The pilot of the Cessna 210 was to be accompanied by five passengers on a flight from Merimbula to Albury. A flight notification was submitted by telephone to the Airservices Australia regional briefing office which indicated that the aircraft would be operating under the instrument flight rules and would track to Albury via Cooma and Corryong at 10,000 ft. The pilot obtained a pre-flight briefing from the Airservices Australia automated pilot briefing system (AVFAX) and selected a product code that provided weather forecasts and operational information for aviation meteorological forecast Area 21.
The Area 21 forecast was applicable for the sector of the flight from Merimbula to approximately 30 NM east of Corryong. At that point the aircraft would enter the eastern part of the adjoining Area 30. The pilot did not order any briefing products for Area 30 from the AVFAX system, which would have included information for his destination aerodrome. No information was requested from the briefing officer during the telephone submission of the flight plan and it was not possible to establish if the pilot had obtained an Area 30 or destination aerodrome forecast from alternative briefing sources. It was reported however, that prior to departing Merimbula the pilot had telephoned a family member to inquire about the prevailing weather conditions in Albury.
The forecast for Area 21 indicated that there would be significant cloud extending up to 8,000 ft over the Snowy Mountain ranges, with some isolated tops to 11,000 ft in the far south of the area. Moderate icing was forecast in the tops of cumulus cloud. The freezing level was forecast to be at 6,000 ft in the south. A hazard alert had been issued for occasional severe turbulence below 10,000 ft over, and to the east of, the ranges. A westerly wind of 30 knots was forecast at the pilot's intended cruise level.
The conditions forecast for Area 30 were similar to those for Area 21. Broken cumulus cloud tops were forecast to extend to 10,000 ft with broken altocumulus/altostratus from 8,000 to 20,000 ft in the east of the area. Moderate icing was forecast in cloud above the freezing level and areas of isolated severe turbulence near the ranges below 10,000 ft. The cloud forecast for Area 30 indicated that flight along the proposed route could possibly require flight in cloud, above the forecast freezing level. The aircraft was not equipped for flight in known icing conditions.
The aircraft departed Merimbula at 1200 Eastern Standard Time and the pilot reported to flight service that he was tracking for Cooma and was on climb to 10,000 ft. Although the aircraft would not enter controlled airspace until just before Albury, an en-route radar controller would provide the pilot with a flight information service from 30 NM south east of Cooma. The pilot was issued with a transponder code for radar identification and was given frequency change instructions. Flight service also passed information to the pilot on a hazard alert that had been issued for Albury aerodrome, due to cloud at 1,200 ft above ground level, which had not cleared as had been forecast.
As the aircraft approached top of climb it appeared on the en-route controller's radar display. The radar return from the aircraft's transponder indicated that the aircraft had levelled off at 10,100 ft and its ground speed was observed to steadily increase from 78 knots and then stabilise for a short period at approximately 140 knots. The ground speed was then observed to commence a gradual reduction, which was accompanied by some minor variations in the radar-recorded transponder altitude.
At 1233 the pilot reported overhead the Cooma non-directional beacon at an altitude of 10,000 ft. The radar-derived groundspeed was reducing through 110 knots at this time and continued to reduce at a constant rate, before stabilising at approximately 95 knots.
When the aircraft was 8 NM northwest of Cooma the controller observed the pilot to be conducting what appeared to be a descending turn to the right. The controller requested that the pilot confirm that aircraft operations were normal and the pilot responded that "operations are not normal" and indicated that he was diverting to Cooma for a landing. The recorded radar data indicated that the initial stage of the descent was uneven, with erratic rates of descent and some increases in altitude. The final part of the descent was conducted at a stable rate.
A short time later, the pilot advised the controller that he was tracking 310 degrees at an altitude of 7,500 ft and that the descent had been necessary due to an accumulation of airframe ice. The pilot indicated that he had "unloaded" the ice and commented that he was able to get over the cloud at Kosciusko without going "to that height". The investigation was unable to determine what the comment "to that height" meant.
The aircraft was observed on radar to be flying a steady north westerly ground track, at a constant altitude of 7,600 ft. The groundspeed stabilised at approximately 145 knots before radar contact with the aircraft was lost at 1243. The controller informed the pilot that radar contact with his aircraft had been lost and nominated a time for the pilot to make an operations normal report.
At 1248 the pilot reported that he was tracking direct to Corryong and had commenced a climb to 10,000 ft. The pilot confirmed that he was tracking north of his original track and again stated that the ice had been "unloaded". He also indicated that the cloud conditions looked much better about 5 or 10 miles north of his planned track.
An unidentified person made several incomplete transmissions, which appeared to be inter-cabin type conversation, on the area VHF frequency. The background noise from these transmissions very closely matched the background noise contained in other reports made by the pilot. At 1252 the person was heard to say, "... you have a standing wave? Well it's ...".
