The DC9 freighter crew performed a missed approach to Melbourne runway 27 when they did not get a landing gear safe indication after gear extension. The crew carried out a manual extension of the gear and obtained the safe indication, then proceeded to a safe landing. Because the landing gear doors remain open after manual extension the crew stopped the aircraft on the runway to allow engineers to secure the doors. This was the second of three similar events (refer BASI occurrences 9805884 and 9805886).

After two failed attempts to re-rig the landing gear system it was found that normal extension could only be achieved if the system was rigged outside of maintenance manual tolerances. The mis-rig problem has been referred to the aircraft manufacturer and the aircraft was cleared for flight. The aircraft has subsequently operated satisfactorily

FACTUAL INFORMATION

VH-TJN, a Boeing 737 (B737), was en route from Melbourne to Brisbane and tracking via air route H29 at flight level (FL) 290 and was estimating overhead Mudgee at 1938 ESuT.

VH-CZK, another B737, had departed Sydney at 1914, tracking via Richmond and Nyngan to Darwin on air route T74. The crew had planned to cruise at FL310 and was instructed by Sydney Air Traffic Control (ATC) to maintain FL280 due to airspace requirements in the Sydney area. Air routes H29 and T74 intersected 113 NM north-west of Sydney.

The crew of CZK was transferred from Sydney ATC to the Melbourne Sector 16 controller (SEC16) approximately 45 NM west of Sydney. The controller asked the crew of CZK if they could meet a requirement to climb to FL310 by 100 NM from Sydney. The crew of CZK responded with "... we are showing it 90 miles to run 310". The controller instructed the crew to climb to FL310, as he understood from their reply that the aircraft would reach that level by 90 NM from Sydney. Shortly after, the crew advised the controller that they would reach FL310 about 140 NM from Sydney. The controller then instructed the crew to maintain FL290. The controller advised the crew that they could expect further climb in approximately 25 NM once they were clear of crossing traffic in their 10 o'clock position at 18 NM.

The controller then observed CZK climbing above FL280 as it was passing TJN. The controller asked the crew of CZK to confirm that they were cleared to maintain FL280. The crew advised the controller that they had been cleared to maintain FL290. As CZK had already passed TJN, the crew of CZK was instructed to climb to FL310. Subsequent investigation of the radar recording found that CZK had passed within 2 NM laterally and 500 ft vertically below TJN. The prescribed vertical separation standard was 1,000 ft, and the lateral standard was 5 NM. There had been an infringement of separation standards.

The flight progress strip for CZK had been annotated with "280" to indicate that the crew was initially instructed to maintain FL280. This annotation had two adjacent ticks. The first tick was placed on the flight progress strip after the crew had made the initial call to SEC16, advising that they were climbing to FL280. The controller wrote "310" on the flight progress strip to record the instruction to climb to FL310, and this was ticked following the correct read-back by the crew. After the crew was instructed to maintain FL290 and they had read the instruction back correctly, the controller placed a second tick next to the existing "280" on the flight progress strip. The controller did not annotate the flight progress strip with "290" following the instruction to the crew to maintain FL290.

The controller had been rostered for one familiarisation shift after having spent 5 weeks instructing in the simulator and a further 2 weeks on annual recreation leave. The controller had been operating under supervision for approximately 4 hours of the shift and his supervisor reported that he was performing satisfactorily. He was subsequently certified to operate solo on sector 16. The controller then had a rest period of approximately 1 hour prior to operating the sector 16 position for the last 2 hours of his shift. The separation infringement occurred approximately 20 minutes prior to the completion of his shift.

The crew of TJN which was fitted with a traffic alert and collision avoidance system (TCAS), was conducting training during that flight and was aware of the crossing traffic. However, they thought that CZK was on climb to maintain FL280. As CZK passed behind them, they realised that CZK had climbed above FL280. The crew did not hear SEC16 advise the crew of CZK of the crossing traffic at 18 NM. The crew of TJN advised that they "also had the traffic sighted and on TCAS".

After receiving the query for the FL310 requirement from SEC 16, the crew of CZK had ascertained from the flight management computer that the aircraft would reach FL310 in 90 track NM. The pilot in command stated that he wished to convert this to, and report it as, a distance from Sydney in accordance with the request. The co-pilot advised the controller that they would reach FL310 in 90 NM from their present position. The pilot in command was not satisfied with that response and manipulated the flight management computer to obtain the top-of-climb distance as 140 NM from Sydney. This was then advised to the controller. The crew sighted TJN after the controller had advised them of the crossing traffic. They thought that the crossing traffic was at FL310. As CZK approached the intersection of the air routes, the crew thought that the crossing traffic, TJN, was approximately 1,000 ft above them. The crew of CZK advised that they had sighted the crossing traffic. CZK was not fitted with TCAS.

