The warning light for the primary electrical inverter illuminated and then re-activated after the stand-by inverter was selected. The pilot decided to return to Mt Isa. A short time later all flight instrument "fail flags" indicated and sparks were observed near the top of the pilot's instrument panel. The avionics master switch was selected off and the aircraft later landed safely.

Later examination found that a section of electrical wiring under the instrument panel had "shorted" and burnt. Both inverters were unserviceable and the 115-volt main fuse was blown. It was determined that the electrical fault was probably initiated by the electrical wiring chaffing and then shorting out.

The student pilot was on his second solo training flight, having completed a one-hour dual training flight immediately beforehand. He reported that on his last landing, which he considered to have been possibly a little heavy, he had heard a crunching noise from the nose gear. Realising that the nose gear was damaged, he tried to keep the nose up as the aircraft decelerated, hoping to minimise damage to the propeller. However, as the aircraft slowed, the nose dropped, and the propeller struck the runway.

Inspection of the failed nose gear revealed it had failed as a result of the previous heavy landing.

The glider released from the tug at about 500 ft and flew a modified circuit, turning on to final approach at about 150 ft. The pilot attempted to deploy the spoilers but operated the cable release lever by mistake. This resulted in the aircraft overshooting the intended landing point. The pilot continued with the landing. At the completion of the landing roll, as the aircraft was turned off the strip, it collided with a termite mound.

The pilot was hand starting the engine of the unoccupied Tiger Moth. After start the power increased unexpectedly. Although tethered, the aircraft broke free and ran about 20 metres before overturning.

The pilot reported that he had failed to ensure the throttle friction nut had been adequately tightened before attempting the hand start.

After take-off at approximately 150 ft above ground level, smoke began to enter the cabin. This was immediately followed by a popping sound and the right engine failed. The pilot shut down the engine, made a Mayday call, and landed the aircraft safely on the departure runway.

Later examination of the engine found that the compressor section had moved rearward and seized. Initial inspection suggests a failure of a compressor bearing support. The engine was later removed and forwarded to the manufacturers overhaul facility in the United States of America.

CIRCUMSTANCES

At the time of the incident, control tower staff comprised an aerodrome controller, a surface movement controller and a coordinator. Aircraft traffic was a Cessna 172 engaged in circuit training, a helicopter operating close to the airport boundary, two other aircraft inbound to the circuit and a Piper PA 28 taxying for take-off. In addition, a maintenance vehicle was working in the vicinity of the runway.

The pilot of the PA 28 requested and was given a clearance, by the aerodrome controller, to line up on runway 32. The aircraft was lined up adjacent to taxiway F which is 430 m from the runway threshold. The PA 28 was held on the runway whilst the controller coordinated requirements for some of the other traffic. Shortly after the PA 28 lined up the pilot of the Cessna 172 requested a clearance to land on runway 32. The controller checked that the runway appeared to be unoccupied and cleared the pilot of the Cessna 172 to land. Shortly before the Cessna 172 touched down, the controller noticed that the PA 28 was still on the runway. He did not give any instructions to the pilot of either aircraft. The Cessna 172 landed on the threshold and turned off the runway at taxiway D, 390 m further on. The controller then cleared the pilot of the PA 28 to take-off.

The Manual of Air Traffic Services indicates that a controller should not clear an aircraft to land unless he or she is assured that the landing area will be available. Similar rules are set out in the Aeronautical Information Publications for pilots. Experience suggests that controllers normally use a combination of situational awareness and visual cues to help meet their runway requirements. The aerodrome controller reported his situational awareness was reduced by the distraction caused by the coordination requirements for other traffic and the maintenance vehicle. As a result, he forgot about the PA 28 after he had cleared it to line up. When the controller checked the runway for obstructions, after the pilot of the Cessna 172 had requested a landing clearance, his vision was partly obstructed by a visual display unit located on the console in front of him. As a result, he did not see the PA 28 until he stood up from his normal operating position. This did not occur until after he had given the clearance to land. At that point the Cessna 172 was about to touch down. The controller considered that any instructions from him might make the situation worse and he decided to say nothing. He knew the pilot of the Cessna 172 was very experienced and would avoid any conflict, if possible.

The other tower staff reported they were busy with their own tasks and were not aware of the impending conflict.

The pilot of the PA 28 was inexperienced and reported that he had not fully assimilated the other circuit traffic when he lined up on the runway. As a result, he did not recognise that the Cessna 172's clearance to land would place that aircraft in conflict with his.

