Behind the Curve: The crash of West Caribbean Airways flight 708
On the 16th of August 2005, a charter flight carrying vacationers home to Martinique after a trip to Panama suddenly plunged out of the sky half way through the flight. After falling 33,000 feet in less than three minutes, the fully loaded MD-82 slammed into the Venezuelan countryside, killing all 160 people on board. As investigators from Venezuela and the United States worked together to uncover the cause, they revealed a harrowing story: battling thunderstorms in the middle of the night, the pilots appeared to lose control of the plane, wallowing in confusion as it fell from the sky. The captain issued a cryptic mayday call, claiming that their engines had failed and the plane was uncontrollable. But there was in fact nothing wrong with the aircraft. Instead, investigators found that the pilots had attempted to fly at a speed and altitude beyond the plane’s performance limits, leading to a high-altitude stall from which they failed to recover. The problems didn’t end there, however: in fact, the entire airline was on its last legs even before the crash. More than anything else, it was the operator’s shocking disregard for safety and for the welfare of its pilots that led to the devastating crash of West Caribbean Airways flight 708.
West Caribbean Airways was a regional airline serving various destinations in Colombia, Central America, and the Caribbean. Founded in 1998, the airline initially operated small twin turboprop Let L-410s, but soon upgraded to jet operations with the introduction of several McDonnell Douglas MD-82s, which it used both for scheduled services and charter flights. By 2005, the airline had already developed a troubled history. In March of that year, a West Caribbean Let L-410 crashed shortly after takeoff from the island of Providencia, killing 9 of the 14 people on board. Investigators found that an engine failure had occurred on takeoff, and the pilots failed to follow established engine out procedures, resulting in a loss of control. Shortly after this accident, Colombian authorities fined the airline twice for safety violations. The first time, they were caught overloading a plane. Then the second fine came after authorities discovered that the airline had been violating crew rest minimums, failing to provide required training, and keeping inconsistent records. All these difficulties caused the airline to fall into serious financial trouble. By August 2005, only one of West Caribbean’s three MD-82s was airworthy, as the other two were grounded pending maintenance for which the airline was unable to pay.
It was against this background that West Caribbean Airways prepared to use its one operational McDonnell Douglas MD-82 to transport a group of tourists from the French Caribbean island of Martinique back home after a trip to Panama. The charter flight from Tocumen International Airport in Panama City to Fort de France Le Lamentin International Airport on Martinique had been booked by a Martinique-based travel agency, and almost all of the 152 passengers consisted of the tourists and their guides. Eight crewmembers also boarded the plane, including 40-year-old Captain Omar Ospina and 21-year-old First Officer David Muñoz, as well as four flight attendants, a maintenance technician, and an airline dispatcher. By the time the plane arrived in Panama City, it was already running late — the preceding flight from Colombia was delayed because West Caribbean Airways had not paid for the fuel.
Before takeoff, the crew filed a flight plan with Panamanian authorities. The plan made no mention of weather conditions, despite a line of storms stretching across Panama’s east coast and down into Colombia and Venezuela. They also specified a cruising altitude of 35,000 feet, which was higher than the MD-82 could safely fly under its current weight and configuration. Nevertheless, West Caribbean Airways flight 708 was cleared to fly, and the plane took off from Panama City at 1:00 a.m. local time.
As flight 708 climbed toward its initial cruising altitude of 31,000 feet, the pilots noted the weather conditions ahead and turned on the engine anti-ice systems. Engine anti-ice diverts hot bleed air from the engines’ compression chambers and cycles it through a system of tubes, heating the outside of the engine to prevent the buildup of ice. However, because the system siphons off some of the airflow though the engine, it causes a reduction in power output while it’s active.
At 1:39 a.m., the pilots received clearance to climb from 31,000 to 33,000 feet. However, at their current weight with engine anti-ice on, it would not be possible for the engines to generate enough power to remain at 33,000 feet. The pilots could have confirmed this using the aircraft performance tables in the flight manual, but they appeared not to have done so.
As flight 708 slowly climbed toward 33,000 feet, Captain Ospina ordered First Officer Muñoz to turn the engine anti-ice off in order to improve climb performance. This proved sufficient to get the plane to 33,000 feet. After leveling off, the pilots changed the autothrottle mode from “climb” to “cruise.” The autothrottle, the system which automatically adjusts engine power over the course of the flight, has variable settings that allow the pilots to set how much power it is allowed to generate. The maximum engine power that the autothrottle can command in cruise mode is less than it can command in climb mode. The pilots also commanded the autothrottle to maintain a speed of 268 knots (496km/h), which it was just barely able to do in cruise mode with engine anti-ice off.
