The DH114 was enroute Undara-Weipa, cruising at 10,000 ft and estimating abeam Cohen at 1505. The C402, Aurukun-Cairns was estimating Holroyd River at 1505, had planned at 9,000 ft but, approaching that level, the pilot advised climbing to 10,000 ft and requested traffic. The flight service operator mentally projected the track of the DH114 on the chart (the Aurukun-Cairns track had already been marked on the chart) and assessed that, based on the respective abeam Cohen and Holroyd River estimates, there would be no traffic confliction. Shortly after reporting abeam Cohen, the pilot of the DH114 advised that another aircraft had passed close by, in the opposite direction, and at the same level. This aircraft was later identified as the C402.

The flight service operator was working area 7 and area 5 combined. The level of activity in these areas had become very busy, but not unmanageably so, in the period leading up to the occurrence. The operator said, that when the pilot of the C402 requested traffic and he had assessed there would be no confliction, the track he had mentally plotted had been incorrect. One reason for this was that the track crossed two charts which were displayed at separate parts of his console. Another was that the position of Undara used by the operator was incorrect. The operator said that he had intended to plot the Undara-Weipa track on the chart to confirm his mental calculation but had forgotten to do this in the time available.

During recovery from a stick shaker exercise, as part of an endorsement sequence, the aircraft departed from controlled flight prior to the speed reducing to the published stick shaker speed. Recovery was reported to have taken approximately 1800 feet. The aircraft was returned to maintenance for investigation.

During the maintenance investigation, three minor leaks were found from butt straps on the left-wing leading edge. Advice from the manufacturer was that such leaks could definitely affect the stalling behaviour of the aircraft. The leaks were rectified and a subsequent test flight confirmed stalling characteristics were normal.

After completing a short flight to check water points on his farm the pilot returned to his 3000 ft landing strip and conducted a low-level inspection to identify any sheep near the strip and frighten away those he saw. This was his normal arrival practice when there were sheep in the home paddock. During the aircraft's landing flare, a single sheep bolted across the landing strip. This happened too quickly for the pilot to take avoiding action. The aircraft hit and killed the sheep whilst the aircraft was still rolling at about 40 knots.

Whilst in cruise at FL310 the cabin altitude commenced to rise. A check of the Engine Indication and Crew Alerting System (EICAS) showed the cabin was rising at 500ft/min, and all air-conditioning packs were off. The check list was actioned, but no packs were able to be reset. The system fault light remained on. At about 8000 feet cabin altitude, which was still climbing at 500ft/min with no packs on, the aircraft was descended to the lowest safe altitude and a diversion to Karachi initiated. A PAN call was made, and Tehran and Karachi were informed.

The Pack Temperature Controllers (PTC) were removed and inspected by the manufacturer who subsequently reported that a capacitor failure on the printed circuit board of the PTC in position 'A' caused all three pack flow control valves to close. The 'B' position PTC took control of the packs, as designed, but could not override the flow control valve closure commands from PTC 'A'. The manufacturer has instituted a modification program to the PTC to eliminate the problem.

The student was performing a dual practice forced landing on to an airfield. Strong winds and gusty conditions prevailed. It was the instructor's intention to allow the student to continue the practice forced landing to a low height for realism. The student forgot to lower the landing gear, and the instructor missed the oversight. On short final the aircraft encountered windshear. The instructor was late in nominating the go-around. The aircraft struck the ground wheels up.

The pilot reported hearing a snapping sound during landing gear retraction and subsequently confirmed that the nose gear had not fully retracted. Flight Service were advised of the problem and the aircraft diverted to Bankstown. An uncertainty phase was declared and emergency procedures implemented. The aircraft subsequently made an emergency landing, during which the nose gear collapsed.

Subsequent investigation determined that the nose gear actuating rod end had failed from fatigue cracking. The fatigue had initiated from a pre-existing crack. It is likely that the original crack had originated from a previous nose gear collapse in October 1993 when the aircraft had collided with a kangaroo.

The pilot flew three passengers out of Geelong on a private pleasure flight. Upon return he performed a normal circuit and approach with the intention of a full stop landing. On touchdown the aircraft bounced slightly. The pilot applied slight forward pressure on the control column. A second slightly higher bounce occurred. A third and final bounce resulted in a heavy landing which broke off the nosewheel.

Both balloons were departing from the same area and commenced inflating their envelopes at about the same time. VH-HJA, the smaller balloon, was ready for launch first and after take-off initially drifted in a south-westerly direction before reversing direction and drifting back towards the take-off point, at about 200 feet above ground level.

