AMOFSG/7-SN No. 16
26/5/08
AERODROME METEOROLOGICAL OBSERVATION AND FORECAST
STUDY GROUP (AMOFSG)
SEVENTH MEETING
Montréal, 9 to 12 September 2008
Agenda Item 6: Aerodrome forecasts
PRODUCTION OF 24-HR TAFS AT ALL UNITED KINGDOM AERODROMES
(Presented by Colin Hord)
SUMMARY
This study note reviews the issues associated with adopting 24 hour TAFs at all
United Kingdom aerodromes and puts forward a number of suggestions on how
this may be achieved without significantly increasing forecasting resources..
1.
INTRODUCTION
1.1
The introduction of meteorological code and related procedural changes associated with
Amendment 74 to Annex 3 — Meteorological Service for International Air Navigation will significantly
change the requirements for the provision of aerodrome forecasts for international air navigation.
1.2
The following amendment to Annex 3 Part I, Chapter 6 related to the issuance of TAF
will be implemented on 5 November 2008.
6.2.6 Recommendation: - The period of validity of a routine TAF should be not less than
6 hours nor more than 30 hours; the period of validity should be determined by regional air
navigation agreement. Routine TAF valid for less than 12 hours should be issued every 3 hours
and those valid for 12 to 30 hours should be issued every 6 hours.
6.2.7 When issuing TAF, meteorological offices shall ensure that not more than one TAF is
valid at any given time.
(10 pages)
106735639
AMOFSG/7-SN No. 16
-2-
1.3
Following consideration at the seventeenth meeting of the Meteorology sub-group
(MET/G/17) of the European Air Navigation Planning Group (EANPG) and subsequently confirmed by
ICAO state letter, the European (EUR) air navigation plan (ANP) Volume 1 Basic ANP, Part VI - MET
has been amended to reflect the global standardization of TAF issuance as follows::
a) routine TAF should be issued as required in respect of operational needs.
They should have a period of validity of 9 hours, or of either 24 or 30 hours and be
issued for designated aerodromes as specified in FASID Table MET-1A.
b) the periods of validity for 9-hour TAF should commence at 00, 03, 06, 09, 12, 15, 18
and 21 UTC, and of TAF valid 24 or 30 hours at 00, 06, 12 and 18 UTC. The periods
of validity should be adapted to the hours of operation of the aerodrome as agreed
between the meteorological authorities and the operators concerned. The scheduled
international exchange of TAF should be completed 30 minutes before
commencement of the period of validity.
c) the forecast maximum and minimum temperature together with their respective dates
and times of occurrence should be included in aerodrome forecasts with a period of
validity of 24 or 30 hours for certain aerodromes as agreed between the
meteorological authority and the operators concerned.
1.4
Additionally, it is noted that United Kingdom operators as well as IATA have requested
24-hour TAF to be produced for all aerodromes, including those non-AOP aerodromes listed in the
SADIS User Guide, Annex 1, whilst MET/G/17 has considered the merits of issuing all TAF every
3 hours.
1.5
This paper reviews the impact of Amendment 74 on United Kingdom TAF production
and considers the issues raised by the new proposals outlined above.
2.
DISCUSSION
2.1
In the United Kingdom from November 2008 there will be 54 aerodromes in receipt of a
TAF, four 30 hour TAF locations, fourteen 24-hour TAF locations and thirty six 9-hour TAF locations (of
which 16 are AOP aerodromes and 20 are non-AOP aerodromes). In the United Kingdom aerodromes that
operate for 24 hours a day are almost all issued with a 24 hour TAF.
2.2
The majority of United Kingdom aerodromes do not operate 24 hours a day and close for
some period overnight, this can range from 3 to over 8 hours at some smaller airports.
2.3
Since November 2007, airports that issue AUTO METARs when the airport is nonoperational have been able to have a TAF issued based on the AUTO METAR without having to wait for
METARs that are produced by an accredited observer. However this requires the aerodrome to produce
AUTO METARs that are compliant with ICAO Annex 3, i.e. contain all the required elements as per
Chapter 4, Para 4.5.1.
