4th of April 2019
A de Havilland Canada DHC-8-402Q (Dash 8) was operating a domestic flight in Austria between the cities of Vienna and Austria on this day in aviation history. During the flight preparation, it became apparent that mild Foehn conditions were foreseen, but wind shears were not forecasted. (Foehn is warm and dry, gusty wind that periodically descends the leeward slopes of nearly all mountains and mountain ranges. The name was first applied to a wind of this kind that occurs in the Alps, where the phenomenon was first studied.) Just after 08.00 local time, the aircraft took off from Vienna under the control of the first officer as pilot flying. Onboard the aircraft 4 crew and 74 passengers.
The damage to the aircraft fuselage (Source: Investigation report © Aircraft Operator)
With the aircraft cruising at 20.000 feet (6000 meters) the latest weather info was obtained from Innsbruck, and it was decided that the first officer could fly the approach, Just after 08.30 lt, the descent toward Innsbruck was initiated. At 08.50 lt the AutoPilot is disconnected due to the turbulence encountered. A short while later the crew receives the landing clearance with the latest wind information, Subsequently, the aircraft id configured for the landing with the gear being selected down and the flaps being extended to 15º. Several EGPWS (Enhanced Ground Proximity Warning System) warnings were given during the approach for excessive vertical speed, the crew took corrective action each time. There was an overshoot of the runway centerline during the turn on to the final approach, this was as expected, due to the wind and the aircraft configuration. Due to the wind conditions, the airspeed over the threshold was ~141 knots, 7 knots above the calculated and briefed Approach Reference speed (Vref), the crew sensed that the aircraft was pushed down and to arrest the descent the first officer added some engine power. This did not prevent the aircraft from touching down at a speed of ~123 knots, the first officer had also increased the angle of attack, which was 7,65º at touchdown, and the vertical acceleration was 2.1 G. AT the same time the "TOUCHED THE RUNWAY" indication illuminated, indicating the tail of the aircraft had struck the runway. The aircraft bounced back into the air and touched down a second time 2 seconds later.
The rollout and taxi were uneventful and the passenger disembarked normally.
Aircraft dimensions and contact point with the runway (Source & © AFM de Havilland Inc.)
According to the aircraft manufacturer, with full compression of the suspension struts of the landing gear, a pitch angle of +7.6° is needed on touchdown in order for a DHC-8-400 to have contact between the tail and the runway. The manufacturer considered the difference between the 6° from the AFM and the 7.6° as a safety factor.
An inspection of the aircraft revealed the following damage, as listed in the accident investigation report issued by the Federal Safety Investigation Authority of Austria;
"The aircraft suffered damage to the outer fairings and panels, an antenna, and to the stringers and frames on the tail. The damage was limited to part of the aircraft tail and had no further effects on the structural integrity of the aircraft or on its systems." The report concluded that the probable cause for the tailstrike was;
"Sudden decrease in wind speed just before touchdown (Low-level negative wind shear"
The full report, as published by the Austrian authorities, in to the tail strike is available by clicking on the file below;