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.

The flight by Tiger Moth VH-AQN was the third in a series of 10-minute joy flights that day from the local airstrip. On board with the pilot were one adult and a 7-year-old child. Both passengers occupied the forward single seat, with the child sitting on the adult's lap. A lap type safety harness attached to the adult harness restrained the child.

The pilot reported that the engine appeared to be slightly harder to start than normal; however, once started, the engine performed normally. At about 150 ft above ground level after takeoff, and without warning, the engine began to run roughly and lose power. The pilot banked the aircraft to the right towards a nearby golf course to avoid the residential area directly ahead. He was able to manoeuvre the aircraft to land on a cleared area of the golf course. However, during the landing roll, the aircraft's left wings came into contact with a tree, which spun it sharply to the left. The aircraft then began to slide sideways and the landing gear collapsed. The aircraft continued to slide until the right wings came into contact with several other trees. After it came to rest, the pilot assisted the passengers from the aircraft. There were no injuries.

The aircraft sustained major structural damage to the upper and lower sections of the wings and the main landing gear separated from the fuselage at the upper attach points.

The aircraft was approved to operate on mogas (automotive gasoline). Examination of the aircraft fuel system indicated that sufficient clean fuel should have been available to power the engine. The engine sustained minimal damage in the accident, which allowed the investigator to conduct a test run of the engine. During the test run, the engine started without difficulty and accelerated normally.

Examination of the carburettor found that the float valve, which was made from natural cork covered with a fuel proof varnish seal, had two large blisters in the varnish. Further examination indicated that the larger of these blisters was binding against the float chamber housing walls. This could have caused either an excessively rich or lean mixture, which would have caused the engine to run rough and stop. When the spark plugs were examined immediately after the accident, they exhibited a slight oil wetness and sooting, which indicated that the power loss was probably due to an excessively rich mixture.

The float was removed and sent for specialist examination. This examination revealed that the blistered lacquer was very fragile, and that it broke easily and peeled in flakes without adhering to the cork. These characteristics were consistent with the use of a non-approved type of nitrocellulose dope, as identified in the Hobson carburettor overhauling and servicing manual. The examination was not able to conclusively determine the cause for the blistering of the varnish. The operator advised that the already varnished float, approved part number CHA31267, was purchased from the UK and was fitted to the Claudel Hobson model A148HIM carburettor approximately 160 flight hours prior to the accident. No other information was available regarding its history, or whether it was recently re-doped or re-lacquered with modern equivalent materials.

A search of the Bureau's database was unable to find any record of a similar event. During the investigation, several experienced Tiger Moth operators were contacted to ascertain their experience with this type of problem. These operators advised that they were aware of several incidents where the varnish surrounding the cork float had cracked and the cork float had then absorbed fuel. However, none had any previous experience of the varnish blistering in this manner.

FACTUAL INFORMATION

The crew of the Learjet registered as VH-SLJ and operating as Spider 14, had flight planned Canberra - Williamtown - Nowra and was preparing to complete the final leg. At the time, the control tower at Williamtown was unmanned and the control zone was operating as a mandatory broadcast zone (MBZ). While parked on the Royal Australian Air Force (RAAF) air movement section tarmac, the crew of SLJ was monitoring the MBZ frequency. They heard traffic information broadcast by the pilot of Navajo, VH-MYG and an Eastern Australia Airlines aircraft that were inbound to Williamtown. The two aircraft were self-separating and MYG elected to land on runway 12 and the Eastern aircraft positioned for a landing on runway 30. The wind was a light easterly from 070 degrees Magnetic.

The pilot of MYG was operating a "bank run" charter and had planned to make a quick turnaround at Williamtown. He landed MYG from a straight-in approach to runway 30 and, while on final approach, had heard Spider 14 make a general taxy broadcast on the MBZ frequency.

