On December 19, 1997, Silk Air Flight 185 suddenly dove from the sky and crashed into the Musi River, killing all 104 people onboard. In episode 79 of Take to the Sky: the Air Disaster Podcast, we explore the investigation that revealed a shocking, but likely scenario that led to the crash: the captain, Tsu Way Ming, intentionally cut power to the cockpit voice recorder and then used his past skills as a top gun pilot to put the plane into an unrecoverable spiral dive. Two agencies investigating the crash, the Indonesian NTSC and the U.S. NTSB, disagreed on that probable cause, with the NTSB publicly opposing the NTSC’s belief that there was not enough proof to determine that the captain sabotaged the flight. The final outcome of the investigations was an “agreement to disagree”, one that left the victims’ families to contend with never knowing definitively what took the lives of their loved ones. 

Silk Air Flight 185 Departs Jakarta for Singapore on Clear, Calm Day 

On December 19, 1997, 97 passengers are boarding a brand-new Boeing 737 known as Silk Air Flight 185, which is a regular 80-minute flight between Jakarta, Indonesia, and Singapore. The plane is being commanded that day by Captain Tsu Way Ming, a former top Singaporean Air Force pilot and former member of the prestigious Black Knights Aerobatic Team. He left the Air Force in 1991 to spend more time with his family and became an experienced commercial captain for Silk Air with 7,173 flight hours, including 3,614 hours on the Boeing 737. 

His co-pilot is First Officer Duncan Ward, who has been flying since a young age, and joined Silk Air in 1996. He has 2,501 flight hours, with 2,311 of them on the Boeing 737 and is noted by supervisors as having above average performance. Joining the flight crew are five cabin crew members, for a total of 104 people onboard Flight 185.

This may be the first mention of this airline. At this time in 1997, SilkAir operated about 100 scheduled flights to about 20 business and holiday destinations in South-East Asia. The routes were generally short haul regional routes, and aircraft and crew usually do not stay overnight outside Singapore. The company operated six Boeing B737 and two Fokker F70 aircraft.

Silk Air Flight 185’s route today would take them mostly over a section of dense rain forest before reaching Singapore, and Flight 185 quickly climbs to its cruising altitude of 35,000 feet (or 10,700 meters). It is a clear, calm day – a day that is perfect for flying. 

About 30 minutes into their flight, and while the cabin crew begins to prepare lunch, Captain Tsu takes this time as a good opportunity to stretch his legs and take a short leave of the cockpit. While he is away, First Officer Ward handles the communications with air traffic control, which has just asked Flight 185 to maintain its cruising altitude and check in with Singapore control in about 5 minutes. First Officer Ward responds by confirming these instructions and then he proceeds with eating his own lunch.

Silk Air Flight 185 Disappears from Radar and is Presumed Crashed

Just a minute later, Flight 185 banks sharply to the right and is soon in a steep dive. The plane is dropping straight through the clouds and begins to invert into a spiral dive. Anything and anyone not buckled down would have been instantly and probably fatally thrown into the ceiling. The plane falls more than 15,000 feet (or 4500 meters) in just 32 seconds and continues to fall. Along its falls toward the ground, parts of the aircraft begin to break away. Just seconds later, the aircraft now traveling at the speed of sound, slams into the Musi River, halfway between Jakarta and Singapore. 

There was no distress call received from the crew or distress signal received from the aircraft transponder. The crash seemed to have happened out of the blue, literally, on a clear day and without warning.

Meanwhile, at 4:13 local time, the flight has just vanished from Jakarta air traffic control radar. Gravely concerned, the controller radios into another pilot on a different flight and asks the pilot to contact Flight 185. The pilot tries to do so but receives no response. 

The fate of the plane seems to be sealed once reports come in from the people who live in the villages along the Musi River – they claim to have seen a large jet slam into the river at a high rate of speed. The fact that the plane is missing from radar, is not responding to calls, and witnesses accounts are now coming in, leads to an intense search for the missing plane. 

Intense Search Launches to Locate Silk Air Flight 185 Plane and Passengers in Musi River

Villagers who had watched in horror as the plane plunged almost vertical into the river began their own search for survivors, but they soon discovered how futile that would be. 

Indonesian Navy divers and ships are brought in to help raise any wreckage from the riverbed, but the search quickly proves to be very difficult. The plane is underneath very murky water with lots of thick mud and clay at the bottom. Divers can only see six inches in front of them and most of the debris is stuck deep in the clay. 