ANALYSIS

The response from the crew of CZK, "... we are showing it 90 miles to run FL310", led the controller to believe that the aircraft would reach FL310 by 90 NM from Sydney. The controller then issued an instruction to climb to FL310 with the intention of monitoring the separation on radar. When the crew later advised that they would reach FL310 by 140 NM from Sydney, the controller intended to revert back to his original plan and maintain CZK at FL280. The investigation could not ascertain why the controller subsequently issued the instruction to CZK to climb to FL290. The controller thought that he had issued an instruction to climb to FL280. However, he incorrectly instructed the crew to climb to FL290 and did not appreciate the error when the crew correctly read back FL290.

By giving CZK an unconditional clearance to climb to the planned level of FL310, the controller did not apply positive separation assurance. From that point on, the prevention of an infringement of separation standards between CZK and TJN depended on the controller remembering that this potential confliction was still unresolved, and then taking timely and appropriate action to positively separate the aircraft. In the event, when the controller returned to resolve the potential conflict between CZK and TJN, an error was made.

The controller did not advise the crew of CZK of the level of the crossing traffic as he thought that the aircraft were vertically separated. The crew of CZK thought that TJN was 1,000 ft above them. The crew of TJN was discussing training issues and was probably not as vigilant in maintaining their situational awareness as if in a non-training situation. If the controller had mentioned the callsign of the crossing traffic, the crew of TJN may have realised that they were in fact the conflicting aircraft.

SIGNIFICANT FACTORS

1. The response from the crew of CZK to the level requirement was ambiguous and misled the controller into believing the aircraft would reach FL290 by 90 NM from Sydney.

2. The controller cleared the aircraft to the incorrect level and did not recognise the error when the crew read back the level.

The DC9 freighter crew performed a missed approach to Melbourne runway 27 when they did not get a landing gear safe indication after gear extension. The crew carried out a manual extension of the gear and obtained the safe indication, then proceeded to a safe landing. Because the landing gear doors remain open after manual extension the crew stopped the aircraft on the runway to allow engineers to secure the doors. This was the second of three similar events (refer BASI occurrences 9805884 and 9805887).

After two failed attempts to re-rig the landing gear system it was found that normal extension could only be achieved if the system was rigged outside of maintenance manual tolerances. The mis-rig problem has been referred to the aircraft manufacturer and the aircraft was cleared for flight. The aircraft has subsequently operated satisfactorily

The DC-9 freighter crew performed a missed approach to Melbourne runway 27 when they did not get a landing gear safe indication after gear extension. 

The crew carried out a manual extension of the gear and obtained the safe indication, then proceeded to a safe landing. Because the landing gear doors remain open after manual extension the crew stopped the aircraft on the runway to allow engineers to secure the doors. This was the first of three similar events (refer BASI occurrences 9805886 and 9805887).

After two failed attempts to re-rig the landing gear system it was found that a normal extension could only be achieved if the system was rigged outside of maintenance manual tolerances. 

The mis-rig problem has been referred to the aircraft manufacturer and the aircraft has been cleared for flight. 

The aircraft has subsequently operated satisfactorily.

After landing, the pilot was manoeuvring his aircraft in the parking area when the right wingtip fuel tank collided with a parked aircraft. The fuel tank was ruptured in the collision and a small fire erupted which was quickly extinguished with portable fire extinguishers. The pilot subsequently reported that, though the area was restricted, there was sufficient room to manoeuvre but he had misjudged the distance between the two aircraft.

Whilst taxiing via taxiway K2 for a night departure from runway 11C, a Piper Archer collided with a preceding Trinidad. Both aircraft were substantially damaged in the accident but neither occupant was injured.

The pilot of the Archer reported that he had arrived at the aerodrome after dark, noticed there was no wind, and assumed that the preferred direction for operations would be from runway 29C. The control tower was not manned. After starting, he made a taxiing broadcast then proceeded to the run-up area for runway 29C. Whilst there he observed other aircraft operating from runway 11C so, in order to conform with the circuit direction in use, he commenced to taxi to the other end of the runway via taxiway K. He did not see any other aircraft on or entering the taxiway.

The pilot subsequently noticed that his taxiing speed had increased so he closed the throttle and momentarily applied the brakes. However, he then saw the dark bulk of an aircraft immediately ahead of him and applied heavy braking, but instead of moving the mixture to the idle cut-off position to stop the engine, he mistakenly applied full power. Realising he could not stop, he steered the aircraft to the left but the right wing collided heavily with the tail of the Trinidad. Both pilots shut their respective aircraft down and vacated without injury.

