The crash of Air France 447 is considered the biggest disaster ever to hit Air France and Airbus since the beginning of their venture into this industry. All of the 228 passengers and crew of the flight were killed in this accident (Palmer, 2013). Due to the delay in the recovery of the black box from the ocean bed, the investigations and final report, published by BEA, took nearly three years for completion (Jonathan, 2011). The final investigation revealed that the accident occurred due to the inconsistent data indicated by the FMC (Flight Management Computer System) regarding the fluid flow velocity concerning the aircraft and the subsequent erroneous actions that the pilots committed to salvage the situation (BEA, 2009a). It was identified that the erroneous data shown by the FMC was due to the formation of ice crystals around the pitot tube possibly causing the sensors to relay wrong information. It could be said that this disaster took place due to the accumulation of a series of unfortunate events that eventually led to the manual errors committed by the pilots. To understand and avoid future instances such as this, it is necessary that we assess this situation further. And by using Barry Turner’s man-made disaster model as a tool, we can ascertain the simplest of errors that eventually led to the demise of over 200 passengers and cabin crew in the flight Air France 447 .
Initial Beliefs and Norms
The pitot tubes are an integral part for the working of many aircraft equipments such as the fly-by-wire control systems, ground proximity warning systems, slat and flap controls, etc. Their primary function is to measure the velocity of the aircraft by using two parameters 1.Total Pressure and 2.Static Pressure (Benson, 2016). They are measured using both Pitot probes and static pressure sensor. The pitot probe systems are provided with drains and electrical heating systems to avoid them icing up. Due to the importance of these sensors, the pitot probes are frequently checked and taken care of to avoid any discrepancies. They are frequently or intermittently, 1.Cleaned using compressed air 2.Cleaned using specific tools (especially the drains) 3.Tested for heating issues using standby power supply systems and 4.Checked for sealants on the circuits (BEA, 2009b).
There is three dedicated Probe Heating Computers monitoring the temperature of the probe to maintain this equipment at an optimum temperature. There is also a force heat button, PROBE/WINDOW HEAT, that can be turned on manually before the flight. During the flight, the probe is continuously heated automatically. In the case of Air France 447, the investigators were not able to find any faults in the pitot tubes or any equipments associated with it. The issue of formation of ice crystals, as a result of the weather conditions and the flight speed, could not be solved by the electric heating equipments in this particular case.
Incubation Period
Erroneous Assumptions: Icing of Pitot tubes in an aircraft is a common phenomenon and have often caused disruptions in the automatic operations of many airplanes. The provision of a heater in the icing tube is only capable of stalling this process in situations where they can be melted as soon as they are formed. But in extreme condensation conditions, such as the one existed in the atmosphere during the flight of Air France 447, this is not possible. The pilots should be capable of identifying such situations beforehand and accept that a possibility for Unreliable Airspeed Condition exist during specific weather conditions. It is also laid down in the policy statements that automated controls should, in all cases, be considered as an aid and not the primary mode of flying an aircraft. But in this case it is notable that the pilots (the two first officers as the Captain had gone to take rest) did not account for this situation due to their erroneous assumptions regarding the reliability of FMC data before heading into the turbulence and lost control of the aircraft.
Information Handling Difficulties: During its flight, at about 0200 hrs UST, Air France 447 ran into severe turbulence from which it never recovered. The turbulence that existed during the flight of Air France 447, detected from 0030 hrs, was identifiable from the on-board weather radar. A cluster of Cumulonimbi clouds, responsible for thunderstorms, had started to form around and reached their maturity around 0200 hrs. This period is usually marked by severe turbulence during flights. The data recorded by TMI instrument, which is a TRMM microwave imager that measures rainfall (water content in the air), has highlighted the issue of condensation in a region below the clouds (Skofronick-Jackson, 2016). It is possible that there was the phenomenon of atmospheric convection in these areas that would lead to turbulence. But the crew failed to assess this weather information and fly around these clouds as the other Air France flights flying over the Atlantic did.
Lack of Accepted standards and Procedures: The crew had failed in following the procedures enlisted for Unreliable Airspeed conditions. The icing of pitot tubes is an event that lasts, in normal conditions, only for a few minutes. During this period the airspeed indications shown by the flight controls are considered to be unreliable. There is two categorized procedures, laid down by Air France, to be followed during such conditions. These two procedures are classified according to the danger the flight is currently in (Barthe, 2009). The listed procedures, as they are different for conditions that usually overlap in most cases, are extremely difficult to choose between. Due to the disengagement of autopilot and other protections such as High Speed and Angle of Attack protections, the pilots are usually overwhelmed by actions that they are supposed to complete to strictly follow these procedures from memory. Investigations revealed that a sum of 8 accidents that hit Air France had been due to situations of Unreliable Airspeed. In fact, the company even had received many suggestions from previous pilots (the subject was even raised in a meeting conducted in technical divisions of Air France and Airbus) about the inability to cope with the conditions caused by faulty airspeed indications. A need for standardization and simplification of these procedures was mooted by Air France and Airbus.