As news of the crash begins to spread, family members converge onto the rescue operation. Two SilkAir flights ferry 200 relatives of the passengers to Palembang, 35 miles (or 56 kilometers) south of the crash site. Dozens of the relatives hired speedboats to watch Indonesian police and navy boats scour a 10-square-mile (or 16-square-kilometer) area of river and swamp for debris and remains. Almost half of the passengers onboard Flight 185 are Singaporean. 

And not just passengers’ families are reacting to the tragic news. First Officer Duncan Ward’s father, Derek Ward, and his family are in complete shock and are devastated by the news. And along with their devastation, they are utterly confused by what could have put the plane into such a deep and deadly descent. Of the moment of realization of what his son and the passengers must have gone through, he said, “It was just horrendous. It has an enormous psychological effect on you.”

It is soon apparent that all 104 people onboard Flight 185 have died on impact. Now it is about finding answers as to why a brand-new Boeing 737 dove out of the sky on a perfectly clear day.

To help find these answers, several agencies converge to make up the investigative team. First, the Indonesian National Transportation Safety Committee (NTSC) will lead the investigation and be aided by members of the U.S. National Transportation Safety Board (NTSB) as the plane was a Boeing, American-made plane. Because Silk Air is the regional wing of Singapore Airlines, the Singaporean Ministry of Communications and Information Technology will also be on hand along with the Australian Bureau of Air Safety Investigation, which is playing an advisory role. 

Initial Silks Air 185 Investigation Rules Out Inflight Fire, Explosion, and Depressurization

One of the first pieces of evidence that investigators review – and that is readily available to them – is the radar data that can be calculated to show the plane’s speed and height during its flight. Everything shows a normal flight course except for the final 36 minutes of the flight, which of course, show the sudden and deep descent. Investigators know that this information only tells them a portion of the story, but nothing that would point to why this occurred.

The team eagerly awaits more evidence from the wreckage site, which is now being combed through by machinery with large buckets that dredge the depths of the river for more airplane parts. Although approximately 73% of the aircraft by weight is eventually recovered, only a small amount of the wreckage is identifiable and in a condition useful for the investigation. And even more tragic than that, searchers collect just 330 pounds (or 150 kilograms) of body parts from the passengers and crew – roughly equal to the weight of two adults. The remains of only six passengers are ever able to be identified.

When investigators inspect the wreckage, there are a few causes they can immediately rule out. The fracture surfaces and wreckage fragments show no evidence of pre-existing structural defects, fire, or explosion in flight. The examination of the recovered passenger oxygen generators, which have not been activated, reveal the aircraft did not experience depressurization in flight. They also rule out most mechanical failures, using the plane parts they have recovered.

Soon, investigators find a clue that puts them on the path of solving the mystery of what brought down Flight 185. While searching for both the flight recorders and more plane debris, investigators are told about pieces of the plane’s tail that have been found beyond the crash site. 

These parts include sections of the horizontal stabilizers, rudder, and elevators – all of which control the position of the plane, including pitching the plane up and down. 

Silk Air Flight 185 Tail Pieces Some of First to Separate from Plane During Fall 

The debris was found scattered on land, with one piece being as far as 2.5 miles (or 4 kilometers) from the impact site and the closest being 2300 feet (or 700 meters) from the impact site. Additional pieces were picked up by local residents and handed over to the police and search and rescue helicopter pilots. The inspection of the recovered wreckage suggests that the aircraft was structurally intact until the outer sections of the horizontal stabilizers, elevators, and sections of the rudder separated from the aircraft. Based on where these pieces have been found, investigators can tell these are among the first parts to break off the plane. The question they need to answer is, did they break off inflight (which would certainly cause the plane to nosedive) and cause the dive OR did the dive happen first, which put aerodynamic pressure on the stabilizers, causing them to break off? 

One of the very first possibilities as to the cause of the stabilizer separation that investigators explore is the concept of a rudder hard over. The previous 737 models had a history of rudder hard over, when the rudder goes all the way to one side or another, or even moves by itself, without being commanded to do so. In some instances, pilots lost control of the plane as the rudder hard over caused a rapid descent. One of those instances was United Airlines Flight 585 in 1991 outside of Colorado Springs, Colorado in the US, which we will eventually cover on the podcast. 

