On March 12, 2009, the flight crew of Cougar Flight 91, a routine, overwater helicopter flight ran into problems when the orange caution message, “MGB OIL PRES” lights up, indicating there is low oil pressure in the main gear box. In episode 101 of Take to the Sky: the Air Disaster Podcast, we explore how the captain initially believed that the true cause of the problem was a faulty sensor, and so he maintains the helicopter’s altitude at 800 feet (244 m) in preparation for making their way back to shore in St. John’s, Newfoundland. But, Cougar 91 will never reach land. The helicopter rapidly loses all its oil, and the flight crew fights with the controls as the aircraft drops back toward the ocean. When the helicopter impacts the waves, only one survivor emerges – the other 15 passengers and 2 flight crew are dead. The Canadian TSB uncovers major problems within the design of the Sikorsky S92 helicopter that was Cougar 91, including titanium studs that became detached due to galling damage, a problem found to exist throughout the entire S92 fleet, unbeknownst to Sikorsky. The second problem was with the FAA’s certification of the S92’s main gearbox. Sikorsky knew the S92 could not meet the FAA requirement of 30 minutes of dry run time, and so it established that a loss of the main gearbox due to lack of lubrication (oil) would be “extremely rare.” However, given the extent to which all S92 studs had galling damage, this certification was based on incorrect assumptions. The TSB also found that decisions made by the pilots prevented Cougar 91 from being adequately prepared for an ocean ditching. Following the crash, sweeping changes were made by Cougar and Sikorsky, and both the TSB and FAA enacted changes that made the S92 much safer. 

Cougar Helicopter Flight 91, a Routine Overwater Flight, Leaves St. John’s with 16 Passengers and 2 Crew

We begin in the North Atlantic Ocean off the coast of Newfoundland, Canada and the many oil rigs at sea. Many of these large ocean platforms are as tall as skyscrapers and weigh sums as large as 750,000 metric tons. The environment surrounding these oceanic oil platforms is incredibly harsh; in fact, crews must battle 80-foot (or 24 m) waves and subzero ocean temperatures. 

One of these such rigs is the Hibernia Oil Field, located 195 miles (or 315km) east of St. John’s, Newfoundland, which is one of the heaviest platforms in the world. And, of course, managing the operations onboard these platforms are hundreds of workers. The Hibernia employs roughly around 185 people at any given time. 

But if you happen to be one of these workers, having your so-called “office” in the middle of the sea poses its challenges, including the fact that it is very difficult work. And, one cannot just hop into a car to get there. For this challenge, the crews onboard Hibernia, and many other platforms just like it, rely on a fleet of over-water helicopters. One of the primary organizations providing offshore transportation in this part of the North Atlantic Ocean is Cougar Helicopters Inc., which transports rig workers using a fleet of Sikorsky S92 aircraft. 

The S92 is an American-made, multi-purpose helicopter powered by twin GE turboshaft engines with an aluminum airframe. It has two rotors, one on top (called the main rotor) and one in back (called the rear rotor). The helicopter is known for several safety features included in its design, and because of those, the FAA certification board called the S92 the "safest helicopter in the world". 

And while this was a state-of-the-art helicopter, it was a “no frills” flight experience without any amenities. Other than the 17 seats behind the cockpit, there was only room for each person’s gear – this is all about optimization of space and getting people to their destinations. 

This is exactly what the 16 passengers and 2 flight crew expected on March 12, 2009, when they boarded a Cougar helicopter at St. John’s Airport for a 90-minute flight known as Cougar 91. Most of the passengers were used to this very flight as all of them worked hard as service workers for the Hibernia or the other various rigs out in the North Atlantic. 

Behind the helicopter controls today, we have two flight crew, one captain and one first officer. Captain Matthew Davis had almost 6,000 hours accumulated over 20 years as a professional helicopter pilot, including 1,067 hours in the S92. First Officer Tim Lanouette had flown a total of almost 3,000 hours during 23 years with the Canadian Forces, and he had been flying with Cougar for 11 months. The first officer also had 97 hours in the S92.

On this cold March morning, once all 16 passengers boarded, the pilots provided them with the required pre-flight safety briefing, which included giving each person an emergency immersion suit for the over-water flight. This is not only an important safety device because of the cold water, but also because if they ditch at sea, a helicopter will not stay float and would sink at a much faster rate than an airplane would. 