At about this time VH-AJB was ready for launch, and after take-off it began to drift to the south-west toward the approaching VH-HJA. The pilot of VH-AJB signalled to the other pilot to climb. Despite the pilot of the smaller balloon operating the burners, the envelope of VH-AJB collided with the basket of VH-HJA. The basket was tilted to an acute angle, but all the occupants managed to maintain hold and remained in the basket. The envelope of VH-AJB became snagged on the basket but was released by a passenger in VH-HJA. Both balloons then separated and continued their respective flights without further incident.

In general, the procedures governing ballooning require that the higher balloon give way to the lower balloon. However, it is also a requirement that aircraft (including balloons) on the ground give way to those that are airborne.

In this case, it would have been prudent for the pilot of VH-AJB to have delayed his take-off until the other balloon was well clear. Equally, the pilot of VH-HJA should have climbed his balloon when he saw that it was drifting back towards the departure point where the other balloon was preparing for take-off.

FACTUAL DATA

VH-CZK and VH-TAZ were both enroute from Melbourne to Sydney on the same track.  CZK departed Melbourne at 0544 UTC and was cruising at flight level (FL)330.  TAZ departed Melbourne at 0546 and was cruising at FL350.  Both aircraft transferred from Melbourne Sector 2 to Melbourne Sector 7 at 0613.  CZK was instructed to hold at Cullerin and was cleared to descend when ready to FL240 with a requirement to be at FL240 by Cullerin.  TAZ was also instructed to hold at Cullerin and cleared to descend when ready to FL250 with a requirement to be at FL250 by Cullerin.  At this time the two aircraft were separated by 18 NM with a closing speed of 20 kts. Both aircraft had previously been issued with standard arrival route (STAR) clearances for Sydney when they transferred from Departures Control to Sector 2.

At 0614 CZK reported leaving FL330 on descent and at 0617 TAZ reported leaving FL350 on descent. At 0617 the distance between the two aircraft had closed to 7 NM and the closing speed had increased to 125 kts. At 0618 the aircraft were 4 NM apart with a closing speed of 160 knots and approximately 4,000 ft vertical separation.

At 0618.44 CZK was instructed to cancel holding at Cullerin, resume the Rivet one STAR, hold at 70 NM Sydney and descend to FL220.  At 0619.06 CZK was instructed to reach FL220 by 70 NM Sydney.  The first requirement to reach FL240 by Cullerin was not cancelled.  By this time the two aircraft were 2 NM apart with a closing speed of 182 kts and 2,800 ft of vertical separation.

At 0619.30 when the radar blips for the two aircraft merged the vertical separation was 2,300 ft, and when the blips parted as TAZ overtook CZK, vertical separation was 1,600 to 1,800 ft. When TAZ was 2 NM ahead of CZK both aircraft were at FL256 just short of Cullerin.  CZK was at FL248 at Cullerin instead of FL240 as instructed.

At 0620.28 the controller noticed for the first time the minimal longitudinal and vertical separation between the two aircraft and instructed TAZ to maintain FL260.  TAZ did not respond so the instruction was repeated at 0620.40. Again, there was no response, and the instruction was repeated at 0620.47. By the time TAZ responded it had descended below FL260. The controller then asked CZK "do you have the traffic sighted in your twelve o’clock at five miles". At this time TAZ was estimated to have been only 2 to 3 NM in front of CZK.

The high closing speed that developed between the aircraft resulted from CZK slowing down in preparation for entering the holding pattern. CZK did not notify the controller of a variation to standard descent profile as required by AIP/OPS CTL 9 and the controller did not notice the speed differential developing between the aircraft.

When the holding requirement for CZK at Cullerin was cancelled and the new holding instruction to be at FL220 by 70 NM Sydney was issued, the crew of CZK believed the Cullerin descent requirement was no longer current.  The controller did not restate, nor was he required to restate, that the first descent requirement was still current.  CZK did not reach FL240 by Cullerin.

Neither aircraft were fitted with a traffic alert and collision avoidance system (TCAS).

ANALYSIS

When the aircraft transferred to Sector 7, they were separated by 18 NM with a closing speed of 20 kts.  As both aircraft were to hold at Cullerin they were issued with descent clearances and descent requirements which were intended to establish vertical separation before turning outbound in the holding pattern.  With 18 NM separation, about 60 NM to run to Cullerin and a closing speed of 20 kts, the controller would normally be confident that the aircraft could maintain sufficient longitudinal separation into the holding pattern.  The controller apparently assessed this to be the case and discounted the need to pay further attention to the closing speed.

