The Sector was operated by a trainee under the supervision of a training officer. The trainee was nearing the final stages of both sector training and the end of training to obtain an air traffic control licence.

Enroute after passing Oodnadatta at Flight Level 260 the crew requested and were approved for climb to Flight Level 280. This change of level was not passed on to Darwin. No loss of separation occurred.

The attention of the controllers on the Melbourne sector was diverted when they received co-ordination on an aircraft for which no details were held. Traffic conditions were busy.

Significant Factors

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

1. Controller attention diverted by another task.

2. Both the trainee and the supervising controller overlooked the need for co-ordination with Darwin.

The pilot reported that at 11,000 feet on climb out of Bangkok the Traffic Collision Avoidance System (TCAS) gave a traffic alert message immediately followed by a 'climb, increase climb' warning. Evasive action was taken. The initial navigation display indicated traffic at a range of one half to one nautical mile ahead in the 12 o'clock position, 300 feet above and in level flight. Air Traffic Control reported no traffic in the area. Visibility was about 10 kilometres in haze and no aircraft was sighted in that position.

Subsequent investigation revealed no defect with TCAS equipment.

After a session in the training area the pilot returned for landing on runway 36. Following an apparently normal touchdown the aircraft slowed, but then the left wing lifted. A correction was made for this, but the aircraft swung left, and the right main landing gear leg collapsed.

During the climb, the aircraft was given an amended clearance to track direct from Bowen to Innisfail. The clearance was read back correctly. The aircraft was later observed to deviate from the cleared track and the air traffic controller asked the crew to confirm their airways clearance. He was told that the aircraft was tracking to Townsville (which was the original planned track). There was no breakdown in separation with other aircraft. The aircraft was then cleared to track direct to Innisfail from its present position.

The pilot-in-command later indicated that the Townsville waypoint had inadvertently been left in the Omega Flight Plan and as a result the aircraft tracked to that position instead of along the revised route.

Simultaneous runway operations were being conducted at the time of the occurrence with departures from runway 16 and arrivals on runways 16 and 07. A busy traffic situation was creating high workload levels for the tower staff. Weather conditions were fine with light winds.

The air traffic situation around the airport was further complicated by an overflying helicopter which had departed from Prince Henry hospital, located 8 km to the east, enroute to Bankstown via overhead Sydney Airport at 1,500 feet.

VH-AJM taxied at 0744 EST and at 0747, reported ready for take-off on runway 16, from the intersection with taxiway Foxtrot, 536 metres south of the runway 16 threshold. VH-MZM taxied at 0750 and was instructed to taxy to and hold at the holding point adjacent to the threshold of runway 16. The planned departure sequence from runway 16 was VH-AJM followed by VH-MZM.

The Tower Controller amended the departure sequence due to the presence of the overflying helicopter, as the departure track of VH-AJM placed that aircraft in potential confliction with the helicopter. He decided that VH-MZM should take-off before VH-AJM.

When VH-MZM was instructed to line up, the crew of VH-AJM mistakenly believed the instruction was addressed to them and commenced to taxy beyond the holding point into the runway strip. They recognised their error when VH-MZM was subsequently cleared for take-off. Although the Tower Controller had not observed VH-AJM move beyond the holding point, as his view of taxiway Foxtrot was obscured by a structural roof support beam, the incursion was immediately noticed by the Tower Coordinator and the Surface Movement Controller who alerted the Tower Controller.

The take-off clearance for VH-MZM was cancelled and both aircraft were instructed to vacate the runway to allow an aircraft on final approach for runway 16 to land.

Significant Factors

1. The crew of VH-AJM expected to depart before VH-MZM.

2. The Tower Controller amended the departure sequence due to overflying traffic in potential conflict with the departure track of VH-AJM.

3. The crew of VH-AJM misinterpreted the callsign when the Tower Controller issued a line up clearance to VH-MZM.

The aircraft was being radar vectored for a right turn onto the ILS (Instrument Landing System) final. It was also on descent to the Radar Lowest Safe Altitude of 4,500 ft and was experiencing moderate turbulence. Just before levelling out at 4,500 ft, its GPWS (Ground Proximity Warning System) Alert activated and the crew immediately initiated a maximum performance climb, levelling at 6,000ft. Air Traffic Control was notified immediately. The aircraft was in cloud at the time of the occurrence.

Investigation has revealed that the GPWS alert was a genuine warning occurring as the result of the aircraft's descent profile and the excessive closure rate to high terrain of Black Mountain which rises steeply from generally lower terrain to 3,493 ft above mean sea level.

A previous incident involving a regular public transport service jet took place some three months earlier where the GPWS gave an alert whilst the aircraft was approaching Black Mountain from the same westerly aspect.

Air Traffic Services has raised the Radar Lowest Safe Altitude from 4,500 ft to 4,700 ft in the area of Black Mountain with the expectation that this will reduce the incidence of alerts.

