Air France Flight 447 Crash

Introduction

Travelling by air presents a quick and safest way to travel from point to point, especially over great distances. Still, a large number of airplane accidents, some tragic, are induced by weather. Owing to decades of developments in aeronautical engineering as well as refinements drawing from past lessons, most modern jetliners are considered safe from the effects of weather. All the same, a large number of weather-related airplane crashes have been reported. As a result, it has been advanced that the problem of weather-related crashes is subject to the influence of other factors, and ought to be addressed comprehensively to ensure no similar accidents occur. Weather-related accidents will be studied by looking at causes of the mishap of Air France flight 447. The continued occurrence of weather-related airplane crashes presents a failure in the most elementary of airplane safety practices given most modern planes are extremely well suited to withstand the effects of adverse weather.

Accident Details

The information and details about the flight path and the descent of the Air France Flight 447 before its plunge into the Atlantic Ocean were reconstructed from the transcripts. The summary of the accident details was that the plane went into an aerodynamic stall high over the Atlantic and despite persistent efforts, the plane course could not be exit the stall. The Airbus A330-200 was en route to Charles De Gaulle Airport in Paris after leaving Rio de Janeiro on via the Galeao International Airport in June 1, 2009 when the high-altitude stall occurred. The plane had on board 12 crew members and 216 passengers all of whom perished in the crash. The primary reason identified was that ice had blocked the plane’s air speed sensors and rendered the rest of the flight instruments unreliable.

The flight began experiencing troubles approximately 2 hours and 10 minutes into the flight. This was made clear when the pilot stated “so we’ve lost the speeds.” The plane had entered the outer extremities of a tropical storm system about 1hr and 36 minutes into flight time, and the weather outside was much warmer than forecast. Since the plane was only a short time into the flight, it still had most of the 70 metric tons of fuel, and as a result, could not climb to a higher altitude to avoid the brunt of the storm. Unlike the crew in other planes plying similar routes in the region on the fateful evening, the crew of AF447 had not studied the storm patterns, and this was the probable cause why they went headlong into the storm, and had not requested a divergence around the area of the most severe storm activity.

Right after the loss of speeds, the plane is known to have entered a state of “Alternate Law” that has been interpreted by investigators to mean flight instruments were no longer relaying accurate information on airspeed. It is worth noting, however, that failure of flight instruments, especially those that measure airspeed does not imply that the plane was losing speed. The flight data recorder captured another four minutes after the “alternate law’ remark by one of the pilots, stopping presumably due to the airplane crash. The plane fell an approximate 38,000 feet in just over four minutes, with the last recorded data points indicating a nose-up attitude of 16.2 degrees, an altitude drop speed of almost eleven times what is considered normal (1000 feet per minute), and a ground speed of 107 knots.

Preliminary reports had indicated that the airplane entered an aerodynamic stall, and due to the conflicting information from the flight instruments the pilots could not tell how accurate the readings were. An aerodynamic stall is characterized by a loss of lift that results when airflow moving over the wings separates from the wing surface. The engines are in no way affected by aerodynamic stall, and it is expected that the plane engines were running even at the point of impact. Transcripts reveal that shortly before the aircraft lost speeds, the auto-thrust and autopilot systems disengaged forcing the pilot to take control of the plane. The experienced pilot who had been taking his regular rest break was back at the cockpits 90 seconds later, but the lesser experienced pilot had made a “nose-up input” from which the plane never recovered (Palmer, 2013).

  According to investigators, the stall warning sounded at least twice in a row before the actual plunge (BEA, 2012). The plane is thought to have been unable to maintain altitude while in the stall, and to have reduced the speeds from about 275 knots to 60 knots. Efforts within the first minute of the fall to regain control of the plane proved unsuccessful, with the airplane’s fly-by-wire system allowing the pilots to exceed certain parameters that manage the flight controls. For instance, the plane’s angle of attack exceeded 40°, at least 5° over acceptable limits. It is believed that the “alternate laws” state prevented the pilot from taking over control and adjusting the angle of attack, a measure usually applied to reduce the chances of entering a stall.

 Figure 1. Lift graph with high and low Mach

Once the experienced pilot returned to the cockpit, he discerned the flight instruments were relaying inaccurate information. This must have presented a dilemma as to what flight instruments were reliable and which were not. Investigators suggest that the Pitot tube, an airflow sensing device outside of the craft must have frozen over, resulting in the false speed readings that led to the pilot believing all flight instruments were damaged (Palmer, 2013). A damning piece of information though was presented in the report from the Bureau d’Enquetes et d’Analyses (BEA), the French civil aviation authority. The report cited the initial pilot reaction of pushing the control stick backward as opposed to forward as being responsible for the plane’s inability to pull out of the stall.

