5-96 This system was later improved and is now called the Phase-3 LLWAS. A typical Phase-3 LLWAS will have enough sensors to be spaced 2 km apart (∼1 NM apart) and cover out to 2 NM from the end of each major runway.
The largest LLWAS is at Denver International Airport, which has 32 wind sensors. Most Phase-3 systems have between 12 and 16 wind sensors. A siting evaluation is done for each airport to determine the network geometry since it depends on terrain, number of runways, obstructions, etc.
The Phase-3 LLWAS alert information is described below.
If a pilot is landing on runway 08, and there is a microburst on his path, the controller would have a display that reads: 08A MBA 30K–3MF 350/25.
This is read to a pilot arriving on runway 08 (08A) by a final controller as “microburst alert (MBA), expect a thirty knot loss (30K–) at three miles final (3MF), threshold wind three–five–zero at 25 (knots).”
If there was a windshear with a wind speed gain at 1 mile departure (headwind gain), for a pilot departing runway 25 left, the final controller’s LLWAS display would show: 25LD WSA 15k+ 1MD. This would be read as “windshear alert, expect a fifteen knot gain at one mile departure.” There are Phase-3 LLWAS systems at 9 U.S. airports and Phase-2 LLWAS at more than 100 airports. Taiwan, Korea, Singapore, Saudi Arabia, and Kuwait are now implementing Phase-3 LLWAS systems. Note, the FAA also has Terminal Doppler Weather Radars (TDWR) for windshear detection at 45 airports and has Airport Surveillance Radar-9 (ASR-9)-based windshear detection systems at another 37 airports. The FAA originally had 110 Phase-1 LLWAS systems, which were upgraded to Phase-2 systems.
A Phase-2 LLWAS has the same number of sensors (5 to 6) as a Phase-1 system (described above), but the windshear algorithm was upgraded to significantly decrease the number of false alarms. As mentioned above, a Phase-1 or Phase-2 LLWAS was not designed to detect microbursts per se, but if the flow is large and strong, it may send an alert.
When NCAR developed the Phase-3 LLWAS, it gave the specifications to the FAA. The University Corporation for Atmospheric Research (UCAR) Foundation owned the intellectual property for the windshear algorithm during the lifetime of the patent. A license agreement was required for companies to implement LLWAS technology until early 2013 when the patent exclusion expired. A license from UCAR Foundation is no longer required to utilize the LLWAS algorithm. The UCAR Foundation does, however, provide technical materials such as test datasets, test airport configuration files, test alert outputs, etc. to aid companies in the implementation and testing of the Phase-3 LLWAS algorithm.
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5.13.2.10.2 Frequently Asked Questions (FAQ).
1. Q. What is LLWAS?
A. A typical Phase-3 LLWAS system includes a network of anemometers (wind sensors) atop tall poles located around the airport (i.e., remote stations) out to no more than 3 NM from the end of the runways, a master station that processes system data and communicates with the remote stations, an archiving system, operator console, alphanumeric alarm displays, and in some instances, graphical displays.
2. Q. How does it work?
A. The wind data at each remote station is processed every 10 seconds to determine if there is divergence or convergence within the network, or station-to-station wind differences between stations aligned with the runways. The divergence/convergence information is processed and if the intensity of the event is large enough, the system will calculate the strength of the along-runway wind losses or gains and generate windshear or microburst alerts (depending on strength), and identify the location of the event.
3. Q. What is a microburst?
A. A microburst is an intense windshear. By definition:
Microburst n: A small, very intense downdraft that descends to the ground resulting in a strong wind divergence. The size of the event is typically less than 4 km across. Microbursts are capable of producing winds of more than 100 mph, causing significant damage. The life span of a microburst is around 5 to 15 minutes.
4. Q. What causes microbursts?
A. Microbursts are strong windshears (greater than 30-knot wind speed losses over distances of 1 to 4 km) that are primarily generated by evaporative cooling and rain loading. When precipitation (rain or snow) descends below the cloud base or is mixed with dry air, it begins to evaporate and this evaporation process cools the air. The cool air descends and accelerates as it approaches the ground. When the cool air approaches the ground, it spreads out in all directions and this divergence of the wind is the signature of the microburst. In humid climates, microbursts can also generate from heavy precipitation. The weight and drag associated with the falling precipitation can result in a downdraft that will descend to the ground and spread out.