Low Oil Pressure Warning and Checklist Creates Confusion, Disagreement Among Cougar Helicopter Flight 91 Crew

Soon, Cougar 91 is at cruising altitude at 9,000 feet (or about 2700 meters) over the open North Atlantic Ocean. Everything was smooth flying, until twenty-eight minutes into the flight. This is when the flight crew receives a very serious warning in the cockpit: the orange caution message, “MGB OIL PRES” lights up, indicating there is low oil pressure in the main gear box. As we mentioned, the S92 has two rotors, one on top and one on the rear tail. The system of gears that control and spin the main rotor (on top of the helicopter) are known as the main gear box. For the main gear box to work properly, it relies on a constant flow of oil to keep all the gears lubricated and functioning effectively. Without oil, the rotor controls could fail, which would be a catastrophic situation. Especially since Cougar 91 is still thirty minutes flying time from land.

Immediately, First Officer Lanouette consults the checklist for this type of emergency while Captain Davis disengages the autopilot, takes control of the helicopter himself, and begins communicating with Gander air control center (or ACC). Captain Davis requests clearance to return immediately to shore, and because he has issued a Mayday call, Gander ACC also contacts search and rescue to be on standby should Cougar 91 need to ditch in the ocean. The flight crew also gets on the PA system and instructs all their passengers to ready their immersion suits should they need to ditch at sea. 

The request to return to shore was approved by Gander control, and Cougar 91 made its turn back toward St. John’s, which was still approximately 62 miles (or 100 kilometers) away. Captain Davis began a descent from 9,000 feet (2,743 meters) to just under 1,000 feet (or 304 m).

Finishing the emergency check list, First Officer Lanouette tells Captain Davis that they are in a LAND IMMEDIATELY condition. 

But Captain Davis says he is going to level off at 1,000 feet (305 meters), and then drop just below that altitude, to just 800 feet (244 meters). This was a strategy that would provide approximately 300 feet (or 91 meters) of terrain clearance over the highest point of land on the direct track from their present position. This strategy, of course, was built on the assumption that Cougar 91 could make it back to shore. 

Another communication that Captain Davis makes is to Cougar dispatch, where he tells the Chief Pilot about the unfolding – and tricky – situation onboard. You see, Captain Davis sees two conflicting pieces of data before him. While the main gear box low oil pressure caution message shows that their oil is below the minimum needed for safe flight operations, the temperature gage is still reading normal. Typically, when oil gets too low, the gears would grind together, creating friction and heat, which should raise the temperature inside the main gear box. It should not read “normal.” Because of this conflicting data, the crew wonders if a sensor problem is the true cause of the low oil pressure reading. The flight crew also considered this situation to be odd because they did not smell any unusual smells or feel any vibrations that one would expect to feel if the main gear box no longer had any oil pressure, and nothing was abnormal in the back of the helicopter.

Cougar 91 Loses All Oil, Plummets into the Ocean 

Suddenly, their fears are confirmed. Captain Davis is suddenly struggling with the controls as the helicopter begins to fall. He quickly relays to Cougar Dispatch that Cougar 91 will need to ditch in the sea – immediately. 

For any helicopter crew, ditching at sea must always be considered a life-and-death situation. At this moment, the conditions at sea were what anyone familiar with the area would expect – but these are not conditions safe for human survival. The winds were at 25 mph (or 40 kph), the waves were cresting as high as 8 feet (or 2.5 meters), and the water temperature was 0 °C (32 °F.). But now, the crew and passengers onboard Cougar 91 have no choice – this is their fate.

As the helicopter is falling back toward the ocean waves, Captain Davis has one goal: to set it down as gently and as level as possible. But, because they are experiencing a loss of lift and directional control, this is difficult to do. They are also higher in the air than a helicopter that is preparing to ditch normally would be. Meaning, as they prepare to ditch, the helicopter is coming down too hard and too fast. 

As the helicopter continued to fall, it pitches and rolls and yaws as the flight crew fights for control. Then, unthinkably, the helicopter begins to roll to the right, reaching a bank angle of 57°. Now just 90 feet (27 meters) above the waves, Flight 92’s rate of descent is 2,300 feet per minute (11.7 meters per second), and possibly much greater, and at an airspeed of 75 mph (or 122 kilometers per hour). At 9:56 AM, Cougar 91 hits the water, a force so great that the fuselage structure fails. The forward section, including the cockpit, is crushed and breaks off, as does the tail boom. The cabin section rolls over and the aircraft sinks immediately. But damage to the fuselage is not the worst part. Remember, 18 people are about to become trapped inside, many of whom just suffered severe stress fractures to their bodies. 