As flight 708 tracked to the south, trying to find a path through the storms, the pilots again became concerned about ice. At 1:48, they turned the engine anti-ice systems back on. In this configuration, the autothrottle could not command enough power in cruise mode to maintain the selected airspeed of 268 knots. Their speed slowly began to decrease, and the autothrottle mode indication changed to “Mach ATL” to alert the pilots to the fact that the autothrottle was unable to reach the desired airspeed. However, neither of them noticed, perhaps because a flight attendant had just brought them dessert.
The plane was now in a dangerously unstable position due to a fundamental principle of fluid dynamics. In basic terms, lift is a function of airspeed (the velocity of the aircraft relative to the surrounding air mass), air density, wing area, and angle of attack (the pitch angle of the plane relative to the direction of airflow). When flying straight and level, air density and wing area are roughly constant, while airspeed and angle of attack can change. To maintain a constant amount of lift (and therefore level flight), any decrease in airspeed must be countered by a corresponding increase in angle of attack. Otherwise, lift will decrease and the plane will descend. On West Caribbean Airways flight 708, the autothrottle was unable to apply enough engine power to maintain the required airspeed. However, the pilots had set the autopilot to “altitude hold” mode, commanding it to maintain an altitude of 33,000 feet. To hold the plane this level, the autopilot had to preserve the amount of lift acting on the aircraft despite the loss in speed. Therefore, it increased the angle of attack to keep the equation balanced.
Over the next several minutes, the plane’s airspeed continued to drop, and the autopilot continued to increase the angle of attack to compensate. At 1:52, the pilots turned the engine anti-ice off. However, within the minute, Captain Ospina turned it back on, and also switched the autothrottle from cruise to climb. But while max climb power would have been sufficient to maintain 33,000 feet earlier in the flight, this was no longer the case.
Perhaps counterintuitively, the amount of engine power needed to maintain a particular speed at a particular altitude follows a parabolic trajectory, which in the case of flight 708 was centered on a speed of 256 knots. Both above and below this critical speed, the amount of engine thrust needed to maintain a constant velocity increases. Therefore, as flight 708 decelerated past 256 knots, the amount of additional thrust needed to prevent the continued loss of speed progressively increased, until the power required was greater than the power available in any configuration. In such a situation, an aircraft is said to be “behind the power curve,” and the only way stabilize the flight is by pitching down to descend. As a result, the pilots’ decision to switch the autothrottle to climb mode came too late, because they had already decelerated too much for the extra power available in this mode to get the plane back ahead of the power curve.
By 1:57, the autopilot had increased the plane’s angle of attack to more than 7.5 degrees, far beyond a normal value for cruise. At this point, First Officer Muñoz suggested that they to descend back to 31,000 feet, although he didn’t voice his reasons for doing so. Captain Ospina agreed, and they received permission from air traffic control to begin the descent. But until they descended far enough to get back ahead of the power curve, their speed continued to decay and the angle of attack continued to increase. 35 seconds into the descent, at an altitude of approximately 31,700 feet, the plane entered a pocket of turbulence. A significant updraft struck the plane from below, causing a further spike in its angle of attack. At the same time, the high angle of attack caused an area of turbulent air to form behind the wings, interrupting airflow into the tail-mounted engines and causing a drop in power output. This put the plane dangerously close to a stall, in which the angle of attack becomes so great that air stops flowing smoothly over the top of the wings and lift begins to decrease. To warn the pilots of the impending stall, an audible “STALL!” warning began to blare, accompanied by the stick shaker, which physically shakes the pilots’ control columns. This was a sign that they needed to immediately pitch down and increase power to gain speed and reduce their angle of attack.
First Officer Muñoz immediately recognized the problem. “It’s a stall, Capi!” he exclaimed. “It’s a stall!”
But Captain Ospina didn’t react to his first officer’s comments. Instead, he seemed to be focused on the engine gauges, which showed a loss of thrust in both engines. The reduction in thrust was in fact a symptom of a stall, but Ospina seemed to believe that the engines were the source of the problem. Instead of taking any action, he ordered his first officer to request a lower altitude from air traffic control, and Muñoz dutifully obeyed!
The plane then stalled and began to fall from the sky, descending at a rate of 5,000 feet per minute, accelerating downward ever faster with each passing moment. Neither pilot took any action to recover from the stall, and in fact Captain Ospina made it worse by adding nose up stabilizer trim. No one started or even mentioned any emergency checklist.
At 1:58, the air traffic controller, perplexed by the crew’s request for a rapid descent, called and asked, “Do you have any problem on board?”
To Muñoz, Ospina shouted, “Affirmative, tell him we have flame out on both engines!” Once again, Muñoz passed this on to ATC.
“Roger, continue descent at pilot’s discretion,” the controller replied.
