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How Plane Crash Forensics Lead to Safer Aviation Read more: Part 1 – Air France Flight 447 – Plane Crash Forensics – Popular Mechanics

April 23, 2012

UPDATE (2:00p.m., April 4): On April 3, French crash investigators—aided by scientists from the Woods Hole Oceanographic Institute in Massachusetts—announced that they had found the remains of Air France flight 447, as well as bodies of some the passengers. According to the Wall Street Journal, this was the fourth mission to hunt for the wreckage of the Airbus 330, which disappeared nearly two years ago after taking off from Rio de Janiero on a flight bound for Paris. This PM special report on the crash and mystery of Air France 447’s whereabouts was published in December 2009.

Seven miles above the empty expanse of the South Atlantic Ocean, on May 31, 2009, an Air France A330 passenger jet cut through the midnight darkness. The plane had taken off 3 hours earlier, climbing from Rio de Janeiro on a northeast heading, its navigation computers hewing to a great-circle route that would take the flight 5680 miles to Paris.

At 10:35 pm local time, one of the co-pilots on the flight deck radioed Atlantico Area Control Center in Recife, Brazil, and announced that the plane had just reached a navigation waypoint called INTOL, situated 350 miles off the Brazilian coast. The waypoint lay just shy of the Intertropical Convergence Zone, a meteorological region along the equator famous for intense ­thunderstorms. Staff at Atlantico acknowledged the transmission and received the airplane’s reply: “Air France Four Four Seven, thank you.”

It was the second time within the past 12 hours that the jet, F-GZCP, had crossed this stretch of ocean, having flown the Paris-to-Rio leg with only 2 hours to refuel and load passengers before departing again. Such was the lot of the four-year-old long-haul plane: a repeated cycle of flight and turnaround, as rhythmic and uneventful as the phases of the moon. But the routine was about to be broken.

After receiving AF 447’s transmission, Atlantico asked for the estimated time it would take the aircraft to reach the TASIL waypoint, which lies on the boundary of the Atlantico and the Dakar Oceanic control areas. At that point communication would pass from Brazil to Senegal. AF 447 did not reply. The controller asked again. Still, there was no reply. The controller asked a third and fourth time, then alerted other control centers about the lapse.

According to the flight plan filed by AF 447, the plane should have crossed into Dakar Oceanic at 11:20 pm, at which point the flight crew would have made radio contact with Dakar to confirm their position. They didn’t. They also failed to contact the Cape Verde controller, whose airspace they were supposed to enter at 12:43 am. As time went on, controllers along the aircraft’s route began to worry that the problem was more than just a communications breakdown.

By 3:47 am, the flight should have appeared on the radar screens of Portuguese air traffic controllers. It didn’t. An hour later, Air France contacted the Bureau d’Enquêtes et d’Analyses pour la Sécurité de l’Aviation Civile (BEA), the French equivalent of the United States’ National Transportation Safety Board. By 8 am, French authorities officially reached what had become a grim, unavoidable conclusion: Air France 447 had disappeared.

Vanishing without a trace is not supposed to happen in this day and age. The globe is crisscrossed by constant ship and air traffic. A constellation of satellites orbits overhead, and communication is nonstop. Yet, for a few days in early June, it seemed that the impossible had happened. Air France 447 and the 228 people onboard were simply gone. There was no distress call or wreckage; there were no bodies.

Within hours, the French government deployed a search-and-rescue airplane near the TASIL waypoint. Over the next few days a flotilla of ships and aircraft arrived to assist the search operation, including a French nuclear submarine and a research vessel withan unmanned deep-water submersible that were dispatched to find the flight data recorder, or black box.

Air France Flight 447 Flight Path

On May 31, at 7:30 pm, Air France 447 leaves Rio de Janeiro on an 11-hour flight to Paris. After 3 hours in the air, the Airbus 330 plunges into a wall of towering storm clouds looming 350 miles off the Brazilian coast. The airplane–with 216 passengers and 12 crew members onboard–never emerges.

Flight 447 Flight Path
8:19 pm
AF 447 contacts air controllers in Recife, Brazil.
9:30 pm
AF 447 passes over the city of Natal, on the Atlantic coast.
10:30 pm
AF 447 reaches INTOL GPS navigation waypoint.
10:35 pm
AF 447 radios final verbal message (to Atlantico Area Control Center): “Air France Four Four Seven, thank you.”
Final Moments
An automatic messaging system onboard AF 447 transmits a torrent of text messages via satellite to the airline’s headquarters in Paris. The 24 encoded texts, reported in just 4 minutes, provide clues about the flight’s final moments.
11:10 pm
The flight control computer receives unreliable sensor data; in response, autopilot disconnects.
11:11-11:12 pm
Speed-limit settings shut down. Safeguards that help pilots prevent rudder damage now fail.
11:13-11:14 pm
Loss of backup instruments that measure pitch angle and velocity. Loss of all internal reference, including heading, vertical speed, flight-path vector and position. Last transmission: a vertical speed advisory, triggered when the cabin drops faster than 30 feet per second.

Yet for days nothing was found. The only clues to the plane’s fate were automatic messages that the onboard maintenance computer transmitted by a datalink system called the Aircraft Communications Addressing and Reporting System (ACARS). The system transmits text messages via satellite to ground stations, which then forward them on land­lines to the intended destination. In just a 4-minute span, the system had broadcast 24 reports to Air France’s dispatch center in Paris, each concerning problems with subsystems onboard the aircraft.

At 11:10 pm, about 35 minutes after AF 447’s last verbal communication, the system sent a message that the autopilot had disconnected. Seconds later, it reported that the flight control system was unable to determine the aircraft’s correct speed. Subsequent messages cited a cascade of other malfunctions. At 11:14 pm, the final message reported that the airliner’s cabin either had depressurized, was moving with high vertical velocity, or both.

ACARS messages are transmitted in a dense alphanumeric code and are used for airplane maintenance, not real-time monitoring of flights by dispatch centers. When investigators realized that the plane was lost, they scrutinized the messages. The story the transmissions told was tantalizing, but inconclusive. Did the error messages suggest a fault in the sensors, or was the flight management system somehow fatally corrupted—perhaps because of a midair lightning strike?

The absence of clues causes concerns that reach beyond the AF 447 investigation. Was the crash a result of pilot error, an unexpected breakdown of vital equipment or a combination of both? Without answers, there is no way to guarantee that another airliner won’t suffer the same fate. 

Read more: Air France Flight 447 – Plane Crash Forensics – Popular Mechanics

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