Cougar Helicopter Flight 91 Sole Survivor Recounts Daunting Escape and Rescue from Ocean

Inside the fuselage, water begins to pour in immediately. At the same time, if conscious, they would find themselves injured from the impact, taking in one final breath before their noses and mouths become submerged in shocking, ice-cold water. If that wasn’t enough, they must find the ability to unbuckle their seat belts in growing darkness, get their bearings, find a window or escape route, and then swim the dozens of feet to the surface of the ocean. 

We have one account that helps us understand what was happening onboard Cougar 91 as it sunk. This comes from passenger Robert Decker, who was a weather observer for one of the rigs, as told by him during an inquiry into the crash. These are his own words, which have been edited by me for conciseness. 

The full transcript is available in an article linked in show notes by The Globe and Mail. Here is Robert:

Shortly after the helicopter took off, I fell asleep. I slept on most of my rides out and back. When I woke up, I realized that we were lower than cruising or flying altitude. We were about 1,000 feet so I knew that we had descended.

Shortly after I was woken the helicopter pilot got on the PA and they asked for everyone to [do up] their survival suits. I've never had to [do up] the survival suit on a flight before, but I still wasn't concerned because everything seemed to be flying normally and everything sounded fine. 

So the pilots got back on the PA and they called "brace" three times, which is a normal command. I trained for that command, and it means that the helicopter is going to attempt to land. After the brace call, pretty shortly after that, the helicopter started making really weird motions. There was some deviation, the heading changed quickly from left to right. There was a high-pitched noise. The helicopter dropped and the high-pitched noise stopped and the helicopter kind of went up again. And that happened about twice.

That's when you realized something really serious was happening, and I think that's why I clung to the seat ahead of me. The helicopter lost control. It instantly had the bow, or the nose, head down and it was just heading straight for the ocean. Just before it crashed, the bow came up a little bit and it turned quickly to the starboard side. I was looking out my window for most of it, so I knew when we were going to hit the water.

The next thing I can remember was waking up in a submerged helicopter. The helicopter was sinking quickly, with its port side down. It was instantly filled with water. It was dark but you could see because everyone's survival suit has a light activated by the water. There was a lot of pressure in the helicopter because [of] the water. It was really hard to operate your arms, it was hard to have any motion at all.

The next thing I instantly did was reach for my seatbelt and undo my seatbelt and I pulled myself out through the [broken] window. The window would have been directly above me because it was sinking on its side.

Then it was a long, I guess, ascent to the surface. I didn't know how deep the helicopter was, at that time I didn't know what was happening. I kind of had my hands above my head and I could look up and I could see it was getting brighter and brighter. Eventually my arms broke the surface, and I could tell that I survived.

When Robert floats up more than 30 feet (or 9 m) to the surface of the ocean, he can see helicopter debris floating around him. Instinctively, he tries to swim back toward the direction of the shore, but he finds that he is badly injured – pains erupt in his chest and back, and he is only able to stay afloat. Overhead, Robert spots the rescue plane, and all he can do is feebly wave his arms. Eventually, the plane tips its wings, indicating that they had seen Robert. 

But he isn’t rescued immediately; in fact, one of the issues encountered during the rescue was that the immersion suits were not easily visible from helicopters, and rescuers had a hard time finding Robert. While he waits, he tries to steady his mind by talking to himself and by singing. Nearby, the lifeless body of another passenger floats in the water. In all, Roberts stays afloat in the freezing water with waves that threaten to overtake him for an hour and twenty minutes before being rescued. 

Robert Decker is the only survivor of the crash of Cougar 91. The remaining 17 people, including the 15 other passengers and the two pilots, have died. And their cause of death is heartbreaking – everyone onboard survived the actual impact only to drown in their seats. 

The flight crew suffered the worst injuries of everyone onboard, with both suffering head and chest injuries when their bodies made contact with the helicopter's instrument panel during impact. Neither pilot was wearing a helmet, nor were they required to by regulation. 

