratus

AMD - Amendment

BKN - Broken

CAVOK - Cloud and visibility and weather ok.

CB - Cumulonimbus

CU - Cumulus

CU/SC - Cumulus and Stratocumulus with bases at the same level

DZ - Drizzle

EMBD - Embedded

FEW - Few

FG - Fog

FM - From (only used in Critical Locations section)

FRQ - Frequent

GR - Hail

GS - Small Hail

INTER - Intermittent variations (only used in Critical section Locations)

ISOL - Isolated

MOD - Moderate

NS - Nimbostratus

OCNL - Occasional

OVC - Overcast

RA - Rain

SC - Stratocumulus

SCT - Scattered

SEV - Severe

SH - Shower

SN - Snow

ST - Stratus

TCU - Towering Cumulus

TEMPO - Temporary variations (only used in Critical Locations section)

TS - Thunderstorm

Z - Code for UTC (universal time)

Example

METAR/SPECI

A METAR is a routine report of meteorological conditions at an aerodrome.

A SPECI is a special report of meteorological conditions, issued when one or more elements meet specified criteria significant to aviation. SPECI is also used to identify reports of observations recorded ten minutes following an improvement (in visibility, weather or cloud) to above SPECI conditions.

Location

The location is indicated by either the ICAO (International Civil Aviation Organization) location indicator or another approved abbreviation.

Date/Time

The day of month and the time of the report is given in UTC (Coordinated Universal Time) using six figures followed by the letter Z. The first two digits are the day of the month; the following 4 digits are the time in hours and minutes, e.g. 291741Z (time of report is 1741 on the 29th of the month UTC).

AUTO

The abbreviation AUTO will be included when the report contains only automated observations.

Surface Wind

The wind direction is given in degrees true, rounded to the nearest 10 degrees. A variable wind direction is given as VRB.

The wind speed, given in knots (KT), is the mean value over the sampling period which is normally ten minutes. The maximum wind speed during the sampling period is reported when it exceeds the mean speed by 10 knots or more. It is indicated by the letter G which is followed by the gust value, e.g. a wind direction of 280°, with a mean speed of 20 knots and a maximum gust of 31 knots, is given as 28020G31KT.

Visibility

The horizontal visibility is given in metres up to 9000 metres; with 9999 being used to indicate a visibility of 10 kilometres or greater.

When the visibility is estimated manually (i.e. by an observer), two groups may be reported when the visibility is not the same in different directions. In these cases, the higher visibility will be given first, followed by the minimum visibility and its direction (using one of the eight points of the compass) from the observing station e.g. 9000 2000N.

When visibility is given by an automated sensor (in fully AUTOmated reports), only one group is reported. The value is followed by the letters NDV (Nil Directional Variation) to indicate that, as there is only one visibility sensor in place, any directional variation in visibility that may exist cannot be detected.

Weather

Weather phenomena are reported using the codes listed in the tables:

Code Weather Descriptor

MI - Shallow

BC - patches

PR - partial

DR - drifting

BL - blowing

SH - showers

FZ - freezing

TS - thunderstorm

Code Weather Phenomena

DZ - drizzle

RA - rain

GR - hail

SN - snow

SG - snow grains

DU - dust

SA - sand

SS - sandstorm

DS - dust storm

GS - small hail/snow pellets

PL - ice pellets

FG - fog

BR - mist

FU - smoke

HZ - haze

PO - dust devil

SQ - squall

FC - funnel cloud

VA - volcanic ash

IC - ice crystals

PL - ice pellets

Intensity is indicated for precipitation, blowing dust/sand/snow, dust storm and sandstorm by appending:

• the prefix - for light, e.g. -DZ
• the prefix + for heavy, e.g. +RA
• no prefix for moderate, e.g. SHRA

One or more codes may be grouped, e.g. +TSGR, -TSRASN

NOTE

• When precipitation is reported with TS, the intensity indicator refers to the precipitation, e.g. -TSRA = thunderstorm with light rain.
• Well-developed dust/sand whirls (dust devils) and funnel clouds are reported using the indicator +

An observation may provide an indication of weather in the vicinity of the aerodrome, i.e. between 8 and 16KM of the aerodrome reference point. In these cases, the weather code is prefixed with the abbreviation VC (vicinity), e.g. VCTS.

Cloud

Cloud information is reported from the lowest to the highest layers in accordance with the following rules:

• 1st group: the lowest layer regardless of amount.
• 2nd group: the next layer covering more than 2 oktas of the sky.
• 3rd group: the next higher layer covering more than 4 oktas of the sky.
• Extra groups: for cumulonimbus and/or towering cumulus clouds, whenever observed and not reported in any of the above.