5. Q. Why is it a problem for airplanes?
A. Windshear is a rapid change of wind speed or direction over a short distance. In general, windshear becomes a hazard for aircraft if the wind changes more than 20 kts over a distance of 1 to 4 km
(0.5 to 2.5 NM). On either takeoff or landing, aircraft are near stall speeds. When going through a windshear, the headwind decreases
5-98 resulting in a loss of lift. If the aircraft is near stall, then a little loss of lift can make all the difference to whether the aircraft can continue the flight.
6. Q. How and what kind of decisions do airports or airlines make using LLWAS?
A. LLWAS provides information on windshear type, location, and intensity. Windshear alerts are issued via radio to arriving and departing aircraft by final air traffic controllers. In the United States, most airlines require that pilots not continue their arrival or departure if there is a microburst alert valid for their operation.
Although most aviation authorities do not close the runways when microbursts are occurring, the air traffic controllers will work with the pilots to reroute aircraft away from the event to a runway that is not impacted by the windshear.
7. Q. How and what kind of decisions do airports make using LLWAS?
A. LLWAS provides information on windshear type, location, and intensity. The pilots get the alert from the controller and the pilot is supposed to determine if they feel comfortable continuing the operation. In the United States, airlines require that pilots do not continue if there is a microburst alert.
8. Q. Where have LLWAS systems been implemented?
A. Phase-3 LLWAS systems have been implemented throughout the United States and at numerous international airports including, but not limited to, Taiwan, Korea, Saudi Arabia, Hong Kong, Kuwait, Italy, Singapore, and Spain. Additional LLWAS procurements are in progress.
9. Q. What are some of the windshear problems associated with airports?
A. Any airport that has thunderstorms will be exposed to Convective windshear. Any airport near mountains will experience terrain-induced windshear from time to time. Any airport near a coast will experience windshear due to sea breezes. In the drier climates, even a light shower (or virga) can produce severe windshears, so in some places, the convection does not have to be as strong as a thunderstorm (e.g., Denver, Phoenix, Reno, Albuquerque, etc.).
Discussion Credit: NCAR.
For m ore information readers can go to:
https://www.ral.ucar.edu/projects/low-level-wind-shear-alert-system-llwas.
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5.13.2.11 Non-Convective Low-Level Wind Shear (LLWS) Group (WShwshwshws/dddffKT).
Windshear (WS) is defined as a rapid change in horizontal wind speed and/or direction, with distance and/or a change in vertical wind speed and/or direction with height. A sufficient difference in wind speed, wind direction, or both can severely impact airplanes, especially within 2,000 ft AGL because of limited vertical airspace for recovery.
Forecasts of LLWS in the TAF refer only to Non-Convective LLWS from the surface up to and including 2,000 ft AGL. LLWS is always assumed to be present in Convective activity. LLWS is included in TAFs on an “as-needed” basis to focus the aircrew’s attention on LLWS problems that currently exist or are expected. Non-Convective LLWS may be associated with the following: frontal passage, inversion, low-level jet, lee side mountain effect, sea breeze front, Santa Ana winds, etc.
When LLWS conditions are expected, the Non-Convective LLWS code WS is included in the TAF as the last group (after cloud forecast). Once in the TAF, the WS group remains the prevailing condition until the next FM change group or the end of the TAF valid period if there are no subsequent FM groups. Forecasts of Non-Convective LLWS are not included in TEMPO or PROB groups.
The format of the Non-Convective LLWS group is:
WShwshwshws/dddffKT WS Indicator for Non-Convective LLWS Hwshwshws Height of the top of the WS layer in hundreds of feet AGL Ddd True direction in 10-degree increments at the indicated height -- VRB is not used for direction in the Non-Convective LLWS forecast Ff Speed in knots of the forecast wind at the indicated height KT Unit indicator for wind Example:
TAF…13012KT…WS020/27055KT Windshear from the surface to 2,000 ft. Surface winds from 130 (southeast) at 12 kts changes to 270 (west) at 55 knots at 2,000 ft.
In this example, the indicator WS is followed by a three-digit number that is the top of the windshear layer. LLWS is forecast to be present from the surface to this level. After the solidus (/), the five-digit wind group is the wind direction and speed at the top of the windshear layer. It is not a value for the amount of shear.