The pilot of the Cessna 172 reported that he was concentrating on his student's performance and was not paying attention to other traffic. Therefore, he was not aware the PA 28 had not been cleared for take-off. He observed that the PA 28 was still on the runway as his aircraft approached touchdown. Assuming it had been given a clearance to take-off, he initially thought the PA 28 would get airborne before his aircraft landed. When the PA 28 did not move he reassessed the situation and decided it was safer to continue with the landing than to attempt a go-around. His student had to apply power to roll through to taxiway D, after landing.

Although the visual display unit obstructed the controller's vision of the runway from his normal operating position (seated), it is not unusual for similar obstructions to exist, particularly in older control towers where roof support-posts are used. Consequently, it is accepted practice for controllers to move their position when checking that a runway is not occupied. In this incident the controller did not do this before he cleared the Cessna 172 to land. It is probably that, in the pressure of the moment, he did not recognise that his vision was obstructed.

SIGNIFICANT FACTORS

The following significant factors were identified as contributing to the incident.

1. The aerodrome controller's situational awareness was reduced, by distraction, to a point where he forgot about the position of an aircraft that was critical to his clearance decision.
2. The aerodrome controllers scan of the active runway was obstructed by a part of the tower equipment, and, in the pressure of the moment, he did not recognise the obstruction. Consequently, the controller did not move to check the complete runway, and he did not observe the runway was still occupied, when he cleared the Cessna 172 to land.
3. The inexperience of the PA 28 pilot was a factor in his not recognising that the Cessna 172's clearance could place that aircraft in conflict with his.
4. The pilot of the Cessna 172 was distracted by his instructional activities and did not recognise that the PA 28 had not been cleared for take-off. Consequently, he allowed the student to continue the approach in anticipation the landing area would be clear before the aircraft touched down.
5. When the pilot of the Cessna 172 realised the landing area would not be clear, he assessed that the safest alternative was to continue to a landing rather than attempt a go-around. As a result, the Cessna 172 landed on an occupied runway.

The Twin Otter took off from runway 16L, on climb to 3,000 ft. Both pilots reported that shortly after entering cloud at 2,000 ft there was a bright flash from the nose of the aircraft, temporarily blinding them. All electrical services had failed, but there was an electrical burning smell and smoke in the cockpit, which cleared when the electrical fire drills were completed. The on-board Emergency Locator Transmitter had also self-activated. Suspecting a lightning strike, and having lost radio communications, the aircraft was flown back for a landing on runway 25, with the crew broadcasting their intentions blind. The aircraft subsequently landed safely.

The departures controller noticed that the radar return from the Twin Otter had lost its altitude display soon after departure and tried unsuccessfully to contact the pilot. He thought the aircraft had suffered a communications failure and, from its track, assumed it was returning to land on runway 25, and immediately cleared the adjacent airspace. The tower controller also noticed the aircraft was landing on runway 25 without communications and issued a landing clearance by flashing a green light signal.

A subsequent inspection revealed the aircraft had sustained a lightning strike on the nose. The nose cone bonding strip had been destroyed, and the resulting heat damage had ruptured the nose cone structure. The current had taken multiple exit paths throughout the aircraft, rendering most electrical services inoperative, before exiting at various points on the tail surfaces.

The strip was grass covered and wet. When the pilot applied the brakes after touchdown, the wheels locked, providing little retardation. The pilot ground looped the aircraft to avoid running off the end of the strip. During the ground loop, however, the aircraft ran slowly backwards into some bushes, causing damage to the right wing and elevator.

VH-PZN was cleared from Mansfield to Melbourne at 4,500 ft. 30 miles northeast of Melbourne, VH-PZN advised approach radar of sighting an unexpected light aircraft, head-on at the same altitude. To avoid a collision, VH-PZN descended immediately and passed approximately 300 ft below and about 100 metres abeam the other aircraft.

The unidentified aircraft did not show up on radar as a secondary surveillance radar (SSR) return. After the breakdown in separation, its primary return was plotted by the radar controller. All attempts by Air Traffic Services (ATS) to contact the aircraft by radio were unsuccessful until the aircraft subsequently called Melbourne radar advisory service (RAS) landing at Wallan. In the meantime, a Piper PA34 assisted ATS by following the aircraft and identifying it as VH-TOF.

The pilot of VH-TOF subsequently advised that he did not see or hear VH-PZN at any time. He advised that he had been viewing property on the ground from above. He did not believe that he had climbed above 4,000 ft at any stage of his flight.