The aircraft reappeared on the controller's radar display at 1253 flying a southwesterly track, climbing through a transponder-indicated altitude of 8,400 ft with a ground speed of approximately 45 knots. At 1254, as the aircraft climbed through 8,800 ft, the climb performance appeared to reduce significantly. The transponder return stabilised at an altitude of 9,000 ft, although the ground speed did not increase as would normally be expected if the aircraft had levelled out at this altitude. The aircraft was then observed to take up a more westerly track and appeared to be tracking direct for Corryong.
The aircraft disappeared from the controller's radar display at 1257. The last return received from the transponder indicated an altitude of 8,800 ft with a radar-derived ground speed of 47 knots. During the last 20 seconds of recorded data, the transponder indicated a descent of approximately 200 ft, without any significant increase in groundspeed.
Prior to disappearing from radar the aircraft was flying directly towards Mt Jagungal (6,760 ft AMSL) and was operating downwind of the mountain. Meteorological conditions were conducive to the formation of mountain waves and this type of activity was evident on meteorological satellite imagery that had been taken a short time before the accident. Mountain waves, also known as standing waves are characterised by "waves" of ascending and descending air in the lee of a mountain range, and can be associated with moderate to severe turbulence. These waves can extend for significant distances downwind of the range and can pose a serious hazard to the safety of light aircraft.
Several witnesses had seen or heard the aircraft shortly before the accident. One witness saw the aircraft fly overhead, making slow progress towards Mount Jagungal. The engine sounded as if it was operating normally and could still be heard even after visual contact with the aircraft was lost. The witnesses described a low layer of broken cloud close to the ground, with the aircraft apparently flying in clear air above this cloud. Several persons on the ground reported that the aircraft noise increased in pitch, as if in a dive, shortly before the sound of an impact. This account of engine operation to the point of impact indicates that there was no significant reduction in engine power during the final stages of the flight.
The following morning the aircraft wreckage was located at a position that was consistent with the last recorded radar data. It had impacted the ground at high speed, in a near vertical attitude, and in an apparent left turn. Impact forces had destroyed the aircraft, and all six persons on board sustained fatal injuries. The accident site was located 3.4 NM directly east of Mt Jagungal, approximately 5,700 ft above mean sea level.
The impact crater contained the engine and the forward section of the fuselage. The remainder of the wreckage was located a short distance away. Examination of the wreckage did not reveal any defect that could have affected the operation of the aircraft prior to impact.
The pilot held a valid single-engine command instrument rating. He had satisfactorily completed the requirements for the renewal of his rating on 11 April 1997. The pilot had logged a total of 2904.4 hours aeronautical experience, of which approximately 580 hours had been flown in Cessna 210 type aircraft. He had regularly operated his aircraft as pilot in command during the previous 12 months and had frequently flown between Albury and Merimbula under instrument flight rules. The passenger who was believed to have been in the co-pilot's seat held a private pilot licence, which was valid for flight under the visual flight rules.
Colleagues of the pilot reported that he was familiar with the use of the systems on-board the aircraft and would normally use the autopilot during cruise. They stated that his usual habit was to hand fly the aircraft during climb/descent and when operating in turbulent conditions.
The pilot had completed a Class 1 flight crew medical examination on 18 November 1997, which had included a requirement for completion of a stress electrocardiogram (ECG). Although this testing did not return an abnormal result, post-mortem examination of the pilot did reveal that he was suffering severe coronary artery disease. The examining pathologist commented that the stress associated with operating the aircraft in difficult weather conditions could have precipitated a sudden deterioration in his cardiac condition, possibly resulting in a sudden medical incapacitation.
Prior to departing from Albury on the outbound leg of the flight, the aircraft had been fuelled with 200 litres of avgas. It was not possible to determine how much fuel was on board the aircraft prior to the commencement of the fuelling operation. Based on a minimum fuel quantity of 200 litres for departure from Albury, at least 70 litres of fuel is estimated to have be on board the aircraft at the time of the accident.
The aircraft departed Merimbula with sufficient fuel to complete the flight to Albury, with the recommended IFR reserves intact. As it has not been established that the pilot had obtained an aerodrome forecast for his destination, the extent to which he may have made provision for holding fuel or flight to a suitable alternate aerodrome was not determined.
The seating position of the passengers could not be positively determined due to the extent of the destruction of the cabin. Estimated pilot and passenger weights and their assumed seating positions were used to calculate the aircraft operating weight and centre of gravity position. The passenger-seating configuration to provide the optimum centre of gravity position was used in the investigation estimation. Based on these assumptions, at the time of the accident the aircraft was operating below its maximum take-off weight, with the centre of gravity in the vicinity of the published rear limit.
The pilot had regularly operated the aircraft when similarly loaded and would have been familiar with its handling characteristics. The published stalling speed (wings-level) for the aircraft at the estimated load configuration was approximately 64 knots indicated air speed (IAS). The published best rate of climb speed was 92 knots IAS.
