For three minutes, as a giant airliner began a plunge to its demise in the ocean, the plane sent out a series of frantic messages - 29 of them - alerting its home base that it was in trouble.
They came not from the pilots, who were struggling to control the wildly bucking aircraft, or the black box that later would reveal their crisis when retrieved from the ocean floor.
Those messages in 2009 came through an automatic system known as ACARS - or more formally, the Aircraft Communications Addressing and Reporting System.
That is the system that US officials said provided data indicating that the twin engines on Malaysia Airlines Flight 370 continued to function for as long as four hours after the transponder sending radar signals went dark.
Though the 2009 flight, an Air France Airbus A330 with 228 people on board, crashed into the Atlantic Ocean largely intact, it was five days before a massive search effort turned up significant wreckage.
The transmissions sent via ACARS in that flight's final minutes were error messages that went to Air France's home base, sent there on the assumption that mechanics would correct the problem once the flight arrived.
The aftermath of the Malaysia Airlines disappearance Saturday has been fraught with confusion and contradictory reports. Officials with the airline and the engine manufacturer, Rolls-Royce, denied that they had received messages from the plane's engines indicating that they had continued to operate.
In addition to its radar transponder, which went dark at 1.07am Saturday, and its radio, which fell silent 26 minutes after takeoff from Kuala Lumpur, the plane may have been equipped with three other modes of nonverbal communication.
It could have sent signals via UHF radio, a line-of-sight system that lacks the capacity to see beyond the horizon and seems unlikely to have been effective on the Malaysia flight. It was almost out of range for the radar used by Malaysian air traffic controllers, whose radar also is a line-of-sight system.
It also might have signalled on VHF radio, which bounces off the atmosphere, carrying a less potent signal much farther.
But ACARS provides the best method for a modern aircraft to send short automatic reports on how its systems are functioning. It is a digital datalink that can be transmitted either by radio or via satellite, and was first deployed in 1978 by Aeronautical Radio (ARINC), a division of US aerospace giant Rockwell-Collins.
There are several places to which the data stream can be directed by ACARS: The manufacturer of the plane - for Malaysia Airlines, that's Boeing - the company that built the engines, or the airline operating that plane.
"That gets down to what the airline chooses to have," said a consultant for another aviation engine maker who asked not to be identified so that he could speak candidly.
Malaysia Airlines has not revealed how its data stream is packaged or where it is sent, adding to the confusion over who might have the best available information.
Air France received that information from the 2009 flight directly, but not all airlines do.
"Air France is a big, sophisticated airline with a very advanced maintenance facility in France," the consultant said. "But some of these less-established airlines have power by the hour."
Under that scheme, an engine manufacturer leases the engines to the airline. In that circumstance, the manufacturer is likely to receive engine data directly.
"The deal is that, for every hour you use this engine, you pay us X thousand dollars," he said. "All the maintenance is included in the package. The engine maker's real profit is in the ongoing service/overhaul. They may sell the engine at break-even just to get the ongoing business."
All of the corporations involved - Malaysia Airlines, Boeing and Rolls-Royce - have reason to be circumspect about the data they release publicly. The history of aviation liability is replete with lawsuits filed against all parties involved in a disaster.
One notable example is the 1997 crash of a SilkAir flight in Indonesia that killed 104 people.
Although the US National Transportation Safety Board concluded that a suicidal co-pilot intentionally caused the crash, families brought suit against Boeing in a California court, claiming the cause was a rudder-control defect. They won an out-of-court settlement with the company.
- Washington Post