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Recommendation issued to: Bureau Of Meteorology

Recommendation details
Output No: R20000040
Date issued: 22 February 2000
Safety action status:
Background:

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.

Output text

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.

Initial response
Date issued: 27 April 2000
Response from: Bureau Of Meteorology
Action status: Closed - Accepted
Response text:

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.

 
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Last update 05 April 2012