Arriving at the destination the landing gear failed to extend when the pilot selected it down.

His attempts to extend it using the manual hand pump were unsuccessful as he was unable to build up enough hydraulic pressure in the system to operate the gear. Hydraulic fluid was then noticed seeping from behind the centre console which he identified as a serious leak from the power pack He was able to replenished the lost hydraulic fluid with spare engine oil carried onboard the aircraft, but this failed to rectify the loss of hydraulic pressure.

After calculating the aircraft's endurance, the pilot decided to return to Darwin where he carried out a wheels up landing.

An inspection revealed that one of the "O" ring seals located at the joint between the landing gear manifold and the power pack was split, causing a hydraulic fluid leak, and loss of hydraulic pressure.

The manifold had been removed the previous day to change the servo-valve, and it is possible the "O" ring was damaged during reinstallation. Several successful gear retraction tests had been carried out after completion of the work, followed by about 9 gear cycles in flight before the leak developed.

The crew of the B737 were cleared to track via PEPPA for a SPUDO 1 arrival for runway 24 at Perth. At PEPPA the aircraft was observed to turn onto a south-westerly heading instead of continuing towards the west. This turn placed the aircraft in potential conflict with outbound traffic and radar instructions were issued to maintain adequate separation. The crew of the B737 later indicated that they had started to fly a PEPPA 1 (218 degrees) arrival instead of the SPUDO 1 (263 degrees) arrival.

Evidence indicates that the B737 crew misunderstood the clearance. As part of the aviation safety net there is a requirement for crews to repeat a clearance back to the controller to confirm they have received it correctly. The crews read-back on this occasion, indicated they would complete a PEPPA 1 arrival rather than a SPUDO 1. This error was not picked up by the controller. The clearance had been given in an abbreviated form, and it is possible this contributed to the crews misunderstanding, particularly, as the arrival procedure had only recently been introduced (5 December 1996) and was not yet easily recognised by flight crews.

Post-accident engine testing indicated the engine should have been capable of normal operation. Inspection disclosed that the internal wall of the air intake duct, located between the filter and the engine, had collapsed restricting airflow to the engine. The restriction in airflow probably led to the reduction in power reported by the pilot. The ducting consisted of an inner and outer cloth-wall sandwich supported by a wire spiral located between the walls. The duct was also bound with string on the outside. The walls were bonded together on either side of the wire. Some of the bonding between the inner and outer walls had delaminated allowing the inner wall to collapse. The ducting did not have the airframe manufacturer’s part number and was a different type to that approved by the aircraft manufacturer.

The ducting fitted was Aeroduct SCEET 16, a duct that is often used in aircraft systems such as air conditioning, but not for negative pressure applications. The manufacturer approved ducting consists of Aeroduct SCAT 16, a heavy-duty ducting suitable for engine intake applications.

The aircraft had been engaged in low level survey work in very hot conditions. It is probable this led to a deterioration in the bond between the duct walls. On the day of the accident the partially clogged air filter probably increased the negative pressure in the intake duct sufficiently to cause the delaminating inner cloth liner to partially detach and block off the intake airflow. The weakened inner duct wall probably detached before the negative duct pressure reached a level sufficient to open the alternate air door. From that point on the emergency landing was inevitable. If the correct SCAT 16 ducting had been fitted it should have prevented the occurrence. The fitment of incorrect ducting was brought to the attention of the maintenance organisation that carried out the work and the regulatory authority.

Over a period of four days the aircraft operated twenty sectors with a high pitch squeal emanating from the L2 door. The squeal reportedly occurred at the top of climb and during cruise and stopped when power was reduced and descent commenced. On some sectors the squeal was not reported. On other sectors it was controlled by lowering the cabin differential pressure. At times the squeal was so loud that earmuffs were worn by the cabin crew, and passengers were seated away from the area. The investigation was unable to determine who issued the verbal instruction which resulted in the earmuffs being issued.

After many attempts at rectification the aircraft was removed from service and ferried to Melbourne. During the flight a licensed aircraft maintenance engineer was able to remove some trim and closely inspect the door. He found that above certain pressure differentials and airspeeds the lower door seal was able to flutter. The door was examined and found to be rigged to the upper limit allowed by the maintenance manual. The door assembly was rerigged to the lower limit. During a subsequent verification flight, the seal was found to be secure. The adjustment required was small, the door being lowered less than four mm.

