Collision with terrain

1. Vacuum pump failure during flight resulted in the loss of suction to the air-driven gyroscopic instruments.
2. Erroneous attitude and heading indications from these inoperative flight instruments.
3. Dark sky conditions with no discernible horizon.
4. The pilot had limited recent experience flying in conditions of reduced external visual reference.
5. Inability of the pilot to control the aircraft by sole reference to the remaining flight instruments.

The circumstances of this accident were consistent with a loss of control by the pilot at night, resulting from inoperative attitude and directional indicators. The combination of a dark night, high level cloud, and limited ground lights would have provided the pilot with few external visual cues. This would have required him to quickly modify his instrument scan to allow him to control the aircraft by sole reference to the remaining flight instruments. One of those instruments, the electric turn coordinator, was probably the 'electric backups' that the pilot referred to in his call to FS.

To achieve a desired flight performance, the aircraft is placed in a particular attitude, together with an appropriate power setting. Precise attitude information can either be gained by reference to the natural horizon, or to a gyro-stabilised attitude indicator, when external indications are either not available or are unreliable. The altimeter, air speed indicator and vertical speed indicator can, in combination, also provide limited attitude information.

The loss of vacuum to the air-driven gyroscopic flight instruments would have resulted in those instruments providing erroneous aircraft attitude and heading indications to the pilot. It is possible that the pilot did not mask the failed attitude and directional indicators. Consequently, the pilot may have inadvertently continued to respond, however briefly, to the erroneous indications from the failed instruments. His instrument scan proficiency, with the attitude indicator as the primary focus, would have been developed over several years. Such a scan could not easily have been modified to ignore the very powerful stimuli from erroneous attitude indications.

The pilot was dependent on alternative instruments for aircraft attitude information and it is likely that while attempting to control the aircraft as well as calculate flight time and distance to Mildura, the pilot became spatially disorientated and lost control.

The following factors were determined to have contributed to the accident:

1. The glare of the sun shining through the aircraft's windscreen may have partly obscured the tree from the pilot's field of vision.
2. The use of the Satloc light bar indicator may have resulted in the pilot focussing his eyes, for at least some of the time, on a close object causing distant objects, such as the tree, to be out of focus and thus more difficult to see.
3. The failure of the cockpit truss to remain in position when the aircraft struck the ground inverted made the accident unsurvivable.

Manoeuvring the aircraft to commence the next swath run was a high workload period for the pilot, requiring precise flying to position the aircraft accurately in both lateral and vertical planes. As the pilot was lining the aircraft up to conduct a swath run in a westerly direction in the late afternoon, the sunlight coming through the windscreen would have created glare in the pilot's field of vision, partly obscuring the tree. When using the Satloc system's light bar indicator to align the aircraft with the line of the next swath run, the pilot's vision would have been focussed, for at least some of the time, on the light bar. When the pilot's eyes were focussed on the light bar, more distant objects, such as the tree, would not have been in focus and would therefore have been harder to see. Although the pilot must have been aware of the tree's presence, the high workload, the glare from the setting sun and the pilot focussing on the light bar indicator all contributed to the pilot temporarily being unaware that the tree infringed his intended flightpath.

The damage to the left wing when it struck the tree would have resulted in a loss of lift and an increase in drag from this wing. This would have caused the aircraft to roll rapidly to the left and, as the ailerons had jammed, the pilot would have been unable to stop the roll. Thus, after impact with the tree, the aircraft was most likely uncontrollable.

When the cockpit truss was tom from the aircraft, the space remaining between the ground and the pilot's seat was too small for the accident to have been survivable.

The witness description of the aircraft's behaviour, along with the evidence at the impact site, indicated that the aircraft probably stalled aerodynamically as the pilot reversed the direction of the procedure turn. It is likely that the aircraft was in a nose-high attitude at the time. This would explain the apparent low forward speed of the aircraft at impact. Assuming that the pilot was conducting the turns at typical altitudes, it is unlikely that there would have been sufficient height available for the pilot to recover the aircraft to normal flight. The pilot's low experience level on turbine powered Air Tractor aircraft compared with piston engine powered models may have contributed to the loss of control.

Details obtained during the investigation did not allow any conclusions to be drawn concerning the security of the pilot's safety harness at impact.

After arriving at the property strip, the pilot was briefed on the spray area by the property owner. In the meantime, the aircraft was loaded with 1,500 litres of spray solution. The pilot subsequently boarded the aircraft and was observed to secure his safety harness, and don gloves and a helmet, before departing for the task.

