Circumstances:

Brisbane Sector 4 is the military (RAAF) sector in the Brisbane Area Approach Control Centre. It is normally manned by two RAAF controllers who rotate between the radar and procedural positions. At the time of the occurrence, however, the sector was manned by one RAAF controller. At 0039 hours UTC, VH-CZD reported to Brisbane Sector 5 its position Longreach, Flight Level (FL) 370, estimating Taroom (165 miles from Brisbane) at 0120 hours. This position was coordinated to the Sector 4 controller as Restricted Area R614, which includes the airspace above and to the east of Taroom, was active and under the control of Sector 4. The Sector 4 controller read back the level correctly but annotated FL 270 on the flight progress strip for VH-CZD. At 0109 hours, VH-TJA departed Brisbane tracking via Taroom on climb to FL 350. At 0120 hours, VH-CZD reported to Sector 4 its position Taroom, FL 370, estimating Brisbane at 0049 hours. The Sector 4 controller did not detect that the flight progress strip had been incorrectly annotated. At 0121 hours, and at about 60 m from Brisbane, VH-TJA transferred to Sector 4 frequency and reported maintaining FL 350 estimating Taroom at 0140 hours. On the controller's request, VH-TJA confirmed cruising at FL 350. At 0127 hours, VH-CZD requested descent and was cleared to descend to FL 210. At 0129 hours, VH-CZD reported left FL 370. The crew of VH-CZD recalled seeing VH-TJA pass below and with a lateral separation of a few hundred metres as descent was initiated. The Sector 4 controller reported that the radar returns of the aircraft merged shortly after VH-CZD reported commencing descent. Investigation of the occurrence revealed that the controller's workload during the period leading up to the occurrence was low, with only two aircraft on frequency. The controller also had engaged in extensive non operational communications during this period. It was further established that the controller was facing a number of significant personal issues which could have had a distracting influence and had experienced disturbed sleep on the night before the occurrence. Low workload is a common predisposing factor in many air traffic control occurrences involving individual controllers. Low workload tends to lead to under-arousal or complacency, causing work performance to suffer. Low workload can also provide the opportunity for personal concerns to intrude and divert attention from the primary task. A fatigued person can generally cope with a short burst of mental effort but can have difficulty in conducting protracted monitoring tasks. The controller's failure to detect the discrepancy between the actual flight level of VH-CZD and that annotated on the flight strip was probably due to the controller having a false mental picture of the traffic situation. Fatigue and personal concerns could have reduced the controller's ability to detect information which contradicted the mental picture. The notion that VH-CZD was at FL 270 had begun as a minor slip, but had grown into a strong idea that was resistant to challenge. Even when VH-CZD reported Taroom at FL 370, the controller heard what was expected rather than the actual words spoken.

Significant Factors:

The following factors were considered relevant to the development of the occurrence

1. Personal concerns, non-operational communications and fatigue probably distracted the controller from the primary task.

2. The controller annotated the incorrect altitude on the flight strip for VH-CZD.

3. The controller failed to detect the flight strip error when VH-CZD reported Taroom.

4. VH-CZD was given descent clearance without adequate separation from the conflicting traffic VH-TJA.

While being towed to the planned launch height, the glider under tow and another glider in the circuit area, collided. The collision caused the tow rope to break and the pilot of the glider, although injured, was able to land his aircraft. The tailplane of the other glider separated in the collision and the aircraft descended uncontrolled into the ground. The tug aircraft was undamaged and landed safely. The glider rejoining the circuit approached the tug and glider under tow from the right rear quarter. Immediately prior to the collision, witnesses reported that the glider attempted avoiding action. The reason the pilot did not see the two other aircraft until it was too late to successfully take avoiding action, could not be determined. However, the combination of a broken cloud cover and a mottled background would have made the pilot's task more difficult.

Circumstances:

