The pilot of a Piper Aircraft Corporation Aerostar (Aerostar)
had been issued with a clearance by the Tamworth aerodrome
controller (ADC) to 'track east of the New England Highway until
intercepting final runway 30R' at Tamworth and, subsequently, to
'report established east of the highway'. The voice recording of
the occurrence confirmed that the clearance issued by the ADC to
the pilot of the Aerostar clearly stated the route to be flown by
that pilot. The pilot correctly read back the clearance and
reported established east of the highway but did not remain east of
the highway. The readback of the clearance, and confirmation from
the pilot that the Aerostar was east of the New England Highway,
enabled the ADC to clear the pilot of the Aerostar to descend below
4,000ft.
Tamworth Air Traffic Control (ATC) provided a non-radar, or
procedural control, service to aircraft operating within the
Tamworth control area and control zone. Controllers used non-radar
information to establish and maintain procedural separation
standards. The ADC intended to establish a lateral separation
standard (between the Aerostar and a Pacific Aerospace CT4B (CT4)
that was departing the Tamworth southern circuit). The standard
used a '1 NM buffer to the track or position of an aircraft
determined relative to a prominent topographical feature' in
accordance with the Manual of Air Traffic Services. In this case
the prominent topographical feature was the New England Highway
that runs approximately south from Tamworth township and which
crossed underneath the inbound track of the Aerostar approximately
12 NM southeast of the airport.
The vertical separation standard applicable between the CT4 and
the Aerostar was 500 ft. However, the ADC applied a vertical
distance of 1,000 ft between the Aerostar and the CT4 until the
pilot of the Aerostar reported established east of the New England
Highway. The ADC was then able to clear the pilot of the Aerostar
for further descent because the ADC believed, based on the
information provided by the pilot of the Aerostar, that a
procedural lateral separation standard had been established between
the Aerostar and the CT4, and between the Aerostar and other
traffic operating in the southern circuit. However, the lateral
separation standard was infringed when the Aerostar crossed to the
west of the New England Highway, and the vertical separation
standard was infringed when the Aerostar left 4,000 ft on descent,
because no other separation standard had been established.
The pilot of the Aerostar was operating under the instrument
flight rules (IFR) and later reported that he would have preferred
to track with reference to his instruments, via IFR tracking
points. The applicable Civil Aviation Regulation stated that the
pilot shall 'ensure that maps and charts applicable to the route to
be flown are carried and are readily accessible to the crew'. The
pilot of the Aerostar carried a current world aeronautical chart
that covered the Tamworth area but reported that he did not have
time to refer to that chart after the clearance to track via the
New England Highway had been issued. He was not carrying a visual
terminal chart for Tamworth. He also reported that his workload at
the time of the occurrence was high due to the combined effects of
the sun in his eyes, the visual tracking instructions issued by the
ADC and because he was unfamiliar with the airport.
The pilot of the Aerostar had a responsibility to advise the ADC
that he was either uncertain about the clearance he had been
issued, or that he was unable to proceed in accordance with the
clearance issued. The ADC could then have issued an alternative
clearance. Such timely notification is particularly important in a
procedural environment where controllers rely on the integrity of
the information provided by pilots to ensure the safe, orderly and
expeditious flow of air traffic.