The spray area was about 800 m from the strip. Witnesses at the strip observed the aircraft as it began spraying and noted that the procedure turns at the end of each run were conducted at a consistent height. The turns were flown initially to the left to offset the aircraft from the previous run, and then reversed to align the aircraft for the next run. About 30 minutes after spraying had commenced, one of the witnesses observed the aircraft rolling right during a turn reversal in a procedure turn. The aircraft continued rolling until it was in an inverted attitude, and then descended into the ground where it immediately caught fire.

Pilot-in-command

The pilot-in-command had a total flying experience of 1,445 hours, of which about 450 were on Cessna 210 aircraft on low level survey tasks.

Aircraft information

The aircraft was manufactured in the USA in 1982 and was entered on the Australian register in 1983. In 1994, it was fitted with approved specialist equipment for geophysical survey operations. The certificate of registration and maintenance release was valid at the time of the accident. The weight and centre of gravity (CG) were within limits.

Meteorological information

A Bureau of Meteorology post-analysis of the weather conditions in the survey area at the time of the accident, indicated that the surface wind was easterly at 5-10 knots. The wind at 2,000 feet was 070 degrees at 25 knots, causing a wind shear of approximately 20 knots between that level and the surface. There was likely to have been significant mechanical turbulence in the Drummond Range area. There was a broken layer of stratiform cloud with a base of 2,000 to 3,000 feet. Visibility beneath the cloud was good and there was no evidence of precipitation in the area. Similar conditions existed on the day following the accident when search aircraft reported severe mechanical turbulence at low level in the area.

Position of the sun

Sunrise at the accident location was 0637. Between 0700 and 0800, the elevation of the sun was between 4 and 16 degrees above the horizon. The azimuth of the sun during that time was between 061 and 068 degrees M.

Examination of the wreckage

Evidence at the accident site indicated that the aircraft had struck several trees while in an 85-90 degree angle-of-bank descending turn to the right. The aircraft heading at that time was about 240 degrees M. Fifteen metres after the initial tree contact, the right wingtip struck the ground. The aircraft then cartwheeled before coming to rest inverted. The wings separated from the fuselage as a single unit and continued beyond the main wreckage. The fuselage remained substantially intact during the impact sequence but was destroyed by the post-impact fire.

Examination of the airframe and powerplant did not reveal any abnormality that might have contributed to the accident. The nature and extent of damage to the propeller indicated that the engine was producing power at impact. The wing flaps were in the retracted position and there was no evidence that the aircraft had suffered a birdstrike. The extent of damage to the survey equipment on the aircraft precluded the recovery of any recorded data that might have assisted in determining the flight path of the aircraft.

Medical and pathological information

There was no evidence of any physiological condition concerning either crewmember that may have contributed to the accident.

Survival aspects

The severity of the impact and subsequent fire were such that the accident was not survivable.

Emergency locator transmitters

The aircraft carried two emergency locator transmitters. One of these was a fixed installation and the other was a portable unit that was normally located under the crewmember's seat. Both units were recovered. The nature and extent of damage sustained by each precluded normal operation.

Other information

Pilot training

At the time of the accident, there was no regulatory requirement which specifically addressed low level survey operations. However, the instrument of approval for low level survey operations issued to the company by the Civil Aviation Safety Authority (CASA) required pilots employed by the company to have either undergone a course in low level flying, or to hold or have held an agricultural rating or an aerial stock mustering approval. This was standard CASA procedure for such approvals.

Civil Aviation Order (CAO) 29.10 addressed low level flying for aerial stock mustering operations. Appendix 1 to the order detailed the syllabus of training. Paragraph 2 referred to aeroplanes and gyroplanes and stated:

1. Aircraft Handling:
   1. level, climbing and descending turns up to 60 degrees angle of bank;
   2. review of stalling symptoms and recovery in both wings level and turning flight up to 60 degrees angle of bank (Aeroplanes);
   3. recovery from high rates of descent at speeds below minimum straight and level speed (Gyroplanes)
   4. slow flying (including use of flap and the effect of changing flap settings);
   5. methods of losing height;
   6. manoeuvring at varying airspeeds and angles of bank.
   7. Note: Before starting low flying training the student is to demonstrate safe aircraft handling of sub-paragraphs (i), (ii), and (iv) below 300 feet but not below 150 feet.
2. Low Flying:
   1. low flying (below 100 feet above ground level);
   2. slow flying (including use of flap);
   3. effect of wind (apparent change in speed in head/tail winds and apparent slip and skid in cross winds);
   4. action in the event of engine failure at low level;
   5. method of losing height;
   6. procedure turns, steep and climbing turns from a fixed ground reference combined with descending turns back to the reference. The obstructed viability inherent in manoeuvring high-wing aeroplanes in descending turns to be a fixed ground reference shall be demonstrated;
   7. low flying in hilly terrain;
   8. effect of false horizons;
   9. effect of the sun, under certain conditions, on visibility;
   10. approach to high ground - use of escape routes; and
   11. avoidance of obstacles."

