In episode 115 of Take to the Sky: The Air Disaster Podcast, we explore the crash of Trigana Air Flight 267, which crashed into the side of Mount Tangok on August 16, 2015, killing all 54 people onboard. The Indonesian KNKT investigation uncovered a host of issues with the performance of the pilot-in-command, Captain Hasanuddin. At the conclusion of the investigation, the KNKT identified several contributors to the crash. First, the minimum safe altitude on the chart was incorrect. Second, the captain deviated from the visual approach guidance for most of the flight to Oksibil Airport, which was not sanctioned by Trigana Air. Third, the CVR did not record any crew briefing and checklist readings from cruising up to the impact.  Fourth, Captain Hasanuddin (and other pilots at Trigana) pulled the circuit breaker to the GPWS, thereby deactivating the system, and Trigana Air had not corrected this behavior in a timely manner.  Fifth, the investigation also found that several maintenance records related to critical elements like the FDR and the GPWS were not well documented, indicating that the maintenance management at Trigana was not well performed. Ultimately, following the crash, several safety recommendations were adopted by Trigana Air and upgrades made to remote airports like Oksibil, but the picture of aviation safety for Indonesia remains troubling to this day. 

Trigana Air Flight 267 Prepares for Landing at Remote Oksibil Airport on August 16, 2015

Trigana Air Flight 267 was a scheduled passenger flight from Sentani to Oksibil in the eastern Indonesian province of Papua. And on August 16, 2015, boarding the ATR 42 Turboprop plane were 49 passengers, many of whom frequently took this forty-minute flight as part of their regular commute back and forth, as many worked for the local government or owned their own businesses. 

Two pilots round out the flight crew. Captain Hasanuddin (aged 60) had joined Trigana Air in 2000, and he has 25,200 hours of total flying experience and 7,300 hours' experience flying ATR 42s. First Officer Aryadin Falani (aged 44) had joined Trigana in 2008 and had a total of 3,800 hours flying experience, of which 2,600 were in ATR 42s. This route was their fifth flight of the day. Their next two legs would take them from Sentani Airport in Jayapura to Oksibil and back, a round trip journey that spanned approximately two hours round trip. This would be their second trip to Oksibil that day. Besides the pilots, there were three other crew members: two flight attendants, and a Trigana Air mechanic. In total, including crew, there were 54 people on board.

At 2:22 PM local time, Flight 267 takes off into the afternoon sky. As we mentioned, this aircraft is an ATR 42 Turboprop, which is a mid-sized commuter plane that is popular for being able to fly in and out of smaller airports, therefore, making flight more accessible to people, especially those individuals who needed to travel across more remote locations.

The airport at Oksibil is situated in a small valley, surrounded by mountains that stretch up to 11,000 feet (or 3300 m) high. It’s also important to note that this airport, due to its location amid mountains, has limited navigational aids, which means pilots must fly into Oksibil on visual approach, which as we know means, pilots must keep the runway in sight at all times during the approach. 

Flight 267 reaches its cruising altitude of 11,500 feet (or 3500 m). And just like any other short flight, this is also the moment the pilots begin planning for descent. 

After Trigana 267 Fails to Respond to AFIS Calls, Search and Rescue Commences

At 2:55, with First Officer Falani at the controls, Captain Hasanuddin contacts the Aerodrome Flight Information Services (or AFIS) officer in Oksibil. Unlike a true controller, the AFIS officer only had the authority to provide information to pilots and could not give them orders. Captain Hasanuddin told the AFIS officer that they were descending from 11,500 feet (or 3500 m) to 8,000 feet (or 2400 m); the AFIS officer acknowledged and asked that the captain confirm when flight 267 was positioned over Oksibil. 

Not surprisingly, given the lack of automated landing systems at the airport, the pilots prepare for a visual approach, an approach flown manually while maintaining continuous visual contact with the airfield. The AFIS officer had reported that there were broken clouds at 8,000 feet (or 2400 m) obscuring more than half of the sky.

As flight 267 descended toward 8,000 feet (or 2400 m), it entered the cloud bank and visibility dropped to zero. The pilots extended the flaps and lowered the landing gear, preparing for an imminent landing. But that is not what happened next. 

