2nd Lead (Adds details)

Media speculation on cause of UAV crash rebuffed

[TamilNet, Monday, 24 October 2005, 00:05 GMT]
Media reports that the Unmanned Aerial Vehicle (UAV) belonging to Sri Lanka Air Force (SLAF) that came down in Vanni on 19 October was downed either by radar-guided gun or by an air-borne attack by the Liberation Tigers were mere speculations not backed up by concrete evidence, experts contacted by TamilNet said. A Virginia (US) based science journalist who covers UAV developments, rebuffed a report that quoted a Sri Lanka Air Force official as saying: "engine failure, generator failure and communications failure warning messages appearing simultaneously at Ground control indicated sudden destruction of the UAV caused by enemy action."

The UAV was on a spy mission over Liberation Tigers controlled territory in Vanni district when it crashed in Vignanakulam. While Liberation Tigers have registered a complaint with the Sri Lanka Monitoring Mission (SLMM) that flight of UAV was a violation of Cease Fire Agreement (CFA), reports in Colombo have alluded to the possession of Surface to Air Missiles (SAMs), multiple fixed-wing aircrafts, and laser/radar guided weapons by the LTTE.

"Catastrophic failure of a UAV will likely have destroyed the communication system, disabling the aircraft's ability to send any valid message, including alerts, relating to the UAV status to ground control. In a catastrophic failure scenario it is unlikely for all key systems to fail and only the communication system to function and correctly indicate failure of other units," a military communications expert working for a US firm told TamilNet.

"Especially, military intelligence communications will have several levels of encryption and protection against bit errors in message formats, and anti-jamming measures to retain the ability to recover data in the presence of intruder signals affecting frequency spectra at the physical transmission layer to the ground. Clearly the communication system was functioning as alerts were displayed, and if we assume that the ground receiver code is defect-free, the most likely scenario is that the subcomponents progressively failed until the UAV lost its ability to fly. The real cause of the system failure cannot be conceivably determined from the one piece of information on alerts. However, improper maintenance of the vehicle has commonly been found to be the primary cause of failures in many of these cases," he said.

Experts also cautioned that advanced and expensive surveillance vehicles such as UAVs can also be fitted with robust independently powered audio transmitters which can withstand the 'crash' impact and continue to transmit audio information to ground control.

Although exact mode of air-to-ground communication in Searcher II UAV in the Sri Lankan theatre of operation is not known, cost considerations and limited area of operation point to likely use of Line-of-Sight (LOS) communication system using C-band, 4.5 Mbps link (up to 100 miles) radio for command and control uplink, and analog data downlink providing full color video.

More advanced and costly UHF SATCOM (Ultra High Frequency Satellite Communications) link (16kbps) and Ku band SATCOM (1.544 Mbps) can provide over-the-horizon (OTH) command and control uplink and frame imagery downlink in large theaters of operation.

Close to six aging UAVs have previously been either brought down by LTTE fire or have crashed due to engine failure.

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