Minimizing Emergent Danger: The unreliability of the Airspeed caused the autopilot to disengage . The flight control mode was shifted from Normal to Alternate 2 which is characterized by the loss of High angle of attack protection and High speed protection (only in the case of failure of two air-data references). Due to the formation of ice crystals in the pitot tubes, the Airspeed data fed to the FMC was no longer reliable and posed serious danger to the aircraft if still proceeded automatically. But the pilot failed to act accordingly while taking into consideration the dangers associated with making erroneous decisions during Alternate 2 control laws, especially due to the absence of angle of attack protections and stall warnings. Figure details the series of events that occurred on June 1, 2009 as of 0200 hrs, which ultimately led to the crash of Flight 447.
Precipitating Event
The event that led to the ultimate demise of all 228 passengers and crew members aboard the Air France 447 was the erroneous actions committed by the PF (Pilot Flying) during the momentary failure of the pitot tubes caused by the formation of ice crystals inside it. This momentary failure caused the aircraft to disengage the Autopilot mode. The control law was shifted from Normal to Alternate 2, due to the abnormality of information displayed by all of the instruments that use airspeed for calculations (such as for altitude, wind speed, etc). Many protections, such as the one that automatically inhibits the aircraft from crossing angle of attack limits and reaching stall conditions, were disabled. This Unreliable Airspeed conditions (or Alternate 2 control law) prevailed for the next two minutes within which the pilots had already lost complete control of the aircraft. The PF pulled his side-stick back, assuming that the indicated altitude (which was lower than true value) was reliable. The aircraft started rising up (with nose-up) and started losing speed causing it to meet the conditions for stall.
Disaster Onset
The shift from Normal control law to Alternate 2 made the controls on the fly-by-wire stick more sensitive to rolling and the pilot struggled to keep the aircraft steady through the turbulence. The aircraft was banking left uncontrollably due to the turbulence it was experiencing (owing to the convective conditions in the atmosphere). The pilot misjudged the sensitivity of the fly-by-wire, partially due to the stressful situations in cabin and partially due to his inability to cope with Alternate 2 control laws, and overcompensated for the banking. During alternate 2 conditions, the aircraft is usually more sensitive to rolling which is what happened in the case of Air France 447 (Driver, 2016).
This control law also disables stall protection and others that prevent the aircraft from crossing angle of attack limits. The PF (Pilot Flying), who was comparatively less experienced than the PNF (Pilot Not Flying) made the erroneous judgment from the invalid airspeed data that the flight was actually gaining speed and losing altitude when the aircraft was actually losing speed and gaining altitude. The instruments, owing to the failure of Pitot tubes, were actually showing residual junk values which were offset from the true values by a large margin. But the PF pulled the side-stick back causing the flight go nose-up and climbing while losing speed and gaining altitude. And therefore, the aircraft registered a continuously increasing angle of attack for the next few minutes (from 0210 to 0211 hrs).
The PNF (Pilot Not Flying), who was more experienced than PF, tried to take over the controls but failed to make a verbal comment about the switch. The PF was still pulling back the side-stick trusting the erroneous data shown by the FMC. The aircraft started displaying stall warning. But alternate 2 laws prevented any automatic control of speed or angle of attack. The airplane eventually reached stall conditions by 0210 hrs. Being more experienced, PNF knew that they had to go nose-down to gain speed to avoid stall conditions. But the PF still had not relinquished his control over the stick. And he continued to hold it back to attempt to increase the altitude (as the FMC was showing lower altitude information) (BEA, 2009b).
All of the aircraft instruments had then started to fail since the upward position of aircraft and rapid decline of speed and altitude of the aircraft (caused by the stall conditions) was providing inconsistent data on all of it. At a time when they should have been nose-diving and gaining speed, the flight was losing altitude quickly while still being nose-up. By the time PF relinquished his control over the stick and passed it to his copilot, the airplane had already crossed safe altitude levels. Even though the new PF tried to recover the control of the flight back, it did not work. Even with the captain’s return to the cabin and also the recovery of pitot tubes as well as associated equipments, the flight never recovered from this fall and crashed into the ocean at about 0214 hrs (when the recording stopped).
Rescue and Salvage
The loss of contact with the aircraft was indicated after 0400 hrs as there was no report from the flight that they had passed into Senegalese Airspace (at 0220 hrs) or into Cape Verdean Airspace (at 0345 hrs). Another flight from Air France (Flight AF459) was asked to contact with Flight 447 to ascertain what had occurred to them. Flight AF459 was not able to establish any contact with Flight 447. Air surveillance from the area too failed to detect the lost aircraft. Even before the end of June 1, the day the accident had occurred, officials were convinced that they had lost the aircraft without any survivors.
