At 1200 local time on 26 October 2005, an A340-600 arrived at Melbourne International Airport (YMML). The approach and landing on runway 16 was conducted in strong crosswind conditions.
The weather data from the flight data recorder examined by the ATSB revealed that the wind direction at 850ft (RALT) was about 250 degrees true; the wind speed between 850ft RALT and 400ft RALT was about 22kts with a peak value of 27kts at 500ft RALT. From 400ft RALT the wind reduced to about 18kts until about six seconds before touchdown when the wind speed began to increase reaching a peak of 40kts about half a second before the right main gear contacted the runway. The aircraft’s heading remained relatively constant between 166 and 168 degrees M from about 850ft and then increased to 175 degrees as the A340 encountered the gust just before touchdown.
June 2006
Cross_Wind_from_07nws02_Jun06.pdf
The Australian Transport Safety Bureau (ATSB) has released the preliminary findings of its investigation into a landing incident at Melbourne (YMML) in October of last year. The text that follows is a pr é cis of the Preliminary Report, the full text of which can be found on the ATSB website http://www.atsb.gov.au/publications/investigation_reports/2005/aair/aair200505311.aspx
At 1200 local time on 26 October 2005, an A340-600 arrived at Melbourne International Airport (YMML) at the end of a scheduled service from Bangkok. The approach and landing on runway 16 was conducted in strong crosswind conditions. Surface conditions reported in the 1130 (local) ATIS (Information Yankee) were winds 230-280 degrees (magnetic) 18 gusting to 30kts with a maximum crosswind component of 14kts. The weather data from the flight data recorder examined by the ATSB revealed that the wind direction at 850ft (RALT) was about 250 degrees true; the wind speed between 850ft RALT and 400ft RALT was about 22kts with a peak value of 27kts at 500ft RALT. From 400ft RALT the wind reduced to about 18kts until about six seconds before touchdown when the wind speed began to increase reaching a peak of 40kts about half a second before the right main gear contacted the runway. The aircraft’s heading remained relatively constant between 166 and 168 degrees M from about 850ft and then increased to 175 degrees as the A340 encountered the gust just before touchdown. The aircraft touched down, yawed 15 degrees to the right of the runway heading and rolled five degrees right wing low. Unsurprisingly, the right main gear (MLG) was the first to make contact with the runway surface followed by the left MLG and then the centre MLG (In normal operations on the A340, the centre bogey will be the last to make contact with the initial load taken by the under wing bogies.) The centre MLG transitioned back from ‘ground’ to ‘air’ mode followed by the right MLG with the right MLG transitioning back to ‘ground’ mode a half second later indicating a bounced landing. The left MLG remained in contact with the runway after touchdown. At touchdown the vertical ‘g’ load was about 1.6 and the lateral load about 0.4 to the left indicating a right sideslip. At the time of touchdown, the outboard bead heel of the number one tire of the left MLG separated
from the rim of the wheel assembly. The tire immediately deflated and then partially disintegrated during the remainder of the landing roll. Fragments of rubber from the disintegrating tire resulted in some minor damage to the undersides of the left wing and fuselage and dislodged an inspection panel on the inboard side of the number two engine pylon. More seriously the debris from the tire fractured a hydraulic brake line on the left MLG and heat from the brake assembly on the rear wheel pair of the left MLG caused the hydraulic fluid from the damaged brake line to ignite resulting in a fire. This fire was quickly extinguished by the airport RFFS thanks to a rapid response to the incident. In addition to the damage to the airframe, the rim of the number one wheel scored the surface of runway 16/34 for some distance after the tire separated. The ATSB is continuing to evaluate data from the FDR and CVR.
Conclusions and recommendations
It is worth noting that the flight crew in this incident did a superb job of controlling the aircraft encountering, as they did, a maximum crosswind component in the flare 3 kts higher than the maximum demonstrated for the aircraft type. This of course was immediately followed by the braking asymmetry as a result of the tire failure. Also worth recalling is effectiveness of RFFS in attending the incident and extinguishing the hydraulic fluid fire. Risks in this incident were mitigated by the fact that, despite the wind, conditions were
otherwise good, daylight, with good visibility. In addition the crew benefited from accurate METAR and ATIS as well as wind data derived from the IRS displayed on the PFDs. What lessons can be drawn from the incident? Is it worth reconsidering your crosswind technique?
Is it best on the aircraft you fly to reduce lateral loads by using a wing down technique in the flare or does this present a greater risk of pod strikes? As already stated this incident took place on a dry runway but what impact might a wet or contaminated runway have on a crews’ ability to maintain directional control, and should this be taken into account when planning or continuing an approach? Or is a more elemental review of ‘maximum demonstrated crosswind’ required? As it stands these limits are ‘for guidance only’. Is there, therefore, a case for a campaign for crosswind limits to be imposed which take into account runway surface conditions? Certainly there is evidence to support this position. In any event a discussion of all these factors is beyond the scope of this article and accordingly a Safety Bulletin is being developed that is intended to address these issues. |
