Air France 447: Investigation, Search and Recovery

AF8

Brigadier Cardoso speaks to the media about the search for the crashed aircraft.

 

Surface search

Flight 447 was due to pass from Brazilian airspace into Senegalese airspace at approximately 0220 (UTC) on 1 June, and then into Cape Verdean airspace at approximately 0345. Shortly after 0400, when the flight had failed to contact air traffic control in either Senegal or Cape Verde, the controller in Senegal attempted to contact the aircraft. When he received no response, he asked the crew of another Air France flight (AF459) to try to contact AF447; this also met with no success.

After further attempts to contact Flight 447 were unsuccessful, an aerial search for the missing Airbus commenced from both sides of the Atlantic. Brazilian Air Force aircraft from the archipelago of Fernando de Noronha and French reconnaissance aircraft based in Dakar, Senegal led the search. They were assisted by a Casa 235 maritime patrol aircraft from Spain and a US Navy Lockheed Martin P-3 Orion anti-submarine warfare and maritime patrol aircraft.

By early afternoon on 1 June, officials with Air France and the French government had already presumed that the aircraft had been lost with no survivors. An Air France spokesperson told L’Express that there was no hope for survivors, and French President Nicolas Sarkozy announced that there was almost no chance anyone survived. On 2 June at 1520 (UTC), a Brazilian Air Force Embraer R-99A spotted wreckage and signs of oil, possibly jet fuel, strewn along a 5 km (3 mi) band 650 km (400 mi) north-east of Fernando de Noronha Island, near the Saint Peter and Saint Paul Archipelago. The sighted wreckage included an aircraft seat, an orange buoy, a barrel, and white pieces and electrical conductors. Later that day, after meeting with relatives of the Brazilians on the aircraft, Brazilian Defence Minister Nelson Jobim announced that the Air Force believed the wreckage was from Flight 447. Brazilian vice-president José Alencar (acting as president since Luiz Inácio Lula da Silva was out of the country) declared three days of official mourning.

 

AF7

Lt. Col. Henry Munhoz describes the recovery of Airbus A330 wreckage from the ocean.

 

 Also on 2 June, two French Navy vessels, the frigate Ventôse and helicopter-carrier Mistral, were en route to the suspected crash site. Other ships sent to the site included the French research vessel Pourquoi Pas?, equipped with two mini-submarines able to descend to 6,000 m (20,000 ft), since the area of the Atlantic in which the aircraft went down was thought to be as deep as 4,700 m (15,400 ft).

On 3 June, the first Brazilian Navy ship, the patrol boat Grajaú, reached the area in which the first debris was spotted. The Brazilian Navy sent a total of five ships to the debris site; the frigate Constituição and the corvette Caboclo were scheduled to reach the area on 4 June, the frigate Bosísio on 6 June and the replenishment oiler Almirante Gastão Motta on 7 June.

Early on 6 June 2009, five days after Flight 447 disappeared, two male bodies, the first to be recovered from the crashed aircraft, were brought on board the Caboclo along with a seat, a nylon backpack containing a computer and vaccination card, and a leather briefcase containing a boarding pass for the Air France flight. The following day, 7 June, search crews recovered the Airbus’s vertical stabilizer, the first major piece of wreckage to be discovered. Pictures of this part being lifted onto the Constituição became a poignant symbol of the loss of the Air France craft.

AF6

The bodies found in the ocean being transferred to the morgue in Brazil for identification

The search and recovery effort reached its peak over the next week or so, as the number of personnel mobilized by the Brazilian military exceeded 1100. Fifteen aircraft (including two helicopters) were devoted to the search mission. The Brazilian Air Force Embraer R99 flew a total of more than 100 hours, and electronically scanned more than a million square kilometers of ocean. Other aircraft involved in the search scanned, visually, 320,000 square kilometres of ocean and were used to direct Navy vessels involved in the recovery effort.

By 16 June 2009 a total of 50 bodies had been recovered from a wide area of the ocean. The bodies were transported to shore, first by the frigates Constituição and Bosísio to the islands of Fernando de Noronha and thereafter by air to Recife for identification. Pathologists identified all 50 bodies recovered from the crash site, including that of the captain, by using dental records and fingerprints. The search teams logged the time and location of every find in a database which, by the time the search ended on 26 June, catalogued 640 items of debris from the aircraft.