Cloud amount is described using the codes in the table:

Code - Cloud Amount

SKC - sky clear

FEW - few (1 to 2 oktas)

SCT - scattered (3 to 4 oktas)

BKN - broken (5 to 7 oktas)

OVC - overcast (8 oktas)

NSC - nil significant cloud

NCD* - nil cloud detected

* NCD is reported (in fully automated reports only) when a cloud sensor detects nil cloud (a human observer will report SKC when the sky is clear.

Cloud height is given as a three-figure group in hundreds of feet above the aerodrome elevation, e.g. cloud at 700 feet is shown as 007.

Cloud type is identified only for cumulonimbus and towering cumulus, e.g. FEW030CB, SCT045TCU.

When an individual layer is composed of cumulonimbus and towering cumulus with a common base, the cloud is reported as CB only.

If the sky is obscured, due to, for example, bushfire smoke, human observers will report the vertical visibility (when it can be estimated) in lieu of cloud. It is reported with the prefix VV followed by the vertical visibility in hundreds of feet, e.g. the group VV003 reports an estimated vertical visibility of between 300 and 399 feet (values are rounded down to the next hundred foot increment).

CAVOK

The abbreviation CAVOK (Cloud and Visibility OK) is used when the following conditions are observed simultaneously:

• Visibility is 10 kilometres or more;
• No cloud below 5000 feet or below the highest 25NM minimum sector altitude, whichever is the higher, and no cumulonimbus and no towering cumulus; and
• No weather of significance to aviation, i.e. none of the weather phenomena listed in the weather tables above.

Temperature

Air temperature and dew point values are rounded to the nearest whole degree. Negative values are indicated by M (minus) before the numeral, e.g. 34/M04

Pressure (QNH)

The QNH value is rounded down to the next whole hectopascal and is given using four figures prefixed by Q, e.g. 999.9 is given as Q0999

Supplementary Information

Supplementary information is used to report:

• Recent Weather - significant weather observed since the last report but not at the time of observation is given after the prefix RE, e.g. RERA.
• Wind Shear - reports of wind shear experienced on take-off or landing are given after the indicator WS, e.g. WS RWY16.

Remarks

The Remarks section (indicated by RMK) may contain the following:

• Quantitative information on past rainfall is given in millimetres in the form RFRR.R/RRR.R or RFRR.R/RRR.R/RRR.R. The former, e.g. RF00.2/004.2, gives the rainfall recorded in the ten minutes prior to the observation time, followed by the rainfall recorded in the period since 0900 local time. The second format, e.g. RF00.2/003.0/004.2, gives the rainfall recorded in the ten minutes prior to the observation, followed by the rainfall in the sixty minutes prior to the observation, followed by the rainfall recorded in the period since 0900 local time.
• Information of operational significance not reported in the body of the message, for example:
  • information about significant conditions (such as bushfires and distant thunderstorms) beyond the immediate vicinity of the aerodrome,
  • any BKN or OVC low or middle cloud present at or above 5000 feet when CAVOK has been included in the body of the message,
  • CLD:SKY MAY BE OBSC may be reported in fully automated reports when the ceilometer (cloud sensor) detects nil cloud and the visibility sensor estimates horizontal visibility as being less than 1000 metres

Elements of report not available

Where an element of a report is not available, solidi will be reported in lieu of the missing element, e.g. //// for visibility, // for weather and ////// for cloud.

SPECI Criteria

SPECI is used to identify reports of observations when conditions are below specified levels of visibility and cloud base; when certain weather phenomena are present; and when temperature, pressure or wind change by defined amounts (outlined in the table on the right).

SPECI is also used to identify reports of observations recorded 10 minutes following an improvement in visibility, weather or cloud to METAR conditions.

Element And Criterion

Wind Direction - Changes of 30° or more, the mean speed before or after the change being 20KT or more

Wind Speed - Changes of 10KT or more, the mean speed before or after the change being 30KT or more

Wind Gust

• Gusts of 10KT or more above a mean speed of 15KT or more
• Gust exceeds the last reported gust by 10KT or more

Visibility - When the horizontal visibility is below the aerodrome’s highest alternate minimum visibility*

Weather - When any of the following begins, ends or changes in intensity:

• thunderstorm
• hailstorm
• mixed snow and rain
• freezing precipitation
• drifting snow
• fog (including shallow fog, fog patches and fog at a distance)
• dust storm
• sand storm
• squall
• funnel cloud
• moderate or heavy precipitation

Cloud - When there is BKN or OVC cloud below the aerodrome's highest alternate minimum cloud base*

Temperature - When the temperature changes by 5°C or more since last report

Pressure - When the QNH changes by 2hPa or more since last report

Other

• Upon receipt of advice of the existence of wind shear
• The incidence of any other phenomenon likely to be significant

*Where no descent procedure is established for an aerodrome, the aerodrome’s alternate ceiling and visibility are 1500 feet and 8 kilometres respectively.