However, following those crashes, Boeing had designed a fix to the rudder before the latest 737 model had even been built. Prior investigations into rudder hard over on the 737 also revealed that the cause was linked to a malfunctioning PCU, or power control unit, on the aircraft. Basically, if a PCU became contaminated or experienced corrosion, it would bind up and malfunction, causing in some cases, the rudder to become stuck in one extreme position. When investigators examine the PCU on the aircraft that was Flight 185, they find it is working properly. They feel confident that a rudder hard over is not the cause of the rapid descent. 

This also means that investigators now believe they have an answer to one of their key questions: it was the aerodynamic forces of the dive that caused the tail parts to break away, and not the other way around. The dive came first. 

Both Flight Data Recorders Stopped Working Before Silk Air 185 Crashed

Investigators are at the point where they need additional data. Luckily, the flight data recorder (FDR) had been found early in the wreckage recovery, but the cockpit voice recorder (CVR) has not yet been located. That was, until the very last day of the dredging and the end of the overall recovery mission – divers found the CVR under 27 feet (or 8 meters) of muddy water.

Both recorders are sent to the NTSB in Washington, DC, for analysis. And what the recorders reveal – or don’t reveal – is shocking: the CVR stopped recording about seven minutes prior to when radar shows the rapid descent begins, and the FDR stopped recording six minutes after the CVR stopped. By the time the rapid descent began, neither recorder was on. The mystery is further deepened when, with the data they do have from the FDR, investigators can tell that everything about the flight was normal – they were at cruising altitude on a clear day on autopilot.  

It’s when they listen to the CVR that alarm bells begin to ring. For the first 35 minutes in air, the CVR shows normal communications between the flight crew and air traffic control as well as with the cabin crew. Then, the final sound recorded is the snap of the Captain’s seat belt being unbuckled. Why did the CVR stop here? It should never stop recording.

Investigators Believe Captain Intentionally Tripped Power to CVR Circuit Before Crash

Investigators know that if the circuit breaker to the CVR had been overloaded, it may send a surge that cuts the power and pops the breaker to the CVR on the panel in the cockpit. So, they conduct tests to try and see how much power would be needed to overload the circuit and make the CVR breaker pop. Instead of answering that question directly, they end up coming upon circumstances that chill investigators. What they found was that when the circuit breaker popped, the CVR kept recording for another split second before cutting off, and during that second, the sound of circuit breaker pop can be heard on the CVR itself. Investigators wonder, then, why did this sound not appear on the CVR for Flight 185? The last sound had been the sound of the Captain’s seat belt unbuckling. 

After more tests, here is what the team found: if the breaker popped, it made a sound that was recorded on the CVR, but if you manually pull the circuit breaker by hand in the cockpit, it does not make an audible sound that then gets captured on the CVR. This means that the circuit breaker did not fail due to a power overload (that would have caused the breaker to pop and that would be found on the CVR). It means it is more likely that the CVR breaker was pulled by hand. And the breakers are located just behind the Captain’s seat. These conclusions lead investigators down a dark path: did one of the pilots intentionally cut power to the CVR to leave no record of a sabotage wherein one of them put the plane into a deadly dive?

As investigators consider this uncomfortable possibility, they continue to seek alternative explanations for the dive. During a simulation using the same data that coincides with the flight parameters of Flight 185, they test 20 different scenarios to see if any of those situations and combinations of mechanical failures could cause the same type of sudden, steep dive. Only one scenario produces the same result as the trajectory of Flight 185: if someone in the cockpit intentionally rolls the column all the way to the right and applies maximum speed. 

One final piece of physical proof supports the theory of sabotage, and this involves the horizontal stabilizer. What follows comes from Air Disasters on the Smithsonian Channel: the trim jack screw is a threaded rod connected to the horizontal stabilizer. It rotates when pilots press a trim switch on their control column. As it turns, it moves the stabilizer up and down, changing the pitch of the aircraft. Based on the jack screw’s final setting at the moment of impact, investigators calculate the final pitch angle on the stabilizer. It was in full nose down trim. To investigators, this evidence confirms that one of the pilots initiated the dive. 

Investigators Identify Captain Tsu as Probable Saboteur of Silk Air Flight 185

Now the investigation turns to the two men flying the plane. And as investigators comb through past performance records and interview colleagues and family and friends, one pilot immediately stands out among the two: Captain Tsu Way Ming. Let’s talk more about the Captain. 

