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143kt established during the approach on which the wind shear encounter occurred is
low, and a final approach speed of 147kt to 152kt is considered appropriate based on the
wind information received by the flight crew because of obtaining speed margin
advantages.
Further, a final approach speed of 147kt to 152kt is also considered appropriate based
on the statements of the air traffic controller as described in the section 2.1.2.3(1) and the
actual wind conditions at the time the accident occurred.
However, it is also necessary to consider that the amount of the pitch-up at flare may
increase and possible to over shoot the touch down point with increasing final approach
speed.
(3) The Method of Calculating the Final Approach Speed used by the First Officer
It is estimated that the first officer established the final approach speed value using
the following formula to simplify the calculation method prescribed in the AOM:
Final approach speed = VLS + ΔV
and in consideration of gusts during approach, while intending to select the maximum
value of 12kt within the range of his ΔV, he used 11kt and thereby arrived at a value of
143kt by the following calculation:
Final approach speed =ＶLS + 11kt = 132kt +11kt = 143kt
The value of final approach speed calculated by the first officer is lower than the value
computed for conditions with strong winds and gusts using the method specified in AOM
and described in section 2.12.6.1. While the method in the AOM distinguishes between a
head wind component and a wind speed variation component to add to VLS, it is thought
that the PF treated these together in the summation. It is necessary to use the
computation formula specified in the AOM to calculate final approach speed.
Also, it could not be clearly determined whether the first officer’s use of 11kt as the
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additional component to the final approach speed in consideration of gusts, rather than
the maximum of 12kt, was due to differences in values of VLS is computed by the
individual FAC and FMGC computers or was the result of a lapse on the first officer’s
part.
(4) On Pilots receiving Information on Wind Speed Variations during Approach
Gust information, which is thought to be regarded by pilots as the most important, was
included in the reports from Hakodate Tower just before landing. While the computed
final approach speed of 143kt was lower than 147kt which is the value obtained following
the gust less than 10kt, it is estimated that it should have been considered inadequate
from the point of view of ensuring speed margin against the wind based on the wind
report issued at around 12:59:46.
Generally, in the case of strong and varying wind speeds where there are large changes
in wind speed over time, it is considered that the final approach speed should be selected
in order to be able to cope with the largest wind speed changes. Accordingly, it is
considered that if there are reports received immediately prior to landing of wind
conditions with gusts greater than the wind speeds expected by the flight crew, as in the
case of the 12:59:46 wind report, the value previously set in the SPD/MACH window
should be changed, or in the case where this cannot be due to the imminence of landing,
thrust should be added to increase CAS to counter the change in wind, and if these
measures are insufficient to cope with the change in wind speed, the crew should execute
a go around without hesitation.
Regarding these matters, given the First Officer’s statements that the CAS was
fluctuating over a range of around 3kt and was stabilized by adding a little excess power,
and that the average CAS from 1,000ft AGL to 177ft AGL was 145kt, it is considered
possible that the approach speed was slightly greater than the 143kt value selected.
(5) Establishment of Final Approach Speed in the Accident to be able to Recover from Wind
Shear
As described in (2) above, the rules in the AOM specify that the value of the final
approach speed be decided by the PF according to conditions.
According to the First Officer’s interview statements, as PF he decided the final
approach speed considering gusts in accordance with the rules. Although consideration of
gusts should result in a greater aircraft speed, as is described in sections 2.12.4.1 (3) and
2.12.6.3 too high a speed results in a nose-down attitude which can impede the proper
execution of approach and landing. According to All Nippon Airways’ technical
information, it is considered that a final approach speed of greater than 149kt, as in the
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case of this accident, would result in a nose-down attitude. However, in conditions where
there is the possibility of a sudden decrease in wind speed following a gust, it is necessary
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