Figure 2. Effect of a drop in total measured pressure on pressure altitude and vertical speed

The submission was that, while weather (ice) was primarily responsible for the onset of the crisis, human error was the ultimate reason for the crash. If the pilots had managed to push the control stick forward long enough, then the crash could have been avoided. The plane recorder’s final readings, 2 hours and fourteen minutes into the flight reflected a ground speed of 107 knots, vertical speed of 10,912 ft/min, the roll angle of 5.3° left, the magnetic heading of 270 degrees, and a pitch attitude of 16.2° nose-up (BEA, 2012). The final descent took place in just over four minutes, and the crew issued no emergency message to the passengers owing to the limited duration of impact. The wreckage was found 6.5 NM and to the north of the last transmitted position at a depth of almost 4,000 meters below sea level on 3 April 2011.

Investigation

The investigation into the factors leading up to the crash of Air France 447 began five days after the disappearance of the plane. The primary concern was the need to understand the reasons for the actions taken by the pilots, and how a loss of airspeed indications alone could have resulted in such a disaster. Initial investigations placed the burden of the crash on an aerodynamic stall, a fact that confounded investigators since how to handle stalls are one of the basics taught in flight school. Accidents such as these are classified as loss of control accidents and have become increasingly common over the last decade. These types of accidents affect both classically designed planes as well as more modern airplanes. Automated in-flight control systems applied in most modern airliners have the capacity to significantly improved safety. However, they are not always used, sometimes deliberately, and at other times when they disconnect involuntarily.

 A stall in aerodynamics refers to the situation where the wing stops producing lift since it has topped the critical angle of attack. Simplified, this means that as a plane slows down, the nose must be raised, thus leading to an increase in the angle of attack, to obtain the necessary lift required to maintain the desired airspeed and altitude. If the angle (of attack) goes too high, the wing no longer produces lift since the smooth flow of air over it is disrupted. In such a situation, the plane’s wing stop soaring and the nose dips downward. To resume normal flight, it becomes necessary to reestablish proper lift by reducing the angle of attack. Since occurrences of aerodynamic stalls are unpredictable, flight control obliges pilots to have perfect situational awareness at all times. This is irrespective of whether they are manning a classic or a modern airplane type, a condition that the pilots of Air France 447 were not able to follow.

Causes Summary

While it is clear that the accident was initiated by the obstruction of the Pitot probes by ice, the more direct cause was due to the crew losing situational awareness (BEA, 2012). The temporary failure in the airspeed indication system of the flight instruments was manageable, at least until the crew was unable to maintain situational awareness resulting in the plane exiting its flight envelope. The situation was further by the “Alternate Law” feature unique to Airbus jets. The feature being on translates to the plane flying in a fly-by-wire system. Under such conditions, the pilot has no direct control over the control surfaces, primarily the elevators, ailerons, and rudder. Whenever the pilot moves the stick or rudder pedals, all he manages to do is send a signal to a computer, which based on metrics collected from the flight instruments chooses what to do. The downside of such a system lies in the Pilot Flying being unable to turn the computer off and assume manual control over the flight.

Human Factor Issues

The preliminary investigations into the fate of Air France flight 447 revealed the possibility of human errors in the crash (BEA, 2012). The reasons were based on the lack of an apparent connection on how a fault in airspeed indication could result in the accident. Consequently, Human Factors (HF) Working Group, in tandem with the BEA joined the investigations three months after they began. The HF analysis was carried out by four Human Factors experts, two of them being pilots. Including pilots in the group provided a basis for reasonable expectations on a fair analysis regarding the reactions and skills of the crew. The other two were experts on the social, emotional, cognitive, psychomotor, and cooperative responses of the airline pilots. The primary concern of the HF working group was to seek an answer to the question of if another crew was substituted for the one in flight AF447, the same responses would be observed.

Subject to their investigation, the Human Factors working group hoped to come up with a better management framework that had the capacity to serve as a basis for improving the safety model and ensuring that similar accidents would not occur as a result of human factors. In the course of their investigations, the HF working group surmised that when crew action was expected, the expectation was that the team, through a rapid diagnosis, could identify the correct course of action. It is not unheard of that crew, faced with a similar situation, have a temporary but profound loss of comprehension. Under such conditions, if the pilot team loses the capacity for basic mastery and are unable to adopt a corrective stance, the safety model is said to be in “common failure mode.” The exact circumstances of flight AF447 were perceived to have been in exactly this state by the Human Factors working group.

