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aborted landing was due to technical consideration. In the second approach at around 00:08
HKT (=UTC + 8 hours), it encountered strong tailwind. Landing was subsequently aborted
and the aircraft diverted to Macao thereafter. Four minutes later, the second aircraft followed
the same glide path of the first aircraft but also failed to land at the HKIA because of the same
reason, i.e. the strong tailwind. The aircraft was also diverted to Macao at 00:12 HKT.
Flight data retrieved from the flight data recorders of the two aircraft was analyzed to reveal
the meteorological conditions encountered by aircrafts. It appeared that the missed
approach was attributable to the strong tailwind which exceeded the airline pre-defined
threshold, namely 15 knots for tailwind landing.
According to the flight data, the first aircraft experienced more than 15 knots tailwind
after it descended to below 1600 feet (Figure 3(a)) in its second approach. The tailwind
increased from 25 knots when the aircraft descended to 780 feet (labeled 'A' in Figure 3(a))
and strengthened to 37 knots at 708 feet at 00:08 HKT (labeled 'B' in Figure 3(a)), which
far exceed the limit for tailwind landing. As a result, diversion to other airport was
conducted.
The second aircraft also experienced the tailwind of around 15 knots when it descended to
around 1600 feet. The tailwind increased and reached 19 knots when the aircraft descended
to 1423 feet (labeled 'C' in Figure 3(b)) but then decreased and fluctuated between 7 to 12
knots when the aircraft further descended to 1028 feet (labeled 'D' in Figure 3(b)). At
around 00:12 HKT, the tailwind started to strengthen again and exceeded 15 knots. The
maximum tailwind experienced by the aircraft was 22 knots, which also exceeded the limit
for tailwind landing, at 859 feet above the runway (labeled 'E' in Figure 3(b)). Similar to the
first aircraft, the second aircraft executed a missed approach due to the strong tailwind and
was diverted to Macao.
The TDWR also captured the wind conditions when the two aircraft conducted missed
approaches. Figures 4(a) and 4(b) showed the radial velocity measured by TDWR at 0008
HKT and 0012 HKT 9 September respectively. Gusts reaching 27 m/s (i.e. around 50 knots)
were captured by the TDWR over the eastern part of the HKIA. The zero isotach, which
marked the leading edge of the shear line, agreed well with that identified based on
anemometer data.
The HKO Windshear and Turbulence Alerting System (WTWS) integrates windshear and
turbulence alerts generated by different algorithms such as Anemometer-based Windshear
Alerting Rules-Enhanced (AWARE) (Lee, 2004), LIDAR Windshear Alerting System
(LIWAS) (Shun and Chan, 2008), TDWR alerts and other algorithms. Alerts are then
generated for 8 runway corridors (north runway and south runway have two arrival and
two departure corridors each) and shown on a graphical display, the WTWS display.
At 0008 HKT, the zero isotach over the HKIA detected by the TDWR was analyzed as a gust
front and was shown on the WTWS display (Figure 5(a)). In addition, microburst alerts,
which represent windshear loss of 30 knots or more with precipitation, were provided by
TDWR to the east of the HKIA; windshear alerts were generated from AWARE over the
runways; turbulence alerts were in force due to the thunderstorm to the north of the HKIA.
Over the 8 corridors of the HKIA, all had windshear alerts with magnitude ranging from
+25 to +30 knots. At 0012 HKT, although the gust front was not detected by the TDWR