5-100 A Non-Convective LLWS forecast is included in the initial time period or a FM group in a TAF whenever:
• One or more Pilot Weather Reports (PIREP) are received of Non-Convective LLWS within 2,000 ft of the surface, at or in the vicinity of the TAF airport, causing an indicated air speed loss or gain of 20 kts or more, and the forecaster determines the report(s) reflect a valid Non-Convective LLWS event rather than mechanical turbulence; or
• When Non-Convective vertical WS of 10 kts or more per 100 ft in a layer more than 200 ft thick are expected or reliably reported within 2,000 ft of the surface at, or in the vicinity of, the airport.
5.13.2.12 Forecast Change Indicator Groups.
Forecast change indicator groups are contractions that are used to subdivide the forecast period (24 hours for scheduled TAFs; less for amended or delayed forecasts) according to significant changes in the weather.
The forecast change indicators FM, TEMPO, and PROB are used when a change in any or all of the elements forecast is expected.
5.13.2.12.1 From (FM) Group (FMYYGGgg).
The change group FMYYGGgg (voiced as “from”) is used to indicate when prevailing conditions are expected to change significantly over a period of less than 1 hour. In these instances, the forecast is subdivided into time periods using the contraction FM, followed, without a space, by six digits, the first two of which indicate the day of the month and the final four, which indicate the time (in hours and minutes Z) the change is expected to occur.
While the use of a four-digit time in whole hours (e.g. 2100Z) is acceptable, if a forecaster can predict changes and/or events with higher resolution, then more precise timing of the change to the minute will be indicated. All forecast elements following FMYYGGgg relate to the period of time from the indicated date and time (YYGGgg) to the end of the valid period of the terminal forecast, or to the next FM if the terminal forecast valid period is divided into additional periods.
The FM group will be followed by a complete description of the weather
(i.e., self-contained), and all forecast conditions given before the FM group are superseded by those following the group. All elements of the TAF (surface wind, visibility, significant weather, clouds, obscurations, and when expected, Non-Convective LLWS) will be included in each FM group, regardless if they are forecast to change or not. For example, if forecast cloud and visibility changes warrant a new FM group but the wind does not, the new FM group will include a wind forecast, even if it is the same as the most recently forecast wind.
The only exception to this involves the significant weather group. If no significant weather is expected in the FM time period group, then significant
5-101 weather group is omitted. A TAF may include one or more FM groups, depending on the prevailing weather conditions expected. In the interest of clarity, each FM group starts on a new line of forecast text, indented five spaces.
Examples:
TAF KDSM 022336Z 0300/0324 20015KT P6SM BKN015 FM030230 29020G35KT 1SM +SHRA OVC005 TEMPO 0303/0304 30030G45KT 3/4SM -SHSN FM030500 31010G20KT P6SM SCT025...
A change in the prevailing weather is expected on the 3rd day of the month at 0230 UTC and the 3rd day of the month at 0500 UTC.
TAF KAPN 312330Z 0100/0124 13008KT P6SM SCT030 FM010320 31010KT 3SM -SHSN BKN015 FM010500 31010KT 1/4SM +SHSN VV007...
Note the wind in the FM010500 group is the same as the previous FM group, but is repeated since all elements are required to be included in a FM group.
5.13.2.12.2 TEMPO (YYGG/YeYeGeGe) Group.
The change-indicator group TEMPO YYGG/YeYeGeGe is used to indicate temporary fluctuations to forecast meteorological conditions that are expected to:
• Have a high percentage (greater than 50 percent) probability of occurrence;
• Last for one hour or less in each instance; and
• In the aggregate, cover less than half of the period YYGG to YeYeGeGe.
The first two digits (YY) are the day of the month for the start of the TEMPO. The next two digits (GG) are the starting hour (UTC). After the solidus (/), the next two digits (YeYe) are the ending day of the month, while the last two digits (GeGe) are the ending hour (UTC) of the TEMPO period.
Each TEMPO group is placed on a new line in the TAF. The TEMPO identifier is followed by a description of all the elements in which a temporary change is forecast. A previously forecast element that has not changed during the TEMPO period is understood to remain the same and will not be included in the TEMPO group. Only those weather elements forecast to temporarily change are required to be included in the TEMPO group.
5-102 TEMPO groups will not include forecasts of either significant weather in the vicinity (VC) or Non-Convective LLWS.