Leading up to the day of Flight 185’s crash, Captain Tsu had been reprimanded by Silk Air three times and demoted for breaches of pilot discipline. During the first instance, Captain Tsu was flying a jet too high into Manado Airport and had to make a second approach. After that, he was required to file a report disclosing the incident, but he did not do so, which caused both him and his co-pilot, Lawrence Dittmer, to be summoned for an investigation by Silk Air. And not only that, but Dittmer was scared by the S-turns that Captain Tsu had been making as they got closer to the airport as a way to rapidly lose speed (like in a fighter jet). On that occasion, some passengers were even made sick in the cabin by the maneuver. 

Three months later, he was scheduled to fly with the same co-pilot. During pre-flight checking, Captain Tsu began to heatedly discuss the prior incident with Dittmer, and just before the plane taxied onto the runway, Captain Tsu triggered the circuit breaker for the CVR. 

But Dittmer saw what he had done, and he refused to fly with him unless he reset the breaker. This caused Captain Tsu to contact ATC and request permission to return to the gate to download the information from the recorder, which operates on a loop. However, he changed his mind, and they proceeded to take off. And not having the CVR recording is against the law. As a consequence of this infraction, Silk Air demoted him from an instructor-pilot to the rank of captain. 

The third incident happened just a month before the crash when Captain Tsu took off from Singapore to China without gaining enough engine thrust. The plane had to return, overloaded with fuel, and Captain Tsu failed to report this incident. In a letter from his then supervisor, he was asked to be more mindful in the future. Apparently, a leaky fuel pipe was the cause, which would have made the airplane unfit for service – he never should have taken off in the first place. 

And, tragically, right before he boarded Flight 185, First Officer Duncan Ward allegedly told a friend that he would plan to meet him that next evening, “if I make it.” Colleagues took that to mean First Officer Ward had concerns about Captain Tsu. 

Captain Tsu was married with three children and was found to have been in financial trouble after losses in the Asian economic crisis. And just 15 days before the crash, he was suspended from trading anymore on the market until he repaid his debts. 

And if these things were not circumstantial enough, here are two more items to add to the list. Shortly before the crash Captain Tsu took out an insurance policy. On December 12, one week prior to the crash, he was notified that this application had been accepted, and then he posted a check for the first premium payment on the 16th. The policy took effect on the 19th.

One more thing. December 19th was also the anniversary of a tragedy that some who knew Captain Tsu said still weighed on him. In 1979, he and four of his Air Force colleagues had gone on a training exercise, but he had to turn around and go back due to troubles with his jet. The remaining airmen were all killed when their jets crashed into a mountain. He is believed to have blamed himself for not being there with the men. 

Investigative Agencies Bitterly Divided Over Captain’s Role in Silk Air Flight 185 Crash

The lead investigator for the Indonesian NTSC said on the Air Disasters episode that when the team submitted its final report, the NTSC Chairman, Oetarjo Diran, overrode the investigation because only circumstantial evidence exists, and the Chairman felt that if you were going to place blame on a pilot, you needed irrefutable physical evidence. The official NTSC report says that the wreckage was highly fragmented, the data was mostly useless, and the investigation could not explain how and why the incident happened. Ultimately, Chairman Diran rejected the theory that Captain Tsu intentionally crashed the plane, because Singaporean police found no suicide note. 

A separate, subsequent criminal investigation conducted by the Singaporean police also found that no evidence existed that the crash was deliberately caused by either pilot or anyone onboard. Also, Indonesian officials asked an accounting firm to review Captain Tsu’s finances, and they came back with a report that said he was solvent and possessed a positive net worth. His income, however, was not enough to cover his monthly household expenses, police found.

However, many people say that inside Silk Air, this disaster was waiting to happen. Mohan Ranganathan was a SilkAir captain who knew both Flight 185 pilots, Tsu and Ward. A veteran 737 pilot himself, Ranganathan said he warned his bosses before the crash that Captain Tsu Way Ming was an unsafe pilot. They refused to listen, he said. Ranganathan quit the airline soon after the disaster. He said, “Tsu Way Ming was very dangerous. A person of Duncan Ward’s experience could never have flown the final profile. It was definitely by a trained aerobatic pilot. Tsu is the only person who could have done it.”

The NTSB, in an unprecedented move, publicly opposes the NTSC and releases its own separate, final report. The editor at Flight Safety Magazine, David Learmont reflected the thoughts of most pilots and experts in the industry, “The amount of circumstantial evidence is pretty overpowering, and frankly, everybody in the business thinks that this is actually what happened. But if you approach this in a completely legalistic way, the evidence that they have simply doesn’t prove what happened.”

