Aviation Safety Council (ASC) release the investigation report of an UNI Airways (UNI Air) MD-90, the flight crew were not acknowledged of dramatic change of wind speed before landing; the ground spoilers were not promptly extended to minimize the wing lift and reduced the right drift from the low level wind impact after landing; the aircraft drift to the right due to the Pilot Flying did not overcome the left wing lift phenomenon when encountering increased left cross wind; the flight crew did not promply use reverser to overcome the weathervane effect, which made the aircraft veer off the runway.
On May 12th, 2011, UNI Air conducted flight BR 806, a MD-90 (bearing national registration number B-17817), wet leased to EVA Airways, the aircraft was on a scheduled passenger flight from Macau Airport to Taoyuan International Airport of Taiwan, Republic of China(ROC). There were 2 flight crew members, 5 cabin crewmembers, and 127 passengers on board.
The aircraft landed at 20:36 at Taoyuan International Airport Runway 06. During landing, the right main gear veered off the runway at 3340 feet from Runway 06 threshold, then back to the runway at 5,100ft. After aircraft taxied via Taxiway S6 and arrived at the parking bay, the inspection found that the aircraft had minor damage, all people on board were safe.
The ASC launched investigation according to the Aviation Occurrence Act after the occurrence. Several organizations were invited for joint investigation, including: Civil Aeronautics Administration (CAA), UNI Airways and Taoyuan International Airport Company, US NTSB and Boeing company. The investigation report was published after approval by the ASC 153rd council meeting and released on May 4th, 2012.
Findings related to probable cause: During landing, there was 10 to 20 knots left crosswind below 500ft; the flight crew were not acknowledged of dramatic change of wind speed before landing; the ground spoilers were not promptly extended after landing, which failed to minimize the wing lift to reduce the aircraft drift to the right from the low level wind impact; after landing, the left crosswind increased to maximum 18 knots which increased the lift of the left wing which made the aircraft drift to the right; the flight crew did not promply use reverser to overcome the weathervane effect, which made the aircraft veer off the runway.
Findings related to risks include：（Flight Operations）At the time when the flight crew informed ATC that the approach preparation was completed, the aircraft configuration, altitude, speed and distance to the airport did not meet the airlines’ requirement; the flight crew did not notice that the aircraft’s altitude was higher than normal descent path with higher speed and did not discuss prior to perform relevant operations; the flight crew did not follow standard operating manual to call out before landing; the flight crew was not acknowledged the most current weather information before landing; the crosswind before landing exceeded the company’s First Officer landing minimum standard; the aircraft landed with 2 main landing gears and nose gear at the same time; the captain did not check the status of spoilers after landing and did not manually extend spoilers when spoilers were not automatically extended; the probable cause of why the spoilers did not automatically extend after landing might be that pilots did not set the speed brake to ARM position and did not check accordingly before landing; and the captain did not take over immediately when the aircraft drifting after landing. （ATC Control）when approach clearance was given by Taipei Approach Taoyuan South controller, the ILS intercepted altitude of the aircraft was 1,000ft higher than Glide Slope and no distance related information was provided to the flight crew; ATC tower controller did not monitor the changes of the low level wind and provide information about the dramatic change of the wind to the flight crew; supervisors and the coordinators did not take the air traffic workload into consideration and re-allocate the Approach Controllers’ manpower; from the fact that controller on duty did not follow ”Air Traffic Management Procedures” to provide the aircraft with important weather information; and the mechanism of audit and inspections to controllers were not yet in placed .
The Aviation Safety Council issued a total of 19 Safety Recommendations.
Safety Recommendations to UNI Air：Reinforce MD-90 fleet captains, when acting as Pilot Monitoring, to take over immediately when discovering Pilot Flying’s abnormal performance; reinforce flight crew’s landing and operating skill under crosswind and wet runway conditions, including the use of thrust reverser when conducting crosswind landing with drifting effect; reinforce flight crew’s crew resources management regarding situation awareness and information exchange; reinforce flight crew training and self audit concerning following standard operating procedures and planning; review and consider revising FOM procedures and operations for speed brake positions check before landing to ensure the extension of the ground spoilers after landing; review fleet operation and training manuals to add the utilization of ND and FMS MCDU Progress page to obtain wind related information; review the assignment of Flight Operations supervisors following Flight Operation Manual; review the annual inspection procedures of FDR and the calibration of its sensing device to ensure the accuracy of the parameters recorded by FDR; review the reasons why flight data analysis system cannot obtain and analyze crucial parameters for runway veering off and enhance the function of the flight data analysis system.
In addition to recommend CAA audit UNI Air perform the safety recommendations above, recommendations to CAA also include：
Review and implement management and policies of ATC services, to ensure that supervisors and coordinators fulfill their duties; supervise and review ATC training, inspection and controller audit regulations to ensure that ATC services meet the regulations; evaluate the workload and work environment of Air Navigation and Weather Services; impplement”Air Traffic Management Procedures” to provide weather information; ensure that ATC shall inform airport authorities and relevant departments when braking condition poor on the runway is reported ; supervise Taoyuan Airport Corporation to Activate unscheduled patrol operating procedures with condition and have special anti-ski inspection or other alternative responses mechanism when pilots report poor braking condition on the runway.
Recommendations to Taoyuan International Airport Company is: Activate unscheduled patrol operating procedures with condition and have special anti-ski inspection or other alternative responses mechanism when pilots report braking condition poor on the runway.
The full investigation report is available for download at http://www.asc.gov.tw (Chinese version only)
Sherry Liu, Engineer