Examples:
TAF KDDC 221130Z 2212/2312 29010G25KT P6SM SCT025 TEMPO 2215/2217 30025G35KT 1 1/2SM SHRA BKN010...
In the example, all forecast elements in the TEMPO group are expected to be different than the prevailing conditions. The TEMPO group is valid on the 17 from 1500 UTC to 1700 UTC.
TAF KSEA 091125Z 0912/1012 19008KT P6SM SCT010 BKN020 OVC090 TEMPO 0912/0915 -RA SCT010 BKN015 OVC040...
In this example the visibility is not forecast in the TEMPO group. Therefore, the visibility is expected to remain the same (P6SM) as forecast in the prevailing conditions group. Also, note that in the TEMPO 0912/0915 group, all three cloud layers are included, although the lowest layer is not forecast to change from the initial time period.
5.13.2.12.3 PROB30 (YYGG/YeYeGeGe) Group.
The probability group, PROB30 YYGG/YeYeGeGe, is only used by NWS forecasters to forecast a low probability occurrence (30 percent chance) of a thunderstorm or precipitation event and its associated weather and obscuration elements (wind, visibility, and/or sky condition) at an airport.
The PRO B30 group is the forecaster’s assessment of probability of occurrence of the weather event that follows it. The first two digits (YY) are the day of the month for the start of the PROB30. The next two digits (GG) are the starting hour (UTC). After the solidus (/), the next two digits (YeYe) are the ending day of the month, while the last two digits (GeGe) are the ending hour (UTC) of the PROB30 period. PROB30 is the only PROB group used in NWS TAFs. Note that U.S. military and international TAFs may use the PROB40 (40 percent chance) group as well.
The PROB30 group is located within the same line of the prevailing condition group, continuing on the line below if necessary.
NWS TAFs do not use the PROB30 group in the first 9 hours of the TAF’s valid period, including amendments. Also, only one PROB30 group may be used in the initial forecast period and in any subsequent FM groups. Note that U.S. military and international TAFs do not have these restrictions.
5-103 PROB30 groups do not include forecasts of significant weather in the vicinity (VC) or Non-Convective LLWS.
Example:
FM012100 18015KT P6SM SCT050 PROB30 0123/0201 2SM TSRA OVC020CB In this example, the PROB30 group is valid on the 1st day of the month at 2300 UTC to the 2nd day of the month at 0100 UTC.
5.13.2.12.4 TAF Examples.
TAF KPIR 111140Z 1112/1212 13012KT P6SM BKN100 WS020/35035KT TEMPO 1112/1114 5SM BR FM111500 16015G25KT P6SM SCT040 BKN250 FM120000 14012KT P6SM BKN080 OVC150 PROB30 1200/1204 3SM TSRA BKN030CB FM120400 14008KT P6SM SCT040 OVC080 TEMPO 1204/1208 3SM TSRA OVC030CB TAF Terminal Aerodrome Forecast KPIR Pierre, South Dakota 111140 Prepared on the 11th at 1140 UTC 1112/1212 Valid from the 11th at 1200 UTC until the 12th at 1200 UTC 13012KT Wind 130 at 12 kts P6SM Visibility greater than 6 sm BKN100 Ceiling 10,000 broken WS020/35035KT Windshear at 2,000 ft, wind from 350 at 35 kts TEMPO 1112/1114 Temporary conditions between the 11 th day of the month at 1200 UTC and the 11th day of the month at 1400 UTC 5SM Visibility 5 statute miles BR Mist FM111500 From the 11th day of the month at 1500 UTC 16015G25KT Wind 160 at 15 kts gusting to 25 kts P6SM Visibility greater than 6 sm SCT040 BKN250 4,000 scattered, ceiling 25,000 broken FM120000 From the 12th day of the month at 0000Z 14012KT Wind 140 at 12 kts P6SM Visibility greater than 6 sm BKN080 OVC150 Ceiling 8,000 broken, 15,000 overcast PROB30 1200/1204 30 percent probability between the 12 th day of the month at 0000 UTC and the 12th day of the month at 0400 UTC 3SM Visibility 3 sm TSRA Thunderstorm with moderate rain showers