The crew of CZK did not advise the controller that the descent speed had been reduced from standard profile in preparation to enter the holding pattern.  When crews wish to vary descent from standard profile by more than 10 kts or M.025, they are required to advise air traffic control in accordance with AIP/OPS CTL-9, para 20.1.

When the holding requirement for CZK at Cullerin was cancelled and new holding and descent requirements were issued, the initial requirement to be at FL240 by Cullerin was not cancelled.  The crew mentally discounted the original Cullerin descent requirement when the new holding and descent requirements were issued.  In such circumstances it is understandable how crews could make such an assumption simply on the basis that the descent requirement was associated with the holding requirement which was cancelled.  With hindsight, it would have been prudent for the controller to have stated that the Cullerin descent requirement was still current.  It may also have been prudent for the crew of CZK to clarify the matter.

When the controller finally noticed the ensuing separation problem with the two aircraft, he instructed TAZ to maintain FL260.  TAZ did not respond until the instruction had been issued three times by which time it was too late to prevent loss of separation between TAZ and CZK.

Neither of these aircraft was fitted with TCAS.  Had TAZ been so fitted, the crew may have received a resolution advisory as they approached CZK.

This occurrence also involves situational awareness considerations.  Both crews were monitoring the same radio frequency, and both should have heard transmissions to/from each other's aircraft. They were under radar control and should have been able to rely on the controller for separation advice. When the crew of CZK varied their descent profile without advising the controller, the potential arose for a reduction in longitudinal separation. Failure to comply with the Cullerin descent requirement then led to a breakdown of separation. The crew of TAZ were not aware of either of these aspects and therefore had no cues pointing to an impending problem.

CONCLUSION

Significant factors

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

1. The controller did not believe that longitudinal separation would be a problem. Consequently, he did not adequately monitor the progress of CZK and TAZ.
2. The crew of CZK did not advise the controller that they were descending at a speed well below the standard profile speed.
3. The crew of CZK incorrectly assumed that the Cullerin descent requirement was cancelled when they were issued with new holding and descent requirement instructions.
4. The status of the Cullerin descent requirement was not queried or clarified by the crew of CZK or the air traffic controller.
5. Neither aircraft was fitted with TCAS.
6. The crew of CZK did not maintain adequate situational awareness.
7. The crew of TAZ did not respond to a control instruction to limit their descent to FL260 until it was too late to prevent the loss of separation.

SAFETY ACTION

As a result of the investigation the Bureau of Air Safety Investigation issued an interim recommendation IR 950088 to the Civil Aviation Authority on 21 June 1995.  It stated:

The Bureau of Air Safety Investigation recommends that the Civil Aviation Authority revise ATS phraseologies and procedures so that whenever a new requirement is issued, the status of the previous requirements is clarified.

The Civil Aviation Safety Authority response was received on 15 August 1995.  It stated:

Reference IR950088

This recommendation relates to the application of subsequent altitude requirements and proposes that ATS phraseologies and procedures be modified to ensure that whenever a new requirement is issued the status of the previous requirement is clarified.

ATS agrees with this recommendation and proposes the inclusion of the following text into MATS/AIP documentation at the next opportunity:

xx.1 Except as stated in xx.2, whenever a level restriction or requirement has been imposed, and subsequently a further level/restriction is imposed, the subsequent instruction will cancel all previous restriction/requirement(s), unless:

1. all restrictions/requirements are re-stated; or
2. the subsequent instruction is prefixed "FURTHER REQUIREMENT";

xx.2 If a STAR or SID has been issued, the level of tracking restrictions will always remain in effect unless: a. the aircraft has been vectored away from the SID or STAR after commencement; or

b. ATC advises "CANCEL STAR/SID"

MATS ONLY

NOTE Controllers should be aware that where level requirements are imposed through a letter of agreement with an adjacent sector, issuance of new requirements may invalidate previous requirements unless the procedures xx.1 and xx.2 are adhered.

The Bureau has classified this response as CLOSED/ACCEPTED.

The aircraft arrived at the country airstrip ten minutes after first light. The pilot reported that there were no signs of animals in the area, but that during the subsequent landing roll a kangaroo jumped out in front of the aircraft. The animal collided with the left mainwheel which collapsed causing the left propeller to strike the ground and the aircraft to veer to the left. The aircraft ran off the strip into a ditch, tearing off the nosewheel. Neither occupant of the aircraft received injuries.