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ELT DOUBTS

Old 11th Mar 2014, 11:33
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ELT DOUBTS

Hi,

I have a few questions about the ELT.

A plane crashes and then the ELT automatically begins sending a signal, ok.

But somebody has to be listening actively that signal in order to find the plane? or that signal is send it to somebody?

I mean, of course with the malasyan plane, i guess everybody is actively monitoring on 121,5 to see if they can listen up the elt.

but is this signal specifically from that plane?
if an small plane has an accident in the alaska tundra, but no body advert it, will somebody go and look for them?
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Old 11th Mar 2014, 11:54
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Angel 121.5 V 406

The current generation of commercial units --as most aviators will know use 406 which is monitored on a continous basis by sat coverage--121.5 can be used by an asset tasked for search to get a directional fix in a local area--the early ELTS has a very high rate of spurious alarms with a low (relatively) automatic activation in a real emergency-thus continuos monitoring of 121.5 was abandoned--having used 121.5 for training/demo purposes in east Anglia(UK) the response was immediate!----121.5 still has its place alongside the newer technology!

Last edited by Dave Sharpe; 11th Mar 2014 at 18:39. Reason: Bad Grammar!!
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Old 11th Mar 2014, 15:29
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As David Sharpe says, 406MHz distress beacon signals are watched by receivers on geostationary satellites.

But radio waves from a smashed beacon trapped in debris on the seabed do not escape to the surface.
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Old 11th Mar 2014, 20:38
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The 406 MHz beacons will be picked up anywhere and are coded with your boat/plane name, owners name, and contact info. If you buy one and register it, you can expect a call within about 5 minutes of turning it on.
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Old 11th Mar 2014, 20:56
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The 406 beacons are also monitoried by low Earth orbiting satellites (LEOSAR). The next generation of monitors are being installed on navigation satellites (GLONASS, GPS and Gallileo), some of which are already in orbit for the MEOSAR system, set for initial operational capability in 2018.


All you want to know about the international Cospas-Sarsat system (Sarsat = Search and Rescue Satellite Aided Tracking, Cospas = equivalent in Russian) is here: International Cospas-Sarsat Programme
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Old 11th Mar 2014, 23:46
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ELTs are not infallibe. The MH one may not have activated automatically (if the circumstances required its activation) and even if it did, there's no guarantee it worked as advertised. If it is under water it maybe shielded or the antenna / skin where it is mounted may have been torn away in any catastrophic event. The ELT maybe transmitting into a short length of coax that could be physically shorted or now water logged. Some signal maybe transmitted but it would be highly compromised as they are pretty low power anyway at about 5 watts. All speculation of course but a few things that may account for non receipt of a distress beacon signal.
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Old 12th Mar 2014, 02:59
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We installed 406Mhz ELT's on our Falcons; always struck me as odd that our (CAA approved) design allowed the unit to be installed in the tail cone of the aircraft while the antenna was installed in the Dassault approved location at the base of the fin forward of the tailcone...
Given that the tailcone is a removable section of the airframe, in some cases a crash followed by an aircraft break-up and tailcone detachment would almost certainly result in the antenna feeder ripping out of its connector, thus rendering the installation useless...
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Old 12th Mar 2014, 04:14
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Helicopter crashed near NZRA a few years ago. Wreckage rolled on impact into a small gully and lay there inverted.

It took (from memory) about a year to find the wreckage, as the trees & shrubs had closed over the wreckage and the 121.5MHz signal could not escape the metal and soil lying on top of it. This was in a low density populated rural area, not wilderness.

So there you go. ELTs in general, 121.5 or 406, are very useful indeed after a forced landing, but dubious after a serious crash.
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Old 12th Mar 2014, 07:14
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A plane crashes and then the ELT automatically begins sending a signal, ok.
I raised this on the MH370 thread, but we never got an answer.

It is my understanding that there is no requirement for all airliners to have crash ('g') activated ELTs. Many have ELTs in the rear cabin that rely on crew removing and activating them after an accident.

The more modern variants do have (additional) 'g' activated ELTs, albeit the 787 ones were deactivated / removed post the LHR incident, and I do not know if they have been reactivated. Partly comes down to requirements of the country of registration.

