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while the aircraft was on final approach at a distance of 250m from the approach end of the
runway, there was an abrupt descent from a height of approximately 100ft AGL, two seconds
after which the wind shear warning sounded.
According to flight crew interview statements and the weather information described in
section 2.7, the possible existence of weather phenomena capable of causing wind shear,
such as fronts, clouds potentially associated with microburst or temperature inversion, was
not recognized in the vicinity of the ground around Hakodate Airport.
Judging from the near-ground wind speed measurements along the approach course to
Hakodate Airport recorded between the approach on which the wind shear encounter
occurred and the second approach of the same aircraft, shown in Figure 9, regarding wind
conditions that would cause an aircraft to abruptly descend and trigger a wind shear
warning, it is considered that there was localized air mass with a wind speed 10kt greater
than the surroundings from 250–100ft above ground level, and below 100ft AGL there was a
wind shear with a marked decrease in wind speed with decreasing altitude. It is considered
possible that wind conditions like these arose due to a combination the strength and
direction of a wind passing over the terrain in the vicinity of the airport at the time affecting
the surface boundary layer that was developing along ground surfaces.
Depends on the DFDR Data, it is considered that intensity of the wind-shear in this
accident could be designated as “severe” that was described in a ICAO Circular 186-AN/122
titled WIND SHEAR.
(Note: While winds generally weaken near the ground due to friction with surface, they
in particular they can suddenly weaken at heights close to ground level such that
there is in no wind at the ground surface. The height range over which this severe
change of wind speed occurs is called the surface boundary layer.)
(See Figs. 6, 9 and Photo 1)
3.1.11 The Impact Absorption Characteristics of Cabin Attendant Crew Seats
Although a vertical acceleration of approximately 1.9G occurred when the lower surface
of the aft fuselage struck the ground, no injuries were sustained by the passengers or flight
crew.
On the other hand, three of the four CAs sustained minor injuries such as lumber
sprains, etc. It is estimated that the reason that only CAs sustained minor injury, as
described in section 2.12.10, is that the CA crew seats had inferior impact absorption
characteristics, with the thickness of the cabin attendant seat cushions being less than one
third that of the passenger seat cushions and the reclining angle of a CA seat was almost
vertical with no armrest might be factors on this accident.
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4 PROBABLE CAUSES
In this accident, it is estimated that while on final approach at a height of
approximately 100ft AGL, the aircraft encountered severe wind shear and although recovery
actions were taken, a sufficient rate of ascent was not attained in time to prevent the lower
surface of the aft fuselage striking the runway, resulting in damage to rear frames and the
aft pressure bulkhead.
Further, the following factors are considered to have contributed to this accident:
(1) A delay in engine thrust response to the thrust levers being advanced to recover from the
wind shear, combined with a reduced approach speed, meant that an increase in speed
could not be obtained immediately. These factors contributed to the fact that sufficient
rate of ascent could not be attained in time to prevent the tail strike.
(2) Factors contributing to the reduced approach speed were the fact that the first officer,
acting as PF, had selected a slightly low value for the final approach speed, and that he
reduced thrust in response to an increase in headwind.
(3) Factors in the reduction of engine thrust in response to the increase in headwind were
that because the pilot was operating the thrust levers manually in “SELECTED SPEED”
mode he was attempting to maintain a constant CAS, and that the flight crew had not
adequately anticipated a increasing followed by a continuing drop in wind speed.
(4) Regarding the selection of a slightly low value for final approach speed, appropriate
consideration was not given to wind speed, and there were concerns over touch down
attitude related to high approach speeds.
(5) Regarding the fact that appropriate consideration was not given to wind speed, the first
officer used a simple calculation formula that did not separately consider the additional
airspeed margins to take account of wind speed changes and the head wind component,
but that treated these together.
(6) Regarding the concerns over aircraft touch down attitude at high approach speeds, the
　
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