SEATTLE: The Malaysian Airlines 777 that has been missing for nearly a week was not tracked for hours by engine maker Rolls-Royce after losing touch with air traffic control, contrary to a report in Thursday’s Wall Street Journal, according to a person knowledgeable about the details.
The Journal reported that “aviation investigators and national security officials believe the plane flew for a total of five hours” based on their knowledge of data automatically downloaded and sent to the ground from the jet’s Rolls-Royce engines as part of a routine maintenance and monitoring program.
On Thursday the Journal revised its story online to say the theory that the plane continued flying for hours was not based on engine monitoring data but on “analysis of signals sent by the … 777’s satellite-communication link designed to automatically transmit the status of some onboard systems to the ground.”
The person with knowledge of the details said no engine transmissions occurred after the plane lost contact with air traffic control, less than an hour after takeoff from Kuala Lumpur on its way to Beijing.
The person, who is familiar with the flight and engine monitoring technology aboard 777s, said data from the jet’s engines is not streamed continuously in flight.
While the technology on newer generation airplanes allows more continuous, real-time tracking of engine performance, the person said that the mid-1990s technology used to monitor the 777 engines does not.
Instead, it sends out only a few short bursts of data about the engine’s performance-measurement of such things as the engine core temperature, the shaft speed, the fuel flow and the condition of the oil _ at a few pre-determined points in the flight: at takeoff, during climb, once during cruise and then upon landing.
The data is relayed to the ground using the standard Aircraft Communications Addressing and Reporting System (ACARS) system, which is a digital datalink system that transmits via a network of VHF ground radio stations or satellite communications.
Earlier Thursday in Kuala Lumpur, Malaysia’s Acting Transport Minister Hishammuddin Hussein, cited both Boeing and Rolls-Royce officials in claiming that the last transmission of engine performance data was at 1:07 a.m. local time on March 8.
Radar contact with the plane was lost at 1:20 a.m.
But the lack of engine data transmissions does not rule out the possibility that the plane did indeed fly on for some considerable time after contact was lost.
The ACARS system could have separately transmitted airplane systems data, which is what the Journal now cites as the reason investigators believe the plane continued to fly.
The revised Journal story cites periodic contacts with this system that “indicate to investigators that the plane was still intact and believed to be flying.”