2.4
TAF verification is carried out routinely for all airports, and provides an important tool
for ensuring that forecasting standards are being maintained. TAFs can only be verified against a METAR
that contains all the required parameters for the verification.
-3-
AMOFSG/7-SN No. 16
2.5
There have been a number of requests from United Kingdom operators and more recently
the International Air Transport Association (IATA) to issue 24-hr TAFs from aerodromes that are not
operational 24 hours a day. This would allow TAFs to be used for longer range flight planning,
especially when planning for multi-sector flights or for flights that may be due to land close to the
reopening of an aerodrome. It should be noted that in this context a TAF only becomes of greater use
when the validity time extends past the reopening of the aerodrome.
2.6
METG/17 considered further additional proposals for simplifying the TAF issuance rules
whereby a TAF is issued every 3 hours regardless of the validity period and a separate study note
discusses these issues.
2.7
Whilst the benefits to airlines and others of having a 24-hr TAF for each aerodrome that
enables improved forward planning are clear, there are 5 key meteorological issues associated with this
proposal and the issuance of such TAF every 3 hours, from both an operational and regulatory
perspective. These issues will be considered in turn:
Issue 1
Nugatory forecasting
When an aerodrome is closed it cannot be used by any operators, as a consequence the
forecast for this period of time is unable to be utilised, while this may be a relatively small amount of time
for some airports it could be as much as half the TAF period in some locations. In the United Kingdom it
is the practise to only forecast for the period when the aerodrome is open. The additional time that the
forecaster would have to spend on forecasting for this unusable period would require additional resources
and ultimately increase TAF production costs.
Issue 2
Constant review
Annex 3 states in Chapter 6:
6.2.4 Meteorological offices preparing TAF shall keep the forecasts under continuous
review and, where necessary, shall issued amendments promptly.
6.2.5 TAF that cannot be kept under continuous review shall be cancelled.
In the United Kingdom a forecaster is required to keep the TAF under continuous review
by monitoring the routine METAR, Should an aerodrome cease to issue METARs United Kingdom
policy states that the forecaster must cancel the TAF. It should be noted that each TAF cancellation is
additional work and would be a significant task if all 36 non H24 aerodromes that currently receive a 9 hr
TAF were to be issued with a 24 Hr TAF and each individual TAF needed to be cancelled upon closure of
the aerodrome.
Issue 3
Verification
Routine verification for all TAFs is carried out in the United Kingdom ensuring that
forecast quality is being maintained, verification is an essential element of any Quality Management
System. If a forecast were issued for a period of time when there might be no observations (i.e. when the
aerodrome is closed) it would not be able to be verified. A change in working practises would be required
to issue a TAF that spanned the time an aerodrome was closed. Ensuring that the forecaster maintained
the level of forecasting quality for that time may prove to be challenging since they would be aware that
the forecast could neither have its accuracy validated nor be used. This could be mitigated by the use of
AUTO METAR, but for a number of States, including the United Kingdom, the cost of aerodrome
AMOFSG/7-SN No. 16
-4-
meteorological equipment is the responsibility of the aerodrome to procure and maintain. Many
aerodromes are not in a position to equip their met offices to be able to produce such observations.
Issue 4
Non standardised TAF issue times
Currently the United Kingdom issues a TAF to an aerodrome once the meteorological
office has received two METARs. It is noted that these times often do not relate to the standard TAF issue
times, for example an aerodrome that becomes operational at 0800 and produces two METARs before
this time would be issued with a 0806 TAF rather than the standard 0606 TAF. In this case the TAF is
issued as a late addition (retarded) to the TAF bulletin. It would only be possible to adhere to the standard
issue times if aerodromes were to issue AUTO METAR.