Both aircraft were flying in accordance with visual flight rules (VFR) in visual meteorological conditions (VMC) with a cloud base of 5,000 ft above mean sea level (AMSL).

Significant Factors

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

1. The pilot of VH-TOF probably inadvertently climbed above 4,000 ft.

2. No SSR transponder returns were received from VH-TOF.

3. VH-TOF was not monitoring Melbourne radar advisory service frequency 135.7 MHZ within 35 miles radius of Melbourne until arrival at Wallan.

The Sector 8 (Oceanic) controllers’ area of responsibility extended from 58 to 320 km east of Sydney. In the period preceding the incident, there was significant military traffic operating in the area above FL300.

VH-TJD was identified on radar 45 km NE of position LOTRA. (LOTRA is a reporting point 071 degrees M, 240 km from Sydney.) VH-TJD was then cleared to track from LOTRA to position CHEZA (084 degrees M, 96 km Sydney) and to descend to 8000 ft.

About 10 minutes later, N188UA departed Sydney. The standard procedure was for this aircraft to intercept the

Sydney-LOTRA track inside 50 km Sydney. On this occasion, however, the Sydney Departures controller asked the Sector 8 (Oceanic) controller if N188UA could track direct to LOTRA. The Sector 8O controller approved the request. As a result, N188UA was in potential conflict with VH-TJD.

At the time of the request from the Sydney Departures controller, the Sector 8 (Oceanic) controller had been distracted by a telephone call concerning a radar technical matter. He checked the radar display for conflicting traffic before agreeing to the request and did not see any confliction. At this time, however, the radar symbol for VH-TJD was amongst the military traffic radar symbols and was not noticed by the controller. The controller approved the request from Sydney Departures on this basis, and without checking the flight progress strips which displayed the flight details of all aircraft under his control at the time, including VH-TJD and the military traffic. In not checking the strips, the controller failed to comply with standard procedures, thus bypassing an element of the safety net which may have alerted him to the conflict.

As N188UA was climbing through about 15000 ft, the crew advised the Sector 8 (Oceanic) controller that they were deviating left as they had sighted descending traffic ahead. Examination of the recorded radar data showed the two aircraft to have been at the same level at 7nm (12 km) lateral separation.  The minimum separation standard which applied in the circumstances was 1000 ft vertical separation, or 5 nm (8km) lateral separation. The 1000 ft standard was infringed when the aircraft were between 8 km and 6 km apart.

AMENDED TEXT

The Sector 8 (Oceanic) controller's area of responsibility extended from 58 to 320 km east of Sydney. In the period preceding the incident, there was significant military traffic operating in the area above FL300.

The B737 was identified on radar 45 km NE of position LOTRA. (LOTRA is a reporting point 071 degrees M, 240 km from Sydney). It was then cleared to track from LOTRA to position CHEZA (084 degrees M, 96 km from Sydney) and to descend to 8,000 ft.

About 10 minutes later, the B747 departed Sydney. The standard procedure was for this aircraft to intercept the Sydney-LOTRA track inside 50 km Sydney. On this occasion, however, the Sydney Departures controller asked the Sector 8 (Oceanic) controller if the B747 could track direct to LOTRA. The Sector 8 controller approved the request. As a result, the outbound B747 was in potential conflict with the inbound B737.

At the time of the request from the Sydney Departures controller, the Sector 8 (Oceanic) controller had been distracted by a telephone call concerning a radar technical matter. He checked the radar display for conflicting traffic before agreeing to the request and did not see any confliction. At this time, however, the radar symbol for the B737 was amongst the military traffic radar symbols and was not noticed by the controller. The controller approved the request from Sydney Departures on this basis, and without checking the flight progress strips which displayed the flight details of all aircraft under his control at the time, including the B737 and the military traffic. In not checking the strips, the controller failed to comply with standard procedures, thus bypassing an element of the safety net which may have alerted him to the conflict.

As the B747 was climbing through about 15,000 ft, the crew advised the Sector 8 (Oceanic) controller that they were deviating left as they had sighted descending traffic ahead. Examination of the recorded radar data showed the two aircraft to have been at the same level at 7 NM (12 km) lateral separation.  The minimum separation standard which applied in the circumstances was 1,000 ft vertical separation, or 5 NM (8km) lateral separation. The 1,000 ft standard was infringed when the aircraft were between 8 km and 6 km apart.