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above the flight deck suffered several dents some to a depth of approximately 0.05 inches with a
diameter of 1 inch. There was also denting to the aircraft skin below the first officer's DV window.
The leading edges of the wings, the engine intake lips, the engine saddle fairings and the horizontal
stabiliser all had dents along their leading edges. The horizontal stabiliser tips exhibited the worst
damage, with the left tip being holed.
The composite structure of the aircraft, the wing to body fairings, pylon to wing attachment fairings
and the leading edge of the vertical fin, were also exposed to hail damage. This damage, however,
resulted only in paint erosion.
Engine damage was limited to the engine intake lips. The fan blades were intact and showed no signs
of impact with the hail. Furthermore, internal boroscope examination did not show any other damage
within the engines.
The Airbus A321 has a system that produces a post flight report on defects recorded by the computer
systems during flight. Faults were recorded for the captain's windscreen heater, the standby pitot
probe heater and due to autopilot disengagement. All these faults were recorded at 1543 hrs and are
directly related to the hail encounter.
Airbus A321-231, G-MIDJ
15
Weather radar system
The weather radar system fitted to the aircraft works on the principle of radio echoing. The radar
operates in the x-band producing energy at very high frequency in the form of electromagnetic pulses.
These pulses are emitted from a flat plate antenna mounted in the radome at the front of the aircraft.
The antenna scans left to right over an angle of 180° with the pulses being emitted at regular intervals
during the scan. When the electromagnetic pulses come in contact with weather they are reflected
back to the scanner. The direction, distance and intensity is then calculated by a transceiver/receiver
unit and displayed to the crew.
A control panel for the weather radar is provided on the cockpit centre console. This incorporates the
ON/OFF selector of the entire weather radar system. In addition there are controls for gain, tilt, mode
and ground clutter suppression. When the weather radar is switched ON the weather information can
be displayed on the captain's and first officer's ND. Each pilot has a separate control panel on the
glareshield where he can not only control his respective ND but also the range of the weather display
up to a maximum distance of 320 nm. Weather is not displayed if the ND selection is to the 'plan'
mode. An additional system allows for the display of terrain data on the ND rather than weather.
Normal practise is for the PNF to have his ND selected to display terrain data and the PF to have his
ND selected to show weather.
The tilt of the weather radar antenna beam, stabilised automatically in pitch and roll to compensate for
the aircraft's attitude, can be controlled manually to point above and below the horizon up to ±15°.
This allows the antenna beam to be moved upwards to reduce the radar returns from the ground or to
scan different levels of the atmosphere ahead. If the tilt is selected to too high or too low an angle
however, some weather activity, that might affect the aircraft on the track ahead, may be missed.
Weather radar system tests
Following the accident the weather radar transmitter/receiver, control panel and the scanner pedestal
were tested by the manufacturer. During the test of the transmitter/receiver there was a single test
failure on the input/output card, however, despite subsequent repeated tests the fault could not be
reproduced and it was thus concluded that the single failure was a 'test glitch'. The remaining
equipment operated without fault.
Operation and limitations of the weather radar equipment
The operating procedures and limitations of the weather radar are comprehensively covered in the
company's Operations Manual (OM). The Supplementary Techniques in the OM, for the operation of
the weather radar, have been reproduced from the manufacturer's instructions.
The capabilities and limitations of the equipment, detailed in the beginning of the instructions, are
summarised below:
GENERAL
The radar is nothing more than a precipitation detector. How much weather it detects
depends upon the raindrops, their size, composition and number.
The radar does not detect:
Clouds, fog or wind (too small droplets or no precipitation at all)
Clear air turbulence (no precipitation)
Wind shear (no precipitation except in microburst)
Lightning.
Airbus A321-231, G-MIDJ
16
The radar does detect:
Rainfall
Wet hail and wet turbulence
Ice crystals, dry hail and dry snow (above 30,000 feet) will only give small reflections.
　
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