Malaysian Airlines plane mystery: how can a flight disappear off radar? Flight MH370s disappearance from tracking could be due to its transponder being stopped deliberately, electrical failure or the planes disintegration Malaysias civil aviation chif Azharuddin Abdul Rahman briefs reporters on the search and recovery Malaysias civil aviation chief Azharuddin Abdul Rahman briefs reporters on the search and recovery efforts. Photograph: Daniel Chan/AP As the search continues for the missing Malaysian Airlines plane, more questions have been asked about how it is possible for a modern aircraft to simply vanish without trace. Some relatives of missing victims are accusing the authorities of withholding information. Theories about what happened remain speculative, but the widening search areas suggest that the authorities are genuinely in the dark about the fate of the plane. How does a plane simply disappear off the radar? Over land, air traffic controllers can use two types of radar, primary, which detects objects by bouncing back a radio signal, and secondary , where the plane sends back an automatic response, identifying itself. Air traffic consultant Doug Maclean, of DKM Aviation, says: Secondary surveillance radar sends out a coded question, the interrogation message will be received and sent back; that requires a degree of co-operation between plane and the ground. In the likes of the 9/11 incident, the aircraft would have received messages but hijackers had switched off the reply. A Vietnamese military helicopter joins the search for flight MH370 A Vietnamese military helicopter joins the search for flight MH370. Photograph: Athit Perawongmetha/Reuters But over longer distances where radar coverage is limited – ie usually when planes are flying across oceans – they use another system, Automatic Dependent Surveillance. Here the aircraft transmits its own signal and gives its position via satellites. Maclean says: Once you go outside primary radar coverage, which would normally be about 100 miles offshore maximum, you are relying on the plane to be transponding. Malaysia Airlines has confirmed its plane had a system called ACARS, or the Aircraft Communications Addressing and Reporting System, which would also automatically alert engineers at base of any mechanical failure. A map of MH370s flight plan is seen on computer screen A map of MH370s flight plan is seen on computer screen. Photograph: Athit Perawongmetha/Reuters So when flight MH370 disappeared from plane tracking websites, it could mean the signals from the planes transponder were stopped deliberately (by pilots or others), or there was a complete electrical failure, or the plane disintegrated. Where the Malaysian plane was flying, the signals are picked up by sites only once a minute and only at a planes cruising height above 29,000 feet. So a dramatic loss of altitude could conceivably also see a plane drop off their radar but potentially continue to travel for some distance.
Posted on: Wed, 12 Mar 2014 14:29:42 +0000
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