The Silent Turn: The crash of Kenya Airways flight 507
On the 5th of May 2007, a Kenya Airways Boeing 737 ran into trouble moments after takeoff from Douala, Cameroon. As the plane climbed away through driving wind and rain, it banked into an ever steepening spiral, turning over into a high-speed dive as the bewildered pilots struggled to understand what was happening. In less than a minute, it was all over: the 737 plunged into a swamp outside the city, killing all 114 passengers and crew.
As a special commission of inquiry pieced together the causes of Cameroon’s worst ever air disaster, it became clear that the pilots were dangerously under-equipped to handle their airplane, leading to panic when it left the normal flight envelope. It was also not the first time this had happened: seven years earlier, a Kenya Airways Airbus A310 crashed into the sea after takeoff from Abidjan, killing 169, after a false stall warning disoriented the pilots. Was there something wrong with the way pilots were trained at Kenya Airways? The investigation would only touch the surface of the problem, but the crash nevertheless held lessons about the importance of seemingly small cultural changes in steeling pilots against a threat that has been claiming lives since the dawn of powered flight: the silent, deadly one-G turn.
Kenya Airways has long been one of the most respected airlines in Africa. Having weathered the 20th century without a fatal accident, the airline was partially privatized in 1996, the first flag carrier on the continent to do so, and in 2010 it became the first and to date only African airline to join the SkyTeam alliance. It operates a modern fleet of Boeing and Airbus aircraft on routes across Africa, providing crucial services to and between poorer countries whose own airlines struggle to meet the demand. But as Kenya Airways expanded rapidly through the 2000s, it found itself caught on a safety learning curve which proved to be tragically steep.
The first fatal accident in the history of Kenya Airways occurred on a dark night in January 2000, off the coast of Côte d’Ivoire. As Kenya Airways flight 431, a wide body Airbus A310, climbed away from the city of Abidjan, a stall warning suddenly began to blare in the cockpit. A cross-check of the airplane’s speed, altitude, and pitch would have shown that it could not possibly be in a stall. But just seconds after takeoff, with the plane barely a few hundred feet above the ground, the First Officer felt he had no time to check. He pitched the nose down, applying the stall recovery procedure in an attempt to regain airspeed that they had not in fact lost. The overspeed warning started to sound, mingling with the stall warning — the plane was telling them they were simultaneously flying too fast and too slow. The radio altimeter called out fifty, forty, thirty, twenty, ten. “Go up!” the captain shouted, but it was too late. Flight 431 slammed into the Atlantic Ocean and broke apart, killing 169 passengers and crew. Only ten survivors would be pulled from the blackened sea.
The crash of flight 431 highlighted an important aspect of quality airmanship: the ability to understand intuitively what an airplane is doing. Only a clear mind and sharp sense of logic, cultivated through rigorous training, could have prompted the crew to question the false warning and continue the climb. This kind of airmanship would have saved many crews who lost control of perfectly controllable airplanes — including another Kenya Airways crew seven years later, whose actions would raise even more troubling questions.
On the evening of the 4th of May 2007, another Kenya Airways flight departed Abidjan, bound for a scheduled stopover in Douala, Cameroon before continuing on to Nairobi. The plane flying the Abidjan-Nairobi route was no longer an Airbus A310, but a Boeing 737–800, the latest version of the world’s most popular passenger jet. In command were two Kenyan pilots: 52-year-old Captain Francis Wamwea, a former Kenya Airways flight attendant who had since racked up over 8,600 flight hours, and 23-year-old First Officer Andrew Kiuru, a new hire who had accumulated only 800 hours since he started flying the previous year.
After flying without incident from Abidjan to Douala, the largest city of Cameroon, flight 507 taxied to the parking area, and the passengers disembarked. Nearby, thunderstorms rolled over the airport, a common occurrence at night in Central Africa.
At Douala, 108 passengers boarded for the flight to Nairobi, which along with the six crewmembers brought the number of people on board to 114. But by the scheduled departure time of 23:00, the plane was not ready, and the delays would only continue to mount. At 23:37, already well behind schedule, Captain Wamwea cancelled his clearance to start the engines because the weather conditions were unsuitable for takeoff. The passengers and crew would spend another twenty minutes sitting on the apron at Douala International Airport waiting for the wind to die and the visibility to improve.
