SUBJECT - RELIABILITY OF NORFOLK ISLAND FORECASTS
SAFETY DEFICIENCY
The meteorological forecasts for Norfolk Island are not
sufficiently reliable on some occasions to prevent pilots having to
carry out unplanned diversions or holding.
FACTUAL INFORMATION
Related Occurrences
During the period 1 January 1998 to 31 March 1999, occurrences
involving unforecast or rapidly changing conditions at Norfolk
Island reported to the Bureau included the following:
199801482
A British Aerospace 146 (BAe146) aircraft was conducting a regular
public transport (RPT) passenger service from Sydney to Norfolk
Island. The terminal area forecast (TAF) for Norfolk Island
indicated that cloud cover would be 3 octas with a cloud base of
2,000 ft. Approaching Norfolk Island, the crew found that the area
was completely overcast. After conducting an instrument approach,
they determined that the cloud base was 600 ft, which was less than
the alternate minima. Fuel for diversion to an alternate airfield
was not carried on the flight because the forecast had not
indicated any requirement.
199802796
Before a Piper Navajo Chieftain aircraft departed for an RPT
passenger service from Lord Howe Island to Norfolk Island, the TAF
for Norfolk Island did not require the carriage of additional fuel
for holding or for diversion to an alternate airfield.
Subsequently, the TAF was amended to require 30 minutes holding and
then 60 minutes of holding. The pilot later advised that he became
aware of the deteriorating weather at his destination only after he
had passed the planned point of no return (PNR). However, the
aircraft was carrying sufficient fuel to allow it to hold at
Norfolk Island for 60 minutes. When the aircraft arrived in the
Norfolk Island circuit area, the pilot assessed the conditions as
unsuitable to land due to low cloud and rainshowers. After
approximately 45 minutes of holding, the weather conditions
improved sufficiently for the pilot to make a visual approach and
landing.
199804317
A BAe146 aircraft was conducting an RPT passenger service from
Brisbane to Norfolk Island. When the crew were planning the flight,
the Norfolk Island TAF included a steady wind of 10 kt and
thunderstorm conditions for periods of up to 60 minutes.
Approximately 30 minutes after the aircraft departed, the TAF was
amended to indicate a mean wind speed of 20 kt with gusts to 35 kt.
As the aircraft approached its destination, the Unicom operator
reported the wind as 36 kt with gusts to 45 kt. The crew attempted
two approaches to runway 04 but conducted a go-around on each
occasion because of mechanical turbulence and windshear. The pilot
in command then elected to divert the aircraft to Auckland. The
wind gusts at Norfolk Island did not decrease below 20 kt for a
further 3 hours.
199900604
While flight planning for an RPT passenger service from Lord Howe
Island to Norfolk Island, the pilot of a Piper Navajo Chieftain
found that the TAF required the carriage of fuel sufficient for a
diversion to an alternate aerodrome. As the aircraft was unable to
carry sufficient fuel for the flight to Norfolk Island and then to
an alternate aerodrome, the flight was postponed. Later in the day,
the forecast was amended to require the carriage of 60 minutes of
holding fuel and the flight departed carrying the additional fuel.
Approximately 20 minutes after the aircraft departed Lord Howe
Island and more than one hour before it reached its point of no
return (PNR), the TAF was amended again to require the carriage of
alternate fuel. The pilot did not request or receive this amended
forecast and so continued the flight.
Following the flight's arrival overhead Norfolk Island, the pilot
conducted a number of instrument approaches but was unable to land
the aircraft due to the poor visibility. After being advised of
further deteriorations in conditions, the pilot made an approach
below the landing minima and landed in foggy conditions with a
visibility of 800m. Subsequent investigation determined that the
actual conditions at Norfolk Island were continuously below
alternate minima for the period from 2.5 hours before the aircraft
departed from Lord Howe Island until 6 hours after the aircraft
landed.
Meteorological information
The Norfolk Island Meteorological Observing Office, which is
staffed by four observers, normally operates every day from 0400
until 2400 Norfolk Island time. When one or more observers are on
leave, the hours are reduced to 0700 until 2400 daily. Hourly
surface observations by the observers, or by an automatic weather
station when the office is unmanned, are transmitted to the Sydney
Forecasting Office where they are used as the basis for the
production and amendment of TAFs and other forecasts.
Weather conditions are assessed by instrument measurements, for
example, wind strength, temperature and rainfall, or by visual
observation when observers are on duty, for example, cloud cover
and visibility. There is no weather-watch radar to allow the
detection and tracking of showers, thunderstorms and frontal
systems in the vicinity of the island. The wind-finding radar on
Norfolk Island is used to track weather balloons to determine upper
level winds six-hourly when observers are on duty. It cannot detect
thunderstorms or rainshowers.
Pilots in the Norfolk Island area can contact the Met Office staff
on a discrete frequency for information about the current weather
conditions.
The reliability of meteorological forecasts is a factor in
determining the fuel requirements. As forecasts cannot be 100%
reliable, some additional fuel must be carried to cover deviations
from forecast conditions.