VH-CAG had taken off from runway 27, turned left, and was climbing through about 1700 ft on the downwind leg when it collided with glider VH-GXO, which was turning right in thermalling flight. The Bonanza lost its right 'Vee' tail on impact and entered an inverted spin, which continued until ground impact. The glider, although sustaining substantial damage to the right wing and lower fuselage, was able to be flown to a safe landing. Tocumwal Aerodrome is provided with sealed runways in the 18/36 and 09/27 directions. Powered aircraft normally use the sealed runways. Gliding operations are conducted during daylight hours from grass strip 18/36 situated west of runway 18/36, or grass strip 09/27 situated north of runway 09/27, dependent on wind conditions at the time. During daylight hours, for traffic separation purposes, contra-rotating circuits are in operation. Right hand circuits apply to runways 09 and 36, and to gliding strips 18 and 27. All other circuits are in a left hand direction. The aerodrome is uncontrolled, and operational information is provided by Melbourne Flight Information Centre on a radio frequency of 118.6 MHz. In addition, gliders operating at Tocumwal monitor a frequency of 122.9 MHz. Radio communications on 118.6 MHz are automatically recorded. The recorded radio communications of VH-CAG were consistent with normal operational procedures. Radio communications on the local glider frequency were not recorded. No evidence was found to indicate that VH-CAG made any transmissions on that frequency in the period leading to the accident. Details of special procedures in use at Tocumwal at the time of the accident were provided in Enroute Supplement Australia (ERSA), a document issued by the Civil Aviation Authority. Although the glider frequency was published in ERSA, there was no requirement for powered aircraft to listen out or broadcast on the glider frequency. On the day of the accident, weather conditions were bright and sunny with no obstructions to visibility. Witnesses reported that the surface wind was light, mostly from the south but occasionally backing to the west. Gliding operations had been conducted throughout the day from strip 18, utilising a right hand circuit direction. The pilot of VH-GXO had been authorised to undertake thermalling flight to the south-west of the aerodrome. At the time of the collision, the glider was being operated in accordance with that authorisation.

The Bonanza had commenced to taxi from the western end of the aerodrome at about the time the glider was aerotowed from strip 18. A few minutes later, the aircraft was observed to backtrack on runway 27 before commencing a take-off roll from the beginning of the runway. Witnesses later reported that, at the time, the wind was from the west at up to 12 kts. The pilot-in-command of the Bonanza was aware that gliding operations using strip 18 had been conducted earlier in the day. After take-off the Bonanza turned left onto an easterly heading, directly into the glider circuit. Why the crew of the Bonanza did not sight the glider can only be surmised; however, a number of factors may have been relevant, including a lack of contrast between the glider and the sky background; the size of the glider as a target; the low rate of movement relative to the Bonanza; the absence of any traffic alert concerning the presence of the glider; and possible distraction from a known inbound aircraft to the north-east of the aerodrome. The pilot of the glider was unaware of the presence of the departing Bonanza, having heard no radio calls concerning VH-CAG on the glider frequency. He also did not see the Bonanza as the glider was turning right, although this could have been difficult as the Bonanza presented a head-on view and would have blended into the ground background as it climbed.

Significant Factors:

The following factors were considered relevant to the development of the accident

1. The crew of VH-CAG were unaware of the presence of the glider.

2. No communications from VH-CAG were heard on the gliding frequency.

3. The pilot of VH-GXO was unaware of the presence of VH-CAG.

4. Fluctuating wind conditions.

5. Conflicting circuit directions.

6. The crew of VH-CAG was possibly distracted by known inbound traffic.

7. Poor conditions for target discrimination, (both aircraft).

8. The pilot-in-command of VH-GXO failed to see the approaching Bonanza.

9. The crew of VH-CAG failed to see and avoid the glider.

The student glider pilot had carried out three previous flights during the day. Her instructor had informed her that she was at a suitable stage of training to be introduced to practice emergency procedures. After sighting her training log book, the instructor for the final flight left the glider to speak to the pilot of the tug aircraft. The instructor returned to the glider and preparations for take-off were then continued. Witnesses observed that the tug and glider became airborne and subsequently carried out normal turns to position the aircraft on a downwind leg at about 500 feet above ground level. The tug aircraft was then seen to waggle its wings sharply three times. Almost immediately this aircraft assumed a steep nose-down attitude, its tail apparently being pulled into a vertical position by the tow rope which was still attached to the glider. The glider then also assumed a steep nose-down attitude and both aircraft spun or spiralled towards the ground. The tow rope was released from both aircraft, but neither pilot regained control before impact with the ground. The subsequent investigation did not disclose any defect or malfunction with either aircraft that might have contributed to the development of the accident. During glider towing operations when the pilot of the tug waggles the aircraft wings it is a signal to the glider to immediately release from the tow. This "wave-off" signal would normally be given when the tug pilot detects some malfunction or when the glider is sufficiently far out of position behind the tug to affect the tug pilot's control of his aircraft. On this occasion it was considered possible that the instructor in the glider had arranged for the tug pilot to simulate an emergency by giving a wave-off signal. The wave-off signal was observed to be given in the normal position relative to the strip for such training manoeuvres to be performed. The reason for the subsequent loss of control of both aircraft could not be determined, however it was evident that when the aircraft released the tow rope there was insufficient height remaining to permit recovery to normal flight.