So whether the MH370 777 had one I open to ideas?
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Old 12th Mar 2014, 08:00
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NOD

Partly comes down to requirements of the country of registration.
AFAIK it may also be a requirement for overflight of some countries - I seem to recall (can't find definitive source) that we had to have hull mounted ELT's installed in "our" 777's because they became mandatory for overflight of the CIS (or remote parts thereof).
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Old 12th Mar 2014, 12:23
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Unfortunately for MH370, 406 lasts 24hrs & 121.5 lasts 50hrs so they are of no use, debris will be the only thing now. Don't think the black boxes have much range but at least once the location is found they should still be pinging away for the next 3 weeks.
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Old 12th Mar 2014, 12:24
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Thanks a lot for your answers. So next time i hear an ELT on 121.5, better don´t say anything by the freq? because somebody will perfectly now from who is that signal coming?

the process is the same with that breitling watch?
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Old 12th Mar 2014, 13:01
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Please DO report 121.5 MHz ELTs! That is the only way they are discovered now. I have reported a few over the years. In the USA at least the CAP or USCG will hunt them down.
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Old 12th Mar 2014, 13:24
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ULB

@ SMOC
...the black boxes .... should still be pinging away for the next 3 weeks.
Or not! Remember 447 pingers . One disappeared (dauphin/shark/ other ?) and it seems that the other one (recovered) never worked.
But, AFAR I did not see recommendation from French BEA for mandatory periodic controls of these beacons.

Last edited by NeoFit; 12th Mar 2014 at 14:02.
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Old 13th Mar 2014, 00:41
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Anyone know what g force is required to set an applicable ELT off?

Had a quick search but no actual figure found.
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Old 13th Mar 2014, 02:33
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CPI: An ELT that works

The questionable utility of an ELT mounted inside the fuselage is an old issue.

Years ago a solution for remote and oceanic crashes was developed called the "Crash Position Indicator" - essentially an ELT that is mounted in a protective "tumbling airfoil" outside the aircraft. On impact the ELT flies away from the aircraft and can float or have a better chance of not being burned/buried. Some were even connected to the CVR/FDR.

It was a technical success and is still found on some aircraft, especially in the RCAF.

Commercially it was a failure, but events like AF447 and MH370 suggest the CPI may need another look.

Crash position indicator - Wikipedia, the free encyclopedia
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Old 14th Mar 2014, 18:22
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and adding to this post, do black boxes have a signal also? or elt is mounted together?
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Old 14th Mar 2014, 23:04
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^^^The black boxes, as in CVR and FDR, have acoustic pingers for underwater search, but not a radio beacon. An ELT is generally not mounted near them.

Anyone know what g force is required to set an applicable ELT off? Had a quick search but no actual figure found.
For current generation 406 MHz beacons, the activation threshold is 2.3 +/- 0.3 G, with a change in velocity (delta V) of 4.5 +/- 0.5 ft/sec (1.4 m/sec +10%). There is also an impulse curve (acceleration vs time) which must be complied with.

For the US, the requirements are contained in FAA TSO C-126b, "406 MHz Emergency Locator Transmitter, (ELT)" which references for specific requirements, document RTCA/DO-204A "Minimum Operational Performance Standards for 406 MHz Emergency Locator Transmitters (ELT)."

Per RTCA, DO-204A is harmonized with EUROCAE ED-62, "Minimum Operational Performance Specification for Aircraft Emergency Locator Transmitters on 406 MHz AND 121.5 MHz (Optional 243 MHz)" The above numbers were taken directly from DO-204A and ED-62.

Regarding carriage of ELTs, the Cospas-Sarsat program, referenced earlier, publishes document C/S S.007 "Handbook of Beacon Regulations" which "...provides a summary of regulations issued by Cospas-Sarsat Participants regarding the carriage of 406 MHz beacons. It also includes practical information on coding and registration requirements in each country, where such information was made available to the Cospas-Sarsat Secretariat." http://www.cospas-sarsat.org/images/...7_sept2013.pdf
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Old 14th Mar 2014, 23:22
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Folks,
From Australian research of actual accidents, fixed ELT have a better than 95% failure to broadcast a useable signal, most commonly because the aerial or aerial cable is damaged in the crash sequence.
For aircraft that go into the water, the failure rate is 100%, the frequencies used for ELT do not propagate any useful distance in water.
Fixed ELT are a total waste of money.
This is why Australian does not mandate the carriage of fixed ELT, although it mandates an ELT on any aircraft traveling more than 50nm.
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Old 15th Mar 2014, 10:54
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I am totally sure this "accident" will make mandatory some sort of gps localizer. They should have done it after the Air France 5 years ago.
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