During the crash sequence of events, the loss of airspeed information as a result of obstruction of the Pitot probes by ice is thought to have completely surprised the crew of Flight 447. Initial responsive reactions to the situation were reliant on basic airmanship, something all jetliner pilots are expected to have. The expectation intimated a rapid diagnosis by the pilots and prompt corrective measures. Due to apparent difficulties with airplane handling due to the high turbulence, the pilots responded to the situation with excessive handling inputs in roll and a nose-up when a nose-down would have been more appropriate. The resulting destabilization from the climb and the change in the pitch attitude and vertical speed further affected the airspeed readings. As a result, the pilots could not quickly diagnose the situation and consequently could not reach a solution. The crew, probably in a state of panic and progressively becoming “destructured,” were utterly unable to realize they had lost “only” three indicators of airspeed information.

The initial reaction of the least experienced pilot was propagated and fed on to the others until a total loss of cognitive control occurred. The plane is then believed to have gone into a state of the sustained aerodynamic stall which, despite the big warnings by in-flight instruments, the pilots could not perceive. Subject to this, the crew was unable to adopt any corrective measures or apply any recovery maneuver. The ergonomics of the airplane warning system is also believed to have played a part. For example, to be able to recognize a stall warning, there is an expectation of having had sufficient previous experience of stalls so as to have the cognitive ability to understanding the situation. Further, it presupposes training on how the particular craft that a pilot is handling handles stall, and a knowledge of protection modes as well as flight physics of the plane. HF working group was unable to identify any reliable indications that current training regimens for airline pilots incorporated sessions meant to aid in the acquiring and maintenance of the said skills (BEA, 2012).

The immediate cause of the crash of the Air France flight was pilot error. Pilot error should not be taken for a lack of experience as the pilots of flight were sufficiently experienced. Joining Air France in 1988, Captain Marc Dubois had by 2009 accumulated approximately 11,000 flight hours, with 1,700 of these hours being specifically on an Airbus A330. The other two, First Officers David Robert, and Pierre-Cedric Bonin had over 9,000 hours of flight time between them. Admittedly, Pierre-Cedric Bonin was a lot less experienced. Bonin had not attained the qualifications specified for first officers on an A330 aircraft by Air France since he had approximately 800 hours in-type. It, therefore, stands to reason he should not have been left at the helm while the other more experienced pilots were asleep.

The summary of the investigation into human factors identified the following direct actions as having played a part in the descent of flight 447.  The pilots never read the storm prediction reports and were therefore constrained to follow a flight path that took them directly to the center of a tropical storm system. Once in the storm, the fact that the plane was loaded with metric tons of highly flammable jet fuel prevented their ascent, forcing then to weather a dangerous storm. The pilot at the helm reacted inappropriately. Where he should have pushed the control stick forward, he pulled back on it. The result was to increase the angle of attack even further, an action that translated into an even steeper climb by the plane. Moreover, the pilots were also unable to realize that they had attained the maximum permissible altitude. Owing to the perceived failure of the flight instruments, the pilot completely ignored the available data on altitude, and vertical velocity.

It confounded investigators that the stall warning system signaled unremittingly for 54 seconds without even the slightest acknowledgments by either pilot. Apparently, they did not realize they were in an aerodynamic stall. To further complicate the situation, the stall warning is designed so as to deactivate whenever temporary adjustments render the angle of attack more in line with the expected values. Consequently, when the stall alternated between sounding and stopping, the pilots may have been confused, or lent to the fact that the warning system was flawed and should be disregarded. In particular, investigations revealed that the stall warning system stopped whenever the pilot was pulling back on the stick, and came on when he pushed forward (BEA, 2012). To add on to the list of pilot concerns, even with the rapid decline in altitude, the pilots could not identify what flight instruments were reliable and which were not. Investigators were of the opinion that it may have been difficult to them to identify what gadgets to depend on and that all were faulty with the values they presented being incoherent.

Another damning observation that lends credence to the opinion that pilot error was the direct cause of the crash is seen on further observation of the flight transcripts. The most experienced pilot, Captain Dubois, is on record saying, “I didn’t sleep enough last night. One hour – it’s not enough,” after which he proceeded to go to slumber, leaving at the helm an inexperienced pilot. As the lead investigator, Chief investigator Alain Bouillard observed that had the captain stayed at the helm for an additional 15 minutes, long enough to see the plane through the tropical storm system, the result may have been different. Bouillard believed that the Captain’s experience would have played a major part in reaching a safe conclusion to the frozen Pitot tube debacle.