The Trinidad was fitted with wing and tail navigation lights which all operated normally after the accident. The aircraft was also equipped with a white flashing strobe light on the top of the rudder, in lieu of a red rotating beacon, in accordance with the requirements of the Civil Aviation Regulations. However, Aeronautical Information Circular H12/95 recommends that, to avoid possible impairment of night vision, white strobe lights should be turned on when entering active runways and turned off when clear of the active runway after flight.

The only light visible to the pilot of the Archer from the Trinidad was the steady white tail navigation light, which would have blended with the background lighting of the surrounding houses and streetlights, and was not seen by the pilot of the Archer. As the Trinidad was not entering an active runway, the white strobe light was not operating, although the navigation lights were turned on. Notwithstanding the actions by the pilot of the Archer, had the Trinidad been required to display an anti-collision light it may have provided a more timely warning for collision avoidance.

SAFETY ACTION

As a result of this occurrence, the Bureau of Air Safety Investigation is investigating a safety deficiency.

The deficiency identified relates to the requirements for anti-collision lights on aircraft.

Any safety output issued as a result of this analysis will be published in the Bureau's Quarterly Safety Deficiency report.

FACTUAL INFORMATION

The BAe 146 aircraft was being operated on a routine passenger flight from Proserpine to Brisbane. When the crew selected full flap during the approach to Brisbane, they noticed an aerodynamic vibration through the airframe which was associated with a tendency for the aircraft to roll to the right. The crew were able to control the roll and continued the approach for an uneventful landing.

Examination of the aircraft revealed that about 600 mm of the forward edge of the bonded and riveted upper surface panel for the right wing flap had partially separated. The failure occurred at about the mid-span position and 38 rivets were found to be either damaged or missing. The panel had a chordwise crack approximately 25 mm long, at the outboard end of the separated section. At rest, the edge of the panel protruded above the leading edge surface by about 10 mm. Preliminary assessment indicated that the rivets had failed progressively over an extended period.

The maintenance documentation for the aircraft showed that the flap was fitted to the aircraft during original manufacture and had accumulated a total of 25,642 cycles and 25,203 hours time in service.

The aircraft had undergone a heavy maintenance "C" check on 19 December 1998, 11 days prior to the incident. Approximately 35 loose or cracked rivets on the outboard section of the flap were replaced at that time.

Examination of the remainder of the flap revealed exfoliation corrosion in the faces of the track link bearing lugs at four locations. Specialist advice was that "the corrosion appears to be substantial and will require removal of the links and bearings at these locations, with treatment, rectification and/or lug bracket replacement as required". The manufacturer's system of maintenance specified a "walk around check" at 2,000 hour intervals, with an "external visual inspection" at 4,000 hour intervals which coincided with the "C" check.

A section of the failed flap panel approximately 540 mm long by 150 mm wide, containing 25 rivet holes including the part containing the crack, was removed from the panel and forwarded for specialist metallurgical examination. Once disassembled it was found that the crack consisted of fatigue fractures emanating from opposite sides of a rivet hole. The fractures had initiated at the hole to countersink transition. The crack then grew under span-wise tension loads. These loads developed progressively after a number of rivets had separated, allowing a part of the panel to lift when subjected to aerodynamic loads. The upward movement of the panel then translated into span-wise tension at the crack location. The examination also found that the mating surfaces of the aluminium sheet panel and flap structure had a thin coat of a light brown coloured sealant applied. It was found that this sealant had penetrated into some rivet holes and countersinks.

The specialist metallugical examination concluded that failure of the riveted joint was precipitated by the presence of the sealant between the joint mating faces. The ATSB was advised that all significant repairs to the flap structure were normally only conducted at the factory. However, under certain circumstances the manufacturer may approve repairs on a one-off basis.

The manufacturer was approached for information relating to the use of the sealant to determine if it was introduced during manufacture or during a subsequent repair action. Despite numerous approaches, no information was received.

The specialist metallurgical report further advised that a fundamental requirement for any effective structural joint is that the clamping force must be high enough to prevent slip and wear of the joined parts and that it must remain stable over the life of the joint. Because the sealant is inherently less stiff than the panel, and the stiffness of the flap structure or the rivet may change over time, the sealant may be expelled from the joint. This would result in a reduction or a loss of the clamping force. Consequently, the joined parts would be allowed to move relative to one another when subjected to service loads. Any movement within a joint would then subject the rivets to higher than normal loads, and progressively wear them to the point of failure. Once one rivet failed, the load it carried would be transferred to the other rivets, triggering a progressive failure of the joint.

It is possible that the sealant may have been introduced after flap manufacture, during an in-service repair. However, no relevant information was available.

SAFETY ACTION

As a result of this incident, and concerns about the effectiveness of certain aspects of the "C" check heavy maintenance inspection, the operator raised two Technical Service Instructions (TSIs). The first called for an immediate fleet inspection to report loose rivets. This fleet inspection revealed that 3 other aircraft of the operators fleet were affected. One of these aircraft required the replacement of between 20 and 30 "working rivets" on both flaps in the same position as for VH-NJQ.