Two minutes later, the AFIS officer became concerned when the crew failed to contact him as expected. At first, the inability to call up the crew did not immediately indicate any sort of emergency. In fact, in that area, for a variety of reasons, sometimes a flight crew needed to divert to another airfield. And in those cases, flight crews may be too busy to answer the call from AFIS. 

But, after trying repeatedly to raise the flight without success, and after confirming with another airfield that Flight 267 was not there either, the AFIS officer sounded the alarm, and a major search and rescue operation kicked into gear. 

Trigana 267 Debris Field Located on Mount Tangok After Difficult Search Period 

The search and rescue (or SAR) team consisted of the Oksibil Airport Authority, local government, police, army, and an investigator from Indonesia’s National Transportation Safety Committee (or KNKT). Hopes of finding the plane at another airfield soon faded as the day dimmed into evening, and the search operation was postponed until the following morning. Then, the next day brought a breakthrough. A pilot flying a Twin Otter aircraft from Oksibil to Sentani Airport saw smoke in the jungle. And then a second pilot flying overhead at a lower altitude also confirmed they saw smoke but this time could also confirm the source of the smoke: it was coming from the debris of an aircraft. This pilot informed the AFIS officer of the location of the aircraft debris, who then communicated with the SAR team. 

While finding the plane’s wreckage location was certainly progress, search and rescue had a very difficult job ahead. The plane was in an area of the mountain without any roads, runways, or clearings. Searchers had to enter the only way possible: by foot. This meant climbing rocks and hacking through jungle vegetation. The SAR assembled a team to proceed to the location of the debris on foot. Finally, more than 24 hours after the crash, and five solid hours of hacking their way through the jungle, flight 267’s last resting place was found in the middle of the jungle forest on Mount Tangok, at an elevation of 8,300 feet (or 2529 m) and 11.5 miles (or 18.5 km) from the airport.

Back at the airport in Oksibil, the victims' families, who had been waiting at the airport, broke down in tears when they heard the news. Many of them accused the airline of taking too long to give them information. Cory Gasper, whose brother Jhon Gasper was on the plane, said, "They are unprofessional ... they play with our feelings of grieving.”

As it happens with so many terrible disasters, the families of those passengers onboard flight 267 had to submit DNA samples so experts could match their profiles to the 54 bodies retrieved from the plane. Through a painstaking process, experts were later able to confirm every passenger onboard and return their loved one’s remains back to the families. 

Just one day following the discovery of the plane’s wreckage, the management of Trigana Air Service announced it would provide compensation to the families equal to about $91,000 USD for each passenger. 

Trigana 267 Debris Located West of Approved Oksibil Airport Approach Path 

Once search and rescue personnel had made the site ready, the remaining investigators with Indonesia’s KNKT began to arrive on foot and by helicopter. Investigators knew they would not be able to transport the wreckage back to a hangar, so they had to meticulously document everything about the site through drawings and photos. 

And the crash site provided plenty of clues as to what happened in the final minutes of flight 267. It was later determined that at 2:58 PM local time that day, the plane, with 54 people onboard, slammed unexpectedly into a fog-bound ridge of Mount Tangok at an elevation of 8,300 feet (or 2529 m). The airplane was completely obliterated upon impact and exploded, scattering charred plane parts and human remains all throughout the jungle floor. Based on the condition of the wreckage, it was clear to investigators that none of the 54 people onboard flight 267 survived the impact. 

What is most curious about the location of the wreckage is that the site is not along the planned flight path of where Flight 267 should have been flying; instead, the plane crashed 11.5 miles west (or right) of the approach path for the airport. This is also a route surrounded by mountains. 

Investigators rush to download data from both flight recorders, including the flight data recorder (or FDR) and the cockpit voice recorder (or CVR). And what they find within the back boxes may be a first that we have talked about: the FDR was not working at the time of the crash. Investigators uncover a history of problems with that FDR on the airplane and evidence that it had not been working consistently for about three years prior to the crash. While this had nothing to do with the crash, it did lead investigators to some troubling discoveries about maintenance practices at Trigana Air. We will come back to this later. 