TSB is Joined by Sikorsky and FAA During Cougar Helicopter Flight 91 Investigation

Wreckage of Cougar 91 was recovered from the sea floor at a depth of approximately 550 feet (168 meters) and returned to a hangar at the airport in St. John’s for analysis by the Transportation Safety Board (or TSB) of Canada. Representatives from Sikorsky, the helicopter manufacturer, and the US’s Federal Aviation Administration (or FAA), join the TSB investigation. 

The investigation ultimately uncovers a host of problems with the S92 helicopter leading up to the crash and a chain of errors, misjudgments, and incorrect conclusions made during the flight. However, it is important to note that the TSB intentionally does not use the phrase “pilot error”. In their view, as the lead investigator for the Cougar 91 investigation, Mike Cunningham, pointed out, “the art and science of accident investigation had determined a long time ago that these complex occurrences often have a lot of underlying factors – in particular, organizational issues which are beyond the control of the flight crew.”

Investigators begin by understanding what led to the main gear box low oil pressure warning the flight crew received. Remember, the main gear box requires a constant supply of oil to keep the gears moving smoothly. Without oil, the helicopter would experience a loss of lift and challenges with directional control. Things that the Cougar 91 flight crew experienced. 

TSB Confirms Cougar Helicopter Flight 91 Oil Rapidly Drained Out when Damaged Studs Became Attached

The TSB discovers that the low oil pressure warning was accurate, and that the issues onboard were not simply from a malfunctioning sensor. And more surprisingly, they discover that oil literally poured out of Cougar 91, which caused a catastrophic loss of power. Investigators discover an issue with the oil filter bowl, which filters oil to the main gear box and is attached to the main gear box by three studs. The investigation revealed two studs from the oil bowl on Cougar 91 had fractured from over-stressed fatigue fractures and subsequently became detached from the gear box, which allowed the transmission oil to rapidly drain out. 

Sikorsky Safety Advisory Urged Operators to Replace Studs on all S92 Fleet

Not only was this finding shocking, but when TSB investigators speak with representatives from Sikorsky, they learn that the Cougar 91 incident is not the first time this happened. Another Sikorsky S92 made an emergency landing in Western Australia less than a year before in 2008 because of the same problems. And similarly, to Cougar 91, the studs on that oil filter bowl had failed, too. The studs on all S92s were made of titanium, which was chosen to withstand the significant loads imposed upon them as highly pressurized oil coursed through the filter bowl. However, when titanium rubs against steel, like on the bowl found on the S92, its surface binds to the steel and begins to strip away — a process referred to as galling. The studs suffered galling damage whenever maintenance workers removed them to replace the oil filters or change the oil, which happened 11 times on the Cougar 91. 

To prevent future incidents of the same nature, Sikorsky issued a safety advisory to all operators, including Cougar, to replace the original titanium studs with steel studs within one year or 1,250 flight hours. Cougar had begun to replace the studs on its fleet but had not made all the replacements; instead, they thought, based on the safety advisory from the manufacturer, that they could wait. And the reason Sikorsky, the manufacturer, told operators to make those changes within a year was because it had not yet received any reports of damaged studs from operators, suggesting that the problem was rare.

Sikorsky also felt it had taken the necessary precautions when it made changes to the Aircraft Maintenance Manual procedures that included an interim inspection procedure for the main gearbox filter bowl assembly. These procedures were aimed at discovering stud damage well before they needed replacing. In November 2008, less than six months before the Cougar 91 crash, these enhanced inspection procedures became mandatory industry-wide. During the investigation, it was determined that Cougar Helicopters had not followed these mandatory inspection procedures for its fleet.

But here is where the problem existed: this galling issue found on these two helicopters was not rare. Investigators found that galling on the titanium filter bowl studs was widespread throughout the entire S92 fleet. This sequence of events meant that Sikorsky had drafted its service bulletin based on inaccurate information about the scale and urgency of the problem. 

FAA Certification of S92 Main Gearbox Based on Wrong Assumptions

The next problem with the helicopter that investigators discovered was related to the S92’s original certification by the FAA. Usually, most helicopters are required to run for at least 30 minutes after a total loss of main gearbox. However, the FAA allowed for an exception to this requirement if the manufacturer could prove that the possibility of a total loss of lubrication was “extremely remote.” Sikorsky initially expected that the S92 would meet the 30-minute rule, but to their surprise, the main gearbox failed after just 11 minutes during a test in 2002. As a result, they decided to have the gearbox certified under the “extremely remote” provision instead. The FAA certified the S92 gearbox based off its analysis of these changes. 

