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Don't ELTs work anymore?

 
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The_Goat
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Joined: 03 Mar 2007
Posts: 2884
Location: South of France

PostPosted: Sun May 01, 2011 11:56 pm    Post subject: Don't ELTs work anymore? Reply with quote

The Arunachal Pradesh CM's helicopter went missing two days ago, and nobody knows where to find it.

http://timesofindia.indiatimes.com/india/No-trace-of-Arunachal-CMs-missing-helicopter-on-Day-2/articleshow/8135324.cms

This is the third incident, the first one involving the AP CM's helicopter, and the second involving the AF A330, where it has taken days to locate the wreckage. Two of those have happened in India. My question is , aren't all the aircraft fitted with ELTs, which should help locate the wreck within no time? If so, why has it taken so long in these three cases?

Can any expert shed some light?
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iflytb20
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Joined: 27 Jan 2007
Posts: 1073
Location: Next to the Airport

PostPosted: Mon May 02, 2011 12:25 am    Post subject: Reply with quote

That depends on what model of ELT was installed.
Quote:
Beacons operating on 121.5 and/or 243.0 MHz simply transmit an anonymous siren tone, and thus carry no information to SAR agencies. Such beacons implicitly rely on the doppler location detection system, or on terrestrial or aeronautical monitoring of the frequency.


So if the chopper was fitted with an older model, it would transmit on 121.5/243 for 24-48 hours [until the battery ran out] and the searcher will have to listen to the tone and use a "hot or cold" type of method to locate it.

Modern system have ELT transmitting on 406Mhz and they :
Quote:
contains the information such as:

*which country the beacon originates from
*a unique 15-digit hexadecimal beacon identification code (a "15-hex ID")
*the encoded identification of the vessel or aircraft in distress, either as an MMSI value, or as, in the case of an ELT, either the aircraft's registration or its ICAO 24-bit address (from its Mode-S transponder)
*when equipped, a GPS position
*whether or not the beacon contains a 121.5 MHz "homer"


Earlier the 121.5 and the 243 Mhz transmission could be located using satellites but this has ceased since 01 Feb 2009.

PS: All the above quotes are from Wiki
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