METAR/SPECI Examples

METAR YPPH 221130Z 28012G23KT 9000 -SHRA FEW005 BKN050 27/22

Q0999 RETS RMK RF00.6/003.4 DISTANT TS

REPORT EXPLANATION

METAR Routine meteorological observation

YPPH ICAO location indicator for Perth Airport

221130Z Time of observation is 1130 on the 22nd of the month UTC

28012G23KT Wind from the west (280 degrees True) at 12 knots; gusting to 23 knots

9000 Visibility is 9 kilometres.

-SHRA Present weather is light rain shower

FEW005 There are 1 to 2 oktas of cloud with base at 500 feet

BKN050 There are also 5 to 7 oktas of cloud with base at 5000 feet

27/22 The air temperature is 27°C; the dewpoint temperature is 22°C

Q0999 The QNH is between 999 and 999.9 hectopascals

RETS Recent weather was a thunderstorm

RMK Remarks section follows

RF00.6/003.4 0.6 mm of rain has fallen in the last 10 minutes; 3.4 mm has fallen since 0900 local time

DISTANT TS Distant thunderstorm (greater than 16 kilometres from the aerodrome reference point)

SPECI YSCB 171515Z AUTO 22015G25KT 9000NDV // NCD 13/09 Q1003 RMK

RF00.8/003.0

REPORT EXPLANATION

SPECI Special meteorological observation (for wind gust)

YSCB ICAO location indicator for Canberra Airport

171515Z Time of observation is 1515 on the 17th of the month UTC

AUTO This report is fully automated

22015G25KT Wind from the southwest (220 degrees True) at 15 knots, gusting to 25 knots

9000NDV Visibility is 9000 metres; from a single visibility sensor, therefore no directional variation (NDV) in visibility can be detected

// Present weather is unavailable

NCD Nil cloud has been detected (by ceilometer)

13/09 The air temperature is 13°C; the dewpoint temperature is 09°C

OVC110 There are also 8 oktas of cloud with base at 11 000 feet

Q1003 The QNH is between 1003 and 1003.9 hectopascals

RMK Remarks section follows

RF00.8/003.0 0.8 mm of rain has fallen in the last 10 minutes; 3.0 mm has fallen since 0900 local time

SIGMETs are issued to provide urgent advice to aircraft of actual or expected weather developments or trends that are potentially hazardous.

SIGMETs are issued to advise of the occurrence or expected occurrence of the following phenomena:

Code and Description

OBSC TS - Obscured thunderstorm(s)

EMBD TS - Frequent thunderstorm(s)

SQL TS - Squall line thunderstorms

OBSC TSGR - Obscured thunderstorm(s) with hail

EMBD TSGR - Embedded thunderstorm(s) with hail

FRQ TSGR - Frequent thunderstorm(s) with hail

SQL TSGR - Squall line thunderstorms with hail

TC - Tropical cyclone

SEV TURB - Severe Turbulence

SEV ICE - Severe icing

SEV ICE FZRA - Severe icing due to freezing rain

SEV MTW - Severe mountain wave

HVY DS - Heavy duststorm

HVY SS - Heavy sandstorm

VA - Volcanic ash

RDOACT CLD - Radioactive Cloud

Pilots in command of aircraft encountering any of the above phenomena not notified by SIGMET advices must report details of the phenomena in an AIREP SPECIAL.

SIGMET for thunderstorms are only issued when they are:

• obscured (OBSC) by haze or smoke
• embedded (EMBD) within cloud layers
• frequent (FRQ), i.e. with little or no separation between clouds and covering more than 75% of the area affected
• squall line (SQL) thunderstorms along a line of about 100 nautical miles or more in length, with little or no separation between clouds

SIGMET for thunderstorms and tropical cyclones do not include reference to icing and turbulence as these are implied as occurring with thunderstorms and tropical cyclones.

Responsibility for the issuance of SIGMET within Australian FIRs

SIGMETs for volcanic ash are the responsibility of the Volcanic Ash Advisory Centre, Darwin.

SIGMETs for tropical cyclones are the responsibility of the Tropical Cyclone Advisory Centres in Perth, Darwin and Brisbane.

SIGMETs for turbulence and icing above FL185 are the responsibility of the Aviation Weather Centre, Melbourne.

SIGMET for all other phenomenon are the responsibility of the Meteorological Watch Offices located in Perth, Darwin, Adelaide, Hobart, Melbourne, Sydney, Brisbane and Townsville.