The second TSI required a once only inspection, with the flap removed at the next heavy maintenance visit, to facilitate an in-depth inspection of the carriage links and attachment bolts.

In reply to concerns raised by the ATSB during the investigation, the Civil Aviation Safety Authority conducted an investigation into the circumstances leading to the flap failure and to assess any possible breakdown in the operator's system of maintenance. The subsequent CASA report stated in part, "investigation revealed there were no special circumstances that led to the flap failure so soon after repair work in the area. The BAe Structural Task Group for Ageing Aircraft have indicated that the flap is a weak area; with corrosion and exfoliation a problem". The report further advised that the manufacturer's corrosion prevention control program will address the deficiencies in the system of maintenance.

At the time of finalising this investigation, no further reports of flap failure, similar to this occurrence, had been reported to the Bureau.

During the take-off ground roll at approximately 90 kts, the left engine ingested a Galah and the gas producer (Ng) speed reduced to below 60% accompanied by the ignition light illuminating. Power was reduced and the take-off was discontinued. Maintenance investigation found a bird carcass and feathers partially blocking the engine air intake. After removal and inspection for damage, ground runs were carried out to verify engine performance parameters, and the aircraft was returned to service.

A formation of two F/A-18A (Hornet) aircraft were tracking from Townsville to Williamtown on airway Y124, maintaining Flight Level (FL) 350. A Boeing 767 (B767) tracking from Brisbane to Darwin on airway A464 was also maintaining FL350. The tracks of the two airways crossed at a position approximately 80 NM north-west of Taroom.

At 1127, the crew of the B767 contacted the sector 5D radar controller, on climb to FL350. At 1135 (approximately 100 NM north of the crossing point) the Hornet formation, also maintaining FL350, made initial contact with sector 5D. Numerous exchanges occurred between the formation and the 5D controller with reference to the formation's track and confirmation of their next waypoint. The controller had a moderate workload due to other traffic operating in the sector at the time.

At 1149, the radar controller recognised that the proximity of the Hornet formation and B767's position symbols might result in a loss of separation, and issued the crew of the B767 with an instruction to immediately descend to FL330. Recorded radar data indicated that the B767 and the Hornet formation were 20 NM apart at that time. Once the crew of the B767 had responded to the descent instruction the controller issued traffic information about the Hornet formation.

The controller then made three attempts to contact the Hornet formation. The first two were to issue a climb instruction, however, no response was received. The controller then issued a traffic statement to the formation regarding the conflicting traffic, but again received no response. The crew of the B767 advised that they had received traffic alert and collision avoidance system (TCAS) indications and questioned whether the Hornet formation had responded to the control instructions to climb.

Radar data showed that the B767 passed behind the Hornet formation with a minimum separation of 4.9 NM. At that point, the B767 was passing FL333 on descent. The required separation standard was either 5 NM lateral or 2,000 ft vertical separation.

From the time the Hornet formation initially reported on frequency, there were at least 16 transmissions with reference to the formation's tracking and controller/aircrew confirmation of a track waypoint. During a subsequent interview, the controller advised that he was concerned that the formation was off-track, and continuing to diverge to the right, because this had the potential to bring the aircraft into conflict with traffic on a northbound route. This distraction may have led to a reduced scan rate on the radar and late recognition by the controller of the impending confliction with the B767.

As the aircraft approached the top of climb the crew received a warning indicating a failure of the equipment cooling system. Ground engineering were contacted and the failure was confirmed. After dumping fuel, the aircraft returned to London and landed without further incident. A post-flight inspection revealed broken wiring within the electrical loom to the equipment cooling valve. The wires had arced and there was evidence of charring to the cargo hold insulation blanket in that area.

Because the aircraft had returned to London, the incident was investigated by the UK Air Accidents Investigation Branch. They reported that the broken wiring was difficult to locate as it had been incorrectly routed beneath the thermal insulation blanket in the forward cargo hold. It was evident that a small fire had occurred to the outer film of the blanket and that this was associated with the broken wiring. The fire had affected an area of about 40 X 15 cm. Water, resulting from condensation, was present in the bilge and it was considered possible that this may have limited the extent of the fire. As the integrity of the blanket had not been compromised, it was not replaced. The blanket had recently been changed for a lighter weight blanket manufactured in-house by the operator and met the flammability requirements. The wiring was repaired by in-line splicing and the aircraft returned to service.

The report added that the maintenance crew considered that the wires may have been inadvertently damaged when they were stepped on whilst hidden from view, possibly when the blanket was replaced. The maintenance personnel reported that it was not uncommon to lose balance whilst working within the cargo bays.