But there in lies the problem with the certification. Sikorsky and the FAA did not consider how a failure of the studs attaching the oil filter bowl to the main gear box would raise the risk of a total loss of the main gearbox. What we now know, of course, is that the damage to the studs was a significant yet unknown factor that should have been considered during certification and that it was a problem that was prevalent on all S92s. This all means the likelihood of a total loss of the main gearbox was way more than “extremely remote”. 

While the investigation uncovered these problems concerning the S92 helicopter itself, they also determined that the decisions made and actions taken by the flight crew contributed to the fatal crash, some of which were not their faults and some which were.

Cougar Flight 91 TSB Investigation Reveals Misleading Checklist, Crew Resource Management Problems 

Investigators found that it took too long for the First Officer to locate the emergency checklist for the low oil pressure main gear box warning, and when he did finally locate it, the checklist did not list all the symptoms the flight crew saw on their panels. Specifically, during a failure of the main gear box due to low oil pressure, the checklist emphasized a rising oil temperature (which they did not have) and vibrations and smells, which they did not experience. Additionally, the pilots’ training reinforced the fact that these symptoms would be present during an oil pressure problem. 

One final issue that the TSB highlighted as a contributor to the crash was a disagreement between the flight crew members about returning to land or ditching immediately. While Captain Davis wanted to return to land, First Officer Lanouette felt that, based on his reading of the checklist, ditching was imminent. At numerous points, the first officer, who had less experience in this type of aircraft but greater overwater flying experience than the captain, can be heard on the cockpit voice recorder stating his concerns over their height, speed, and lack of preparedness for a ditching. Captain Davis, known to have the stronger personality, dismissed these concerns. This dynamic suggested a lack of appropriate crew resource management.  

Because Captain Davis thought they had a sensor problem and could make it back to land, he decided to level off at 800 feet instead at 100 feet, which is much safer distance from which to initiate a sea ditching. Had they been at 100 feet when the final drop oil poured out, they could have descended all the way to the water before the rotor failed and had a much safer ditching instead of an actual crash. This was the decision that ultimately made the crash of Cougar 91 so deadly. Because of the high rate of speed and hard impact with the water, the helicopter’s emergency floatation system was destroyed and unable to deploy. If it had, it could have bought everyone onboard precious time to escape. An easier landing may have also prevented so many fracture injuries.  

Cougar Helicopter Flight 91 Crash Leads to Tangible, Industry-Wide Changes

As a result of the accident, many changes came about.

• The FAA required S92 helicopter operators to immediately replace their titanium studs with steel versions. It also ordered Sikorsky to change the S92 flight manual to clearly indicate that the helicopter’s “run dry” time could be as little as 10 minutes or less; and mandated a design change to the filter bowl which would prevent it from coming apart due to a failed stud. 

• Cougar Helicopters introduced a new safety management system; mandated the use of helmets among its pilots; amended its low oil pressure warning checklist; and updated and delivered a new crew resource management program. 

• Sikorsky increased the number of oil filter bowl studs from three to six. 

• Helicopter passengers in the Canadian offshore oil fields were provided with underwater breathing apparatuses and helicopter ditching survival training was improved to mimic real sea conditions. And finally, S92 pilots are now taught that oil temperature readings may appear normal even if all the oil is gone.

• The TSB also issued several recommendations, including that the FAA require all helicopters to adhere to the 30-minute run dry rule.

Cougar Flight 91 Book Author Hopes to Honor the Crash Victims

Ten years after the tragedy, CBC reporter Rod Etheridge wrote a book called 18 Souls: The Loss and Legacy of Cougar Flight 491 about the Cougar 91 tragedy, with the goal of highlighting the victims. 

Of his time interviewing the victims’ families, Etheridge said, "Every single one of them wanted to tell their story, because they want people to know how hard it is — how hard it is to get that phone call, how hard it is to turn around to your six-year-old and say 'Dad's not coming home. And they want that to be part of the legacy, in the sense they want the public to know that the offshore life is not easy." 

Etheridge hopes the book honors the legacy of those who died. What stays with him the most is the fact that the passengers were all people who were just doing their best to raise a good family and have a good salary to do that with. Of their legacies he said, “No one wants to remember how they died. They want to remember how they lived."

And THAT is the sad story of the crash of Cougar Helicopter Flight 91.