By now they were plunging downward at an astonishing rate of 12,000 feet per minute. At 1:59, Muñoz reported to ATC, “We are at 14,000 feet!”
“And going down!” said Ospina. “The airplane is uncontrollable!”
“The airplane is uncontrollable!” Muñoz repeated to ATC.
“Roger, confirm people on board, intention, and distance from any nav aid if possible,” said the controller.
“One hundred and fifty two!” Muñoz gasped. “The airplane is uncontrollable!”
The plane had now entered what is known as a deep stall. On T-tail aircraft like the MD-82, it is possible to enter a stall attitude in which the wings completely block the flow of air over the elevators, preventing the pilots from controlling the plane’s pitch. Once a plane has entered such a condition, recovery is impossible.
“I understand, 152 people on board,” the controller replied.
“Affirmative!” said Muñoz.
“Confirm what level are you crossing at this time, Whiskey Charlie Whiskey 708?” asked the controller. But there was no reply.
Inside the cockpit, the pilots said nothing, sitting like deer in the headlights as the plane plunged toward the ground. The ground proximity warning blared, “WHOOP WHOOP PULL UP, SINK RATE, WHOOP WHOOP PULL UP!” But there was nothing they could do. At 2:00 a.m. and 31 seconds, West Caribbean Airways flight 708 slammed belly-first into a marshy field west of Lake Maracaibo, triggering a massive explosion that sent debris flying high into the air. The impact obliterated the aircraft and instantly killed all 160 people on board. In a rural area in the dead of night, there were no witnesses to attest to their final moments.
Upon hearing the crash, local residents rushed to help, but they were confronted with a grisly scene: little was left of the airplane, besides the tail; much of the wreckage was burning and bodies were scattered everywhere. By the time emergency services arrived, it was clear that no one had survived. That made West Caribbean Airways flight 708 the deadliest plane crash in the history of Venezuela. The French overseas department of Martinique was also left reeling — almost all the passengers hailed from there, and few people on the island were more than a degree or two of separation from one of the victims. Under pressure to uncover the cause quickly, Venezuela’s Aircraft Accidents Investigation Committee (CIAA) invited its French, American, and Colombian counterparts to take part in a massive international inquiry.
Early media reports focused on the pilots’ frantic distress call, in which they claimed that both of their engines had failed. But an examination of the ruined engines suggested that they were generating power at impact, and the readout from the flight data recorder confirmed this. The real sequence of events appeared to be much more subtle. On the most basic level, the pilots tried to fly at an altitude that exceeded the aircraft’s performance limits. With the autothrottle unable to maintain the selected airspeed, the autopilot kept increasing the angle of attack to compensate, until the AOA exceeded the critical point and the aircraft stalled.
However, this was not the first time this had happened. In 2002, a Spirit Airlines MD-82 encountered much the same set of circumstances, only in that case, the pilots reacted correctly to the stall warnings and regained control of the airplane. The flight diverted to Wichita, Kansas and no one was hurt. In the wake of the incident, Boeing issued a bulletin to all MD-80 series operators informing them that when flying at an altitude above the aircraft’s performance limit, the autopilot could keep increasing the AOA until it stalled the airplane. However, there was no evidence that West Caribbean Airways had ever passed this bulletin on to its pilots. (Note that Boeing took over production of former McDonnell Douglas aircraft types after the two companies’ merger in 1997.)
Normally, the autopilot on the MD-82 will disconnect before reaching a stall. This situation proved to be an exception to that rule. But that hardly absolved the pilots, who barely did anything to fly the airplane. Upon hearing the stall warning, they should have instinctively pitched the nose down and increased power without even having to think about it. Instead, Captain Ospina became fixated to the point of delusion on a perceived loss of engine power. It seemed that he completely tuned out not just the obvious stall warnings, but also his copilot’s exhortation that “It’s a stall, Capi!”
But if First Officer Muñoz knew they were stalling, why didn’t he take control? Interviews with people who knew the pilots revealed that Muñoz had a very submissive personality, while Ospina was very much a dominant figure in the cockpit. Compounding this dynamic was the fact that Muñoz was only 21 years old, barely half the age of his captain. Not only would he have been hesitant to defy Ospina, he could have convinced himself that he was the one reacting incorrectly after Ospina ignored the stall warnings. Furthermore, the pilots’ statements and actions (or lack thereof) were suggestive of a dissociation from reality. In the middle of the night, confused by what their plane was telling them, they might have lost the ability to think rationally and determine whether they situation they were in was real. As they plummeted downward from 31,000 feet, they might have been asking themselves: is this reality, or just a bad dream?
