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2.3.4. Had the flight crew progressively increased the negative tilt angle,
with an ND setting of 160 NM for the PNF and 80 NM for the PF
as recommended in FCOM 3, it is likely that they would have
obtained a reasonable profile of any storm cell by observing the
returns from the icing level.
2.3.5. At a cruising level of FL410 with an ND range scale setting of 80
NM, there will be surface returns at downward radar tilt angle
settings of 5 degrees and greater, covering the outer range
segments of the ND display. However, any storm cell ahead of the
aircraft, ‘masked’ by these surface returns will progressively
emerge from the returns as the distance from the cell reduces. By
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approximately 40 NM it should be identifiable as a cell, enabling
avoidance action to be taken. It is essential that the radar tilt be
adjusted continuously and positively when the presence of CB cells
is forecast or suspected so that an effective track deviation around
weather returns can be initiated in sufficient time.
2.3.6. Having reviewed the company procedures on the use of weather
radar, the investigation team consider that, for the purpose of crew
training, FCOM 3 is not sufficiently clear in its description of the
recommended technique for operating the radar for weather
avoidance. On the other hand, the Honeywell RDR-4B Forward
Looking Windshear/Weather Avoidance Radar System User’s
Manual gives a clearer and more detailed description of the subject.
However, both pilots stated that the Honeywell RDR-4B user’s
manual was not used during training and that they had not been
given a copy of the manual.
2.3.7. At a tilt angle setting of –1.75°, the radar beam was probably
scanning above the level necessary to give more significant
weather returns. Hence it is likely that the most significant areas of
weather were not properly presented on the radar display and the
aircraft inadvertently flew into an area of turbulent weather caused
by strong convective activity associated with Tropical Depression
‘Koni’. Based on information provided by Manila ATC, no other
aircraft were known to be in sufficient proximity to the position of
HDA060 to have caused wake turbulence. There was no other
form of known turbulence that conceivably could have affected the
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aircraft, in a manner consistent with the circumstances.
2.3.8. The DFDR record showed that just before NOBEN, the aircraft
commenced a 23° right turn at time 0508:48, from a heading of
013°M to 036°M to avoid weather. At 0510:47, just 2 minutes
after commencement of the track deviation, when the aircraft was
14 NM north-northeast of NOBEN, the first onset of severe
turbulence was encountered. At that time, the aircraft was only 6
NM right of track. The investigation team is of the view that given
the radar setting selected prior to the turbulence encounter, it was
highly probable that the way in which the weather radar was
operated precluded optimum detection and indication of the
position and intensity of the weather in the vicinity of the aircraft.
As a result, the deviation around weather was not initiated early
enough, nor was the deviation large enough to avoid the weather.
2.4. Standard Operating Procedures (SOP) for Turbulence Penetration
2.4.1. Both the cabin and flight crew stated that shortly before the
turbulence encounter the aircraft experienced “light chop”. This
was consistent with the DFDR data readout. The PF stated that the
aircraft was cruising at M 0.80. The DFDR record showed that,
prior to the initial encounter with the severe turbulence, the
indicated Mach Number was M 0.81. This rapidly increased
thereafter to M 0.86; the ‘G’ loading increased to +1.89 and the
aircraft climbed to a maximum pressure altitude of 41,628 feet.
The DFDR record showed that at that point, the Autopilot
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disengaged. The PF then disengaged the Autothrust and reduced
both engines to idle thrust.
2.4.2. The PIC stated that the climb from FL 370 to FL 410 was
requested in an attempt to fly above the weather so as to improve
the ‘ride’. At that level, prior to the encounter, the aircraft was in
IMC and in cloud.
2.4.3. The operating ceiling of the A330 is FL 411. The optimum level at
which an A330 can be flown is dependent on the aircraft weight,
the cruising Mach Number and the ambient temperature. The
aircraft Flight Management System (FMS) will compute the
optimum and maximum cruising levels, which will increase as the
aircraft weight decreases. The aircraft weight at the time of the
encounter was estimated to be approximately 165,000 Kg. At this
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