At 23:54, the crew again requested clearance to start, and shortly thereafter flight 507 finally taxied to the runway. Rain was falling over the airport. “Put on your wipers,” Captain Wamwea suggested to First Officer Kiuru.
Kiuru flipped the switch, and the wipers swished to life.
“You’re struggling to look? And you got wipers,” Wamwea said, admonishing his young First Officer.
“Kenya 507, after takeoff runway 12 EDEBA 1E departure, you are cleared level three seven zero to Jomo Kenyatta,” the controller said, issuing a route clearance.
First Officer Kiuru read back the clearance, then said, “Call you ready next, 507.”
“Wait first,” said Captain Wamwea. Kiuru made some kind of gesture. “No, I mean wait till we line up.”
“Okay, things usually happen in a hurry, that’s why,” said Kiuru.
Wamwea chuckled. “Okay, you’re keeping up with it, eh?”
“Yes, I’m trying to keep up,” said Kiuru.
Two minutes later, having completed routine checks and secured the cabin, the crew lined up with the runway for takeoff. Although it was First Officer Kiuru’s job as the monitoring pilot to work the radios, Captain Wamwea took it upon himself to request a weather diversion from air traffic control. “Ah, tower from Kenya five zero seven, after departure we would like to maintain ah… slightly left of runway heading due to weather ahead.”
“Right,” Kiuru corrected him. Their weather radar clearly showed that they would encounter less intense storms if they turned to the right.
“Ah, sorry, slightly right,” Wamwea said to the tower.
“Approved,” the controller replied.
“Okay, all done,” said Wamwea.
Once Kiuru had made his standard departure announcement over the public address system, the pilots pushed the thrust levers forward to takeoff power, and flight 507 began to accelerate down the runway. Thirty seconds later it was in the air, climbing out over the mangrove swamps southeast of the city. Neither pilot noticed that they had just taken off without clearance from air traffic control. It was a bizarre mistake that would turn out to have nothing to do with the catastrophe which followed.
As soon as flight 507 lifted off the runway, it began to turn slowly to the right without any input from the pilots. Like cars, airplanes often have a natural tendency to pull to one side, and this one was no exception. The cause of the right roll would later be put down to inherent asymmetry in the construction of the wings, along with a very slight right rudder trim setting left over due to play in the rudder trim system. But in any case, the roll was so sedate that it presented the pilots with no great difficulty — Captain Wamwea simply turned the plane a little bit to the left whenever he noticed it slipping to the right.
Meanwhile, the crew focused on their plan to divert around the thunderstorms near the airport. “Heading select,” Wamwea announced, selecting a target heading of 132 degrees. Seconds later he changed it to 139 degrees. His flight director, an overlay on his attitude indicator, instructed him to fly right to assume the new heading.
“Selected, check,” said Kiuru, confirming the selection.
“I will keep somewhere around here,” Wamwea said.
“Alright.”
Thirteen seconds later, Captain Wamwea announced, “Okay, command.” This was an order to engage the autopilot in command mode, the primary mode in which the autopilot has full authority to control the airplane. Pressing the CMD button on the autopilot panel would engage command mode and cause the autopilot to fly the plane on the already selected heading.
But First Officer Kiuru never replied, nor did he ever press the CMD button. The autopilot remained off, and the plane kept turning by itself, rolling slowly to the right as it had been ever since it took off. And yet nobody said a word.
Even though no one was flying the plane, the pilots continued as normal.
“Standard?”
“Check.”
“Two four, climbing.”
“Checks.”
Rain drummed against the windscreen. “Now we are getting into it,” said Captain Wamwea.
The plane rolled through 139 degrees and kept right on going. The pilots’ flight directors instructed them to fly left to return to the target heading. First Officer Kiuru, who was monitoring the instruments, thought Wamwea had made this sharper turn on purpose. “I continue with the heading,” he announced, changing the target heading to 165 degrees in accordance with what he assumed were Wamwea’s intentions.
“Through here is okay isn’t it?” Wamwea asked.