On 2, June, a Brazilian aircraft from their Air force detected possible debris of Air France 447 at around 1520 hrs. The presence of oil, presumably jet fuel, along with an aircraft seat, a barrel and some debris of conductors and electrical equipments were also detected. The remaining recovery operations were conducted on the assumption that this site was probably the crash site for Air France 447. Five days after the wreckage of the aircraft two male bodies were recovered from the crash site. By June 16, almost fifty bodies had been recovered from the site. The possibility of having lost all lives aboard the plane was by now ascertained. By this time, the recovery was primarily focused on the flight data recorder and cockpit voice recorder. It was only on May 1, 2011 that the flight data recorder and cockpit voice recorder were finally recovered from the ocean bed. Between May and June of 2011, about 150 bodies were recovered by the team.
Cultural Readjustments
Following the accident of Air France 447, the BEA made a series of new recommendations while reinstating the importance of some of the recommendations they had made in the past. The dangers caused by the brief blockage of pitot tubes due to icing was the primary discussion of these recommendations. Air France subsequently adopted a new pitot tube and replaced every old ones from all of their flights. The new pitot tube (identified as BA; the old was called AA) had fared better in their tests in resisting condensation. Air France also made sure that a universal copy of the procedures to be followed during Unreliable Airspeed was kept in the cockpit and that too in English to avoid inconsistencies caused by translation.
The next big step that was caused by this crash was the assessment of the role of copilots. The PF (Pilot Flying) and PNF (Pilot Not Flying) in the case of Air France 447 had a brief conflict between who should be controlling the plane during the events that led to its crash. The duty of the copilot should have been more elaborately defined to avoid such situations. The choice of the Captain and his first officer to leave the control of the aircraft to the third officer (aid; PF during the crash), who was much less experienced than the others, during severe turbulent conditions were also criticized. He (PF) had exhibited lack of knowledge in the field of flying during Alternate Law conditions. This also meant that the pilots should be given elaborate and thorough training in dealing with situations where the automatic controls of the aircraft might be lost. Some of the technical recommendations included the provision of a direct readout of Angle of Attack during flights, especially during Alternate laws when the vulnerability of the aircraft to roll is much higher. Aircraft manufacturers such as Airbus realized that the increased reliability on automation has significantly reduced the skills of pilots in dealing with situations where automation failed. They succumbed to the false mental images that they had about the aircraft’s position and failed to look for the facts (Learmount, 2012). The captain had retired to rest even though he saw that the flight was running into some turbulence. It appears as though he might have overestimated the ability of his copilots especially because of his experience in flying much less sophisticated airplanes through harder weathers. The weather conditions prevailing in the Atlantic was not that exceptionally dangerous but the copilots, due to their lack of knowledge in flying non-automated flights, failed to manage this situation (CNN, 2012).
Conclusion
The story of the crash of Air France 447 had come as a shock to the world as well many airlines. The Airbus A330s were always praised for its efficient automatic controls and the ease that it provided the pilots in flying the plane. But this confidence had blinded both pilots and the manufacturers in assessing and preparing for situations where these automatic controls were unreliable. The crash of Air France 447 is a sad reminder of this false presumptions about flying airplanes. It was easily observable from the Cockpit Voice Recorder that the failure of automatic controls had thrown the pilots (PF and PNF) into a frenzy that made them make erroneous judgments which ultimately caused the demise of 228 passengers and crew along with the flight. Both the airline and Airbus realized that human finesse and knowledge cannot be excluded from flights even with the maximum level of automation.
References
Barthe, J. (2009, June 24). Air France Airbus 330 – Unreliable Airspeed Problems Since 2006. Retrieved July 20, 2016, from https://luckybogey.wordpress.com/2009/06/24/air-france-airbus-330-unreliable-airspeed-problems-since-2006/
BEA. (2009). Final Report. Retrieved from https://www.bea.aero/docspa/2009/f-cp090601.en/pdf/f-cp090601.en.pdf
Benson, T. (2016). Pitot Tube. Retrieved July 20, 2016, from https://www.grc.nasa.gov/WWW/k-12/VirtualAero/BottleRocket/airplane/pitot.html
CNN. (2012, July 5). Final Air France crash report says pilots failed to react swiftly - CNN.com. Retrieved July 20, 2016, from http://www.cnn.com/2012/07/05/world/europe/france-air-crash-report/index.html
Driver, A. (2016). Airbus Flight Control Laws. Retrieved July 20, 2016, from http://www.airbusdriver.net/airbus_fltlaws.htm
Jonathan. (2011, May 27). Information on The Crash of Air France Flight 447. Retrieved July 20, 2016, from http://www.airfrance447.com/
Learmount, D. (2012). IN FOCUS: After AF447, what now? Retrieved July 20, 2016, from https://www.flightglobal.com/news/articles/in-focus-after-af447-what-now-377433/
Palmer, B. (2013). Understanding Air France 447. William Palmer.
Skofronick-Jackson, G. (2016). Precipitation Measurement Missions. Retrieved July 20, 2016, from https://pmm.nasa.gov/trmm/tmi
