Two aircraft were being used to suppress bushfires in the Perth basin. At approximately 1027 WST, the aircraft were called to a fire near Maddington, an outer suburb of Perth approximately 6 NM south-east of Perth airport. The pilot of VH-JTD reported that no problems were identified during the pre-takeoff checks.
Both aircraft departed at approximately 1035 towards the south. Air traffic controllers in the tower noted that JTD, the accident aircraft, flew a shallower departure profile than the other aircraft. The pilot later reported that the profile resulted from his operating technique and not from any problem associated with the aircraft.
Because the bushfire was relatively close to the airport, both aircraft climbed to only 1,200 ft before descending to conduct the inspection circuit at about 1,000 ft. While communicating with the bushfire ground controllers, the pilots positioned their aircraft in a left circuit pattern to reduce the time during which the aircraft were climbing out over populated areas. The pilots then approached the fire from the south-east. The first aircraft dropped its load of fire retardant without incident.
The pilot of JTD reported that he set up the approach slightly tighter and steeper than usual due to the proximity of housing. Just prior to the base turn, he selected full flap and set the propeller to a fine-pitch setting.
During the base turn, the pilot reported that he needed more elevator control back pressure than usual to maintain the aircraft's nose attitude. The pilot initially thought that the aircraft's trim setting needed adjusting, until the nose dropped further. The pilot levelled the wings and fully opened the throttle: this appeared to have little or no effect and he decided to immediately dump the load of retardant. He could not recall any engine instrument indications. Because the dump system had been set up for a partial dump only, he decided to use the manual lever rather than the electric switch to dump all the fire retardant. Following the loss of engine power, the pilot turned on the emergency fuel pump as required in the emergency checklist, but did not apply carburettor heat.
The pilot reported that the aircraft appeared to travel further than expected during the descent. He flew the aircraft close to the stall at approximately 60 kts during the forced landing, using rudder to control wing drop. Having passed over several streets, the pilot decided to attempt to land the aircraft on a small street, parallel and close to the aircraft's flight path.
The aircraft severed a set of powerlines at the northern end of the street before its right wing struck and broke a power pole. The aircraft then veered right, glanced off the roof of an occupied house, and embedded itself into the next house, which was unoccupied at the time.
Once the aircraft had come to rest, the pilot switched off the fuel and electrical systems. There was no fire. He then exited the aircraft and signalled to the other pilot that he was okay. The pilot was wearing a four-point harness and a flying helmet, both of which were undamaged. However, the pilot received minor injuries to his left leg during the impact sequence. The nature of the impact sequence appeared to have progressively slowed the aircraft, thereby lessening the peak forces suffered by the pilot.
When the other pilot saw that JTD had crashed, he advised air traffic services of the accident and gave directions to enable emergency services to locate the accident site. Emergency services arrived about 5 minutes later. The pilot switched off the operating emergency locator transmitter.
The aircraft's forward fuselage was substantially damaged and the main landing gear had collapsed. The wings remained attached to the fuselage although powerlines had severed 2 m of the left wing. The cabin was penetrated by two pieces of wood from the house roof trusses. The engine was torn from its mounts, moving 1 m forward and rotating approximately 90 degrees to the left.
The on-site examination of the engine revealed no abnormality. The carburettor was firmly attached and all four butterfly valves were fully open although their positioning may have resulted from the impact. The propeller remained attached to the engine with all blades bent backwards. The general appearance of the blades indicated that the propeller was rotating at low power at impact.
The Bureau of Meteorology reported that there was 2 octas of cumulo-form cloud at 4,500 ft. The temperature was approximately 35 degrees C, dewpoint was 16.5 degrees C, and there was a relative humidity of 38% at Perth airport. There was a light wind from the north-east.
The fuel system included two wing tanks connected to a header tank. Fuel from the header tank was drawn by the engine-driven fuel pump and fed through a firewall-mounted filter before entering the carburettor.
The operator reported that the aircraft departed with a fuel load of approximately 700 L and that approximately 40 L of fuel was drained from the left tank soon after the accident. It was estimated that about another 20 L was spilled during the aircraft wreckage recovery. The right wing tank contained no fuel when it was inspected after the accident; however, the fuel would have drained from the fuel lines that were damaged during the collision sequence.
A sample of fuel was drained from the left wing tank and analysed. The analysis confirmed the fuel as Avgas 100/130. Apart from an extremely low Reid Vapour Pressure, it complied with the fuel specification requirements. The fuel sample was taken almost 24 hours after the accident. The fuel manufacturer reported that due to the hot weather in Perth at the time, the lighter fuel fractions may have evaporated from the ruptured tank, resulting in the low vapour pressure.
A small amount of clear water was found in the fuel sample drained from the fuel pump.