SIGMET Structure

Bulletin Identification

• WCAU01 for SIGMET on tropical cyclones
• WVAU01 for SIGMET on volcanic ash cloud
• WSAU21 for SIGMET for other phenomena

Originating Office (WMO Indicator)

The World Meteorological Organisation (WMO) location indicators for Australian Meteorological Watch Offices are:

APRM - Adelaide Regional Forecasting Centre

APRF - Perth Regional Forecasting Centre

ABRF - Brisbane Regional Forecasting Centre

ASRF - Sydney Regional Forecasting Centre

ADRM - Darwin Regional Forecasting Centre

AMRF - Melbourne Regional Forecasting Centre

AMHF - Hobart Regional Forecasting Centre

ABTL - Townsville Meteorological Office

AMMC - Melbourne Aviation Weather Centre

Note: These differ from the ICAO indicators (beginning with Y) used elsewhere in the message.

Issue Date/Time

Issue date/time is given in UTC in the form DDHHMM, where DD is day of month, and HHMM is time in hours and minutes.

Flight Information Region

Gives the abbreviation for the FIR (YMMM or YBBB) in which the phenomenon is located.

Identifier

The message identifier is SIGMET.

Daily Sequence Number

The four-character sequence number consists of:

• a two-letter designator to indicate the general location of the event (as given in the two maps below), and
• a two-digit number, giving the sequence number of SIGMETs issued by the relevant office within the FIR (Brisbane or Melbourne) since 0000 UTC.

The tropical cyclone and low-level SIGMET two-letter designators and their associated geographical extent are:

The high-level (above FL185) icing and turbulence SIGMET two-letter designators and their general associated geographical extent are:

Validity Period

The validity period is given in the format DDHHMM/DDHHMM, where DD is the day of the month and HHMM is the time in hours and minutes UTC.

Tropical cyclone and volcanic ash SIGMETs can have a validity of up to six hours. SIGMETs for other phenomena can be valid for up to four hours.

Originating Office (ICAO Indicator)

The International Civil Aviation Organization (ICAO) location indicators for Australian Meteorological Watch Offices are:

YPRM - Adelaide Regional Forecasting Centre

YPRF - Perth Regional Forecasting Centre

YBRF - Brisbane Regional Forecasting Centre

YSRF - Sydney Regional Forecasting Centre

YPDM - Darwin Regional Forecasting Centre

YMRF - Melbourne Regional Forecasting Centre

YMHF - Hobart Regional Forecasting Centre

YBTL - Townsville Meteorological Office

YMMC - Melbourne Aviation Weather Centre

Flight Information Region

This gives the abbreviation and full name for the FIR in which the phenomenon is located.

Meteorological Information

This section includes:

• type of phenomenon
• observed or forecast
• location, both horizontal and vertical extents
• movement or expected movement
• expected change in intensity
• SIGMET for tropical cyclone and volcanic ash cloud include a forecast position for the end of the validity period
• message status

Cancel SIGMET

If during the validity period of a SIGMET, the phenomenon for which the SIGMET is no longer occurring or is no longer expected, the SIGMET is cancelled by issuing a SIGMET with the abbreviation CNL in lieu of meteorological information.

SIGMET Status

The status line indicates whether the SIGMET is:

• NEW - the SIGMET is for a new phenomenon.
• REV - the SIGMET reviews an earlier SIGMET for the phenomenon.
• CNL - cancels a current SIGMET.

The following abbreviations are used in SIGMET:

Code and Description

A - Altitude

ABV - Above

APRX - Approximately

BLW - Below

CNL - Cancel

DS - Dust storm

EMBD - Embedded

FIR - Flight Information Region

FCST - Forecast

FL - Flight level

FRQ - Frequent

FZRA - Freezing rain

GR - Hail

HVY - Heavy

ICE - Icing

INTSF - Intensifying

LOC - Location

MOV - Moving

NC - No Change (intensity)

OBS - Observed

OBSC - Obscured

RDOACT CLD - Radioactive cloud

REV - Review

SEV - Severe

SQL - Squall line

SS - Sand storm

STNR - Stationary

STS - Status

TC - Tropical cyclone

TS - Thunderstorm

TURB - Turbulence

VA - Volcanic ash

WI - Within (area)

WKN - Weakening (intensity)