The BEA documented the timeline of discoveries in its first interim report

AF5

Colour bathymetry relief map of the part of Atlantic Ocean into which Air France Flight 447 crashed. Image shows two different data sets with different resolution. 

Underwater search

On 5 June 2009, the French nuclear submarine Émeraude was dispatched to the crash zone, arriving in the area on the 10th. Its mission was to assist in the search for the missing flight recorders or black-boxes that might be located at great depth. The submarine would use its sonar to listen for the ultrasonic signal emitted by the black boxes pingers, covering 13 sq mi (34 km2) a day. The Émeraude was to work with the mini-sub Nautile, which can descend to the ocean floor. The French submarines would be aided by two U.S. underwater audio devices capable of picking up signals at a depth of 20,000 ft (6,100 m).

Following the end of the search for bodies, the search continued for the flight data recorder and the cockpit voice recorder, the so-called black boxes. French Bureau d’Enquetes et d’Analyses (BEA) chief Paul-Louis Arslanian said that he was not optimistic about finding them since they might have been under as much as 3,000 m (9,800 ft) of water, and the terrain under this portion of the ocean was very rugged. Investigators were hoping to find the aircraft’s lower aft section, since that was where the recorders were located. Although France had never recovered a flight recorder from such depths, there was precedent for such an operation: in 1988, an independent contractor recovered the cockpit voice recorder of South African Airways Flight 295 from a depth of 4,900 m (16,100 ft) in a search area of between 80 and 250 square nautical miles (270 and 860 km2). The Air France flight recorders were fitted with water-activated acoustic underwater locator beacons or pingers, which should have remained active for at least 30 days, giving searchers that much time to locate the origin of the signals.

France requested two towed pinger locator hydrophones from the United States Navy to help find the aircraft. The French nuclear submarine and two French-contracted ships (the Fairmount Expedition and the Fairmount Glacier, towing the U.S. Navy listening devices) trawled a search area with a radius of 80 kilometres (50 mi), centred on the aircraft’s last known position. By mid-July, recovery of the black boxes still had not been announced. The finite beacon battery life meant that, as the time since the crash elapsed, the likelihood of location diminished. In late July, the search for the black boxes entered its second phase, with a French research vessel resuming the search using a towed sonar array. The second phase of the search ended on 20 August without finding wreckage within a 75 km (47 mi) radius of the last position, as reported at 0210.

The third phase of the search for the recorders lasted from 2 April until 24 May 2010, and was conducted by two ships, the Anne Candies and the Seabed Worker. The Anne Candies towed a U.S. Navy sonar array, while the Seabed Worker operated three robot submarines AUV ABYSS (a REMUS AUV type). Air France and Airbus jointly funded the third phase of the search. The search covered an area of 6,300 square kilometres (2,400 sq mi), mostly to the north and north-west of the aircraft’s last known position. The search area had been drawn up by oceanographers from France, Russia, Great Britain and the United States combining data on the location of floating bodies and wreckage, and currents in the mid-Atlantic in the days immediately after the crash. A smaller area to the south-west was also searched, based on a re-analysis of sonar recordings made by Émeraude the previous year. The third phase of the search ended on 24 May 2010 without any success, though the BEA says that the search ‘nearly’ covered the whole area drawn up by investigators.

2011 search and recovery

In July 2010, the U.S.-based search consultancy Metron, Inc. had been engaged to draw up a probability map of where to focus the search, based on prior probabilities from flight data and local condition reports, combined with the results from the previous searches. The Metron team used what it described as “classic” Bayesian search methods, an approach that had previously been successful in the search for the submarine USS Scorpion and SS Central America. Phase 4 of the search operation started close to the aircraft’s last known position, which was identified by the Metron study as being the most likely resting place of flight 447.

AF3

Cable ship Île de Sein was assigned to assist in the recovery of materials from the ocean floor. 

Within a week of resuming of the search operation, on 3 April 2011, a team led by the Woods Hole Oceanographic Institution operating full ocean depth autonomous underwater vehicles (AUVs) owned by the Waitt Institute discovered, by means of sidescan sonar, a large portion of the debris field from flight AF447. Further debris and bodies, still trapped in the partly intact remains of the aircraft’s fuselage, were located at a depth of 3,980 metres (2,180 fathoms; 13,060 ft). The debris was found to be lying in a relatively flat and silty area of the ocean floor (as opposed to the extremely mountainous topography that was originally believed to be AF447’s final resting place). Other items found were engines, wing parts and the landing gear.

