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DHC6, en-route, Mount Elizabeth Antarctica, 2013

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Summary
On 23 January 2013, a Canadian-operated DHC6 on day VFR positioning flight in Antarctica was found to have impacted terrain under power and whilst climbing at around the maximum rate possible. The evidence assembled by the Investigation indicated that this probably occurred following entry into IMC at an altitude below that of terrain in the vicinity having earlier set course en route direct to the intended destination. The aircraft was destroyed and there were no survivors.
Event Details
When January 2013
Actual or Potential
Event Type
Controlled Flight Into Terrain (CFIT), Human Factors
Day/Night Day
Flight Conditions IMC
Flight Details
Aircraft DE HAVILLAND CANADA DHC-6
Operator Kenn Borek Air
Domicile Canada
Type of Flight Public Transport (Non Revenue)
Origin Jack F. Paulus Skiway
Intended Destination Terra Nova Bay Skiway
Take off Commenced Yes
Flight Airborne No
Flight Completed No
Flight Phase Cruise
ENR
Location En-Route
Origin Jack F. Paulus Skiway
Destination Terra Nova Bay Skiway
Location
Approx. Mount Elizabeth, Antarctica
Loading map...
CFIT
Tag(s) Into terrain,
VFR flight plan
HF
Tag(s) Authority Gradient,
Plan Continuation Bias,
Procedural non compliance
Outcome
Damage or injury Yes
Aircraft damage Hull loss
Fatalities Most or all occupants (3)
Causal Factor Group(s)
Group(s) Aircraft Operation
Safety Recommendation(s)
Group(s) Aircraft Operation,
Aircraft Airworthiness
Investigation Type
Type Independent

Description

On 23 January 2013, radio contact was lost with a DHC6-300 (C-GKBC) being operated by Kenn Borek Air on a day non revenue positioning flight from South Pole Station to Terra Nova Bay under Visual Flight Rules (VFR). After a search and rescue effort based on transmissions from the ELT, the aircraft was subsequently found to have crashed whilst en route in Instrument Meteorological Conditions (IMC) resulting in the three occupants being killed.

The location of the wreckage (reproduced from the Official Report)

Investigation

An Investigation was carried out by the Canadian TSB. The Cockpit Voice Recorder (CVR) and a satellite tracking unit were recovered from the wreckage but the CVR was subsequently found to be inoperative. Recorded data of considerable significance to the Investigation was recovered from the satellite tracking unit, a SkyTrac ISAT-100. This unit yielded recorded flight data in 5-second intervals, including position, altitude, ground speed and true track.

It was noted that flight operations by Kenn Borek in the Antarctic were conducted in accordance with Canadian Aviation Regulations.

It was established that the aircraft commander had been employed by Kenn Borek Air for over 20 years and had accumulated over 22000 flying hours including 7770 hours were on the DHC6. It was his eighth summer season operating in the Antarctic and it was noted that he had previously flown the route of the accident flight approximately 16 times. The First Officer had been with Kenn Borek Air for just over two years and had accumulated almost 800 flying hours including about 450 hours on the DHC6. It was his first summer season operating in the Antarctic. The passenger was an aircraft maintenance engineer employed by the Company.

It was found that after take off from South Pole Station, the aircraft had climbed to 11000 feet asl and initially proceeded along a track of 358°T (see map below). Just over an hour after take off, the aircraft had descended to 10000 feet asl. After almost a further hour, the aircraft turned just over 30°T and began a descent to 9100 feet asl. An hour after this, the last position report was received by South Pole Station. Just over 20 minutes after this, a climb was initiated to 12500 feet asl followed by a turn to the left of just over 40° was made. A final GPS position was transmitted 12 minutes later and when the hourly radio position report expected at 0827 was not received, an emergency response was initiated.

Positions along the track from South Pole Station towards destination Terra Nova Base (based on a Google Earth image and reproduced from the Official Report)

The final stages of the aircraft track can be deduced from the second diagram below.

Positions along the track from South Pole Station towards destination Terra Nova Base (based on a Google Earth image and reproduced from the Official Report)

Extreme weather conditions prevented the search and rescue team from accessing the site for 2 days. When this was possible, the wreckage was found at approximately 13000 feet asl on a steep slope below the 14700 feet asl summit of Mount Elizabeth. Only limited parts of the aircraft were visible and it was noted that there was no evidence that fire had occurred.