By now you may be thinking of similar stories we have covered on the podcast, including episode 5, Germanwings 9525, which was intentionally flown into a mountain; and we also saw two other incidences, once with an attempted takeover onboard Fed Ex 705 in episode 9 and an airline employee who shot the pilots and put the plane into a fatal dive onboard PSA 1771, which we covered in episode 69. Also, during episode 12, Egypt Air 990, it was never fully determined if the pilot intentionally brought down the plane or not. 

NTSB Firmly Believes Captain Tsu Caused the Fatal Dive that Killed 104 People On board Silk Air 185

Here is what the NTSB deduces happened onboard Flight 185. 

No one will ever know what happened in the cockpit after the voice recorder went dead. It is likely that Captain Tsu might have left the cabin, as he said he was going to do, and come back a few minutes later. Or he might never have left at all.

One theory is that after First Officer Ward talked with air traffic control, Captain Tsu took command of the plane, sent his co-pilot out of the cockpit on a ruse, and locked the door.

But even if First Officer Ward was in his seat when the plane began to dive, there was little he could have done if Captain Tsu was determined to crash the aircraft. It would have taken Captain Tsu eight to 10 seconds of continuous thumb pressure on a hand-held button to change the horizontal stabilizer to the maximum nose-down setting. While he was pressing the button, First Officer Ward could not have overridden the command, according to a former military aerobatic pilot. And even if First Officer Ward immediately realized what Tsu was doing, he couldn’t have reached Captain Tsu’s control from his seat.

Flight plans, dishes and manuals would have flown around the cockpit as warning alarms sounded and the plane flipped over or began to spiral. The two pilots might have battled for the controls, but without command of the horizontal stabilizer, First Officer Ward would have been powerless to pull out of the dive. In the cabin, many experts say the terrified passengers would have remained conscious. They would have known they were about to die as the plane plunged earthward. Others say the g-forces would have made them pass out. 

Families Unsettled by Differing Views on Probable Cause of Silk Air Flight 185 Crash 

Most of this story has been about Captain Tsu, and understandably so. But if he did what the NTSB believes he did, then he also committed murder. Derek Ward, father to First Officer Duncan Ward, believes that the evidence is clear and that the grimness of the situation should not be minimized or forgotten. Of the cause of the crash, he says, “Tsu intentionally flew the plane directly into the ground. I call that mass murder. What else can it be called?”

Following the crash, victims’ families reluctantly accepted compensation from Silk Air for the loss of their loved ones, yet the money provides little comfort given how the investigation turned out. Some victims’ families contend that Singapore and Indonesia have tried to cover up the cause of the disaster to protect the airline’s reputation. SilkAir is a subsidiary of Singapore Airlines, after all, and one of the city-state’s most prominent businesses and one in which the Singaporean government owns the controlling interest.

And because this may have been a mass murder, we cannot forget about the victims, who should be front and center in this story.

Silk Air Flight 185 was carrying passengers from 14 countries, including 46 from Singapore, 23 from Indonesia and five from the United States. The oldest was 77; the youngest, 2. Three Indonesian children were traveling onboard without their parents.

First Officer Derek Ward was dating a SilkAir flight attendant and living his dream as an airline pilot. Associates described the New Zealander as friendly, honest and “full of life.”

Passenger Bonnie Hicks’ was a well-known model and author and even penned a column on the brevity of life just before she was killed. Hours after her final article was printed on that Friday, Bonnie and her American boyfriend then boarded Flight 185.

An entire family was killed in the crash. Liauw Ali Gunawan, 37, his mother, wife and two daughters were all killed onboard the flight that they were taking to Singapore for the wedding dinner of his younger sister.

Soen Lay Heng, 41, had developed a phobia of flying after being aboard Singapore Airlines Flight 117 when it was hijacked in 1991. This time, Soen, a businessman, had just clinched a $100 million deal in Jakarta and was heading home to Singapore en route to San Francisco to join his wife and three children, ages 5 to 12, who were on vacation.

Yee Pui Leng, Koh Poh Kwee and Tan Chay Hoon were teachers at Singapore’s Fairfield Methodist School. Close friends who shared school meals and holidays, they went to Indonesia for a week’s vacation. But they cut it short by a day when they heard a 33-year-old colleague, Soon Ching Lin, had died of a sudden heart attack. They wanted to be back in time for the funeral Sunday.

A memorial for the victims was erected at the burial site, which is located within the Botanical Gardens near Palembang. Another memorial is located at Choa Chu Kang Cemetery in Singapore.