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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.

 

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.

 

Both pilots were aware that two downwind radio calls had been made close together and consequently, that two aircraft were possibly operating in close proximity to each other. Neither pilot had attempted to clarify the relative position of the other aircraft or establish their position in the landing sequence.

The pilot of ZIR had made his downwind broadcast before the pilot of ZIB and at this stage, was most probably ahead of ZIB. The pilot of ZIR believed that the other aircraft would follow him. It is possible that during the second circuit, ZIR was slightly wider downwind than normal and that this may have contributed to the pilot of ZIB not sighting the aircraft ahead.

In addition, the pilot of ZIB was inexperienced in non-controlled aerodrome operations. His previous solo flying had been completed at an aerodrome where an air traffic controller would provide sequencing instructions. He was also at a very early stage of his flying training and had accumulated only 2.0 hours solo flying. It is possible that this level of experience had contributed to the pilot of ZIB not clarifying the position of the other aircraft when he became aware of the possible conflict on the downwind leg of the circuit.

The training organisation's technique of using a continuous turn from late downwind onto final could have contributed to the pilot's view of aircraft on a wide base and long final being partially obstructed by the outboard wing. Furthermore, the pilot's view from the left control seat would have also restricted visibility towards the outside of the turn.

It is probable that the relative positions of the two aircraft on final approach had prevented the pilot of the higher aircraft from seeing the lower aircraft ahead.

 

Local safety action

Following the occurrence, the training organisation introduced a requirement for pilots to make a radio broadcast when established on final approach.

Additionally, the training organisation has equipped an observation platform at Merredin for an instructor to monitor students operating solo in the circuit. It is the organisation's policy that an instructor is to be in attendance during circuit operations by solo students.

The training organisation subsequently discontinued the practice of oval circuits requiring continuous turns from upwind onto downwind and downwind onto final.

 
General details
Date: 18 September 2000 Investigation status: Completed 
Time: 1610 hours WST Investigation type: Occurrence Investigation 
Location   (show map):Merredin, (ALA) Occurrence type:Airborne collision 
State: Western Australia Occurrence class: Airspace 
Release date: 01 August 2002 Occurrence category: Accident 
Report status: Final Highest injury level: Minor 
 
Aircraft 1 details
Aircraft manufacturer: Grob - Burkhart Flugzeugbau 
Aircraft model: G115 
Aircraft registration: VH-ZIB 
Serial number: 82079/C2 
Type of operation: Flying Training 
Damage to aircraft: Substantial 
Departure point:Merredin, WA
Departure time:1550 hours WST
Destination:Merredin, WA
Crew details
RoleClass of licenceHours on typeHours total
Pilot-in-CommandStudent/Passenger3030
Aircraft 2 details
Aircraft manufacturer: Grob - Burkhart Flugzeugbau 
Aircraft model: G115 
Aircraft registration: VH-ZIR 
Serial number: 82084/C2 
Type of operation: Flying Training 
Damage to aircraft: Substantial 
Departure point:Merredin, WA
Departure time:1400 hours WST
Destination:Merredin, WA
Crew details
RoleClass of licenceHours on typeHours total
Pilot-in-CommandStudent/Passenger7070
 
Injuries
 CrewPassengerGroundTotal
Minor: 1001
Total:1001
 
 
 
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Last update 13 May 2014