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information reported.
According to ATIS issued at 12:38, the average wind speed was 29kt with a maximum
momentary wind speed of 42kt.
At around 12:56:14, Hakodate Tower reported a wind speed of 28kt with no gust
information.
At around 12:59:46, Hakodate Tower reported a wind speed of 28kt with a maximum
momentary wind speed of 34kt.
According to ATIS issued at 13:00, the wind speed was 28kt with no gust information
reported.
Although some of these reports included gust information while others did not, given
that in principle gust information is reported where gusts exceed 10kt, it is considered
that even if some reports contained no gust information, wind speed fluctuations could
have been expected to some extent judging from the facts that that gust information had
been included in previous reports and that the wind speeds were continuously high.
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Therefore, while the flight crew did not receive information related to wind shear prior
to the accident, it is estimated that because they had received information on strong
winds accompanied by gusts, they could have recognized the existence of large
fluctuations in wind speed.
Further, regarding the fact that the flight crew received gust information over
company radio at around 13:01:07, the flight crew stated in their interviews that they
could not have clearly grasped this information because it was received during a period
just before landing, while they were concentrating on the landing. However, it is thought
that the flight crew should have been able to monitor this information through workload
sharing etc, because it is still 3 nm on the final approach course thus the flight crew could
have enough time until their landing.
(3) Trigger Conditions of the Wind Shear Warning System
As described in section 2.12.5, the wind shear warning system installed in the aircraft
had two types of detection function: predictive and reactive.
In this accident, the reactive detection system issued an aural alert, but the predictive
system did not.
The wind shear switch had been set to “AUTO” and the predictive system was enabled.
The weather radar used for the predictive wind shear function has a pulse width of 1.5
μs and cannot detect turbulent air currents of a size less than half a pulse width, 220m,
in the direction of flight. The radar has a pencil beam approximately 3° wide, and at a
range of 0.5nm (around 930m) from the aircraft the resolution limitations of the
equipment mean that it is unable to detect turbulent air currents with a width or height
less than the beam width of around 170ft (around 50m) at that distance. In this accident,
despite the fact that the predictive wind shear detection system was operative and that
rainfall required for detection was existed, it could not be ascertained why the predictive
system did not issue an alert. However, it is considered possible that the wind shear
could not be detected due to the system’s performance limitations, including the
possibility that the wind shear could not be detected because of weak reflections due to a
low level of precipitation.
Regarding the reactive type system, as described in the section 2.12.2, the synthetic
aural alert of “WINDSHEAR, WINDSHEAR, WINDSHEAR” was recorded by the CVR at
around 13:02:58. At that moment a wind speed of 14kt was recorded. A maximum wind
speed of 47kt was recorded during the 30 seconds immediately prior to this, a difference
of 33kt from the wind speed at the time the alert was annunciated. From this variation in
wind speed, it is considered that wind shear was detected.
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(4) The Crew’s Grasp of Information related to Wind Shear
In the event that a preceding aircraft encounters wind shear on approach, or that
specified conditions relating to the presence of thunderstorms are satisfied, information
that there is the possibility of wind shear is circulated. However, in this accident, no such
information was provided.
Moreover, Hakodate Airport was not equipped with a ground radar facility capable of
detecting wind shear.
Furthermore, although the predictive wind shear warning system installed on the
aircraft was operating normally, as described in (3) above, the warning system did not
issue an alert.
Based on these facts, while it is considered that the flight crew could not anticipate the
wind shear encounter before the event, it is thought that considering that there were
strong winds with large variations in wind speed just before the accident, the crew should
have been wary of the range of CAS variation and the amount of wind variation.
(Refer to Figures 3-1, 3-2 and 5)
3.1.6 Final Approach Speed
　
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