“Okay,” Kiuru replied.
Suddenly, Wamwea noticed that they were banking steeply to the right, causing him to make an exclamation of surprise. Less than one second later, the plane rolled through 35 degrees of bank, triggering a loud alarm. “BANK ANGLE,” the warning blared. “BANK ANGLE!”
The steepening bank and the warning caught Wamwea completely by surprise. He immediately grabbed his control column and instinctively wrenched it to the right, then back to the left, then hard to the right again. The plane rapidly rolled to the right, approaching fifty degrees of bank, way beyond the normal flight envelope.
Only now did Wamwea notice that the autopilot was not engaged. He reached up and pressed the CMD button, hoping to engage it in command mode, but due to the pressure on the captain’s control column, it engaged in “control wheel steering” (CWS) mode instead. In this mode, the autopilot simply holds whatever roll and pitch attitude the pilot applies using the control column. When engaged at bank angles beyond the standard limit, the autopilot in CWS mode will slowly roll the plane back to a safe 30 degrees of bank, but no farther.
If Captain Wamwea had let go of the controls and let the autopilot fly the plane, even in CWS mode, it would have recovered. But when the autopilot did not immediately level the wings, he became frustrated and grabbed the control column again, overpowering the autopilot. Swinging the control column back and forth while mashing the rudder, he sent the plane rolling to the right again, reaching 90 degrees within seconds. As the plane rolled inverted, he shouted, “We are crashing!”
“Right, yes, we are crashing, right!” Kiuru said. Looking at his attitude indicator, he could see they were in a right roll. “Right, captain… left, left, left! Correction, left!”
Kiuru grabbed his controls and tried to roll back to the left, but Wamwea was still turning to the right. The plane quickly turned over into a spiral dive, corkscrewing down from 2,000 feet at a high rate of speed, completely out of control. The cockpit voice recording captured First Officer Kiuru shouting an expletive, the brief sound of an alarm, and then silence.
Kenya Airways flight 507, pitched steeply downward and banked 60 degrees to the right, slammed into a mangrove swamp deep in the estuary of the Wouri River. Traveling at 530 kilometers per hour, the 737 gouged a massive crater in the swamp, sending mangled debris, chunks of mud, and pieces of trees billowing out over a vast area. Much of the wreckage penetrated up to five meters into the waterlogged ground, while the rest rained down over an area 2,000 meters square, coating the trees with a toxic sludge of mud and jet fuel. For the 114 passengers and crew, there was no hope: all died instantly on impact.
Even though the plane had crashed just a few kilometers outside Douala, a city of two million people, the crash in a dense swamp shortly after midnight passed largely unnoticed. No alarm was raised until the plane failed to arrive in Nairobi five hours later, and even then no one was sure where to look for it. Authorities seized on reports of a flash in the sky and a loud noise near the village of Lolodorf 160 kilometers southeast of Douala, and a major air and ground search was launched in the region, but nothing was found. It took the better part of two days before authorities discovered that the plane had barely even made it out of the city. The wreckage was found on the 6th of May, shattered into thousands of pieces inside a muddy crater in the swamp about five kilometers southeast of the airport. Nearby villagers had apparently known about the crash for some time, but due to a lack of communication, this information didn’t come out until the search was already well underway.
When reports came in that the plane had been found, relatives initially prayed for survivors, but those hopes were quickly dashed when the first aerial images revealed the desolate crash site. It was clear that no one could possibly have survived. 114 people, hailing from 26 different countries, were dead — the worst air disaster in the history of Cameroon.
Cameroon, being a very poor country lacking in robust institutions, did not have an agency which was responsible for investigating aircraft accidents. Facing a disaster of unprecedented scale, the government acted quickly to form a special commission of inquiry comprised of Cameroonian and foreign experts, who would be charged with a singular goal: to explain the crash of Kenya Airways flight 507.
The first task facing investigators was the recovery of the black boxes from the riven swamp. The flight data recorder was located quickly, but finding the cockpit voice recorder proved much more complicated. A special scanning device had to be flown in to penetrate the swamp water, and even after detecting the box’s locator beacon, their job wasn’t done. The CVR had split into four pieces, and the pinger was no longer attached to the section containing the memory module, forcing investigators to dig by hand through the mud in search of the chip. The memory module was finally recovered on the 15th of June, more than a month after the crash. Only then could the commission of inquiry begin to explain what happened to the ill-fated flight.
