page_title: Airlines PNG Flight 4684
section_title: Investigation
hierarchical_section_title: Airlines PNG Flight 4684 / Investigation
caption_attribution_description: Early morning at Alola, Kokoda Track, Papua New Guinea. Photographed on Day 3 of Trek - 8 September 2008.
context_page_description: Airlines PNG Flight 4684 was a scheduled domestic passenger flight, operated by Papua New Guinean airliner Airlines PNG, flying from Jacksons International Airport in Papua New Guinea's capital Port Moresby to Kokoda Airport in Oro Province, Papua New Guinea. On 11 August 2009, the aircraft operating the flight, a de Havilland Canada Twin Otter, crashed and exploded into a forest in Kokoda Valley, a popular trekking site in Papua New Guinea while carrying 13 people in bad weather.
  A search and rescue operation was conducted by authorities and found the wreckage of the crashed plane on the next day, 12 August 2009. The aircraft was pulverized, and searchers found no signs of life. Papua New Guinean Search and Rescue Agency then announced that everyone on board was killed instantly in the crash.
  The Australian Transport Safety Bureau were involved in the investigation to the cause of the crash and released its final report, concluding that the plane crashed due to pilot error. The plane deviated from its original flight path and the visual reference in Kokoda Gap was obscured by clouds, causing the pilots to not be aware of their proximity with the ground.
context_section_description: The Australian Transport Safety Bureau (ATSB) were requested by Papua New Guinean Government in assisting the crash investigation. However, the ATSB could only determine the cause of the crash without the FDR and the CVR, as both flight recorders were not mandatory to be equipped on a Twin Otter, based on aviation regulations. The lack of both flight data and cockpit voice recorders adversely affected a full understanding of the accident by the investigation.
  The weather in Kokoda Gap at the time was poor. Based on eyewitnesses accounts and photographic evidence retrieved by ATSB, at the time of the accident, Kokoda Gap was obscured by clouds, making it difficult for the pilots to know if they were in close proximity with the ground. Given the surrounding mountainous terrain, the evident cloud in the Kokoda Gap, as in this instance, had the potential to severely limit the crew's escape options, increase their workload, and test their situational awareness. A reduction in situational awareness and the presence of mountainous terrain during an approach are known risk factors in instances of controlled flight into terrain (CFIT).
  Later investigation found that only one pilot had an IFR rating, while one of them did not. The co-pilot, First Officer Rodney Souka, had been assessed for instrument approach procedures; however, he was not qualified for flight under the IFR. Although the crew had planned to fly under the IFR with visual procedures, the forecast cloud in the area ought to have alerted them that, under those procedures, visual flight in the Kokoda Gap could prove problematic. The visual descent into the Kokoda Gap required 5 km visibility, while at the time of the accident, the visibility was less than 5 km.
  The Australian ATSB then turned their attentions to Souka. They examined his postmortem and medical history. Investigators found that Souka had critical coronary artery heart disease, and the examining pathologist considered that Souka could have had a medical emergency at any time. Souka's relatives reported that they were not aware of any significant medical condition affecting him. If an emergency occurred in mid-air as the aircraft approached the cloud to the north of the Kokoda Gap would have instantly increased Moala's workload and distracted her from the primary task of flying the aircraft. Both those factors are known to increase the risk of CFIT.
  Investigators noted that Kokoda Airport was lacking with its navigation infrastructure. The lack of ground-based navigation aids at Kokoda Airport meant that the only potential navigation assistance for the crew during their approach to Kokoda was from the GPS, or via the ground-based non-directional beacon/distance measuring equipment (NDB/DME) located at Girua.
  The investigation concluded that the accident was probably a controlled flight into terrain: that is, an otherwise airworthy aircraft was unintentionally flown into terrain, with little or no awareness by the crew of the impending collision.
caption: High terrain in the surrounding area of Kokoda Valley.
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