Z - Universal Time

SIGMET Examples

WSAU21 AMMC 180357

YMMM SIGMET MM01 VALID 180439/180839 YMMC-

YMMM MELBOURNE FIR SEV TURB FCST WI S3200 E12800 - S3200 E13000 - S4700 E13600 - S4700 E13400 FL260/400 MOV E 25KT NC

STS:NEW

WSAU21 AMMC 180720

YMMM SIGMET MM02 VALID 180720/180839 YMMC-

YMMM MELBOURNE FIR CNL SIGMET MM01 180439/180839

STS:CNL SIGMET MM01 180439/180839

WCAU01 APRF 180217

YMMM SIGMET PH01 VALID 180215/180815 YPRF-

YMMM MELBOURNE FIR TC ILSA OBS AT 0000Z S1330 E11324 CB TOP FL500 WI 120NM OF

CENTRE MOV WSW 17KT INTSF FCST 0815Z TC CENTRE S1418 E11036

STS:NEW

WVAU01 ADRM 200100

YBBB SIGMET BT04 VALID 200100/200700 YPDM-

YBBB BRISBANE FIR VA ERUPTION LOC S0416 E15212 VA CLD OBS AT 200100Z A100/180 APRX 120NM BY 40NM S1130 E14530 - S1330 E14900 - S1030 E15030 - S0830 E14700 - S1130 E14430 MOV SW 20KT FCST 0700Z VA CLD APRX S110 E144530 - S1230 E14930 - S1050 E15130 - S0800 E14700 - S1130 E14400 STS:REV SIGMET BT03 191900/200100

Aerodrome Forecast (TAF)

A TAF is a coded statement of meteorological conditions expected at an aerodrome and within a radius of five nautical miles of the aerodrome reference point.

Explanation of TAF Elements

Identifier and Description

TAF - Aerodrome Forecast

TAF AMD - Amended Aerodrome Forecast

TAF COR - Corrected Aerodrome Forecast

TAF .. CNL - Cancels Aerodrome Forecast

TAF .. NIL - Aerodrome Forecast will not be issued

PROV TAF - Provisional Aerodrome Forecast

Location

The location is given by either an ICAO location indicator or an approved Airservices Australia abbreviation.

Issue Time

The issue time of the TAF is expressed in a six-figure group followed by the code letter Z, e.g. 202230Z, which gives an issue time of 2230 on the 20th day of the month UTC.

Validity

The period of validity is given in the format ddhh/ddhh, where dd is day of the month and hh is hour UTC, e.g. 2100/2206, which gives a 30 hour validity period from 0000 the 21st to 0600 on the 22nd UTC. Note that 00 is used to indicate periods of validity beginning at 0000 UTC; and 24 is used to indicate periods of validity ending at 2400 UTC.

Wind

The wind direction is given in degrees True, rounded to the nearest 10 degrees. A variable wind direction is given as VRB (used when the forecasting of a mean wind direction is not possible).

The wind speed is given in knots (KT).

The maximum wind gust is included, after the letter G, if it is expected to exceed the mean by 10 knots or more, e.g. a wind direction 280° True, with a mean speed of 20 knots, and a maximum gust of 30 knots, is given as 28020G30KT

Visibility

The horizontal visibility is given in metres in increments of 50 metres when visibility is forecast to be less than 800 metres; in increments of 100 metres when forecast to be 800 metres or more but less than 5,000 metres; and in increments of 1,000 metres when forecast to be 5,000 or more but less than 10,000 metres . Visibility is always given in a four figure group: eg 500 metres is given as 0500. Forecast visibilities of 10 kilometres or more are given as 9999. Visibility is not given when CAVOK is forecast.

Weather

Forecast weather is expressed using the following abbreviations:

MI - shallow

BC - patches

PR - partial

DR - drifting

BL - blowing

SH - showers

FZ - freezing

TS - thunderstorm

DS - duststorm

GS - small hail/snow pellets

DZ - drizzle

FG - fog

RA - rain

BR - mist

GR - hail

FU - smoke

SN - snow

HZ - haze

SG - snow grains

PO - dust devil

DU - dust

SQ - squall

SA - sand

FC - funnel cloud

SS - sandstorm

VA - volcanic ash

IC - ice crystals

PL - ice pellets

Intensity is indicated for precipitation, blowing dust/sand/snow, duststorms and sandstorms. In these cases, the weather group is prefixed by - for light and + for heavy; moderate intensity has no prefix, e.g. +TSRA means thunderstorm with heavy rain; DZ means moderate drizzle; -RA means light rain.

After a change group, if the weather ceases to be significant, the weather group is replaced by NSW (nil significant weather) or CAVOK if appropriate.

Cloud

Cloud information is given from the lowest to the highest layers in accordance with the following rule:

• 1st group: the lowest layer regardless of amount.
• 2nd group: the next layer covering more than 2 oktas.
• 3rd group: the next higher layer covering more than 4 oktas.
• Extra group for cumulonimbus and towering cumulus when forecast but not at any of the layer heights given above.