The debris field was described as quite compact, measuring 200 by 600 metres (660 by 1,970 ft) and located a short distance north of where pieces of wreckage had been recovered previously, suggesting that the aircraft hit the water largely intact. The French Ecology and Transportation Minister Nathalie Kosciusko-Morizet stated the bodies and wreckage would be brought to the surface and taken to France for examination and identification. The French government chartered the Île de Sein to recover the flight recorders from the wreckage. An American Remora 6000 remotely operated vehicle (ROV) and operations crew from Phoenix International experienced in the recovery of aircraft for the United States Navy were on board the Île de Sein.

Île de Sein arrived at the crash site on 26 April, and during its first dive, the Remora 6000 found the flight data recorder chassis, although without the crash-survivable memory unit. On 1 May the memory unit was found and lifted on board the Île de Sein by the ROV. The aircraft’s cockpit voice recorder was found on 2 May 2011, and was raised and brought on board the Île de Sein the following day.

On 7 May the flight recorders, under judicial seal, were taken aboard the French Navy patrol boat La Capricieuse for transfer to the port of Cayenne. From there they were transported by air to the BEA’s office in Le Bourget near Paris for data download and analysis. One engine and the avionics bay, containing onboard computers, had also been raised.

By 15 May all the data from both the flight data recorder and the cockpit voice recorder had been downloaded. The data was subjected to detailed in-depth analysis over the following weeks, and the findings published in the third interim report at the end of July. The entire download was filmed and recorded.

Between 5 May and 3 June 2011, 104 bodies were recovered from the wreckage, bringing the total number of bodies found to 154. Fifty bodies had been previously recovered from the sea. The search ended with the remaining 74 bodies still unrecovered.

Investigation and safety improvements

 

 

AF2

East-west cross-section of Atlantic Ocean portion in which Air France Flight 447 was thought to have crashed, showing depth of the sea floor. The vertical scale is exaggerated by a factor of 100 relative to the horizontal.

The French authorities opened two investigations:

  • A criminal investigation for manslaughter began 5 June 2009, under the supervision of Investigating Magistrate Sylvie Zimmerman from the Paris Tribunal de Grande Instance. The judge gave the investigation to the Gendarmerie nationale, which would conduct it through its aerial transportation division (Gendarmerie des transports aériens or GTA) and its forensic research institute (the Institut de Recherche Criminelle de la Gendarmerie Nationale, FR). As part of the criminal investigation, the DGSE (the external French intelligence agency) examined the names of passengers on board for any possible links to terrorist groups.

In March 2011, a French judge filed preliminary manslaughter charges against Air France and Airbus over the crash.

  • A technical investigation, the goal of which is to enhance the safety of future flights. As the aircraft was of French registration and crashed over international waters, this is the responsibility of the French government, under the ICAO convention. The Bureau d’Enquêtes et d’Analyses pour la Sécurité de l’Aviation Civile (BEA) is in charge of the investigation. Representatives from Brazil, Germany, the United Kingdom, and the United States became involved under the provisions of ICAO Annex 13; representatives of the United States were involved since the engines of the aircraft were manufactured there, and the other representatives could supply important information. The People’s Republic of China, Croatia, Hungary, Republic of Ireland, Italy, Lebanon, Morocco, Norway, South Korea, Russia, South Africa, and Switzerland appointed observers since citizens of those countries were on board.

On 5 June 2009, the BEA cautioned against premature speculation as to the cause of the crash. At that time, the investigation had established only two certain facts: the weather near the aircraft’s planned route included significant convective cells typical of the equatorial regions; and the speeds measured by the three pitot tubes had differed from each other during the last few minutes of the flight.]

On 2 July 2009, the BEA released an intermediate report, which described all known facts, and a summary of the visual examination of the rudder and the other parts of the aircraft that had been recovered at that time. According to the BEA, this examination showed that:

  • The airliner was likely to have struck the surface of the sea in a normal flight attitude, with a high rate of descent;
  • There were no signs of any fires or explosions.
  • The airliner did not break up in flight. The report also stresses that the BEA had not had access to the post-mortem reports at the time of its writing.