The pilot advised that at the time of the incident he was carrying out a last +fly around; of his property which had recently been sold. The pilot's three year old son was the only other passenger on board. While manoeuvring at low level the pilot's attention was diverted into the cockpit for a period of time, assisting his son who had become ill. During this period of distraction the pilot had inadvertently allowed the aircraft to descend. He recalls looking outside the aircraft again just as it impacted the ground. The pilot confirmed that the aircraft's engine and flight controls were operating normally at the time. The pilot received serious injuries to both ankles in the accident. The passenger received only minor cuts and bruising. The aircraft was damaged beyond economical repair.

The pilot was taking off from the 020 degree grass strip but was using only the last 700 feet of the available 2200 feet. Partial engine failure occurred when the take-off roll was well established. The engine surged. The pilot applied carburettor heat, full rich fuel mixture and full throttle without regaining full power. The pilot continued the take-off and became airborne. He advised that he had to turn to avoid trees. The aircraft stalled from somewhere between 50 and 100 feet. The wings were damaged. The engine was pushed back into the firewall and the undercarriage collapsed.

The owner subsequently advised that no fault has been found with the airframe, engine or fuel system. He believes that the likely cause of the loss of engine power was carburettor icing.

Significant Factors

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

1. The engine suffered a partial engine failure probably because of carburettor icing.

2. The pilot did not reject the take-off.

FACTUAL INFORMATION

Circumstances

At the completion of flying on 8 February 1993, the aircraft underwent scheduled maintenance at Melbourne. Included in the maintenance was an Engineering Instruction which required that both the left outer and the right inner engine fan cowls be removed for inspection and rectification.

In order to return VH-TAK promptly to service, the right engine inboard fan cowl was borrowed from VH-TAI which was undergoing heavy maintenance.

On 13 February, the borrowed cowl was returned to VH-TAI and the cowl which had been removed from the VH-TAK left engine outer position on 8 February was returned from maintenance.  This cowl was then fitted to the right engine inner position on VH-TAK.

The aircraft was released for service on 14 February, and through to the end of flying on 16 February it operated 19 sectors. At 0600 on 17 February, during a pre-flight inspection in Hobart, it was noticed that the Vortex control device (VCD) was not fitted to the right engine inboard cowl.

The VCD, which is a large blade-shaped nacelle chine, is required to be fitted to the engine inner fan cowls on Boeing 737-376 series aircraft. At large angles of attack in the landing configuration, the engine nacelle causes an airflow vortex spill which disrupts the boundary layer flow from the upper wing surface downstream to the extended flaps behind the engine.  The chine produces a vortex which mixes with the nacelle vortex to increase wing lift by improving the boundary layer flow over the flaps.

Following advice that the VCD was not fitted, Maintenance Control in Melbourne issued an authorisation for the aircraft to be operated for one revenue sector back to Melbourne where the VCD was to be fitted.

Maintenance Aspects

The cowl was fitted to the aircraft in accordance with Boeing 737 maintenance manual (MM) section 71-11-02. That section defines the procedures to be used for removal and fitment of the cowl by either the manual method or the sling method. The operator of the aircraft utilises the manual method.

Section 71-11-02 page 401 Paragraph 2 is headed 'Remove the Fan Cowl Panel (Manually)' and at sub para (2) states 'If you replace the inboard fan cowl panel, first remove the VCD'. It is by this procedure that all fan cowls, irrespective of position on the aircraft, are received into store with the VCD removed.

In Paragraph 3, on page 404, headed 'Remove the Fan Cowl Panel (Sling Method)', the sub para (2) is not included.

On page 407, Paragraph 4 is headed 'Install the Fan Cowl Panel (Manually)'. This paragraph does not include a requirement to fit the VCD.

On page 410, Paragraph 5 is headed 'Install the Fan Cowl Panel (Sling Arrangement)' and at page 412, sub para E is headed 'Put airplane back in its usual condition'. At E (1) is the requirement 'If you replaced the inboard fan cowl panel, install the VCD on the replacement panel'. Sub para E is not listed as a requirement when the panel is replaced manually per Paragraph 4. Accordingly, there was no trigger to alert the maintenance crew to fit a VCD.

The effect of non-fitment of the VCD was not advised in either the Maintenance Planning Document, the MM or the Operations manuals.

The only specification under which the cowl is held in store is P/N 314A1110.  To provide for fitment to either engine nacelle, this specification does not include a VCD.  The cowls were not labelled to indicate that the VCD was required to be fitted to cowls placed on the nacelle inner position.

There was no requirement on the daily or preflight inspection procedures to specifically check for the presence of a VCD on the inboard cowls.  During the time that the aircraft had operated without the VCD, 22 maintenance and 19 pilot inspections had been conducted.