The data from the black boxes revealed a scenario which was, at its core, not so different from a large number of previous accidents. In fact, everything about the brief flight strongly indicated that this was a case of spatial disorientation in roll, a problem which has been plaguing aviators ever since the airplane was first invented.
Because it is impossible to distinguish acceleration from gravity without a visual frame of reference, pilots flying at night and in clouds must keep a close eye on their artificial horizon, or attitude indicator, in order to maintain a proper mental picture of their position in space. Pilots are trained to rely on the artificial horizon at the expense of the body’s internal balance system, which will often lie to the brain when the real horizon cannot be discerned.
A constant roll in one direction is particularly insidious because of a fundamental principle of aerodynamics known as the one-G turn. In the absence of any inputs, an airplane rolling to one side will naturally begin to turn in that direction as well. Due to conservation of angular momentum, objects inside the plane will resist the turn, causing them to be pulled in the opposite direction with equal force. Mathematically, this means that the force being exerted on the occupants in a normal banked turn will always remain equal to the force of gravity and will always continue to pull straight down through the floor. This fact can be demonstrated easily next time you’re on an airplane: when the plane enters a turn, drop an object onto your lap, and you will see that it always falls straight down relative to the floor, not relative to the ground. Perhaps most famously, various aviators have used this principle to pour coffee during a barrel roll without spilling a drop, as demonstrated above (with iced tea).
For a pilot, this means that a steady roll in one direction, without reference to a horizon, is completely undetectable using normal human senses. A pilot can however notice a sudden change in the rate of roll, known scientifically as “jerk.” This fact would play a key role in the fate of flight 507.
As the 737 climbed away from the runway in Douala, the pilots would have stared into a black hole: the bad weather and uninhabited swamps provided no visual horizon. Simultaneously, the plane naturally rolled to the right at a slow, steady rate, detectable only using their attitude indicators. Captain Wamwea corrected this roll at first, but he would not have been able to feel it. Instead, he would have felt the change in acceleration as the plane went from rolling right to rolling left every time he made a correction. The vestibular system in his inner ear, which regulates one’s sense of balance, would have interpreted this as the plane turning left from a horizontal position. Although his artificial horizon would have showed the wings level, his brain would not have agreed. Initially he was able to overcome this disorientation, as all pilots do, by flying the plane by his instruments.
The problem came when Captain Wamwea asked First Officer Kiuru to engage the autopilot. The investigators could not say for sure why the autopilot was not engaged at this point, but the most likely explanation was that Kiuru, busy interpreting the weather radar to find the best course, simply never heard him. However, the technical log had recorded a fault with the autopilot back in February, so it could not be ruled out that Kiuru pressed the button, only for the autopilot to remain off.
Either way, it was a lack of communication which turned this into a serious problem. If he was aware of his captain’s order, First Officer Kiuru should have checked the autopilot annunciator panel and announced whether or not the autopilot had engaged, and if he was not, Captain Wamwea should have inquired as to the status of the autopilot when Kiuru didn’t respond. In the event, neither of these callouts was made. Instead, a misunderstanding developed, as Wamwea assumed the autopilot was now in control, while Kiuru thought Captain Wamwea was still flying the plane. The result was that nobody touched the controls for 55 seconds, allowing the smooth, steady one-G turn to continue until the bank angle reached 35 degrees.
At this point, approximately coincident with the activation of the bank angle warning, Captain Wamwea suddenly realized that the plane was in a turn. But his physiological instinct would have told him that the plane was banking left, because he had felt the leftward corrections during the climb but not the right roll that prompted them. Faced with conflicting cues about which way the plane was turning, along with sudden confusion about the status of the autopilot and a loud alarm, Wamwea simply panicked and turned the wrong way. His artificial horizon was right there in front of him, indicating a steepening right bank. He had a first officer whose job was to call out unexpected indications. And yet neither of these safeguards prevented him from rolling right until the plane turned over and entered in irrecoverable dive toward the ground. First Officer Kiuru did eventually intervene, but by then it was too late.