On 16 May 2011, Le Figaro reported that the BEA investigators had ruled out an aircraft malfunction as the cause of the crash, according to preliminary information extracted from the flight data recorder. The following day, the BEA issued a press release explicitly describing the Le Figaro report as a sensationalist publication of non-validated information. The BEA stated that no conclusions had yet been made, that investigations were continuing, and that no interim report was expected before the summer. On 18 May the head of the investigation further stated that no major malfunction of the aircraft had been found so far in the data from the flight data recorder, but that minor malfunctions had not yet been ruled out.

On 27 May 2011, the BEA released a short factual report of the findings from the data recorders without any conclusions.

Airspeed inconsistency

In the minutes before its disappearance, the aircraft’s onboard systems had sent a number of messages, via the Aircraft Communications Addressing and Reporting System (ACARS), indicating disagreement in the indicated airspeed (IAS) readings. A spokesperson for the BEA claimed that the airspeed of the aircraft was unclear to the pilots and, on 4 June 2009, Airbus issued an Accident Information Telex to operators of all its aircraft reminding pilots of the recommended Abnormal and Emergency Procedures to be taken in the case of unreliable airspeed indication. French Transport Minister Dominique Bussereau said, Obviously the pilots [of Flight 447] did not have the [correct] speed showing, which can lead to two bad consequences for the life of the aircraft: under-speed, which can lead to a stall, and over-speed, which can lead to the aircraft breaking up because it is approaching the speed of sound and the structure of the plane is not made for enduring such speeds.

Pitot tubes

Between May 2008 and March 2009, nine incidents involving the temporary loss of airspeed indication appeared in the Air Safety Reports (ASRs) for Air France’s A330/A340 fleet. All occurred in cruise between flight levels FL310 and FL380. Further, after the Flight 447 accident, Air France identified six additional incidents which had not been reported on ASRs. These were intended for maintenance Aircraft Technical Logs (ATLs) drawn up by the pilots to describe these incidents only partially, to indicate the characteristic symptoms of the incidents associated with unreliable airspeed readings. The problems primarily occurred in 2007 on the A320 but, awaiting a recommendation from Airbus, Air France delayed installing new pitot tubes on A330/A340 and increased inspection frequencies in these aircraft.

When it was introduced in 1994, the Airbus A330 was equipped with pitot tubes, part number 0851GR, manufactured by Goodrich Sensors and Integrated Systems. A 2001 Airworthiness Directive required these to be replaced with either a later Goodrich design, part number 0851HL, or with pitot tubes made by Thales, part number C16195AA. Air France chose to equip its fleet with the Thales pitot tubes. In September 2007, Airbus recommended that Thales C16195AA pitot tubes should be replaced by Thales model C16195BA to address the problem of water ingress that had been observed. Since it was not an Airworthiness Directive, the guidelines allow the operator to apply the recommendations at its discretion. Air France implemented the change on its A320 fleet where the incidents of water ingress were observed and decided to do so in its A330/340 fleet only when failures started to occur in May 2008.

After discussing these issues with the manufacturer, Air France sought a means of reducing these incidents, and Airbus indicated that the new pitot probe designed for the A320 was not designed to prevent cruise level ice-over. In 2009, tests suggested that the new probe could improve its reliability, prompting Air France to accelerate the replacement program, which started on 29 May. F-GZCP was scheduled to have its pitot tubes replaced as soon as it returned to Paris. By 17 June 2009, Air France had replaced all pitot probes on its A330 type aircraft.

In July 2009, Airbus issued new advice to A330 and A340 operators to exchange Thales pitot tubes for tubes from Goodrich.

On 12 August 2009, Airbus issued three Mandatory Service Bulletins, requiring that all A330 and A340 aircraft be fitted with two Goodrich 0851HL pitot tubes and one Thales model C16195BA pitot (or alternatively three of the Goodrich pitot tubes); Thales model C16195AA pitot tubes were no longer to be used. This requirement was incorporated into Airworthiness Directives issued by the European Aviation Safety Agency (EASA) on 31 August and by the Federal Aviation Administration (FAA) on 3 September. The replacement was to be completed by 7 January 2010. According to the FAA, in its Federal Register publication, use of the Thales model has resulted in reports of airspeed indication discrepancies while flying at high altitudes in inclement weather conditions, that could result in reduced control of the airplane. The FAA further stated that the Thales model probe has not yet demonstrated the same level of robustness to withstand high-altitude ice crystals as Goodrich pitot probes P/N 0851HL.