The investigation disclosed that many factors had inhibited the early detection and rectification of the problem.

These included:

• an inadequate system of recording cabin defects,
• flight crews did not always record that the defect existed,
• flight attendants gave incomplete reports to flight crews, - a lack of timely advice to maintenance management, and
• the difficulty in visually identifying the seal flutter.

The investigation also found there had been inadequate communication links between:

• flight attendants and the company's cabin safety management,
• the flight attendants union and the company cabin safety management,
• cabin safety management and maintenance, and
• flying operations, cabin safety management and maintenance.

While it is undesirable to have a defect existing for so many sectors, this particular defect was difficult to detect in normal service and was not found until after the door trim was removed and the seal closely inspected in flight. The major safety concern was that on some sectors the cabin crew wore earmuffs which could have prevented them from immediately responding to some other problem, should one have occurred.

Safety actions taken

The operator is introducing a system of recording cabin defects that will stand alone from the technical report used by flight crews. This will require appropriate certification to transfer technical items into the maintenance log and will also enable cabin crews to have access to a running history of cabin reports.

The operator has also instituted an enhanced communications structure that will allow pilot reports to be rapidly conveyed to maintenance management, ensuring direct contact between operations, maintenance and cabin safety management. The operator's cabin safety management has advised cabin crews to make immediate telephone contact with them in the event of similar problems occurring.

The BAe146 was inbound to Kununurra from Curtin and the crew had been listening on both the area and the MBZ frequencies. They heard the pilot of the C207 make contact with Perth and discuss SARTIME arrangements and give his destination as Broome. This information indicated the C207 might be conflicting traffic for their arrival. They assumed the C207 was still on the ground at that time. As nothing further was heard from the pilot of the C207, the crew of the BAe146 made several attempts to contact him. When contact was established the C207 was 12 NM from Kununurra on the 242-degree radial at 5,500 ft. The BAe146 was 14 NM from Kununurra on the 250-degree radial at 3,800 ft, on descent.

The pilot of the C207 reported that his aircraft was fitted with one VHF set. After making his departure report on the MBZ frequency he changed to the area frequency and became engaged in a discussion with Perth flight service about his SARTIME. The discussion took longer than expected and during that time he could not hear any transmissions from the BAe146 on the MBZ frequency. When he changed back to the MBZ frequency he heard the transmission from the BAe146, and he answered immediately. He had tracked south of the Kununurra - Broome track to remain clear of cloud. He does not believe he came close to the BAe146.

It is likely that the discussion between the pilot of the C207 and Perth flight service, which the crew of the BAe146 assumed had taken place whilst the C207 was still on the ground, was the one that occurred after the C207 had departed. Consequently, the BAe146 crew did not hear the taxi and departure transmissions that preceded that discussion. The fitment of only one VHF set prevented the pilot of the C207 from adequately monitoring the MBZ frequency and, as a result, separation between the two aircraft could not be arranged in a timely fashion.

The pilot of the PA28 called Essendon tower completing a left orbit of the central business district and requested a clearance direct to Point Ormond.  His clearance was conditional on remaining clear of the DC3 which he believed he had in sight.  Shortly thereafter, the pilot of the DC3 reported a 200 metre near miss with the PA28.

The PA 28 pilot explained that at the time he was asked by the tower controller if he had the DC3 sighted, he saw an aircraft some distance off to the right, which soon passed abeam.  He presumed this was the DC3.  Believing that DC3 traffic had passed, he was shocked to see aircraft navigation lights directly ahead.  Immediately he altered heading slightly to the right but as the navigation lights continued to approach at about the same altitude, he banked steeply right and descended to 1,700 ft.

The PA28 pilot subsequently advised that judging distance to the head-on DC3 lights was difficult because of the background blackness of Port Phillip Bay.   For the DC3 pilot, the near miss was so sudden he did not achieve any evasive action.  Until the PA28 banked steeply, the DC3 pilot did not see it, probably because the PA28 navigation lights merged with the myriad of background lights of Melbourne suburbia.

