de Havilland Canada DHC-8-201, VH-SDE, Emerald, Queensland, on 1 May 2003

The recorded flight data indicated that the influence of the left to right lateral acceleration immediately prior to, and just after, touchdown was sufficient to overcome the countering influence of the aircraft's orientation and the rudder position. Information regarding the prevailing weather conditions, along with the recorded flight data, indicated that the aircraft encountered significant windshear immediately before touchdown. The crew were unable to prevent the aircraft from touching down prior to their intended touchdown point. The windshear was accompanied by very heavy rainfall which reduced visibility to such an extent that the crew lost visual reference with the runway centreline and were unable to maintain directional control of the aircraft. Both the windshear and the heavy rain were characteristic of thunderstorm activity. The wet runway would have reduced the coefficient of friction between the aircraft's tyres and the runway surface.

The crew was surprised by the sudden and significant change in the weather conditions at the time of landing. Had they been aware of the proximity of the thunderstorm to the aerodrome, they would probably have delayed their landing until conditions improved. Against that background, it is relevant to discuss the information the crew was aware of regarding the thunderstorm.

1. The 1827 SPECI that the crew received at 1831 indicated that the Emerald weather had changed significantly from that reported in the 1800 Emerald METAR. Subsequent events indicated that the crew took a number of steps to gain further information regarding the Emerald weather.
2. The dark night conditions and absence of lightning activity when the aircraft was on final approach prevented the crew from visually assessing the location, size, and movement of the thunderstorm. The crew therefore had to rely on other sources of information regarding the storm.
3. The crew confirmed the presence of weather, consistent with a thunderstorm, near Emerald from the aircraft's weather radar, which provided an explanation for the change in conditions advised in the 1827 SPECI.
4. The dark conditions may have limited the value of the company agent's assessment regarding the movement of the thunderstorm. Nevertheless, the agent's advice that the storm would pass west of the aerodrome probably contributed to the crew's decision to continue the approach.
5. The crew's report that they could see the runway lights throughout the approach indicated that there was little, if any, rain or cloud between the aerodrome and the aircraft during that period. Those conditions would have strongly reinforced the crew's apparent perception that the thunderstorm posed no hazard to the progress of the flight.

Considering what the crew knew about the weather conditions at Emerald, their decision to continue the approach was reasonable. However, BoM and Airservices were aware of additional information about the weather conditions at Emerald, and further information was probably available from the aircraft's onboard weather radar. This additional information was potentially significant in the context of the flight crew's decision-making.

1. Despite the lack of detailed information available to the investigation regarding the speed and direction of movement of the thunderstorm, it seems very likely that it was close to the aerodrome during the aircraft's final approach. Therefore, it is possible that additional use of the aircraft weather radar during that period may have enabled the crew to better assess the conditions ahead.
2. Had the crew received all the SPECI reports as transmitted by the Emerald AWS (including all the wind gust data), their awareness regarding the significance of the thunderstorm activity may have been greater. In turn, that may have prompted them to seek more information, for example by reference to the weather radar, and/or amend their arrival procedure.
3. Because the controller did not have visibility or cloud height data for Emerald (the two parameters that generally determine alternate minima), the information available to the controller to assess whether the SPECI reports justified a hazard alert was incomplete and reduced the likelihood that a hazard alert would be issued. Even if visibility and cloud height information was available, the additional information the controller required to determine if a weather report such as a SPECI indicated that conditions had deteriorated below the alternate minima was not easily accessible, and reduced the likelihood that a hazard alert would be issued.
4. BoM removed from SPECI reports data on wind gusts that were not 10 kts or more greater than the mean wind speed. Therefore, information was not available to the air traffic controller, which may have influenced the controller's decision whether or not to pass the SPECI reports to the flight crew.
5. The 1842 and 1846 SPECI reports indicated a rapid and significant change in wind direction, characteristic of thunderstorm activity. The MATS requirement that a hazard alert should only have been issued if conditions were unexpected and critical reduced the likelihood that such SPECI reports would be passed to flight crew, even though there are occasions when such information constitutes a safety hazard. For example, if the wind had backed after 1827 rather than veered, the aircraft would have encountered a significant tailwind during the landing.
6. At 1852, four minutes after the crew advised that they were changing to the Emerald MBZ frequency, and coincident with the aircraft's estimate for arrival at Emerald, Airservices received a SPECI report which indicated that the wind had veered a further 20 degrees and the gust strength was 31 kts. The controller did not pass that SPECI report to the crew. The MATS requirement that hazard alerts be directed to aircraft maintaining continuous communications with ATS reduced the likelihood that the SPECI report would have been passed to the crew. The crew were still monitoring the area frequency, even though they had earlier advised that they were changing to the Emerald MBZ frequency.

The occurrence resulted in minor damage to the aircraft. Had the aircraft encountered the windshear slightly earlier in the approach, at a point where there was insufficient altitude available for the crew to establish a positive rate of climb and go around, the consequences of this occurrence could have been far more serious.

The recorded rainfall rate was within the BoM classification of `violent'. Visibility in such conditions would have been very limited and the benefit of windscreen wipers in such conditions was probably marginal at best, as indicated by the loss of visibility reported by the crew when they encountered the heavy rain. Therefore, the failure of the first officer's wiper when high wiper speed was selected was unlikely to have contributed significantly to the loss of directional control.