Cloud amount is given using the following abbreviations:

SKC - sky clear

FEW - few (1 to 2 oktas)

SCT - scattered (3 to 4 oktas)

BKN - broken (5 to 7 oktas)

OVC - overcast (8 oktas)

NSC - nil significant cloud

Cloud height is given as a three-figure group in hundreds of feet above the aerodrome, e.g. cloud at 700 feet above the aerodrome is shown as 007.

Cloud type is identified only for cumulonimbus and towering cumulus, e.g. FEW030CB, SCT040TCU.

CAVOK

The abbreviation CAVOK (Ceiling and Visibility and weather OK) is used when the following conditions are forecast simultaneously:

• Visibility is 10 kilometres or more,
• No cloud below 5000 feet or the highest 25 nautical mile minimum sector altitude, whichever is the higher; and no cumulonimbus or towering cumulus at any height,
• No weather of significance to aviation, i.e. none of the weather listed in the weather table

Significant Changes and Variations (FM, BECMG, INTER, TEMPO)

Significant changes and variations will be included when the changes and variations are expected to satisfy the amendment criteria. It should be noted that these changes relate to improvements as well as deteriorations.

The term FM is used when one set of prevailing weather conditions is expected to rapidly change to a different set of prevailing weather conditions. The indicator is the beginning of a self-contained forecast, with the new conditions applying until the end period of the forecast or until the commencement time of another FM or BECMG group.

The term BECMG is used when one set of prevailing weather conditions is expected to gradually change to a different set of prevailing weather conditions. The indicator is the beginning of a self-contained forecast, with the new conditions applying until the end period of the forecast, or until the commencement time of another BECMG or FM group.

Following any change group (FM or BECMG) there will be information on wind, visibility, weather and cloud; except when CAVOK is given or when fog is forecast.

Following any change group (FM or BECMG) where there is nil significant weather forecast the abbreviation NSW is used. In some cases where the sky is forecast to be clear after a change group the abbreviation SKC is used.

The terms TEMPO and INTER are used to indicate significant temporary or intermittent variations from the prevailing conditions previously given in the TAF. TEMPO is used for periods of 30 minutes or more but less than 60 minutes. INTER is used for periods less than 30 minutes.

Change and variation groups (FM, BECMG, TEMPO, INTER) are not introduced until all information necessary to describe the initial forecast conditions of wind, visibility, weather and cloud have been given.

Variation groups (TEMPO, INTER) follow at the end of all change groups (FM, BECMG) and before any PROB or TURB.

PROB

The term PROB[%] is used if the estimated probability of occurrence is 30 or 40 percent (probabilities of less than 30% are not given), and is only used with reference to thunderstorms or poor visibility (less than the alternate minimum) resulting from fog, mist, dust, smoke or sand. If the estimated probability of occurrence is greater than or equal to 50 percent, reference is made to the phenomenon in the forecast itself, not by the addition of a PROB. When using PROB with thunderstorms, INTER and TEMPO are also included whenever possible to indicate the probable duration. Where PROB is used without one of these, the likely period of occurrence will be deemed to be one hour or more. For example:

PROB30 INTER 1205/1211 5000 -TSRA BKN040CB indicates a 30% probability of deteriorations of less than 30 minutes due to thunderstorms with light rain between 0500 and 1100 UTC on the 12th.

PROB40 TEMPO 1102/1113 3000 TSRA BKN040CB indicates a 40% probability of deteriorations of 30 minutes or more but less than 60 minutes due to thunderstorms with moderate rain between 0200 and 1300 UTC on the 11th.

PROB30 1005/1014 1000 +TSRA BKN040CB indicates a 30% probability of deteriorations of one hour or more due to thunderstorms with heavy rain between 0500 and 1400 UTC on the 10th.

RMK

RMK (remarks) precedes Turbulence (if forecast) and Temperatures and QNH

Turbulence.

Special reference is made in TAF to hazardous turbulence that may endanger aircraft or adversely affect their safe or economic operation. The TAF contains information on commencement time (FMddhhmm), the expected intensity (moderate [MOD] or severe [sEV]) and the vertical extent (BLW.... FT). TILLddhhmm is used to indicate the cessation of the turbulence when this is expected before the end of the TAF validity.

Air Temperature

Temperature, preceded by the letter T, is given in whole degrees celsius using two figures. If the temperature is below zero Celsius, the value is prefixed by the letter M (minus). In Australia, forecasts of air temperature are given at three-hourly intervals, for a maximum of nine hours, from the time of commencement of validity of the forecast. They are given for the times HH, HH+3, HH+6 and HH+9, where HH is the time of the commencement of the TAF validity. They are point forecasts for these times but are valid for, in the case of the first value, ninety minutes after the time point HH; and, for subsequent values, ninety minutes each side of the time point.

QNH

QNH, preceded by the letter Q, is given in whole hectopascals using four figures.