5-104 BKN030CB Ceiling 3,000 broken with cumulonimbus FM120400 From the 12th day of the month at 0400 UTC 14008KT Wind 140 at 8 kts P6SM Visibility greater than 6 sm SCT040 OVC080 4,000 scattered, ceiling 8,000 overcast TEMPO 1204/1208 Temporary conditions between the 12 th day of the month at 0400 UTC and the 12th day of the month at 0800 UTC 3SM Visibility 3 sm TSRA Thunderstorms with moderate rain showers OVC030CB Ceiling 3,000 overcast with cumulonimbus
TAF AMD KEYW 131555Z 1316/1412 VRB03KT P6SM VCTS SCT025CB BKN250 TEMPO 1316/1318 2SM TSRA BKN020CB FM131800 VRB03KT P6SM SCT025 BKN250 TEMPO 1320/1324 1SM TSRA OVC010CB FM140000 VRB03KT P6SM VCTS SCT020CB BKN120 TEMPO 1408/1412 BKN020CB TAF AMD Amended Terminal Aerodrome Forecast KEYW Key West, Florida 131555Z Prepared on the 13th at 1555 UTC 1316/1412 Valid from the 13th at 1600 UTC until the 14th at 1200 UTC VRB03KT Wind variable at 3 kts P6SM Visibility greater than 6 sm VCTS Thunderstorms in the vicinity SCT025CB BKN250 2,500 scattered with cumulonimbus, ceiling 25,000 broken TEMPO 1316/1318 Temporary conditions between the 13 th day of the month at 1600 UTC and the 13th day of the month at 1800 UTC 2SM Visibility 2 sm TSRA Thunderstorms with moderate rain showers BKN020CB Ceiling 2,000 broken with cumulonimbus FM131800 From the 13th day of the month at 1800 UTC VRB03KT Wind variable at 3 knots P6SM Visibility greater than 6 sm SCT025 BKN250 2,500 scattered, ceiling 25,000 broken TEMPO 1320/1324 Temporary conditions between the 13 th day of the month at 2000 UTC and the 14th day of the month at 0000 UTC 1SM Visibility 1 sm TSRA Thunderstorms with moderate rain showers OVC010CB Ceiling 1,000 overcast with cumulonimbus FM140000 From the 14th day of the month at 0000 UTC VRB03KT Variable wind at 3 knots P6SM Visibility greater than 6 sm VCTS Thunderstorms in the vicinity
5-105 SCT020CB BKN120 2,000 scattered with cumulonimbus, ceiling 12,000 broken TEMPO 1408/1412 Temporary conditions between the 14 th day of the month at 0800 UTC and the 14th day of the month at 1200 UTC BKN020CB Ceiling 2,000 broken with cumulonimbus
5.13.3 Issuance.
Scheduled TAFs prepared by NWS offices are issued four times a day, every 6 hours, according to the following schedule:
Table 5-19. TAF Issuance Schedule
SCHEDULED ISSUANCE VALID PERIOD ISSUANCE WINDOW 0000 UTC 0000 to 2400 or 0600 UTC 2320 to 2340 UTC 0600 UTC 0600 to 0600 or 1200 UTC 0520 to 0540 UTC 1200 UTC 1200 to 1200 or 1800 UTC 1120 to 1140 UTC 1800 UTC 1800 to 1800 or 2400 UTC 1720 to 1740 UTC
5.13.3.1 Minimum Observational Requirements for Routine TAF Issuance and Continuation.
The NWS forecaster must have certain information for the preparation and scheduled issuance of each individual TAF. Although integral to the TAF writing process, a complete surface (METAR/SPECI) observation is not required. Forecasters use the “total observation concept” to write TAFs with data including nearby surface observations, radar, satellite, radiosonde, model data, aircraft, and other sources.
If information sources, such as surface observations, are missing, unreliable, or not complete, forecasters will append AMD NOT SKED to the end of a TAF. The use of AMD NOT SKED indicates the forecaster has enough data, using the total observation concept, to issue a forecast but will not provide updates. This allows airport operations to continue using a valid TAF.
In rare situations where observations have been missing for extended periods of time (i.e., more than one TAF cycle of 6 hours), and the total observation concept cannot provide sufficient information, the TAF may be suspended by the use of NIL TAF.
5.13.3.2 Sites With Scheduled Part-Time Observations.
For TAFs with less than 24-hour observational coverage, the TAF will be valid to the end of the routine scheduled forecast period even if observations cease prior to that time. The time observations are scheduled to end and/or
5-106 resume will be indicated by expanding the AMD NOT SKED statement.