Issue 5
3-hourly updates
The proposed move to 3-hourly updates of all TAF leads to a significant increase in the
number of TAF that would be required to be produced in the United Kingdom, with the associated
resource implications. Clearly the forecaster must be in a position to issue amendments to forecasts if they
reach the agreed amendment criteria but this is based on a continuous evolution of the forecaster’s
understanding of the meteorological conditions and has a high priority over routine work. This is very
different to a routine issue of a large number of TAF, which even though modern IT systems can be used,
still takes a significant amount of input from the forecaster and diverts their attention from other work and
monitoring of conditions. Further information on the additional amount of TAFs produced is given in the
appendix to this paper.
2.8
Notwithstanding the above, the United Kingdom supports the intentions of IATA’s
proposal for improved flight planning but suggests that in order to address the issues above, some
additional changes are considered by the group:
a) remove or amend the requirement to keep the forecast under continuous review
(an amendment to Annex 3 could state only keep the TAF under continuous review if
(i) the aerodrome is operating during its notified hours of operation or (ii) there is a
continuous supply of observations
This is not favoured as it appears to dilute the current Annex 3 standard to maintain a
high-quality TAF and to issue amendments to it as soon as the forecaster becomes aware
that the forecast has or will fall outside appropriate amendment critieria;
b) not all aerodromes produce 24-hr TAF
It is speculated that there may be a difference of opinion between users over which
aerodromes should have 24-hr TAF and which should not, particularly in light of cost
recovery issues pertaining to the nomination of diversion aerodromes;
c) use of NIL within a TAF
At present it is only possible to use NIL with a TAF, as the missing forecast identifier
(see Annex 3 Appendix 5 Table A5-1). However, it (or some other indication) could be
used within the body of the text to indicate that for a given period no forecast has been
prepared, i.e. when the aerodrome is non operational for that time.
-5-
AMOFSG/7-SN No. 16
An example could be seen as follows, for an aerodrome that is closed between 2200 and
0500 UTC:
TAF EGNH 060510Z 0612/0712 35010KT 7000 -RASN BKN020
TEMPO 0612/0614 2500 -SN BKN008
BECMG 0613/0615 9999 NSW
PROB30 TEMPO 0615/0621 5000 SHRASN SCT030CB
0622/0705 NIL FM 060500 4000 BR BECMG 0706/0708 9999 NSW
PROB40 TEMPO 0709/0712 3000 -SNSH SHRASN BKN010; and
d) permit the use of non-standard validity times but only in the case of aerodromes that
open between standard validity periods
3.
CONCLUSION
3.1
Aerodromes should be encouraged by the operators to install automated observing
equipment that enable AUTO METARs to be issued during non-operational hours, so ensuring that the
TAF can be kept under constant review and not cancelled as soon as the aerodrome closes.
3.2
Increasing the TAF length for both AOP and non AOP aerodromes to 24 hours is likely
to have a significant impact on the forecasting resources required to complete this task and would likely
lead to increase costs for production. Careful consideration should be given to which aerodromes should
be provided with 24 hr TAFs.
3.3
Consideration should be given to allow a the TAF to contain a “NIL” enabling the
forecaster the ability to only provide a forecast for the period in which the aerodrome is operational. This
would ensure that the forecast provided could be kept under constant review, since there was no forecast
for the period when there were no observations were being provided as the aerodrome was closed This
would also ensure that there was no nugatory forecasting, which as been noted can be significant for
aerodromes that only open for relatively short periods of the day.
3.4
In view of the significant increase in the number of “TAF hours” that are required when a
24-hour TAF is issued every 3 hours, there should be careful consideration of the costs versus the benefits
before such a requirement is introduced.
4.
ACTION BY THE GROUP
4.1
The group is invited to consider the issues raised in this paper and, if necessary, ask the
Secretary to develop appropriate revisions to the appendix to this paper.