KNKT Finds Crew of Trigana 267 Took Left Base Leg Approach Across Mountainous Terrain

Thankfully, though, the CVR did record. And on the CVR, during the pilots’ conversations with the AFIS officer, investigators discover that the pilots chose to take a different approach path into the airport. As we have mentioned already, all aircraft landing in Oksibil must execute a visual approach. However, airport authorities had not published an official visual approach procedure for pilots to follow. As a result, Trigana Air devised its own procedures, which called for approaching aircraft to overfly the airfield, make a loop to the southeast, fly past the airport to the west, then turn around and land on runway 11. But this is not the path Captain Hasanuddin chose to fly that day. 

Instead of flying what he and many other Trigana pilots felt was an overly complicated loop around the airport, he often flew directly to the west end of the airfield, made a single left turn, and then lined up with the runway. 

This approach was known as a “left base leg,” and the reason for taking it was that it saved considerable time and effort. There is a downside, or risk, to taking this approach, however: it takes a plane closer to the top of the mountainous terrain, some of which exceeded 9,000 feet (or 2700 m). And since the AFIS officer did not have the same authority as an air traffic controller, they could not deny this flight path. And this was the same flight path these two pilots had used on one of their earlier legs that same day. 

Cloud Cover Conditions on Trigana 267 Flight Path Violated VFR Approach Rules 

Something else was revealed through the CVR. While the engines sound like they’re operating normally, investigators don’t hear something they would expect to hear at the moment of impact, which is the reaction from the pilots. But there is no screaming, no startled response. Nothing. And here is why. 

Investigators identified almost immediately that clouds were obstructing the view of the mountains along the flight path. As flight 267 descended toward 8,300 feet (or 2500 m), investigators believe it probably entered clouds, which brought visibility to zero. The clouds were so thick and the impact so sudden that neither the crew nor the passengers ever knew what hit them.  

The AFIS officer had reported to the pilots that there were broken clouds at 8,000 feet. But, Captain Hasanuddin probably believed that since the cloud base was at 8,000 feet, and according to his approach charts, this was also the minimum safe altitude, he thought he could descend and remain clear of the terrain while also giving himself a chance to catch sight of the airport. This is problematic for a key reason: a visual approach cannot be performed under cloudy conditions because a pilot must always always maintain visual contact. 

But in 2015, a commercial plane colliding with a mountain is highly unlikely to happen because of the ground proximity warning system (GPWS) in the airplane. But the CVR transcript showed the alarms from this system never sounded on flight 267. Maintenance records for the GPWS showed no issues with the system as of two days before the crash, which leads investigators to assume that the system was working properly on the day of the crash. 

KNKT Discovers Visual Approach Guidance Charts used by Trigana Showed Wrong Safe Minimums

But where the investigation goes next ends up uncovering two key contributors to the crash of flight 267. The first contributor was that the visual approach guidance charts used by Trigana pilots on this same flight path showed the minimum safe altitude over terrain to be 8,000 feet (or 2400 m), but we know that the plane crashed into Mount Tangok at 8,300 feet height (or 2529 m). The KNKT examines the charts and find that they are incorrect. The information the pilots were using was wrong and this is one of the reasons that flight 267 was put on a collision course with the mountain. The minimum safe altitude threshold should have been much higher. 

The second contributor to the crash is uncovered when the KNKT interviews other Trigana pilots about whether they received GPWS warnings over this same flight path. In those interviews, the pilots tell them that, yes, the system worked properly over the mountains and even gave off several false warnings, which were caused by a lack of good data being fed to the system about the surrounding terrain. GPWS continuously checks an airplane’s position against a computerized terrain database to predict when it is in danger of striking terrain. The resolution of the database showing the terrain on the flight path was so low that it would often and incorrectly activate even if a plane was not actually in danger of striking terrain. 

KNKT Investigation Reveals Trigana 267 Captain Likely Deactivated EGPWS 

So, if the system was functioning properly and the system was so sensitive that it even gave false alarms, how did the pilots not know about what was coming? The answer lies in how Trigana pilots historically responded to the false terrain warnings: they did so by pulling the circuit breaker to the GPWS, and thereby, deactivating the system. 

The KNKT believes that during an earlier flight, when the GPWS generated a false warning, Captain Hasanuddin probably pulled the circuit break to the system – and never reset it again for the next flight. Obviously, this action was considered to be a grave oversight and one that investigators say can be attributed to overconfidence on the part of the captain, who had flown this route so many times in the past that he simply and tragically forgot to push the breaker back in. 