The pilot's records indicated that he had completed sub-paragraph (a) "Aircraft Handling" training in August 1995. This indicated that the pilot had completed the section of the syllabus relating to aircraft handling. There was no record of him having completed the sub-paragraph (b) "Low Flying" section of the syllabus.

Additional information and training provided by the company to pilots

The survey company issued to all its pilots, a publication titled "The Survey Pilots Guide". The guide outlined the techniques and procedures to be used when flying survey operations. Some of the topics covered included hazards such as the sun, terrain, and powerlines. Paragraph 3.1.4 of the Guide addressed "Terrain". Paragraph 3.1.4(b) was titled anticipation and stated:

"Due to the aircraft's speed and inertia it is vital to anticipate commencement of climb and descent when following terrain. Terrain over 1,500 feet above normal survey level needs further anticipation as the inertia dissipates above this height, the aircraft relies on climb performance alone. For example approaching a hill of 2,500 feet commence climb at five nautical miles before the base of the hill."

Paragraph 3.1.4(a) stated that "kinetic energy of the aircraft provides some assistance when flying over terrain up to 1,500 feet above ground level".

There was no information in the guide, nor was there training provided to pilots, on specific manoeuvres such as minimum radius turns which might need to be flown as an escape manoeuvre from a valley.

For any aircraft flying at an airspeed of 140 kts, the radius of turn for a constant altitude, steady turn, is as follows:

The elevation of the wreckage was between 2,100 ft and 2,250 ft above mean sea level. The width of the valley at this elevation was between 500 and 850 m. The valley width at 2,000 ft elevation was 300 m, and reduced to about 200 m at 1,800 ft elevation.

The factors contributing to this accident could not be conclusively determined.

In the absence of any witnesses or recorded flight data, the events leading to the accident could not be determined. However, the right turn the aircraft was apparently performing at impact could indicate that the pilot had been flying towards the northeast, into the valley (perhaps following survey line 11124) and was attempting to turn back down the valley. It is possible that the wind and turbulent conditions in the valley affected the climb performance of the aircraft sufficiently to create doubt in the pilot's mind that the aircraft possessed enough residual performance to outclimb the valley floor.

Cloud on the range may have affected visibility and limited or delayed the pilot's appreciation of the terrain ahead. Similarly, if the weather was clear, the elevation and azimuth of the sun relative to the aircraft's track may also have affected the pilot's perception of the terrain ahead. Either of these possibilities may have caused him to attempt to turn back.

The outcome of a turn in the valley would have depended on the aircraft's speed and altitude when the turn was initiated, its position in the valley (that is, the manoeuvring area available), and the pilot's skill level, as well as any turbulence and/or windshear which was present. A comparison of turn radii at various bank angles against the width of the valley indicates that the aircraft could have been in a position where there was insufficient room in which to safely complete a turnback.

The completion by the pilot of only the "Aircraft handling" section of the Aerial Stock Mustering Syllabus may have influenced his actions in the events leading to the accident. However, the limited information available concerning the final stages of the flight made any meaningful assessment in this regard impossible.

The Cessna 210 was involved in a geophysical survey task west of Emerald. The survey task included flying a number of pre-planned survey lines. A line number identified each line. The survey lines to be flown on the day of the accident were a block between lines 11118 and 11125. Line 11127, south of this block, was to be re-flown as previous data collected on the line was flawed. The lines were oriented 070/250 degrees M and were about 110 km (60 NM) long. From the southwest, the lines traversed flat, open terrain initially, and then crossed the Drummond Range. The range rises about 400 m above the level of the surrounding terrain and is a rugged area, which includes a number of narrow valleys.

The aircraft was equipped with a satellite navigation system, which provided information on the track to be flown to the pilot via a display on the glare-shield above the instrument panel. A radio altimeter provided aircraft height above ground level. Survey lines were to be flown at 140 kts indicated airspeed and, where possible, at 80 m above ground level. Accuracy in horizontal track keeping had priority over vertical navigation accuracy. For considerations of safety and ease of flying, the flying technique over rough terrain involved "smoothing" of the flight path rather than attempting to follow terrain contours.

The aircraft departed Clermont at 0638 EST. Because radio transmissions interfered with the recording of survey data, none were normally made during survey operations. Consequently, no contact was expected from the aircraft until about 1130, when it was due to return from the survey task. When no communication had been received by this time, the company reported that the aircraft was overdue and a search was commenced. Three days later, the burnt wreckage of the aircraft was located in the Drummond Range approximately 58 NM west of Emerald. The wreckage was about 30 m below the top of a ridge, which formed the southern side of the same valley followed by survey line 11124. It was approximately 400 m south of that line.

There were no witnesses to the accident.