During the launch by a tug aircraft for the pilot's first flight of the day, turbulence was encountered at about 40 feet agl. The pilot released from the tow and attempted to land straight ahead, however the right wing struck a post of the aerodrome boundary fence and the aircraft ground looped before coming to rest. The pilot had earlier experienced difficulty in fitting the all-moving tailplane to the glider during the pre-flight assembly. Shortly after becoming airborne the turbulence led the pilot to believe he had elevator control problems and he released from the tow. He then planned to land straight ahead, controlling the rate of descent with the air brake and making virtually no elevator movements. The use of air brake shortened the gliding distance to the point where the aircraft could not clear the boundary fence. Subsequent investigation revealed no defect with the elevator controls or the tailplane.

Upon arrival at Mitta Mitta the pilot performed a touch and go on the 1000 metre long gravel strip, before approaching for the full-stop landing. After touchdown, the aircraft veered to the right but was repositioned on the centreline within a short distance. However, it again veered to the right and departed the hard packed gravel surface of the strip and entered an area of long, damp grass. The pilot was unable to control the direction of travel and the aircraft encountered a drainage ditch, an earth mound and a fence before coming to rest with its noseleg collapsed. No fault was found with the aircraft systems that may have contributed to the accident. The pilot had not flown the aircraft for 18 months and it is probable that the veer was caused by differential braking in combination with the damp, slippery grass on the sides of the strip. Weather conditions were fine and calm and were not considered a factor.

The pilot was engaged in dropping sweets at a Children's Christmas party. As the pilot was completing the third run over the area at an altitude of about 50 feet, the cord on the sweet bag became tangled. The pilot diverted his attention from the operation of the aircraft as he freed the cord. The aircraft descended and the left wing struck a tree, it continued on colliding with a power line before coming to rest on the verandah of a house.

The pilot was conducting a soaring flight when deteriorating lift conditions made an outlanding necessary. A paddock was chosen and the pilot carried out a standard approach pattern, aiming to land into wind. He noted a powerline pole on a hill some 500 metres away, but could not see any other poles near the intended landing area. However, as he was about to turn onto final approach, he noticed a single powerline directly ahead of the aircraft. There was insufficient time available to take any avoiding action, and the wire struck the aircraft canopy. The aircraft subsequently impacted the ground and cartwheeled to a stop 87 metres beyond the point of collision with the wire. The powerline struck by the glider was particularly difficult to see from the air. The pole on the hill was prominent, but the other pole was situated amidst a group of farm buildings. The distance between the poles was one kilometre. The pilot had been at a lower height than normal for a turn onto final approach, however there was little doubt that the intended landing would have been successful had the wire been avoided.

Circumstances:

The pilot had not flown for over four months and planned to sell the aircraft. On the day of the accident, he decided to conduct a check flight before the arrival of a prospective buyer. The aircraft took off into a very light breeze and remained in the circuit area for a short time. It then departed to the east, climbing to about 300 feet. It was then seen to commence a left, level (yawing) turn, both wings seemed to come together at the same time and the aircraft fell in a level attitude to the ground. During the sequence, the engine was heard increasing and decreasing power. It was determined that the left wing spar failed under load at about 1.6 metres from the keel tube. Following this failure, both wing spar tubes failed at the attachment points. No pre-existing fault could be found which could have initiated the left wing spar outboard failure. No other fault was found which could have contributed to the accident. Extensive engineering analysis has shown that at a weight of 160 kilograms, wing spar failure could be expected at about 2.3g. Brochures and other literature on the aircraft claim the airframe will withstand up to 8g.

Significant Factors:

The following factors were considered relevant to the development of the accident:

1. For undetermined reasons, the left wing spar failed 1.6 metres from the keel tube.

2. Both wing spars buckled at the keel attachment points.

Circumstances:

The aircraft was approaching 1000 feet, on departure, when it began to vibrate significantly. The pilot declared an emergency and carried out a precautionary landing in open country. An inspection of the aircraft disclosed that two of the three main rotor blades had begun to delaminate along their trailing edges, and the foam core of one blade had begun to break up. Subsequent inspections of the blades indicated that all three had suffered a foliage strike on their lower surface. The strikes had caused sufficient damage to the blade material to allow delamination to occur; however, they had not been sufficiently heavy to damage the blades' leading edges or penetrate the skin except where the blade body joins the trailing edge insert. It was evident from the strike marks that the blades had been positioned at a high angle of attack at the time of the strike. Debris found in the skin fracture indicated that the strikes had occurred some time prior to the delamination but not more than two to four flying hours. The light nature of the strikes indicates that the pilot and crew were possibly unaware that a strike had occurred. The high angle of attack on the blades indicates that the strikes occurred either during an approach to land or whilst the aircraft was manoeuvring at low level in the vicinity of tall trees.