On 20 December 2010, Airbus issued a warning to roughly 100 operators of A330, A340-200 and A340-300 aircraft, regarding pitot tubes, advising pilots not to re-engage the autopilot following failure of the airspeed indicators. Safety recommendations issued by BEA for pitot probes design, recommended that they must be fitted with a heating system designed to prevent any malfunctioning due to icing. Appropriate means must be provided (visual warning directly visible to the crew) to inform the crew of any non-functioning of the heating system.

Findings from the flight data recorder

On 27 May 2011, the BEA released an update on its investigation describing the history of the flight as recorded by the flight data recorder. This confirmed what had previously been concluded from post-mortem examination of the bodies and debris recovered from the ocean surface: the aircraft had not broken up at altitude but had fallen into the ocean intact. The flight recorders also revealed that the aircraft’s descent into the sea was not due to mechanical failure or the aircraft being overwhelmed by the weather, but because the flight crew had raised the aircraft’s nose, reducing its speed until it entered an aerodynamic stall.

While the inconsistent airspeed data caused the disengagement of the autopilot, the reason the pilots lost control of the aircraft remains something of a mystery, because pilots would normally try to lower the nose in case of a stall. Multiple sensors provide the pitch (attitude) information and there was no indication that any of them were malfunctioning. One factor may be that since the A330 does not normally accept control inputs that would cause a stall, the pilots were unaware that a stall could happen when the aircraft switched to an alternate mode due to failure of the airspeed indication.

In October 2011, a transcript of the voice recorder was leaked and published in the book Erreurs de Pilotage (Pilot Errors) by Jean Pierre Otelli. The BEA and Air France both condemned the release of this information, with Air France calling it sensationalized and unverifiable information” that “impairs the memory of the crew and passengers who lost their lives. The BEA would subsequently release its final report on the accident, and Appendix 1 contained an official cockpit voice recorder transcript that did not include groups of words deemed to have no bearing on flight.

Third interim report

On 29 July 2011, the BEA released a third interim report on safety issues it found in the wake of the crash. It was accompanied by two shorter documents summarizing the interim report and addressing safety recommendations.

The third interim report stated that some new facts had been established. In particular:

  • The pilots had not applied the unreliable-airspeed procedure.
  • The pilot-in-control pulled back on the stick, thus increasing the angle of attack and causing the aircraft to climb rapidly.
  • The pilots apparently did not notice that the aircraft had reached its maximum permissible altitude.
  • The pilots did not read out the available data (vertical velocity, altitude, etc.).
  • The stall warning sounded continuously for 54 seconds.
  • The pilots did not comment on the stall warnings and apparently did not realize that the aircraft was stalled.
  • There was some buffeting associated with the stall.
  • The stall warning deactivates by design when the angle of attack measurements is considered invalid, and this is the case when the airspeed drops below a certain limit.
  • In consequence, the stall warning came on whenever the pilot pushed forward on the stick and then stopped when he pulled back; this happened several times during the stall and this may have confused the pilots.
  • Even though they were aware that altitude was declining rapidly, the pilots were unable to determine which instruments to trust: it may have appeared to them that all values were incoherent.

The BEA assembled a human factors working group to analyze the crew’s actions and reactions during the final stages of the flight.

A brief bulletin by Air France indicated that the misleading stopping and starting of the stall warning alarm, contradicting the actual state of the aircraft, greatly contributed to the crew’s difficulty in analyzing the situation.

 

 

2


Building 153, the head office of the Bureau d’Enquêtes et d’Analyses pour la Sécurité de l’Aviation Civile (BEA) at Le Bourget Airport, where the flight recorders were analysed 

Final report

On 5 July 2012, the BEA released its final report on the accident. This confirmed the findings of the preliminary reports and provided additional details and recommendations to improve safety. According to the final report, the accident resulted from the following succession of major events:

  • temporary inconsistency between the measured speeds, likely because of the obstruction of the pitot tubes by ice crystals, causing autopilot disconnection and reconfiguration to alternate law;
  • the crew made inappropriate control inputs that destabilized the flight path;
  • the crew failed to follow appropriate procedure for loss of displayed airspeed information;
  • the crew were late in identifying and correcting the deviation from the flight path;
  • the crew lacked understanding of the approach to stall;
  • the crew failed to recognize that the aircraft had stalled and consequently did not make inputs that would have made it possible to recover from the stall.