A delay of one hour or more can exist between a change occurring in
the weather conditions and advice of that change reaching a pilot.
The change has to be detected by the observer or automatic weather
station and the information passed to the Forecasting Office. After
some analysis of the new information in conjunction with
information from other sources, the forecaster may decide to amend
the forecast. The new forecast is then issued to Airservices
Australia and disseminated to the Air Traffic Services (ATS) staff
who are in radio contact with the pilot. It is then the pilot's
responsibility to request the latest forecast from ATS.
Alternate minima
Alternate minima are a set of cloud base and visibility conditions
which are published for each airfield that has a published
instrument approach procedure. The alternate minima are based on
the minimum descent altitude and minimum visibility of each of the
available instrument approaches. When the forecast or actual
conditions at an airfield decrease below the alternate minima,
aircraft flying to that airfield must either carry fuel for flight
to an alternate airfield or fuel to allow the aircraft to remain
airborne until the weather improves sufficiently for a safe landing
to be conducted.
A pilot flying an aircraft that arrives at a destination without
alternate or holding fuel and then finds that the weather is below
landing and alternate minima is potentially in a hazardous
situation. The options available are:
1. to hold until the weather improves; however, the fuel may be
exhausted before the conditions improve sufficiently to enable a
safe landing to be made;
2. to ditch or force-land the aircraft away from the aerodrome in a
area of improved weather conditions, if one exists; or
3. attempt to land in poor weather conditions.
All of these options have an unacceptable level of risk for public
transport operations.
The alternate minima for Norfolk Island are:
1. cloud base at or above 1,069 ft above mean sea level (AMSL) and
visibility greater than 4.4 km for category A and B aircraft;
and
2. cloud base at or above 1,169 ft AMSL and visibility greater than
6 km for category C aircraft.
The available alternate aerodromes for Norfolk Island are La
Tontouta in Noumea (431 NM to the north), Lord Howe Island (484 NM
to the south-west) and Auckland NZ (690 NM to the south-east). Lord
Howe Island may not be suitable for many aircraft due to its short
runway. Flight from Norfolk Island to an alternate aerodrome
requires a large amount of fuel, which may not be carried unless
required by forecast conditions or by regulations.
Australian regulations
Prior to 1991, the then Civil Aviation Authority published specific
requirements for flights to island destinations. For example,
flights to Lord Howe Island were required to carry fuel for flight
to an alternate aerodrome on the mainland Australia, and flights to
Norfolk Island and Cocos Island, where no alternate aerodromes were
available, were required to carry a minimum of 2 hours of holding
fuel.
In 1991, Civil Aviation Regulation (CAR) 234 was enacted. This
regulation provided that an aircraft would not commence a flight
unless the pilot in command and the operator had taken reasonable
steps to ensure that the aircraft was carrying sufficient fuel and
oil to enable the proposed flight to be undertaken in safety. The
regulation did not specify the method for determining what was
sufficient fuel in any particular case. Civil Aviation Advisory
Publication (CAAP) 234-1(0) dated March 1991, provided guidelines
which set out one method that could be used to calculate fuel
requirements that would satisfy CAR 234. CAAP 234-1 did not contain
any special considerations or requirements when planning a flight
to an island destination.
In August 1999, Civil Aviation Order 82.0 was amended to require
all charter passenger-carrying flights to Norfolk Island and other
remote islands to carry fuel for the flight to their destination
and to an alternate aerodrome. The alternate aerodrome must not be
located on a remote island. This requirement to carry additional
fuel does not apply to regular public transport flights to a remote
island.
European Joint Aviation Regulation
The European Joint Aviation Regulation (Operations) 8.1.7.2 states:
"at the planning stage, not all factors which could have an
influence on the fuel used to the destination aerodrome can be
foreseen. Consequently, contingency fuel is carried to compensate
for ... deviations from forecast meteorological conditions."
Traffic levels
In February 2000, approximately 11 regular public transport
aircraft land at Norfolk Island every week, including Boeing 737
and Fokker F100 aircraft. An additional 20 instrument flight rules
and 12 visual flight rules flights are made to the island every
week by a variety of business and general aviation aircraft.
ANALYSIS
Reports to the Bureau, including those detailed in the factual
information section above, indicate that the actual weather
conditions at Norfolk Island have not been reliably forecast on a
number of occasions. Current regulations do not require pilots of
regular public transport aircraft to carry fuel reserves other than
those dictated by the forecast weather conditions. The safety
consequences of an unforecast deterioration in the weather at an
isolated aerodrome like Norfolk Island may be serious.
The present level of reliability of meteorological forecasts and
the current regulatory requirements are not providing an adequate
level of safety for passenger-carrying services to Norfolk
Island.
SAFETY ACTION
As a result of these occurrences, the Civil Aviation Safety
Authority has commenced a project to review the fuel requirements
for flights to remote islands.