————————
APPENDIX
EXAMPLE FORECAST TIMELINES
Some example forecast timelines are provided below (see Tables 1 & 2) for two typical airports in
the UK that currently receive a 9 hr TAF, Blackpool (AOP listed) which closes from 2200 – 0600 and
Campbeltown (non AOP listed) which has limited traffic and is closed from 1700-0800.
For each airport three example timelines are shown, a 9 Hr TAF and a 24 Hr TAF issued at 6 and 3
hourly intervals.
Each timeline is colour coded, orange shows when the aerodrome is open and the TAF is valid, red
indicates the aerodrome is closed for that period of the TAF and white indicates that no TAF has been issued
as the aerodrome is not open.
At present the total number of hours for which a TAF should be produced each day for Blackpool is
54, however this is reduced to 47 hours by only issuing the TAF for the hours when the aerodrome is open.
At Campbeltown there are 38 hours for which the 9 Hr TAF should be produced each day, here a
reduction to 26 hours is made by only issuing the TAF for the operational hours.
For the 24 hour TAFs, it can be seen that when issuing the TAF 6 hourly the number of hours to be
forecasted at Blackpool rises to 90, however 26 hours (29%) are for when the aerodrome is closed and the
forecast cannot be utilised.
In the case of Campbeltown there are 36 hours of the TAF that would not be able to be utilised
which represents 49% of the 74 hours for which a TAF is produced.
Were the forecast be issued every 3 hours the number of TAF hours that are required to be forecast
rises significantly, for Blackpool this becomes 183 hours of which 55 hours are for when the airfield is
closed (30%). In the case of Campbeltown the number of TAF hours is 154 of which 80 are for when the
airport is closed (52%).
AMOFSG/7-SN No. 16
A-2
Appendix
To summarize:
Total Hours of TAF
required in each 24 hour
period
9 Hour TAF
Blackpool
54 hours
Campbeltown
38 hours
24 Hour TAF
24 Hour TAF
issued 6 Hourly
issued 3 Hourly
90 hours
183 hours
29 % when closed
30 % when closed
74 hours
154 hours
49% when closed
52% when closed
AMOFSG/7-SN No. 16
Blackpool
9Hour TAF
0
6
0
8
Hours
forecasted
A-3
1
0
1
2
1
4
1
6
1
8
2
0
2
2
24 Hour TAF
6 hourly
0
0
0
2
0
4
0
6
0
8
1
0
1
2
1
4
1
6
1
8
2
0
2
2
0
0
0
2
0 0
4 5 TAF CNL
Hours
forecasted
while
aerodrome
open
9
9
9
9
9
9
X
9
7
X
9
4
0
0
3
3
6
6
54
47
7 hrs forecasted when closed
X
X
X
X
24 hour TAF
3 hourly
24
16
24
16
24
16
18
16
90
64
26 hrs forecasted when closed
X
X
X
X
X
X
X
X
24
16
24
16
24
16
24
16
24
16
24
16
18
16
21
16
183
128
55 hrs forecasted when closed
Table 1 - Forecast Timeline for Blackpool
Table 2 Forecast Timeline for Campbeltown
Appendix
Campbelltown
Hours
forecasted
9 Hour TAF
AMOFSG/7-SN No. 16
Appendix
0
0
6
8
1
0
1
2
1
4
1
6
1
8
2
0
2
2
0
0
0
2
0
4
0
6
0
8
1
0
1A-41
2
4
1
6
1
8
2
0
2
2
0
0
0
2
0 0
4 5
Hours
forecasted
if TAF
ceases at
airport
closure
6
6
X
9
8
X
9
5
X
9
2
0
0
0
0
1
1
4
4
38
26
12 hrs forecasted when closed
24 Hour TAF
6 hourly
X
X
X
X
24
11
24
24
10
9
16
9
74
53
36 hrs forecasted when closed
24 Hour TAF
3 hourly
X
X
X
X
X
X
X
X
24
11
24
24
24
24
24
24
10
9
13
9
16
9
19
9
154
119
80 hrs forecasted when closed
— END —