These events resulted from the following major factors in combination:

  • feedback mechanisms on the part of those involved made it impossible to identify and remedy the repeated non-application of the procedure for inconsistent airspeed, and to ensure that crews were trained in icing of the pitot probes and its consequences;
  • the crew lacked practical training in manually handling the aircraft both at high altitude and in the event of anomalies of speed indication;
  • the two co-pilots’ task sharing was weakened both by incomprehension of the situation at the time of autopilot disconnection, and by poor management of the startle effect, leaving them in an emotionally charged situation;
  • the cockpit lacked a clear display of the inconsistencies in airspeed readings identified by the flight computers;
  • the crew did not respond to the stall warning, whether due to a failure to identify the aural warning, to the transience of the stall warnings that could have been considered spurious, to the absence of any visual information that could confirm that the aircraft was approaching stall after losing the characteristic speeds, to confusing stall-related buffet for overspeed-related buffet, to the indications by the Flight Director that might have confirmed the crew’s mistaken view of their actions, or to difficulty in identifying and understanding the implications of the switch to alternate law, which does not protect the angle of attack.

 Independent analyses

Before and after the publication of the final report by the BEA in July 2012, there were many independent analyses and expert opinions published in the media about the cause of the accident.

 Significance of the accident

In May 2011, Wil S. Hylton of The New York Times commented that the crash was easy to bend into myth because no other passenger jet in modern history had disappeared so completely – without a Mayday call or a witness or even a trace on radar. Hylton explained that the A330 “was considered to be among the safest” of the passenger aircraft. Hylton added that when Flight 447 seemed to disappear from the sky, it was tempting to deliver a tidy narrative about the hubris of building a self-flying aircraft, Icarus falling from the sky. Or maybe Flight 447 was the Titanic, an unsinkable ship at the bottom of the sea. Dr. Guy Gratton, an aviation expert from the Flight Safety Laboratory at Brunel University, said, This is an air accident the likes of which we haven’t seen before. Half the accident investigators in the Western world – and in Russia too – are waiting for these results. This has been the biggest investigation since Lockerbie. Put bluntly, big passenger planes do not just fall out of the sky.

Angle-of-attack indication

In a July 2011 article in Aviation Week, Chesley Sully Sullenberger was quoted as saying the crash was a seminal accident and suggested that pilots would be able to better handle upsets of this type if they had an indication of the wing’s angle of attack (AoA). By contrast, aviation author Captain Bill Palmer has expressed doubts that an angle-of-attack indicator would have saved AF447, writing: as the PF seemed to be ignoring the more fundamental indicators of pitch and attitude, along with numerous stall warnings, one could question what difference a rarely used AoA gauge would have made.

Following its investigation, the BEA recommended that EASA and the FAA should consider making it mandatory to have an angle-of-attack indicator on the instrument panel. In 2014, the FAA streamlined requirements for AoA indicators for general aviation without affecting requirements for commercial aviation.

Human factors and computer interaction

On 6 December 2011, Popular Mechanics magazine published an English translation of the analysis of the transcript of the cockpit voice recorder controversially leaked in the book Erreurs de Pilotage. It highlighted the role of the co-pilot in stalling the aircraft while the flight computer was under alternate law at high altitude. This “simple but persistent” human error was given as the most direct cause of this accident. In the commentary accompanying the article, they also noted that the failure to follow principles of crew resource management was a contributory factor.

The final BEA report points to the Human Computer Interface (HCI) of the Airbus as a possible factor contributing to the crash. It provides an explanation for most of the pitch-up inputs by the pilot flying (PF), left unexplained in the Popular Mechanics piece: namely that the Flight Director (FD) display was misleading. The pitch-up input at the beginning of the fatal sequence of events appears to be the consequence of an altimeter error. The investigators also pointed to the lack of a clear display of the airspeed inconsistencies even though the computers had identified them. Some systems generated failure messages only about the consequences but never mentioned the origin of the problem. The investigators recommended that a blocked pitot tube should be clearly indicated as such to the crew on the flight displays. The Daily Telegraph pointed out the absence of angle of attack information, which is so important in identifying and preventing a stall. The paper stated that “though angle of attack readings are sent to onboard computers, there are no displays in modern jets to convey this critical information to the crews”. Der Spiegel indicated the difficulty the pilots faced in diagnosing the problem: One alarm after another lit up the cockpit monitors. One after another, the autopilot, the automatic engine control system, and the flight computers shut themselves off. Against this backdrop of confusing information, difficulty with aural cognition (due to heavy buffeting from the storm as well as the stall) and zero external visibility, the pilots had less than three minutes to identify the problem and take corrective action. The Spiegel report asserts that such a crash could happen again.