Based on his statements captured by the CVR, First Officer Kiuru appeared to be aware of the plane’s attitude throughout the flight and was not suffering from spatial disorientation. Only Wamwea, it seemed, was caught off guard by the subtle one-G turn. So why did a supposedly experienced captain succumb to an illusion that had been known since the 1910s? And why didn’t Kiuru take corrective action sooner? These questions would open an entirely new avenue of inquiry.
Looking into the pilots’ records, a number of red flags appeared in Captain Wamwea’s training history. His skills were assessed as below average but acceptable, allowing him to pass his examinations, although not without difficulty. Instructors had written that he struggled with crew resource management, knowledge of systems, respect for standard procedures, instrument scans, situational awareness, and planning and decision-making. In a 2004 training flight, he was cited for failing to properly discuss a failure with the first officer, and on another occasion he was reprimanded and sent to retraining after diverting a flight due to a failure of the standby attitude indicator, a backup instrument not normally used in day-to-day operations. Furthermore, after Wamwea performed poorly during a routine line check in 2006, the Kenya Airways Manager of Product Training wrote, “A review of the entire training program will be carried out to see if complacency or incompetence is the issue.” But after Wamwea passed a remedial check three months later, no further action was taken.
Most worryingly, however, Wamwea displayed several personality traits which might have made him difficult to work with. Despite the fact that his abilities were not especially stellar, instructors and colleagues described him as overbearing, verging on arrogant, with a tendency to belittle first officers for their mistakes. In fact, the cockpit voice recording revealed that on the flight into Douala from Abidjan, Wamwea had called Kiuru “stupid” and told him to “shut up” — shocking words for a supposedly professional airline pilot. The effect of this behavior on the relationship between the two pilots was undoubtedly disastrous. Cowed by the insults to his intelligence, Kiuru would have been hesitant to correct the captain, who was more than twice his age and had ten times as much experience. When such an authority gradient already exists, belittling language can make it all but impossible for the junior crewmember to overcome the difference in seniority, even in an emergency situation. Considering this background, it was unfortunately not surprising that Kiuru failed to intervene to correct the steep bank until the plane had already rolled past the point of recovery.
With all these factors in mind, a picture begins to emerge of a flight which was in danger from the moment it took off. At night in bad weather, with an overbearing but below average captain and a young, unsure first officer, the situation was ripe for confusion. The problems had already begun on the ground, when the flight took off without clearance. After that, all they needed was one moment of miscommunication, a little bit of bad luck, and disaster became inevitable.
Nevertheless, it was not possible to blame the accident wholly on the crew — the airline had to take its share of responsibility. Kenya Airways had all the information it needed to determine that Captain Wamwea was especially at risk of disorientation due to his history of poor communication and situational awareness, but nobody ever looked at his entire training history in a holistic manner until after the accident. Instead, each training flight was reviewed individually, preventing the pattern from being discerned. Investigators felt that Kenya Airways should have been more aware of Wamwea’s shortcomings, and should have avoided pairing him with a new first officer whose own training record was decidedly less than perfect.
Furthermore, Kenya Airways operating procedures contained ambiguities which contributed to the poor communication on flight 507. The procedures did not say who was responsible for engaging the autopilot, or at what altitude, and they did not require anyone to call out whether the engagement was successful, even though this was recommended by Boeing. Had Captain Wamwea been trained to expect such a call, the crash might have been prevented.
Since the crash of flight 507, Kenya Airways hasn’t had another fatal accident, but the two that it did suffer are linked in several key ways. Both involved pilots who lacked awareness of the positions of their airplanes in space, a key skill which can only be cultivated through training and experience. The fact that Kenya Airways had two spatial disorientation accidents in a seven year period suggests that the airline was not instilling in its pilots the innate qualities of airmanship, those intangible skills which separate good aviators from the merely passable. At an airline with an effective training system, Captain Wamwea would either have been forged into a better pilot, or forced to find another career. Instead, he did neither, and 114 people lost their lives. As for what caused this cultural problem at Kenya Airways, and what was done to resolve it — that story is yet to be told.
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