Flybe E145 at Stuttgart on Jan 5th 2009, overran runway on landing
Last Update: August 16, 2012 / 16:02:46 GMT/Zulu time
The serious incident was caused by the fact that the crew did not brake the aircraft consistently down to a safe speed.
The fact that the braking action on the runway did not correspond with the classification "good" and that this information had not been transmitted to the crew, contributed to this situation.
The BFU reported that the captain (52, ATPL, 9,500 hours total, 6,000 hours on type) was pilot flying for the landing, the first officer (26, CPL, 722 hours total, 564 hours on type) was pilot monitoring.
When the crew checked ATIS on approach to Stuttgart the braking action was reported good.
The aircraft performed a CAT II approach to runway 07 with flaps at 22 degrees and a Vref of 124 KIAS. The approach was stable, the aircraft crossed the runway threshold at 54 feet AGL at 127 KIAS and touched down 680 meters past the runway threshold at 118 KCAS, engines were at 26% N1 at that point with the thrust levers at idle. Ground spoilers deployed automatically, the aircraft oscillated around its vertical axis prompting the captain to correct with opposite rudder inputs.
The crew had not intended to use taxiways D to B due to those taxiways being described slippery by air traffic control. The captain therefore did not apply maximum brakes and relaxed the brakes causing the brakes pressure to drop to 0 for about 8 seconds during roll out before brakes pressure was increased again. Deceleration values, initially measured at about 0.1G and decreasing to 0.05G until brakes release, increased again to below 0.1G after brakes pressure was increased again. Tower queried "Are you braking?", shortly before the aircraft went past the runway end the first officer applied the park brake as emergency brake, which however did not noticeably improve deceleration but deactivated anti-skid. The aircraft overran the end of the runway at about 20 knots ground speed and came to a stop on the paved surface of the overrun area.
The BFU reported that about 8 minutes after landing the captain commented that she had been braking and it seemed fine, then she was braking again because they would have missed the turn querying the first officer for confirmation they had been reported braking action good.
The runway had been cleared from snow about 20 minutes to landing, a subsequent measurement of friction values recorded 87, 84 and 89 for the three thirds of the runway. Following the overrun two more measurements were conducted resulting in values of 46, 38 and 51. Values at and above 40, according to ICAO Annex 14 Appendix A, are classified as good braking action and values 36-39 as medium to good.
The BFU however analysed that the SNOWTAMs were contradictory in themselves, a SNOWTAM released prior to the incident indicated good braking action however 50% slush coverage which can not be correct. Equally, a later SNOWTAM indicating the runway was wet and braking action was medium, was also contradictory indicating better runway conditions than the braking action suggested. The BFU analysed: "These differences suggest uncertainties with respect to the classification and the description of the runway condition by the responsible personnel."
The BFU however also analysed, that the crew could have recognized the deterioration of runway condition through the release time of ATIS message, which went live about 20 minutes prior to the landing indicating good braking action and continuous snow fall.
The BFU analysed that during the first 20 seconds of braking the aircraft achieved an average deceleration of 0.08G which was sufficient to stop within the boundaries of the runway. Had the intial average deceleration during the first 11 seconds of 0.12G been maintained throughout the landing roll the aircraft would have stopped 750 meters short of the runway end. The BFU continued: "The inconsistent braking of the aircraft in the first rollout phase and the interruption of braking in the area of taxiways B and C resulted in the extension of the rollout distance."
The BFU analysed that the crew opted to perform a CAT II approach which however was in contradiction of the operations manual for contaminated runways. The operations manual required a flap setting of 45 degrees for landing on contaminated runways while the operations manual required 22 degrees of flaps for a CATII approach. Weather conditions did not require a CAT II landing as the visibility and cloud base were significally above limits, nor did the aerodrome indicate low visibility procedures were in progress. The BFU concluded: "The decision of the crew to conduct a Cat II landing including the requirement to set the flaps to 22 degrees resulted in an extended landing distance although there was no need for it."
The BFU analysed that the aircraft oscillated around its vertical axis (yaw) by about 6 degrees requiring the crew to counteract the yaw with rudder inputs showing the crew had difficulty to maintain directional control during roll out. The BFU stated: "An effective use of the brakes was impaired under these conditions. The data show that the oscillations around the vertical axis were minimized initially with reduced and later complete interruption of braking pressure."
Three safety recommendations, two to Stuttgart Airport and one to the operator, were released as result of the investigation.
This article is published under license from Avherald.com. © of text by Avherald.com.
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