Investigators also had to ask why the pilots attempted to fly at 33,000 feet in the first place, and why they didn’t notice that they were losing speed. During the critical 10-minute period where their airspeed was decaying, they appeared to be distracted by the ongoing meal service, as well as several communications with air traffic control as they were handed off from the Colombian sector to the Venezuelan sector. They also might have simply placed too much trust in the autothrottle’s ability to maintain whatever speed they asked of it.
Another red flag was that their filed flight plan called for a cruising altitude of 35,000 feet, which showed that they were unfamiliar with the capabilities of their aircraft. Many of their actions over the course of the flight suggested that they also had a poor understanding of how the plane would react to their inputs. This called into question the quality of the training at West Caribbean Airways, which had already been cited for major training violations earlier that same year. It was clear from looking at the pilots’ records that little had changed as a result of the citation. Neither pilot had been trained to anticipate or recover from a high altitude stall. Their knowledge of aircraft systems was rudimentary at best. And they had not received comprehensive Crew Resource Management (CRM) training. But that was not the only disadvantage that the pilots had going into this flight.
As investigators looked into the pilots’ daily lives, they discovered that flying was probably not the only thing on their minds. West Caribbean’s dire financial situation had left it unable to pay pilots on time, and Captain Ospina had not received a paycheck in six months. He had recently started a restaurant as a second source of income, without which he would have been unable to feed his family. Running this business consumed much of the time that he was supposed to spend resting. Both also faced looming uncertainty about the long-term prospects of their careers. With West Caribbean Airways teetering on the brink of insolvency, they feared waking up one morning to discover that their employer no longer existed. The level of stress brought on by these factors was probably high, but Captain Ospina’s latest recertification included no check of his psychoemotional state, so the precise manifestation of this stress couldn’t be determined.
Within a day of the accident, Colombian authorities indefinitely suspended West Caribbean Airways’ operating certificate. For such a small airline to have two deadly crashes in a single year proved beyond all doubt that it should not be flying. In October 2005, West Caribbean went bankrupt and sold off its four remaining airplanes.
The case of West Caribbean Airways flight 708 illustrates the importance of close monitoring, or even preemptive grounding, of small airlines that are struggling financially. This was neither the first nor the last case of an airline on the edge of bankruptcy cutting corners at the cost of lives. For example, in December 2005, Chalk’s Ocean Airways flight 101 crashed after takeoff from Miami after a wing fell off in flight, killing all 20 people on board. The company’s finances were deep in the red, its owners had been trying to unsuccessfully to sell it, and maintenance had fallen by the wayside in an effort to save money. And in 2016, LaMia flight 2933 crashed in Colombia, killing 71 of the 77 people on board, including most of Brazil’s Chapecoense football team. LaMia, a Bolivian charter airline with only one operational airplane, had been in such deep financial trouble that it deliberately underfueled its airplanes in order to save money. On flight 2933, they cut it too close, and the plane ran out of gas. After both of the aforementioned accidents, the airlines in question were grounded, but a closer examination might have led authorities to shut them down earlier.
West Caribbean Airways flight 708 was also not the only accident involving a high altitude stall from which the pilots failed to recover. Most famously, on the first of June 2009, Air France flight 447 disappeared over the Atlantic Ocean with the loss of all 228 passengers and crew. While flying through a storm, the Airbus A330’s pitot tubes, which measure airspeed, froze and stopped providing valid information. The first officer reacted incorrectly, pitching the plane up until it stalled. He continued to pitch up all the way until the plane hit the sea, apparently never realizing that he was in a stall and needed to pitch down. Several other similar accidents have occurred in recent years, including the 2014 crashes of Air Algerie flight 5017 and Indonesia Air Asia flight 8501, which claimed a combined 278 lives. It is hard to explain why all of these pilots failed to perform one of the most basic emergency maneuvers, taught from day one of flight training. But the answer could lie in the powerful ability of the human brain to discard any information that does not support its preconceived picture of the situation. On West Caribbean flight 708, Captain Ospina’s initial determination that there was something wrong with his engines could have prevented him from assimilating information that pointed to a different source for the problem.
In its final report, released in 2010, the Venezuelan CIAA recommended that pilots receive better training on how to use aircraft performance tables; that airlines be required to provide training in recovery from high-altitude stalls; that authorities continually monitor the financial state of every airline to ensure that it is capable of providing an adequate margin of safety; that MD-80 series pilots be taught about accidents involving the aircraft’s various autopilot and autothrottle modes; that pilots receive new training on strategies to maintain situational awareness; that Boeing add an alarm or warning to inform crews that the aircraft is exceeding its performance limits; and that the model of flight data recorder used on the plane be modified to record the aircraft’s angle of attack. It remains to be seen whether these efforts, and those following the similar crashes that have occurred since, will effect a long-term reduction in pilot errors involving high altitude stalls.
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