In an article in Vanity Fair, William Langewiesche noted that once the angle of attack was so extreme, the system rejected the data as invalid and temporarily stopped the stall warnings. However, this led to a perverse reversal that lasted nearly to the impact: each time Bonin happened to lower the nose, rendering the angle of attack marginally less severe, the stall warning sounded again—a negative reinforcement that may have locked him into his pattern of pitching up, which increased the angle of attack and thus prevented the aircraft from getting out of its stall.

 

In April 2012 in The Daily Telegraph, British journalist Nick Ross published a comparison of Airbus and Boeing flight controls; unlike the control yoke used on Boeing flight decks, the Airbus side stick controls give little visual feedback and no sensory or tactile feedback to the second pilot. Ross reasoned that this might in part explain why the pilot flying’s fatal nose-up inputs were not countermanded by his two colleagues.

In a July 2012 CBS report, Sullenberger suggested that the design of the Airbus cockpit might have been a factor in the accident. The flight controls are not mechanically linked between the two pilot seats, and Robert, the left-seat pilot who believed he had taken over control of the aircraft, was not aware that Bonin had continued to hold the stick back, which overrode Robert’s own control.

 

Side-stick control issue

 

AF1

Right-hand side-stick control on an Airbus A380 flight deck (similar to Airbus A330 side-stick)

 

Fatigue

Getting enough sleep is a constant challenge for pilots of long-haul flights. Although the BEA could find no objective indications that the pilots of Flight 447 were suffering from fatigue, some exchanges recorded on the cockpit voice recorder (CVR), including a remark made by Captain Dubois that he had only slept an hour, could indicate that the crew were not well rested before the flight took off. The co-pilots had spent three nights in Rio de Janeiro.

Other incidents

Shortly after the crash, Air France changed the number of the regular Rio de Janeiro-Paris flight from AF447 to AF445. The route still uses Airbus A330-200’s. Six months later, on 30 November 2009, Air France Flight 445 operated by another Airbus A330-203 (registered F-GZCK) made a mayday call because of severe turbulence around the same area and at a similar time to when Flight 447 had crashed. Because the pilots could not obtain immediate permission from air traffic controllers to descend to a less turbulent altitude, the mayday was to alert other aircraft in the vicinity that the flight had deviated from its normal flight level. This is standard contingency procedure when changing altitude without direct ATC authorization. After 30 minutes of moderate-to-severe turbulence, the flight continued normally. The flight landed safely in Paris six hours and 40 minutes after the mayday call.

Inaccurate airspeed indicators

There have been several cases where inaccurate airspeed information led to flight incidents on the A330 and A340. Two of those incidents involved pitot probes. In the first incident, an Air France A340-300 (F-GLZL), en route from Tokyo to Paris experienced an event at 31,000 feet (9,400 m), in which the airspeed was incorrectly reported and the autopilot automatically disengaged. Bad weather, together with obstructed drainage holes in all three pitot probes, were subsequently found to be the cause. In the second incident, an Air France A340-300 (F-GLZN), en route from Paris to New York, encountered turbulence followed by the autoflight systems going offline, warnings over the accuracy of the reported airspeed and two minutes of stall alerts.

Another incident on TAM Flight 8091, from Miami to Rio de Janeiro on 21 May 2009, involving an A330-200, showed a sudden drop of outside air temperature, then loss of air data, the ADIRS, autopilot and autothrust. The aircraft descended 1,000 metres (3,300 ft) before being manually recovered using backup instruments. The NTSB also examined a similar 23 June 2009 incident on a Northwest Airlines flight from Hong Kong to Tokyo, concluding in both cases that the aircraft operating manual was sufficient to prevent a dangerous situation from occurring.

Following the crash of Air France 447, other Airbus A330 operators studied their internal flight records to seek patterns. Delta Air Lines analyzed the data of Northwest Airlines flights that occurred before the two companies merged and found a dozen incidents in which at least one of an A330’s pitot tubes had briefly stopped working when the aircraft was flying through the Intertropical Convergence Zone, the same location where Air France 447 crashed.

 

Courtesy of Wikipedia.org

 

 

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