Fuel lines to and from the fuel filter, mounted on the firewall, were severed at the filter. The fuel filter did not have an external or cockpit warning to indicate when the filter was blocked and operating in bypass. The aircraft's flight manual noted that the fuel pressure indication dropped when the filter was blocked, but the pilot reported that he did not observe such an indication. A mixture consisting of 50% fuel and 50% black-coloured water was drained from the filter. Chemical analysis of the water found the presence of dissolved impurities.
Examination of the filter element found the lower part saturated with water and heavily contaminated with rust particles to the point that the lower half of the filter was blocked. On the fuel inlet side, there was a significant accumulation of large, flat rust pieces. The lower half of the steel coil inside the element was severely corroded. Analysis indicated that the large rust pieces probably originated from a fuel storage tank. Specialist examination of the filter indicated that the water and subsequent corrosion had been present for an extended period.
Approximately 250 mL of fuel and a similar quantity of water were drained from the carburettor bowl. Both samples were free of sediment. The carburettor was a standard float type, where the pressure difference between the chamber and venturi regulated the amount of fuel drawn. The carburettor was opened and inspected. No sediments, or evidence that water had been present for an extended period, were found. The examination of the carburettor found no defect that may have adversely affected its operation.
The aircraft was manufactured in 1993 and operated in the USA before its purchase by the Australian owner in 1996. The aircraft Certificate of Registration holder made a valid election to use the Civil Aviation Safety Authority (CASA) maintenance schedule, CAR42B Schedule 5, as the aircraft maintenance schedule and the aircraft had undergone a periodic maintenance inspection prior to the issue of an Australian maintenance release. A subsequent periodic maintenance inspection would then be required at the completion of 100 flying hours or 12 calendar months.
An option available to the aircraft Certificate of Registration holder was to elect to use the aircraft manufacturer's maintenance schedule, which would require that the fuel filter be inspected every 50 (+/- 5) flight hours.
On 5 February 1999, CASA informed the Bureau that the aircraft maintenance schedule, CAR 42B Schedule 5 Part 1, required that a fuel sample drain of aircraft fuel filters be conducted each day the aircraft was flown, except when not applicable to the aircraft. In the case of the PZLM18A aircraft, CASA stated that the engine firewall fuel filter would not be required to have a fuel sample drain carried out during the daily inspection.
The Civil Aviation Safety Authority confirmed that the firewall fuel filter should have been inspected during the initial periodic inspection for the issue of the aircraft maintenance release.
At the tiine of the accident, the aircraft had accumulated approximately 53 flying hours since the completion of the periodic inspection. The investigation could find no evidence that the firewall fuel filter had been inspected at any time prior to or during flying operations in Australia.
Pilot and eyewitness descriptions of events immediately prior to the accident suggest that the engine lost a substantial degree of power, but did not completely fail.
It is likely that the engine power loss was gradual. This was evidenced by the pilot's report of the aircraft's increasing nose-down tendency and its extended flight profile. Examination of the engine indicated that it was producing limited power at impact. There was no evidence of any pre-existing condition that may have adversely affected the serviceability of the engine.
A significant amount of water and other contaminants were found in the firewall fuel filter.
Inspection and testing indicated that the water had been in the filter a significant length of time. The water in the carburettor bowl and the fuel pump was clear and the lack of corrosion or other damage inside the carburettor and the pump indicated that the water had only recently been introduced to those components, possibly during the post-accident firefighting operations. No factors, other than water contamination and the deterioration of the fuel filter, were disclosed during the investigation. Consequently, it is considered that the deterioration of the filter most likely contributed to the engine's loss of power.
There was no evidence to indicate that the fuel filter had been removed and inspected during the periodic inspection conducted for the initial issue of an Australian aircraft maintenance release or at any subsequent time prior to the occurrence. The aircraft maintenance schedule elected by the Certificate of Registration holder would not have required a further inspection of the filter until 100 flight hours had been completed after the initial inspection.
During the investigation, it became apparent that there was a general misunderstanding of the intent of certain aspects of the CASA maintenance schedule contained in CAR42B Schedule 5.
As a result of this occurrence, The Bureau of Air Safety Investigation is further investigating a safety deficiency involving the misinterpretation of the Civil Aviation Safety Authority maintenance schedule, CAR42B Schedule 5.
Any recommendation issued as a result of this deficiency analysis will be published in the Bureau's Quarterly Safety Deficiency Report.
|Date:||03 February 1997||Investigation status:||Completed|
|Time:||1043 hours WST|
|Release date:||19 March 1999||Occurrence category:||Accident|
|Report status:||Final||Highest injury level:||Minor|
|Aircraft manufacturer||PZL Warszawa-Okecie|
|Type of operation||Aerial Work|
|Damage to aircraft||Destroyed|
|Departure point||Perth, WA|
|Departure time||1035 hours WST|
|Role||Class of licence||Hours on type||Hours total|