Flight crew are generally in the best position to assess the significance of operational information such as weather reports. However, currently the responsibility for assessment and transmission of such information remains with air traffic controllers. This situation is likely to exist until advanced technology systems for the provision of operational information direct to flight crews are available. One such system, an airborne internet communication system, is part of the US National Aeronautics and Space Administration-led Small Aircraft Transportation System project.

The crew lost directional control of the aircraft on the runway after landing due to thunderstorm-related strong wind and reduced visibility in heavy rain.

The crew did not refer to the on-board weather radar during final approach.

The crew was not provided with relevant information regarding the Emerald weather of which BoM and Airservices were aware.

BoM processing of METAR and SPECI information, along with Airservices procedures for passing operational information to flight crew during flight, reduced the likelihood that SPECI reports would be transmitted to the crew.

Local Safety Action

Airservices Australia

Airservices Australia has advised the ATSB that they are conducting an in-depth review of Hazard Alerting procedures.

Bureau of Meteorology

The Bureau of Meteorology has advised the ATSB that they are considering including all wind gust information in METAR and SPECI reports.

The Operator

The aircraft operator has provided a report on this incident to all flight crew to remind them of the dangers of operating near thunderstorms at night, and to monitor the weather radar in these conditions, even when there are no visual cues that a thunderstorm is present. The operator also provided a weather radar training CD to all company flight crew.

Previous occurrences and recommendations

The ATSB recently released reports of the investigations into three occurrences that involved flight by regular public transport aircraft into convective weather. For further information, readers are directed to ATSB occurrence investigations 200100213, 200105157 and 200201228 and associated safety recommendations. Copies of these reports are available from the ATSB website, , or from the Bureau on request.

The following recommendations, along with responses and the current ATSB classification of those responses, also relate to the circumstances of this occurrence.

R20020170 - The Australian Transport Safety Bureau recommends that Airservices Australia increase the emphasis in its controller training programs to ensure that all appropriate sources of weather information, such as meteorological forecasts, controller observations, radar information, and pilot reports are provided to pilots.

The following response dated 29 January 2003 was received from Airservices Australia:

It is believed that current procedures already adequately cover the issues identified in the recommendation, however a Review of controller weather training will be undertaken by ATCC and upgrade action taken as required.

A further response, dated 13 April 2004, was received from Airservices Australia. That response advised:

A training package has been developed which is used in ab-initio course and is also included as a topic available for refresher training.

Response status: Closed - Accepted

R20020175 - The Australian Transport Safety Bureau recommends that the Civil Aviation Safety Authority ensure that operators increase the emphasis in their initial and periodic recurrent training programs on the effective use of all available sources of weather information, such as pre-flight meteorological briefings, ATIS broadcasts, controller-provided reports, airborne weather radar, and visual observations, and provide detailed guidance to pilots regarding the degradation on aircraft performance during flight through intense convective weather, and operational decisions involving take-off and landing operations which could expose a flight to hazardous weather conditions.

The following response dated 22 March 2003 was received from the Civil Aviation Safety Authority:

CASA acknowledges the intent of this recommendation and advises that while this is normal practice within the industry, the Authority will consider including an article on this topic in a future edition of the Flight Safety Australia magazine.

ATSB Note: The August 2002 edition of CASA's Flight Safety Australia magazine included an article on the 1 June 1999 McDonnell Douglas MD-82 convective weather-related accident at Little Rock, Arkansas. The October 2002 edition of the Flight Safety Australia magazine included an ATSB article on the effects of microburst events on aircraft performance.

Response status: Closed - Accepted

R20020177 - The Australian Transport Safety Bureau recommends that the Civil Aviation Safety Authority place greater emphasis on the hazards of low-level flight through thunderstorms and on the effect of windshear encounter during initial and periodic recurrent training programs for all pilots.

The following response dated 22 March 2003 was received from the Civil Aviation Safety Authority:

The Authority acknowledges the intent of recommendations R20020175 and R20020177. It addresses the matters raised in these recommendations through its education programs. A meteorological module is included in the Authority's programs. For example, a module called WeatherWise is included in the Flight Safety Roadshows. It covers a wide range of adverse weather situations including thunderstorms and microbursts and emphasises the importance of pre-flight weather briefings.

Response status: Closed - Accepted

R20020179 - The Australian Transport Safety Bureau recommends that the Civil Aviation Safety Authority ensure that operators of aircraft equipped with weather radar provide pilots with initial and periodic recurrent training on the use and interpretation of weather radar, and its limitations.

The following response dated 22 March 2003 was received from the Civil Aviation Safety Authority:

CASA acknowledges the intent of this recommendation and advises that while this is normal practice within the industry, the Authority will consider including an article on this topic in a future edition of the Flight Safety Australia magazine.

A further response from CASA, dated 10 May 2004, advised that an article on the use and interpretation of weather radar and its limitations would be included in a future edition of the Flight Safety Australia magazine.

Response status: OPEN

¹ Global Positioning System/Non-precision Approach