As aviation safety analyst Todd Curtis said during an interview for the Mayday Air Crash Investigation episode for this crash, “Overconfidence and complacency, they are two of the issues common in aviation. And what that leads to is certain equipment could be turned off because the pilots think that their experience and other aspects of flight will more than compensate.” 

Ultimately, in a situation like this, pilot overconfidence and complacency leads to great risk. And that risk is to the lives of their passengers. Prior to the accident, the management at Trigana Air had scheduled a briefing with Captain Hasanuddin and other pilots about not pulling the GPWS circuit breaker. 

KNKT Investigators Find Captain Mostly to Blame for Trigana Air 267 Crash 

At the conclusion of the investigation, the KNKT identified several contributors to the crash. First, the minimum safe altitude on the chart was incorrect. Second, the captain deviated from the visual approach guidance for most of the flight to Oksibil, which was not sanctioned by Trigana Air. Third, the CVR did not record any crew briefing and checklist readings from cruising up to the impact.  Fourth, Captain Hasanuddin (and other pilots) pulled the circuit breaker to the GPWS, thereby deactivating the system, and Trigana Air had not corrected this behavior in a timely manner.  Fifth, the investigation also found that several maintenance records related to critical elements like the FDR and the GPWS were not well documented, indicating that the maintenance management at Trigana was not well performed. 

Following the crash, the KNKT issued several safety recommendations that addressed all the issues found during the investigation calling for comprehensive pilot briefings about safe behaviors and visual approach landings; enhanced oversight of maintenance and training at Trigana Air; and updated visual approach guidance for several airports in remote areas, including Oksibil.  On an even larger scale, the Indonesian government vowed to upgrade the infrastructure and runways in Papua at twelve small airports, including Oksibil Airport. Updated weather reports would also be issued by the local weather station more frequently than they had been issued to flights before the crash. 

Trigana Air Flight 267 Crash Highlights Ongoing Challenges in Indonesian Aviation Safety 

The crash of flight 267 also brought the spotlight back on Indonesian aviation safety. Arnold Barnet, a statistician focusing on aviation safety at the Massachusetts Institute of Technology (or MIT), told the New York Times in December 2014 that the death rate in Indonesian airline crashes over the previous ten years was one in every million passenger-boardings, compared to one death for every 25 million passengers for airlines in the United States. According to the Aviation Safety Network’s database, the country has experienced 104 commercial airline accidents with over 1,300 fatalities since 1945, and at least one hull loss every year from 2010 to 2019, ranking it as the most dangerous place to fly in Asia.

Since 2002, Trigana Air has itself experienced 13 major incidents. Ten of the 13 were listed as “hull loss,” a term used when an aircraft is damaged beyond repair and at the time of the crash, were blacklisted by the EU as an unsafe airline to fly. 

Despite that blacklist designation, when the crash of flight 267 happened, news networks repeatedly asked the question, why was this airline being allowed to operate at all? The answer is nothing less than unsatisfying: Sovereign nations set their own aviation standards and practices, and while the UN-affiliated International Civil Aviation Organization (or ICAO) can audit airlines and their home country’s regulatory climate, outside entities and other nations can’t do anything to stop an unsafe carrier from operating, except to bar a particular company from its own territory. It’s not just the airline that's to blame; in dozens of developing countries, air-traffic control and airport infrastructure is minimal, and many pilots and air controllers lack the latest technology and necessary training. Among the other outliers on the EU blacklist are airlines from countries whose aviation sector has been ravaged by prolonged military conflicts.

However, blacklists can provide some guidance. But flyers should consider it along with other sources such as the U.S. State Department’s travel advisories, according to Bruce McIndoe, president of iJet in Annapolis, Maryland, which specializes in travel risk management. While his firm’s analysts are watching the rapid growth of aviation in Asia closely, overall, flying is still the safest way to travel. Perhaps keeping the bigger picture in mind is the right way to go. Afterall, each of us has a one in 25 million chance of dying in a commercial airliner worldwide, while our lifetime odds of dying in a car crash, at least in the United States, is 1 in 101. 

And THAT is the story of yet another crash that never had to happen, Trigana Air Flight 267.