In Australia, forecasts of QNH are given at three-hourly intervals, for a maximum of nine hours, from the time of commencement of validity of the forecast. They are given for the times HH, HH+3, HH+6 and HH+9, where HH is the time of the commencement of the TAF validity. They are point forecasts for these times but are valid for, in the case of the first value, ninety minutes after the time point HH; and, for subsequent values, ninety minutes each side of the time point.

TAF Examples

TAF YMAY 022230Z 0300/0312 35010KT CAVOK

FM030800 31018KT 9999 SHRA BKN025 OVC100

INTER 0308/0312 31020G40KT 3000 +TSRA BKN010 SCT040CB

RMK FM030600 MOD TURB BLW 5000FT

T 23 24 28 33 Q 1012 1013 1014 1009

Decoded:

TAF - Aerodrome Forecast

YMAY - ICAO location indicator for Albury Airport

022230Z - TAF issued at 2230 on the 2nd day of the month UTC

0300/0312 - Validity period of TAF is from 0000 to 1200, on the 3rd day of the month UTC

35010KT - Wind will be from the north (350 degrees True) at 10 knots

CAVOK - Cloud, visibility and weather ok

FM030800 - Significant changes to the mean conditions are expected to commence from 0800 on the 3rd UTC, and to persist (at least) until the end of the forecast period

Note that there will be intermittent variations to these new mean conditions (refer INTER below)

31018KT - Wind will be from the northwest (310 degrees True) at 18 knots

9999 - Visibility will be 10 kilometres or more

SHRA - Weather will be moderate showers of rain

BKN025 - Cloud will be broken (5 to 7 oktas) with base at 2500 feet above the aerodrome

OVC100 - There will also be overcast cloud (8 oktas) with base at 10000 feet

INTER 0308/0312 - There will be intermittent (periods of less than 30 minutes) variations to the previously given mean conditions. Period of INTER is 0800 to 1200 on the 3rd UTC

31020G40KT - Intermittently the wind will be from the northwest (310 degrees True) at 20 knots gusting to 40 knots

3000 - Visibility will be 3000 metres

+TSRA - Weather will be thunderstorms with heavy rain

BKN010 - Cloud will be broken (5 to 7 oktas) with base at 1000 feet above the aerodrome

SCT040CB - There will also be 3 to 4 oktas of cumulonimbus cloud with base at 4000 feet

RMK - Remarks section follows

FM030600 MOD TURB BLW 5000FT - From 0600 on the 3rd UTC, expect moderate turbulence below 5000 feet

T 23 24 28 33 - Forecast air temperatures at 00, 03, 06 and 09 UTC are 23, 24, 28 and 33

Q 1012 1013 1014 1009 - Forecast QNH at 00, 03, 06 and 09 UTC are 1012, 1013, 1014 and 1009.

TAF COR YMLT 212240Z 2200/2218 31015G28KT 6000 -RA BKN010 OVC100

TEMPO 2209/2218 2000 +TSRA BKN005 SCT040CB

RMK

T 25 21 18 15 Q 1014 1013 1013 1011

Decoded:

TAF - Aerodrome Forecast

COR - This TAF is a correction to the previously issued TAF

YMLT - ICAO Location Indicator for Launceston Airport

212240Z - TAF issued at 2240 on the 21st day of the month UTC

2200/2218 - Validity period of TAF is from 0000 until 1800 on the 22nd of the month UTC

31015G28KT - Mean wind is expected to be from 310 degrees True at 15 knots with gusts to 28 knots

6000 - Visibility will be 6000 metres

-RA - Weather will be light rain

BKN010 - Cloud will be broken (5 - 7 octas), with base at 1000 feet above the aerodrome

OVC100 - There will also be overcast cloud, with base at 10,000 feet above the aerodrome

TEMPO 2209/2218 - There will be temporary variations (periods of 30 to 60 minutes), to the previously given mean conditions, during the period 0900 to 1800 on the 22nd.

2000 - Visibility will be 2000 metres

+TSRA - Weather will be thunderstorms with heavy rain showers

BKN005 - There will be broken (5 to 7 oktas) cloud with base at 800 feet above the aerodrome

SCT040CB - There will also be scattered (3 to 4 oktas) cumulonmbus cloud with base at 2000 feet above the aerodrome

RMK - Remarks section follows

T 25 21 18 15 - Forecast air temperatures at 06, 09, 12 and 15 UTC are 25, 21, 18 and 15

Q 1014 1013 1013 1011 - Forecast QNH at 06, 09, 12 and 15 UTC are 1014, 1013, 1013 and 1011

TAF AMD YMML 292330Z 3000/3106 14008KT 9999 NSW SCT030

FM301100 14003KT 3000 HZ BKN009

PROB40 3017/3023 0400 FG

RMK

T 14 15 17 14 Q 1016 1014 1013 1014

Decoded:

TAF - Aerodrome Forecast

AMD - This TAF amends the previously issued TAF

YMML - ICAO location indicator for Melbourne Airport

292230Z - TAF issued at 2230 on the 29th day of the month UTC

3000/3106 - Validity period of TAF is from 0000 on the 30th until 0600 on the 31st UTC

14008KT - Mean wind is expected to be from the southeast (150 degrees True) at 8 knots

9999 - Visibility will be 10 kilometres or more

NSW - There will be nil significant weather

SCT030 - Cloud will be scattered (3 to 4 oktas), with base at 3000 feet above the aerodrome

FM301100 - Significant new mean conditions are expected from 1100 on the 30th UTC;

14003KT - Mean wind is expected to be from 150 degrees True at 3 knots

3000 - Visibility will be 3 kilometres

HZ - Weather will be haze

BKN009 - Cloud will be broken (5 to 7 oktas), with base at 900 feet above the aerodrome

PROB40 3017/3023 - There is a 40% probability of conditions being the following during the period 1700 to 2300 on the 30th:

0400 - Visibility of 400 metres

FG - Fog

RMK - Remarks section follows

T 14 15 17 14 - Forecast air temperatures at 00, 06, 09 and 12 UTC are 14, 15, 17 and 14

Q 1016 1014 1013 1014 - Forecast QNH at 00, 06, 09 and 12 UTC are 1016, 1014, 1013 and 1014

Pitot tubes are crucial components onboard aircraft used to measure a range of important data. The tubes are popularly known as speedometers, giving pilots a gauge on their airspeed, and also measure altitude and altitude trend. Pitot tubes are usually found along the front fuselage or along the wing of an aircraft.

What exactly are pitot tubes?

Pitot tubes aren’t just inventions innovated for aviation; they’re also commonly found in industrial machinery, boats and even Formula 1 cars. A pitot tube is essentially a flow sensor instrument. Simple pitot tubes have one hole at the front; however, planes will often use pitot-static tubes with two openings rather than separate pitot tubes and static ports.

Pitot-static instrumentation on an aircraft. Photo: Getty Images

A simple pitot tube can measure stagnation pressure only due to its single opening. The advantage of a pitot-static tube is its ability to measure static pressure in addition to stagnation pressure. Static ports along the side of the pitot tube give it this all-in-one capability, meaning there is no need to install separate static ports elsewhere.

How pitot tubes work

Pitot tubes work as flow sensors to measure the speed and pressure of air, liquid or gas. These readings allow pilots to gauge airspeed and altitude and have a wide variety of applications in other equipment. The tubes can usually be spotted beneath the cockpit on the front fuselage or along the wing.

Pitot tubes clearly visible on a 737NG. Photo: Simple Flying/Dylan Ashe

The pitot-static tube has two openings, one in the front and one along the sides, used to measure air, gas or liquid flow. This system involves placing a pitot tube inside another tube with static ports. The front hole measures the stagnation pressure, while the side openings (static ports) gauge static pressure. The difference between these two measurements is called dynamic pressure – this is what is used to calculate airspeed.

Pitot tubes are critical instruments

Measuring airspeed is an indispensable part of flying and essential for all pilots to keep a gauge of. Pitot tubes provide indicated airspeed (IAS), based upon measuring the dynamic pressure. This is different from groundspeed, as planes can encounter resistance during flight, such as headwind and air density.

Pitot tubes provide pilots with vital data on airspeed and altitude. Photo: Getty Images

Planes flying too slowly won’t generate enough lift and risk spiraling into a stall, while aircraft flying too quickly risk damage as they aren’t built to withstand certain speeds. Airspeed is also vital in estimating flight length – inaccurate estimations may cause pilots to run out of fuel mid-journey if the flight goes on longer than expected.

Incidents involving pitot tubes

As a critical part of an aircraft’s instrumentation, pitot tubes have been at the center of several accidents. As the tubes are exposed to the elements, they are in danger of icing over, which has led to several fatal accidents. Pitot tube failures will always force a plane to divert – in October, an Airbus flight over Russia was forced to land after its pitot tubes were not heating up adequately.

Testing the pitot-static system is important for ensuring safety. Photo: Lufthansa

In one case, wasps nested inside a pitot tube, which later led to a fatal crash onboard Birgenair Flight 301. The aircraft had been grounded for 20 days and its pitot tubes were left uncovered, allowing wasps to burrow inside. Australia is to this day combating nuisance wasps that are nesting inside pitot tubes. Another high-profile case involved a disgruntled American Airlines mechanic tampering with a pitot tube, which led to an emergency landing.