At 1718 ESuT On 5 November 2002, VH-TJG, a Boeing 737-476 aircraft, encountered turbulence 1718 ESuT during the landing flare on runway 35 at Canberra International Airport. The aircraft was operating a scheduled fare-paying passenger service from Melbourne, Victoria to Canberra, ACT. The pilot in command was the handling pilot for the flight.
At 1700, the wind direction and speed at Canberra was 280 degrees T at 18 kts, gusting to 23 kts. At 1730, it was 280 degrees T at 18 kts, gusting to 26 kts. Runway 35 was aligned on magnetic heading 348 degrees, which was equivalent to 360 degrees T.
The automatic terminal information service (ATIS) at Canberra airport provided information on the prevailing weather conditions. At the time of the occurrence, information "Sierra" was current. It included information that runway 35 was in use, and that the wind direction and speed was 270 degrees M, with a minimum speed of 15 kts and maximum speed of 25 kts.
The aircraft was equipped with a solid-state digital flight data recorder (SSFDR). The flight data plots revealed that the pilot in command applied left control wheel to achieve a left wing low attitude of about 3 degrees as the aircraft descended through a radio altitude of about 60 ft. At about 6 ft radio altitude, the aircraft suddenly rolled left to a left wing low attitude of about 6 degrees, and the pilot in command rapidly applied right control wheel input to arrest the roll to the left. The aircraft landed about one second later in a slightly right wing low attitude.
The landing was completed without further incident, and there were no reported injuries to any of the 34 occupants of the aircraft.
The pilot in command subsequently reported that the turbulence encountered during the landing flare appeared to have resulted from a hangar located adjacent to, and to the west of, the touchdown zone of runway 35.
Construction of the hangar was completed in April 2002. The airside (eastern) face of the hangar was located 283.5 metres from the centreline of runway 35, and the roof height on the airside face of the hangar was 21.7 metres.
Turbulent wake eddies may be generated downwind of obstacles by wind flowing over and around them. The turbulent effects will depend on the size and location of an obstacle or group of obstacles, such as a cluster of buildings, as well as the direction and speed of the wind. If obstacles are located close to runways, turbulent wake eddies from those obstacles may have the potential to affect safety of flight if they result in aircraft experiencing difficulties during takeoff or landing.
The International Civil Aviation Organization (ICAO) has published standards and recommended practices that relate to aircraft, personnel, airways and auxiliary services. Those standards and recommended practices are contained in various Annexes to the Convention on International Civil Aviation, which was signed at Chicago on 7 December 1944 (the Chicago Convention). Australia is a contracting State to the convention. It is obliged under Article 37 of the convention to conform to standards and to endeavour to conform to recommended practices unless a difference has been filed with ICAO.
Annex 11 contained the standards and recommended practices that relate to the provision of air traffic services to the aviation sector. Paragraph 4.3.7 of Annex 11 detailed the information to be included in ATIS messages, and paragraph 4.3.7 k) required that messages contain:
`…other essential operational information.'
Paragraph 4.3.7 s) required ATIS messages to contain:
`…any available information on significant meteorological phenomena in the approach, take-off and climb-out areas including wind shear, and information on recent weather of operational significance.'
ATIS "Sierra" contained no information regarding the likelihood of turbulence in the touchdown zone of runway 35 at the time of the occurrence.
Canberra International Airport is a licensed aerodrome, and particulars about the aerodrome are required to be published in the Aeronautical Information Publication (AIP) Enroute Supplement Australia (ERSA).
The Civil Aviation Safety Authority (CASA) publishes Civil Aviation Advisory Publications (CAAPs) which provide guidance on the preferred method for complying with the Civil Aviation Regulations. CAAP 89O-1 (2), issued in November 2000, related to publishing aerodrome information and reporting changes to that information. That information included any event that affected the safety of aircraft using the aerodrome.
At the time of the occurrence, both the ERSA and the location briefing material for Canberra aerodrome contained no information to caution pilots of the likelihood of turbulence from the hangar located adjacent to, and to the west of, the touchdown zone of runway 35.
There have been two similar events of building-induced turbulence in the UK. One resulted in a B747 leaving the runway at London Heathrow airport, and was described in the UK Air Accident Investigation Branch (AAIB) Bulletin No. 5/2002. The other involved an A300 that sustained a podstrike at London Gatwick airport, and was described in AAIB Bulletin No. 6/2002.
The National Transportation Safety Board (NTSB) of the USA has had no reported occurrences of building-induced turbulence, nor has the NTSB identified that condition as a safety concern.
There are presently no building codes or standards in Australia that address the phenomena of building-induced turbulence with respect to proposed buildings to be located on or adjacent to aerodromes.
At the time of the occurrence, the wind direction and speed at Canberra aerodrome was 280 degrees T at 18 kts, with gusts exceeding 20 kts at times. The wind direction was therefore 80 degrees removed from the runway direction, providing a left crosswind of about 18 knots.
It is probable that the prevailing wind conditions at the time of the occurrence resulted in turbulent downwind wake eddies from the hangar located adjacent to, and to the west of, the touchdown zone of runway 35.
The downwind convergence of those turbulent wake eddies was probably in the vicinity of the touchdown zone of runway 35, and was likely to have been the source of the turbulence encountered during the landing flare.
As a result of this occurrence, the following safety actions were initiated:
The operator of Canberra International Airport requested Airservices Australia to include a caution note in Canberra aerodrome information contained in the ERSA, as follows:
`During strong westerly winds down stream of buildings, severe turbulence may be experienced in the touch down area while landing Runway 35.'
The operator also requested Airservices Australia to issue a Notice to Airmen (NOTAM) to reflect that cautionary advice until the ERSA was amended, and to give consideration to making:
`…necessary caution announcements on the ATIS during similar strong wind conditions.'
Airservices Australia issued a local instruction to air traffic controllers at Canberra Tower. The instruction contained information that when the crosswind component (including gusts) from the west equals or exceeds 12 kts and runway 35 or 17 is nominated, the following shall be included on the ATIS:
`Expect turbulence over runway south of runway intersection.'
The instruction included information that controllers were to make a directed broadcast to aircraft operating on runway 35, or departing runway 17, when this crosswind condition exists and runway 35 or 17 were not nominated on the ATIS.
Airservices reported that it did not consider the issue of a NOTAM providing cautionary advice of turbulence was warranted, as directed broadcasts would provide pilots with information of the meteorological phenomenon.
Airservices Australia also reported that it would conduct a survey of the turbulence phenomenon until 1 July 2003 to determine the extent of the condition, including:
a. occasions when the westerly crosswind component, including gusts, equals or exceeds 12 kts,
b. pilot reports of turbulence / shear at touch down or take-off, including aircraft type,
c. pilot comments, and
d. pilot reports of turbulence when the crosswind is less than 12 kts.
|Date:||05 November 2002||Investigation status:||Completed|
|Time:||1718 hours ESuT|
|Location:||Canberra, Aero.||Investigation type:||Occurrence Investigation|
|State:||Australian Capital Territory||Occurrence type:||Turbulence/windshear/microburst|
|Release date:||13 March 2003||Occurrence class:||Environment|
|Report status:||Final||Occurrence category:||Incident|
|Highest injury level:||None|
|Aircraft manufacturer||The Boeing Company|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure point||Melbourne, VIC|
|Departure time||1615 hours ESuT|