An expert review of the likely weather conditions in the vicinity of Mount Elizabeth at the time of the accident was commissioned by the Investigation. This indicated that "it was likely that there was a widespread cloud layer over the Beardmore Glacier from 13100 feet asl to 14700 feet asl" and that the cloud base over the Ross Shelf at the foot of the Beardmore Glacier "may have been at approximately 9800 feet asl". It was noted that a SAR aircraft which had been in the vicinity of Mount Elizabeth 4 ½ hours after the accident had observed a solid cloud layer in the area with a top at approximately 16 000 feet asl and "a break in the cloud in the east grid". Mountain wave conditions with high winds and associated turbulence were also reported to have prevailed.

It was ascertained that the aircraft had been equipped with a TAWS Class B but, since the installed database was not valid beyond 70°S, the forward-looking functionality would have been inoperative with the unit displaying “Terrain Fail”. However, it was noted that the two Garmin GNS 430W navigation receivers installed did have a Forward Looking Terrain Avoidance (FLTA) capability and the error which would have applied to GPS position at the time of the accident was subsequently determined to have been "less than 2.2 metres" with "no significant solar or geophysical weather events that would have affected GPS accuracy". It was noted that the installed terrain database did cover Antarctica - being the first such database to include worldwide terrain data. It was noted that the unit generates FLTA alerts using a comparison of GPS altitude with the data in the terrain database. The diagram below shows the minimum FLTA advisory and warning criteria for the terrain in the area of the accident. It was concluded that the apparent commencement of a climb 45 seconds prior to impact "may correlate with receipt of a 30-second terrain advisory". However, it was calculated, based on the aircraft type operating data manual that, at an altitude of approximately 12500 feet asl and (at the prevailing aircraft weight), the aircraft would (only) have been capable of a 700 fpm rate of climb.

The Garmin GNS 430W FLTA function superimposed on the rising terrain as the aircraft approached the crash (reproduced from the Official Report)

It was concluded overall that "the circumstances surrounding the accident were difficult to determine given the limited access to the accident site and lack of data, which could have revealed details of the last moments of the flight". However, it was apparent that the final turn to the left approximately 12 minutes prior to impact had put the aircraft on a track "that would have led directly to Terra Nova, but the aircraft’s altitude was insufficient to clear Mount Elizabeth". The evidence available suggested that the aircraft would have entered IMC at some point so that "the crew’s view of Mount Elizabeth was likely to have been obscured". The initiation of a climb approximately 45 seconds prior to impact co-incident with the probable generation of a terrain alert by the Garmin FLTA system "suggests that the crew might have responded to a terrain warning" to the extent possible given available aircraft performance.

The formally stated findings of the Investigation as to Causes and Contributory Factors were as follows:

The crew of C-GKBC made a turn prior to reaching the open region of the Ross Shelf. The aircraft might have entered an area covered by cloud that ultimately led to the aircraft contacting the rising terrain of Mount Elizabeth.

Other findings were formally documented as:

  • The CVR was not serviceable at the time of the occurrence.
  • The company did not have a practice in place to verify the functionality of the CVR prior to flight.
  • The rate of climb recorded in the SkyTrac ISAT-100 tracking equipment prior to contacting terrain was consistent with the performance figures in the DHC-6 Twin Otter Series 300 Operating Data Manual 1-63-1, Revision 7.

Safety Action taken as a result of the accident findings by Kenn Borek Air was recorded as follows:

  • flight-following in the Antarctic has been taken back 'in-house' from a contractor "so as to maintain greater operational control"
  • GPS standard operating procedures have been amended to prevent incorrect data input
  • "the accuracy of aviation navigational charts in the Antarctic has been improved" and standard VFR routes for flights exceeding 400 nm have been introduced.
  • a GPWS/TAWS limitation awareness program for flights above the 70th parallel north and below the 70th parallel south has been introduced
  • the pre-start checklist has been amended so as to confirm that an adequate oxygen supply is on board the aircraft and that the cockpit voice recorder is functional
  • the administrative oversight of daily aircraft inspections has been "improved"

The Final Report was authorised for release by the Board on 21 May 2014 and officially released on 20 June 2014. No Safety Recommendations were made as a result of the Investigation.

Further Reading