Security Considerations Adopted Since

As a direct result of the investigation of the crash of flight AF447, the French civil aviation authority BEA, proposed some far-reaching intervention measures to ensure no repeat of an accident like that ever happens again. The first recommendation was the immediate removal from service of all Thales Avionics P/N C16195AA Pitot probes (Palmer, 2013) The second was to extend to 90 days the transmission time for ULB’s installed on flight recorders on airplanes that traversed maritime areas. This was meant to ease recovery of flight recorders. BEA also recommended an additional locator beacon that transmitted over a second frequency to further aid towards this end. Moreover, the aviation body was looking into the possibility of making it mandatory for all flights involved in public transportation to transmit basic flight parameters like their altitude, heading, speed and position. Furthermore, there was an undertaking to study the appropriate precision the composition of cloud masses at high altitude.

BEA also advocated a change in the Flight Manual to specify the recommended procedure when auto-thrust and autopilot are automatically disconnected. The emphasis here was on handling the event of flight controls having reverted to alternate law. Another recommendation was that the European Aviation Safety Agency (EASA) and the Federal Aviation Administration (FAA) look into instituting a provision that would make it mandatory that plane manufacturers integrate an angle of attack pointer in plain view of the pilot. Similarly, the International Civil Aviation Organization (ICAO) was asked to look into the requirement that all public transport aircraft be equipped with an image recorder that enables a pilot look at the whole instrument panel. BEA further advanced that EASA and ICAO make mandatory, and as quickly as possible, for public transport planes with flights over maritime or remote areas incorporate data transmission mechanism to facilitate their localization in case of emergency situations. Also, BEA advanced that the EASA ought to define additional criteria on the rules regarding how the Relief Captains are chosen to ensure that there is better task sharing among the different crew members.

Safety Considerations

The measure outlined above are by no means the comprehensive list of recommendations by the BEA. The BEA provided over 40 items for consideration on how to prevent future crashes. What is concerning is that this was not the first crash arising from a similar set of conditions. Many accidents that have occurred recently have been similar, and after analysis has had recommendations that would have prevented the occurrence of the crash of flight AF447. The failure to incorporate these endorsements into the standard operating procedures (SOPs) is what is damning. Some airplane accidents are striking in that they could have been prevented using basic airmanship. Recent research points to the loss of control accidents being the primary cause of accidents in the commercial fleet (Palmer, 2013). Even more concerning, the numbers are not improving, if anything they are static. Despite this easily identifiable and correctable flaw, not much has been done to ensure it is mitigated. Safety regulators are calling for better pilot training and more comprehensive instructions for dealing with unusual circumstances.

Cases of failure to enforce regulations that would improve flight safety are rife, with corrective measures largely ignored. As early as 1998, a Lufthansa Airbus lost its airspeed indicator while circling the Frankfurt airport. The potential tragedy was only averted when the ice melted as the plane descended leading to BFU, German Federal Bureau of Aircraft Accident Investigation demanding specifications of the pitot tubes be altered to allow “unrestricted flight in severely icy conditions.” In 2005, Thales, the company that manufactures the Pitot tubes on flight AF 447, started research on possible replacements for the pitot tubes (Palmer, 2013). A Thales document identifies the potential loss of the airspeed indicators that “could cause aircraft crashes, especially in cases in which the sensors ice up” as the primary reason for the research. Further, Airbus, the manufacturer of the ill-fated flight was aware of the shortcomings of the Thales pitot tubes. Internal documentation point to nine incidents involving faulty pitot tubes between May and October 2008 alone.

Conclusion

To conclude, the design and engineering of modern airplanes precludes the possibility of air crashes as a result of adverse weather. That these accidents still happen, can be attributed to human error and a failure to implement the safety measures in place meant to prevent such tragic consequences. The occurrences of such accidents also belie the effectiveness of some of the preventative measures in place to watch against this. To avert future recurrences of similar crashes, pilot training should be improved, and safety measures once adopted should be implemented. It is only by learning from past accidents that future mishaps can be prevented.

References

BEA,. (2012). Final Report On the accident on 1st June 2009 to the Airbus A330-203 registered F-GZCP operated by Air France flight AF 447 Rio de Janeiro – Paris. Paris: Ministère del’ Écologie, du Développement du rable, des Transpott set du Logement.

Palmer, B. (2013). Understanding Air France 447.