The crew of SLJ decided to depart from runway 12, which necessitated a long taxi on taxiway Alpha but less manoeuvring on departure. They made a general broadcast and reported lining up on runway 12. When approaching the threshold, they heard a taxi call broadcast by MYG so they broadcast on the MBZ frequency that their aircraft was rolling. As they commenced their take-off run from runway 12, they sighted MYG entering the runway 30 threshold from taxiway Juliet. The pilot in command considered aborting the takeoff but elected to continue because the aircraft was lightly loaded and would be airborne quickly. The crew saw the Navajo cross the runway and vacate into the operational readiness platform at the threshold of runway 30.

The pilot of MYG reported that during the turnaround at the civil apron, he remained in the aircraft and monitored the Williamtown MBZ frequency 118.3 MHz on the primary radio and the national advisory frequency 127.7 MHz on the secondary radio. After a short stop to offload one bag, he taxied MYG for a runway 30 departure and made a general broadcast to advise that he was taxiing. He reported that prior to entering runway 30, he scanned the runway and checked the final approach path and that on entering the runway, he made an entering and lining up broadcast. After making the broadcast he noticed the Learjet rolling towards him from the other end, and so vacated the runway to the operational readiness platform. The pilot of MYG did not hear crew of SLJ report lining up on runway 12.

A replay of the audio recording of the MBZ frequency indicates that the crew of SLJ did report lining up on runway 12 but that the pilot of MYG overtransmitted the last portion of the transmission. The crew of SLJ did not hear MYG report lining up on runway 30. Military staff informed the investigation team that the tower radio frequency at Williamtown (used as the MBZ frequency) had some gaps in its coverage.

Neither the crew of SLJ nor the pilot of MYG submitted an air safety incident report, which was required in accordance with AIP Australia ENR 1.14, paragraph 1.3.2.

ANALYSIS

The wind was a light easterly from 070 degrees magnetic and did not favour any particular runway. Mandatory radio broadcasts made on the MBZ frequency by the crews of both aircraft were appropriate and timely.

The pilot of MYG did not hear the "lining up" or the "rolling" broadcast made by the crew of SLJ due to limitations in the MBZ radio coverage. The crew of SLJ also did not hear the pilot of MYG report entering and lining up on runway 30 due to limitations in the MBZ radio coverage. The basis of this analysis is the tape recording of the event, where the pilot of SLJ had been transmitting for sometime before that transmission was overridden by the taxying broadcast made by the pilot of MYG. As a result of the limitations of the radio coverage of the Williamtown MBZ frequency, the crews of both aircraft were prevented from developing accurate situational awareness.

The pilot of MYG did not adequately scan the runway prior to entry for take-off.

SIGNIFICANT FACTORS

Neither crew heard the transmission of the other crew reporting lining up on the reciprocal runway.

The radio coverage of the Williamtown MBZ frequency was limited: the tower radio frequency at Williamtown (used as the MBZ frequency) had some gaps in its coverage.

The pilot of MYG did not adequately scan runway 12/30 prior to entry.

SAFETY ACTION

Local Safety Action

Williamtown ATS authorities issued a Notice to Airmen on 10 December 1998, alerting pilots of the unreliability of the MBZ frequency for ground-to-ground communications due to possible shielding.

Bureau of Air Safety Investigation Safety Action

As a result of this occurrence, the Bureau of Air Safety Investigation is investigating a perceived safety deficiency relating to limitations of the MBZ frequency.

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

As the aircraft descended through 7,500 ft, the controller informed the pilot that radar services were terminated. Below 8,500 ft the aircraft was in `Class G demonstration airspace' and the pilot was responsible for separation from other aircraft. To assist him in this task, he was advised of radar-observed traffic by the controller, within the limits of radar coverage and as the controller's workload permitted. The pilot had expected that such assistance would not be terminated at 7,500 ft but would be provided to a much lower altitude. Recorded data from three radar sites covering the area was examined during the investigation. 

Returns from the aircraft to one site were reliable down to 7,500 ft, while returns from the other two sites were broken for varying periods of time on a number of occasions during the descent. The radar system software utilised a built-in matrix to determine which radar data was used in specific geographical areas. The matrix had recently been changed as technicians attempted to obtain the best possible coverage for the area. The investigation found that radar coverage in the area the aircraft was operating was unreliable below about 7,500 ft.