Expanded statements will include the observation ending time (AFT Y1Y1HHmm, e.g., AFT 120200), the scheduled observation resumption time (TIL Y1Y1HHmm, e.g., TIL 171200Z) or the period of observation unavailability (Y1Y1HH/YeYehh, e.g., 2502-2512). TIL will be used only when the beginning of the scheduled TAF valid period coincides with the time of the last observation or when observations are scheduled to resume prior to the next scheduled issuance time. When used, these remarks will immediately follow the last forecast group. If a routine TAF issuance is scheduled to be made after observations have ceased, but before they resume, the remark AMD NOT SKED will immediately follow the valid period group of the scheduled issuance. After sufficient data using the total observation concept has been received, the AMD NOT SKED remark will be removed.
Examples of Scheduled Part-Time Observations TAFs.
TAF AMD KRWF 150202Z 1502/1524 {TAF text} AMD NOT SKED 1505Z-1518Z= No amendments will be available between the 15th day of the month at 0500 UTC and the 15th day of the month at 1800 UTC due to lack of a complete observational set between those times.
TAF AMD KPSP 190230Z 1903/1924 {TAF text} AMD NOT SKED= Amendments are not scheduled.
5.13.3.3 Automated Observing Sites Requiring Part-Time Augmentation.
TAFs for automated stations without present weather and obstruction to vision information and have no augmentation or only part-time augmentation, are prepared using the procedures for part-time manual observation sites detailed in the previous paragraph, with one exception. This exception is the remark used when the automated system is unattended. Specifically, the time an augmented automated system is scheduled to go into unattended operation and/or the time augmentation resumes is included in a remark unique to automated observing sites: AMD LTD TO CLD VIS AND WIND (AFT YYHHmm, or TIL YYhhmm, or YYHH-YYhh), where YY is the date, HHmm is the time, in hours and minutes, of last augmented observation and hhmm is the time, in hours and minutes, the second complete observation is expected to be received. This remark, which does not preclude amendments for other forecast elements, is appended to the last scheduled TAF issued prior to the last augmented observation. It will also be appended to all subsequent amendments until augmentation resumes.
5-107 The AMD LTD TO (elements specified) remark is a flag for users and differs from the AMD NOT SKED AFT Z remark for part-time manual observation sites. AMD LTD TO (elements specified) means users should expect amendments only for those elements and the times specified.
Example:
TAF AMD KCOE 150202Z 1502/1524 text AMD LTD TO CLD VIS AND WIND 1505-1518= The amended forecast indicates that amendments will only be issued for wind, visibility, and clouds, between the 15th day of the month at 0500Z and the 15th day of the month at 1800Z.
An amendment includes forecasts for all appropriate TAF elements, even those not reported when the automated site is not augmented. If unreported elements are judged crucial to the TAF and cannot be adequately determined
(e.g., fog versus moderate snow), the TAF will be suspended (i.e., an amended TAF stating “AMD NOT SKED”).
AWOS systems with part-time augmentation, which the forecaster suspects are providing unreliable information when not augmented, will be reported for maintenance and treated the same as part-time manual observation sites. In such cases, the AMD NOT SKED AFT YY/aaZ remark will be used.
5.13.3.4 Non-Augmented Automated Observing Sites.
The TAF issued for automated observing stations with no augmentation may be suspended in the event the forecaster is notified of, or strongly suspects, an outage or unrepresentative data. Forecasters may also suspend TAF amendments when an element the forecaster judges to be critical is missing from the observation and cannot be obtained using the total observation concept. The term AMD NOT SKED will be appended, on a separate line and indented five spaces, to the end of an amendment to the existing TAF when appropriate.
5.14 Route Forecasts (ROFOR).
5.14.1 Issuance.
ROFORs are only issued by the NWS WFO in Honolulu, HI, twice per day for two routes: San Francisco, CA (KSFO), to Honolulu, HI (PHNL), and Santa Barbara, CA (KSBA), and PHNL. ROFORs are available on the NWS WFO Honolulu website.
5.14.2 ROFOR Amendments.
ROFORs are not required to be amended.
5.14.3 ROFOR Corrections.
ROFOR corrections are issued as soon as possible when erroneous data has been transmitted.