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segment of flight), so the pilot-flying must have manually controlled the speed with the throttles. This may be
obvious from the rather irregular, step-like pattern of response of the throttle positions in Figure 8 (under autopilot
control a much smoother, more continuous pattern would have emerged).
Figure 8 Throttle activity versus distance to touchdown for the B747 flight
Therefore the pilot-reported “wind change of +40 knots” was actually an airspeed change of +40 knots due to a) a
wind change of only 20 knots and b) a ground speed increase also of 20 knots because of pilot action.
The second case illustrates the application of the corrective gain for sideslip (section 2.5) and the determination
of turbulence level for a flight with a B777 aircraft. With the application of the corrective gain it is apparent that the
variations in the crosswind component are reduced, although the general trend remains the same, see Figure 9.
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Figure 9 Crosswind component with (red)/without (blue) sideslip corrective gain for theB777 flight
The reduction in the wind variation, viz. turbulence, brought about by the application of the corrective gain, also
shows up in the TKE plots, see Figure 10.
Figure 10 Turbulent kinetic energy with (red)/without (blue) sideslip corrective gain for the B777flight
The TKE without the application of the gain correction reached peak values of 16 m2/s2, which corresponds to
heavy turbulence (Ref. 6). With the corrective gain the peak TKE gets to about 5.5 m2/s2 only, which is a medium
turbulence level (Ref. 6). The EDR1/3 is not affected very much by the corrective gain for sideslip, see Figure 11.
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K_beta=1
K_beta=0.551
0 50 100 150 200 250 300 350 400
TIME [S]
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Eddy Dissipation Rate (EDR)1/3 [m2/3.s-1]
Figure 11 Eddy dissipation rate with (red)/without (blue) sideslip corrective gain for the B777 flight
The EDR1/3 peaks to about 0.28 m2/3s-1, which corresponds to a light-to-moderate turbulence level. This is more
consistent with the TKE profile with the application of sideslip correction.
A final example case to show is the computed eddy dissipation rate compared against the LIDAR data measured
at the airport (Ref. 7). The comparison result is shown in Figure 12. The median EDR1/3 values (between the runway
threshold and 4 nautical miles away from the threshold) are considered here. The comparison involves 185 flights
arriving at the north runway of HKIA from the east in 2006 and 2007. Technical details of the computational
method of LIDAR EDR can be found in Ref.7.In general, the comparison between the two datasets shows a
reasonable correlation.
Figure 12 Comparison of median EDR1/3 values from the aircraft and from the LIDAR
5 Conclusions and future work
A sophisticated algorithm has been developed jointly by NLR and HKO to calculate the meteorological
paramet ers crucial for the study of low-level windshear and turbulence by taking into account the aerodynamics of
the aircraft. The estimated α and β values appear to be realistic for the aircraft types under consideration (Ref. 6).
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The resulting windshear and turbulence parameters as calculated from the QAR data, such as headwind change,
windshear hazard factor (F-factor), TKE and EDR, are found to give valuabl e insights into the low-level windshear
and turbulence events at HKIA. The algorithm has been implemented on a standalone software package so that
batch processing of a large amount (in the order of hundreds) of aircraft QAR data can be completed within several
minutes.
The QAR data analysis software is under further refinement to cover other aircraft types. A special version is
being prepared to handle missed approach events because there could be a number of aircraft conducting missed
approaches in turbulent flow situation at HKIA, e.g. under the influence of a tropical cyclone. The F-factor and EDR
calculat ed from QAR data will also be compared more extensively with the estimates of these quantities from
ground-based remote-sensing meteorological instruments, such as the TDWR and LIDARs, and pilot reports.
6 Acknowledgments
The authors gratefully acknowl edge the support of Cathay Paci fic Airways Ltd which provided the QAR data
used in this study and the assistance of pilots for filing windshear reports to HKO for the purpose of enhancing flight
safety.
7 References
1Haverdings, H.,“ Updated specification of theWINDGRAD algorithm”, NLR-TR-2000-623, 68 pp, 2000.
2Bryson Jr., A.E., and Ho, Y.C., “Applied optimal control. Optimization, estimation and control”, Ginn and Company,
Waltham, Mass., 1969.
3Haverdings, H.,“ Improved sideslip estimation for application to FDR data delivered by theHong Kong Observatory”, NLRCR-
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Quick Access Recorder (QAR) Data Analysis Software(8)