The circumstances of this occurrence are consistent with the aircraft being flown at the limit of its performance capabilities, in the prevailing weather conditions. In addition, the reported medical condition of the pilot and the stress associated with operating an aircraft in such weather conditions, requires balanced consideration of the possibility of pilot incapacitation being a factor in the accident.
The Area 21 forecast indicated that the first part of the flight could be conducted clear of cloud during the climb and cruise, with the cloud tops forecast to extend to 8,000 ft in the area through which the aircraft was flying. The recorded radar data indicates that the aircraft was not significantly affected by airframe ice on initially reaching the planned cruising altitude of 10,000 ft.
However, the aircraft did appear to encounter icing conditions as it approached Cooma. The progressive reduction in aircraft groundspeed and the minor altitude variations from the aircraft transponder are consistent with the aircraft operating in convective cloud and accumulating airframe ice. A short time later, the aircraft was observed on radar to conduct a descending orbit and the pilot indicated that he was diverting to Cooma for a landing.
It is likely that during the descent, the aircraft broke clear of cloud and the pilot considered that he was able to continue towards his planned destination. The pilot was familiar with the route sector being flown and would have been aware of the height of terrain in the vicinity. It is unlikely that the pilot would operate the aircraft in cloud, below the lowest safe altitude and continue to fly towards rising terrain.
The apparent improvement in the stability of the radar recorded descent profile also suggests that the pilot had established visual reference during the latter stages of the initial descent from 10,000 ft. The radar recorded data, particularly the groundspeed that the aircraft achieved after levelling off, supports the pilot's report of having "unloaded" the airframe ice. It is likely that the aircraft was no longer operating in cloud and was not significantly affected by airframe ice at this time. The pilot had also commented about being able to get over the cloud at Kosciusko which further suggests the aircraft was established clear of cloud at this time.
Approximately eleven minutes before the accident the pilot reported that he had commenced climbing to 10,000 ft. The aircraft subsequently reappeared on radar and was observed to take up a track that would pass directly overhead Mt Jagungal, in conditions that were conducive to the formation of mountain waves and the forecast probability of occasional severe turbulence. The reported weather conditions at the time of the accident suggest that Mt Jagungal was probably covered by cloud and the pilot may have been unaware of his proximity to the mountain peak.
Based on the reported wind direction and strength, the radar-recorded low groundspeed suggests that the aircraft was climbing at a lower than normal airspeed. This would have provided the pilot with a reduced safety margin above the stalling speed. The apparent reduction in climb performance as the aircraft approached 9,000 ft can be attributed to the aircraft flying into the descending air associated with mountain wave activity. Had the pilot elected to level out at this altitude, it would be reasonable to expect that a measurable increase in groundspeed would be associated with the setting of a flight attitude for straight and level flight.
The witness sighting of the aircraft a short time before the accident indicates that at this point, the aircraft was established clear of cloud, but with a broken layer of cloud below. It was not possible to determine if the aircraft was significantly affected by airframe ice at the time of the accident. The presence of any ice on the airframe would have further increased the aircraft's stalling speed and further reduced the margin for any airspeed fluctuations due to turbulence.
It is possible that while attempting to continue climb to 10,000 ft the aircraft encountered moderate to severe turbulence. The unpredictable fluctuation in airspeed could have resulted in an inadvertent stall. The aircraft departed controlled flight immediately prior to the accident and impacted the ground at high speed in a near vertical attitude, consistent with an uncontrolled spiral dive. The reason for the loss of control could not positively be established.
Furthermore, the possibility of pilot incapacitation cannot be excluded as a contributing factor in the occurrence. The reported operation of the aircraft engine to the point of impact, together with the uncontrolled nature of the descent, indicates that there had been no effective response initiated to counter the rapid descent of the aircraft.
- The planned route was over mountainous terrain, in adverse weather conditions, and at an altitude above the forecast freezing level.
- Moderate to severe turbulence had been forecast in the vicinity of the Snowy Mountain ranges and the meteorological conditions were conducive to the formation of mountain waves.
- At the time radar contact with the aircraft was lost, the pilot was attempting to climb the aircraft to an altitude of 10,000 ft and appeared to be flying it at a lower than normal climb speed. The reason for the observed loss of climb performance as the aircraft approached 9,000 ft could not be positively determined.
- The aircraft impacted the ground in an attitude consistent with a loss of control. The reason for the loss of control could not be established.
|Date:||26 April 1998||Investigation status:||Completed|
|Time:||1258 hours EST|
|Location:||16 km W Eucumbene|
|State:||New South Wales||Occurrence type:||Collision with terrain|
|Release date:||24 September 1999||Occurrence category:||Accident|
|Report status:||Final||Highest injury level:||Fatal|
|Aircraft manufacturer||Cessna Aircraft Company|
|Type of operation||Private|
|Damage to aircraft||Destroyed|
|Departure point||Merimbula, NSW|
|Departure time||1200 hours EST|
|Role||Class of licence||Hours on type||Hours total|