The Australian Transport Safety Bureau (formerly the Bureau of
Air Safety Investigation) recommends that the Bureau of Meteorology
should review the methods used and resources allocated to
forecasting at Norfolk Island with a view to making the forecasts
more reliable.
In response to your letter of 25 February 2000 relating to Air
Safety Recommendation 20000040 and the reliability of
meteorological forecasts for Norfolk Island, the Bureau of
Meteorology has explored a number of possible ways to increase the
reliability of forecasts for flights to the Island.
There are several factors which determine the accuracy and
reliability of the forecasts. The first is the quality and
timeliness of the baseline observational data from Norfolk Island
itself. The second is the information base (including both
conventional surface observational data and information from
meteorological satellites and other sources) in the larger Eastern
Australia-Southwest Pacific region. The third is the overall
scientific capability of the Bureau's forecast models and systems
and, in particular, their skill in forecasting the behaviour of the
highly localised influences which can impact on conditions on
Norfolk Island. And the fourth relates to the speed and
responsiveness with which critical information on changing weather
conditions (forecast or observed) can be conveyed to those who need
it for immediate decision making.
As you are aware, the Bureau commits significant resources to
maintaining its observing program at Norfolk Island. While the
primary purpose of those observations is to support the overall
large-scale monitoring and modelling of meteorological conditions
in the Western Pacific, and the operation of the observing station
is funded by the Bureau on that basis, it is staffed by highly
trained observers with long experience in support of aviation. As
far as is possible with available staff numbers, the observers are
rostered to cover arrivals of regular flights and rosters are
adjusted to cover the arrival of notified delayed flights.
The Norfolk Island Terminal Aerodrome Forecast (TAF) is produced by
experienced professional meteorologists located in the Bureau's New
South Wales Regional Forecasting Centre in Sydney. The terminal
forecast provides predictions of wind, visibility, cloud amount and
base height and weather routinely every six hours. Weather
conditions are continuously monitored and the terminal forecast is
amended as necessary in line with air safety requirements. The
forecasters have full access to all the Bureau's synoptic
meteorological data for the region and guidance material from both
Australian and overseas prediction models. As part of the
forecasting process, they continuously monitor all available
information from the region including the observational data from
Norfolk Island itself. When consideration of the latest
observational data in the context of the overall meteorological
situations suggests the need to modify the terminal forecast,
amendments are issued as quickly as possible.
Despite the best efforts of the Bureau's observing and forecasting
staff, it is clear that it is not always possible to get vital
information to the right place as quickly as it is needed and the
inherent scientific complexity of weather forecasting means that
occasional serious forecast errors will continue to be unavoidable.
That said, the Bureau has carefully reviewed the Norfolk Island
situation in order to find ways of improving the accuracy and
reliability of its forecasts for aviation through a range of short
and longer-term means.
As part of its strategic research effort in forecast improvement,
the Bureau of Meteorology Research Centre is undertaking a number
of projects aimed at increasing scientific knowledge specifically
applied to the provision of aviation weather services. Research
projects are focussed on the detection and prediction of fog and
low cloud and are based on extensive research into the science of
numerical weather prediction. However, with the current level of
scientific knowledge, the terminal forecasts for Norfolk Island
cannot be expected to be reliable 100 percent of the time. Based on
figures available for the period January 1998 to March 2000 (some
12 000 forecast hours), the Bureau's TAF verification system shows
that for category A and B aircraft when conditions were forecast to
be above the minima, the probability of encountering adverse
weather conditions at Norfolk Island airport was 0.6%.
As part of its investigations, the Bureau has considered the
installation of a weather watch radar facility at Norfolk Island
with remote access in the NSW Regional Forecast Centre. Although
routine radar coverage would enable the early detection of
precipitation in the vicinity of the Island, investigations suggest
that the impact of the radar images in improving forecast accuracy
would be on the time-scale of one to two hours. This time frame is
outside the point of no return for current aircraft servicing the
route. It was concluded that the installation of a weather watch
radar would be relatively expensive and would only partially
address the forecast deficiencies identified in Air Safety
Recommendation R20000040. The Bureau will however keep this option
under review.
To increase the responsiveness of the terminal forecasts to changes
in conditions at Norfolk Island, the Bureau has issued instructions
to observing staff to ensure forecasters at the Sydney RFC are
notified directly by telephone of any discrepancies between the
current forecast and actual conditions. This arrangement will
increase the responsiveness of the system particularly during
periods of fluctuating conditions. In addition the Bureau has
provided the aerodrome manager with access to a display of the
latest observations to ensure the most up to date information is
relayed to aircraft.
The Bureau is actively participating in the review of fuel
requirements for flights to remote islands being undertaken by the
Civil Aviation Safety Authority.
I regret the delay in replying to your letter but the Bureau has
felt it important to look carefully at all aspects of the Norfolk
Island forecast situation and consider the full range of
possibilities for forecast improvement within the resources
available to us. We will continue to work on forecast improvement
for Norfolk Island as resources permit.
