Air France Flight 447
Disappearance Of Air France Flight 447
On June 1, 2009, Air France Flight 447 departed on an overnight flight, from Rio de Janeiro, Brazil destined for Paris, France. The plane carried 228 lives. While crossing the Equator, near the middle of the Atlantic Ocean, the aircraft left radar and voice coverage during what should have been a routine handoff between air traffic controlling agencies. A few hours into the flight, the plane hit bad weather and the aircraft’s Aircraft Communications and Address Reporting System (ACARS) radioed over satellite links a series of system errors indicating a possible failure of the pilot static system. This system supplies critical flight data to the computer. The aircraft ceased communicating shortly afterwards. Immediate and continued efforts to raise the Airbus 330 were unsuccessful. A frantic search and rescue effort was initiated at daybreak the following morning, but AF447 had mysteriously vanished. The disappearance kicked off one of the most exhaustive and technologically sophisticated searches in modern history.
After five days, initial surface searches discovered floating wreckage, and a passive acoustic search was undertaken to detect the Underwater Locator Beacons (ULBs) installed on the two “black boxes” on the aircraft. This search revealed no detections in the beacons’ 30-day battery lifetime, and the Bureau d’Enquêtes et d’Analyses pour la sécurité de l’aviation civile (BEA), the French equivalent to the NTSB, was faced with the difficult question of where to look next.
In July 2009, Metron was engaged by the BEA to help better define the underwater search area. Metron’s expertise in applying Bayesian Search Theory to real world problems, such as the 1968 hunt for the missing submarine Scorpion and the 1986 search for the SS Central America, made us uniquely suited to the complicated underwater search for the missing plane. After examining the available data, talking with experts in Paris, and running computer simulations of the currents in the search area, we formed a prior distribution of the location of the impact point which summed up everything that was known about the incident before search operations began. We then evaluated search efforts to date (both surface search for drifting wreckage and the underwater search for the ULBs) and employed the principles of Bayes’ Theorem to update the prior distribution with the negative search information, generating a posterior distribution probability map. This displayed the likelihood of the locations of the impact point considering all that was known to date. This map was provided to the BEA and was used to assist one underwater search conducted that summer. Additional searches a year later were based on data provided by other sources.
In December 2010, the crash site remained unlocated despite significant (and costly) searches which employed unmanned underwater vehicles (UUVs) with side scan sonar and cameras. The BEA intended to attempt another search the following spring and they turned to Metron to update the probability map. We incorporated the latest search efforts and generated an update to the map. At this point, we also considered another possibility: that the black box beacons had been damaged in the impact and were not functioning when the ULB search had occurred.
The search so far had been exhaustive, assessed to result in a high probability of detection given the presence of a signal to detect. But what if there was no signal present? We re-ran the analysis eliminating the credit originally given to the ULB searches, and generated a new probability map as an alternative. The new map showed high probability areas just north of the last known point of the plane. The BEA conducted their last search in late spring 2011, and within five days the UUVs’ sonar detected a debris field on the bottom at around 10,000′ which was quickly verified to be the wreckage of AF447.
Recovering The Wreckage
Significant portions of the wreckage and remains were recovered in the ensuing salvage operation, and both the Flight Data Recorder and the Cockpit Voice Recorder (the “black boxes”) were recovered. The data that was removed from these units painted a stark picture of equipment failures and confusion in the cockpit during the final moments of the flight. The lessons learned from these data sources have prompted changes in avionics and in pilot training that will help avoid similar disasters in the future.
Metron’s role in the search was summed up by this statement from BEA, “This [Metron] study published on the BEA website on 20 January 2011, indicated a strong possibility for discovery of the wreckage near the center of the circle. It was in this area that it was in fact discovered after one week of exploration …” 1
1. Troadec, Jean-Paul, “Undersea search operations to find the wreckage of the A 330, flight AF 447: the culmination of extensive searches,” note from BEA director, April 8, 2011, on the BEA website at: http://www.bea.aero/en/enquetes/flight.af.447/note.from.bea.director.end.phase4.pdf.