A 'Permit to Operate' document was used by the airline to authorise the operation of an aircraft with damage or unservicabilities outside the scope of the appropriate Minimum Equipment List, Schedule of Permissible

Unserviceabilities or Configuration Deviation List. The permit was issued by the Aircraft Maintenance Manager as a Delegate under Civil Aviation Regulations 37(1) and 37(2).

The Aircraft Maintenance Manager discussed the issue with the Engine Type Specialist and with the pilot but did not consult the manufacturer or an aerodynamics specialist, nor did the operator's procedures require this. The operator's procedures required that the Delegate seek the agreement of the Flight Standards Manager prior to signing the permit. However, this agreement was not obtained.

The manufacturer advised that flight with a VCD missing had not been assessed and therefore was not approved.

ANALYSIS

The aircraft industry operates under a system of checks and balances designed to ensure safety through accountability and traceability in maintenance and operations. That accountability and traceability is effected through detailed procedures which have been written, assessed, and approved, and is introduced to the user through a series of manuals. Check sheets are used to call up those procedures and a certification is required to indicate that a given procedure has been accomplished.  However, when errors or omissions in procedural documentation occur, as in this incident, quality assurance becomes dependent upon the depth of systems knowledge of the personnel involved.

The lack of specific check item requirements alone does not explain why maintenance and flight crews, during the course of numerous inspection procedures, did not recognise the absence of the VCD.  The circumstances of this occurrence suggest that there is a need for operators to ensure that training programs promote appropriate systems appreciation, in order that inspection procedures provide the intended system safety.

The procedures laid down for issue of a Permit to Operate did not ensure that the signatory must refer to relevant, qualified persons before signing the Permit. Consequently, the decision to authorise the flight to Melbourne was based on information which was insufficient to ensure that the signatory was fully aware of the implications of his decision.

FINDINGS

1. The maintenance personnel who fitted the cowl did not realise that a VCD was required to be fitted.
2. Pilots and engineers conducting the daily and pre-flight inspections did not recognise that the VCD was not fitted.
3. The operator's procedures for the issue of a Permit to Operate did not require that the permit signatory consult either the aircraft manufacturer or an engineer relevant to the discipline in question, prior to issuing the permit.

SIGNIFICANT FACTORS

1. Cowlings, when released from stores, were not required to have the VCD fitted.
2. Those sections of the B737 Maintenance Manual applicable to the manual installation of the cowl did not call for the VCD to be fitted.
3. The daily and pre-flight inspection procedures did not call for the VCD to be inspected.
4. No warnings were contained in the Maintenance Planning Document, the Maintenance Manual or the Operations Manual as to the effect of non-fitment of the VCD.
5. An apparent lack of awareness by both maintenance and operational personnel concerning the function of the VCD.

SAFETY ACTION

As the result of problems identified during this investigation the following changes to maintenance and operational documentation have been made:

1. The Aircraft Maintenance Manual has been amended to highlight the requirement to install the VCD (71-11-02pages 411 & 414).
2. The operator's Operations Manual has been revised to include an additional check for VCD condition during crew 'walk round' inspections.
3. Ancillary maintenance check lists have been amended to include a check for fitment of fan cowl vortex control devices.
4. Changes have been made to the operator's procedures to ensure that appropriate persons are consulted prior to the granting or issue of permits to operate.

Barwon Heads Airfield has two strips. The main strip is aligned 350/170 degrees, has a level gravel/grass surface and is approximately 760 metres long. The shorter strip is aligned 080/260 degrees, has a grass surface, is approximately 470 metres long and slopes down to the east. When the aircraft arrived in the circuit area the wind was calm. The pilot intended to land into the north, but he noted that there were several power chutes operating from that strip, so he opted for an approach into the east.

The first approach resulted in a go-around due to a power chute landing into the north. This chute was pulled up just prior to the intersection. The second approach resulted in a touchdown which was later measured to be 73 metres in from the threshold markers. Full flap was used. The pilot reported that the aircraft skipped over a small mound at the intersection of the two strips. Braking then seemed to be ineffective. The aircraft felt as though it was skidding. The pilot applied some rudder correction and checked the brakes and hand brake were both off.

He said that he then decided to go around but delayed power application due to the proximity of a power chute. Power was then applied, and the aircraft became airborne with full flap still selected. It clipped the top strand/strands of a wire fence at the end of the strip. Because the pilot did not know what damage may have been done, he closed the throttle and mixture controls and landed beyond the fence. The aircraft touched down, ran through another fence, entered thick tussocks in a swamp and overturned.

The investigation found that the short grass strip was wet with dew and had an uneven surface due to cracks in the ground and a tufty grass surface. This would have provided a very poor braking surface. In addition, the strip had an increasing down slope, the last third of its length measured as approximately 3% downhill. The pilot reported that he landed on the same strip the previous week in similar conditions and stopped in about two thirds of the strip length.