Two Grob G115-C aircraft, VH-ZIR and VH-ZIB collided at low
altitude while on short-final approach to runway 18 at Merredin WA.
Each aircraft was being flown by a student pilot on a solo training
exercise and was being operated under visual flight rules.
Several witnesses had sighted the two aircraft as they converged
on short final. They recalled that the lower aircraft was closest
to the runway threshold, but was being approached from above and
behind by the second aircraft, which was travelling slightly
faster. One of the witnesses, a pilot in a taxiing aircraft, made a
broadcast on the aerodrome's Common Traffic Advisory Frequency
(CTAF) for the aircraft on final to `go around'. Moments later the
two aircraft collided. The collision occurred in the vicinity of
the runway threshold and at a height that was estimated to be less
than 50 ft.
Neither pilot was able to maintain control of their aircraft
following the collision. The nose of ZIR pitched steeply upwards
and the aircraft became inverted before it impacted the runway. The
nose of ZIB pitched downwards and the aircraft landed heavily nose
first. Both aircraft came to rest on the runway. The pilot of ZIR
received minor injuries and was trapped in the cockpit until
bystanders lifted the wreckage and helped him clear. The pilot of
ZIB was not injured.
Although the investigation could not positively determine the
sequence of impact between the two aircraft, the physical evidence
was consistent with ZIR being initially struck from above and
behind by ZIB. The lower rear-right fuselage of ZIR sustained
several propeller strikes. There was additional evidence of
secondary contact between the two aircraft as ZIR became inverted
and prior to impacting the ground. The VHF radios in both aircraft
were tuned to the CTAF frequency and the altimeters were set to a
QNH of 1022 hPa.
Merredin is a privately owned, non-controlled aerodrome. It is
operated by a Jandakot-based flying training organisation and was
used as a satellite aerodrome to supplement training operations.
The weather conditions at the time of the accident were described
as generally fine, with good visibility and a 20-25 kts southerly
wind.
The pilot of ZIB had recently transferred to Merredin after
completing his early ab-initio training at Jandakot (a General
Aviation Aerodrome Procedures controlled aerodrome). Since arriving
at Merredin he had completed 1.9 hours of dual circuit training and
an additional 2.8 hours of dual flying in the local training area.
The student was described as an above average student who displayed
a good level of situational awareness for his level of experience.
The accident occurred during the student's first solo flight at a
non-controlled aerodrome.
The pilot of ZIR was reported to be an above average student and
had completed most of his flying at Merredin. The accident occurred
at the end of his first solo cross-country navigation exercise.
The pilot of ZIR had joined the circuit crosswind as the pilot
of ZIB had lined up for take-off on runway 18. Although the pilot
of ZIB was aware there was circuit traffic ahead, he did not see
the aircraft at any stage. When his aircraft bounced during the
first landing attempt, the pilot of ZIR discontinued the approach
and broadcast on the CTAF that he was going around. The pilot of
ZIB completed his first touch and go without incident. He did not
hear the transmission from the pilot of ZIR, indicating that he had
gone around, and assumed that the aircraft had already landed.
On the second circuit, the pilot of ZIR broadcast his position
downwind. The pilot of ZIB recalled that he was turning crosswind
when he heard this broadcast and realised that there was an
aircraft ahead. In turn, he broadcast his position downwind and
received no response to his transmission. Although he could not see
the aircraft he was following, the pilot of ZIB surmised that this
situation was similar to his first circuit and concluded that the
other pilot was probably not making his downwind broadcasts in the
standard position. The pilot of ZIR subsequently recalled that his
second circuit was slightly wider than normal.
The pilot of ZIR recalled that he heard the downwind broadcast
from the other pilot and had noticed that this call was made
shortly after he had made his transmission. He assumed that the
other aircraft was behind him and would follow him in the
circuit.
Neither pilot sighted the other aircraft at any stage during
downwind, base or final legs of the circuit. Both pilots were
conforming to the standard oval circuit pattern recently introduced
by the training organisation. That procedure involved a climbing
turn from 500 ft above ground level (AGL) on the upwind leg to
position the aircraft downwind at 1,000 ft AGL. The base turn was
commenced 30 seconds after the aircraft had passed abeam the
landing threshold and consisted of a descending turn onto final
approach.