In hindsight, the PA28 pilot believes each aircraft would have been more easily sighted if aircraft landing lights were on.

The Air Tractor 502 was conducting spraying operations late at night in fine conditions, with scattered cloud, no moon, and a barely discernible horizon.  After levelling at approximately 200 ft from a pull up and procedure turn, the pilot reported that his attention was drawn to another aircraft which was spraying a nearby property.  Whilst the pilot was watching the other aircraft the Air Tractor struck the ground at an estimated airspeed of 95 knots.

Wreckage distribution and pilot evidence indicated that, following the initial impact, the aircraft became airborne for a further 200 metres, with no engine or electrical power, before again striking the ground and sliding to a stop. The pilot, who had been wearing a full harness, escaped without injury.  The aircraft was destroyed.

The instructor reported that a normal approach was flown, with the student as the handling pilot. The aircraft was subsequently flared normally but was not held off, descending onto the runway in a level attitude and touching down on its three wheels simultaneously. The nose of the aircraft continued to lower onto the runway until the propeller struck the ground.

The operator subsequently reported that the lugs on the nose gear upper housing, which retain the hinge pin for the lower fork assembly, had failed. The nosewheel, complete with its fork assembly, had separated from the nose leg. There was no evidence of any pre-existing defects with the leg. The instructor reported that the landing did not appear to have contributed to the failure. The reason for the failure was not determined.

The pilot reported that it was the first time he had flown the type of glider, and it had been over 3 years since he had flown a glider with water ballast. Prior to the flight he had forgotten to drain the water, and he had departed with the ballast tank about half full.

As he made his approach to land, during an out-landing, the water shifted causing one wind to drop suddenly. The wing tip hit the top of a fence, yawing the aircraft to the right. The landing gear was torn off on touchdown and the left-wing tip then dug in causing the aircraft to ground loop to the left.

The pilot reported that there had been some nosewheel vibration, described as slight, during the take-off and that the aircraft had wanted to yaw away from the centreline. He had been able to regain the centreline with the use of moderate rudder input. Otherwise, the take-off was reported as normal.

During the landing roll, following the completion of a solo navigation exercise, the nose of the aircraft descended further than expected when the pilot attempted to lower the nosewheel onto the runway. He opened the throttle to complete a go-round; however, the propeller began striking the runway before this could be completed. The go-around was abandoned and the aircraft brought to a stop on the grass to the left of the flight strip.

Inspection found that the nosewheel and folk were missing and that the aircraft had slid to a stop on the nosewheel-folk attachment plate at the bottom of the nosewheel strut. The nosewheel tyre had made contact with the lower fuselage at some stage. The nosewheel was not located during an inspection of the airfield. The left main-gear leg was found to be bent slightly rearwards. Both propeller blades were scored and bent at the tips. No other damage to the landing gear was evident.

The nosewheel and folk were found on a beach north of Perth/Jandakot, one week after the occurrence. It was apparent the nosewheel had fallen from the aircraft during the navigation training flight.

The nosewheel folk was made of carbon-fibre material and information from a composite expert indicates some the carbon fibres had been damaged when an excessive side-load had been applied to the nosewheel structure. Despite the damage, the folk did not fail completely at that time. It is likely this initial damage occurred prior to the flight on which the nosewheel fell off.

It is possible the damage was not evident to the pilot during his preflight inspection prior to the navigation training flight. Delamination of composite structures, following excessive loading, usually shows up as a white discolouration of the naturally black material. The black, composite, folk had been painted white to match the aircrafts colour scheme. This probably disguised any signs of delamination.

Additional loads, during the take-off and possible movement in flight, caused the damaged folk structure to fail completely and the nosewheel was then able to fall free, colliding with the lower fuselage on the way.

The type and extent of damage to the left main gear and the lack of any other damage to the nose structure indicates that the side loads were applied either during a landing with the aircraft yawed to the right or when the aircraft was turned to the right, on the ground, at too high a speed. It is unlikely the damage was the result of a heavy landing or collision with an object. The initial damage probably occurred during night flying training on the evening prior to this occurrence although, nothing unusual was reported. Neither of the possible reasons may have appeared worth reporting to the maintenance section at the time, particularly if there was no apparent loss of function.