Problems in locating the lost helicopter (equipped with ELT) at dense forest.

[muralishan89]

Dear Friends,

Inspite of Helicopters fitted with Emergency location transmitter (either manual or automatic), why there is delay in finding the exact position of the lost helicopters?

For example- US marine helicopter lost recently in Nepal on May 13 2015 during the relief supply which was found only after two days (15th may).

What makes the delay for satellites to receive a distress signal?

Even though with the sophisticated communication & location finder instruments, what parameters make the delay to find the exact accident spot?

Awaiting for your replies.

Thank you in advance.

With regards,
Muralidharan.

[Reely340]

My guess: ETL signal ist radiowave and nothing more. No GPS data embedded in the signal, You need a bunch of directional antennae around the country and a good knowledge of how their directions and singal receive strengs indicate where the sender might be.

[ericferret]

Modern Beacons such as the HR Smith CPI have a GPS locator signal embedded in the transmission signal. It is actually possible to locate a beacon with little in the way of technical equipment as was proved a several years ago.

A beacon was inadvertantly deployed and landed in a field of standing wheat.
The satellite fix probably gave a search area of about a square mile.
The only location equipment available was a hand held tranceiver tuned to 121.5.
By listening to the signal strength they were able to cut the search area to a couple of hundred square yards. They then retracted the aerial to detune the transceiver further.
They eventually reached a point where they could not determine a direction, looked down and there it was!!!!

Sounds simple, on a hot summers day it was a great effort tramping around the fields and much applauded.

I suspect that weather in the search area and difficult terrain are generally more of a problem than the signals themselves.

[[email protected]]

Eric - not far off a technique we used for audio only beacon homing when needle indications were poor or confusing or the signal was very weak.

Muralishan - depends on what type of beacon it was, most ELTs are now 406 Mhz and have an embedded GPS to give an accurate location to the satellite. Then you use the 121.5 signal also produced to fine tune the position if required once you are really close.

However, the digital hexadecimal transmission can be corrupted (ISTR the position reference is in the second part of the message) and not quite as accurate as expected. It will also depend on the condition of the beacon if it has been in a crash.

[EN48]

ELT's are notorious for failing to operate in a crash, either because they are destroyed or fail to transmit for any of several reasons. The newer breed of COSPAS 406 MHz ELT's are more reliable and some but not all transmit GPS position info within a few meters. Good idea is to carry one or more PLB's (personal locator beacon) in addition to the ELT. These also work on 406 MHz and virtually all have an embedded GPS to transmit position info. These are now quite affordable (about $250 U.S. an up) and a case can be made for having one for each seat in the helicopter. However, PLB's depend on a survivor in a condition to deploy them. Perhaps best of all is a real time satellite based tracking system such as SkyTrac or Spider Tracks (there are many others). These are independent of the aircraft in the sense that if the transceiver in the acft fails to provide a position report every minute (this time interval is adjustable), alert messages are sent from a central monitoring station to a list of user selected parties (SAR, company, girlfriend, etc). Someone will know withing 1-2 minutes that something has happened and where it happened.This kind of system is also quite affordable, with initial equipment cost starting below $1000 and monthly service charges ranging from $30 per month and up depending on usage.

[EN48]

Just some food for thought

Like much else in aviation, helps to know what one is doing. Some training appropriate. Based on the frequencies stated, these do not seem to be COSPAS 406 MHz PLB's, which may not be subject to the same issues. Maybe others here know more about this. One of the benefits of transmitting GPS position via ELT or PLB is that homing may only be necessary for the last few (or few tens ) of meters.

[AnFI]

Consequently, although each antenna was reported to have been correctly pivoted to an angle close to the vertical, the telescopic sections were not extended.

Every uneccessary complexity is an opportunity for human error, poor design to lazily leave the systematic hazards possible (like having six fuel pumps, with switches) KISS

[John R81]

I used to fly with just a PLB. The only one in the aircraft, no chance of conflicting signal, and it stayed with me if separated from the aircraft.

Now mandated to fit ELT to the machine, so risk of conflicting signals, expense, etc.

And where is it mounted - right above the fuel bladder.

[[email protected]]

John - it is only smart ELTs that might inhibit their 121.5 transmission in the presence of a 'dumb' PLB transmitting on the same frequency.

Your ELT will be 406 mHz with a 121.5 transmitter embedded as well - this is because you can't home to a 406 Mhz transmission very effectively as it only does a burst transmission every 50 seconds, unlike a 121.5 beacon which transmits continuously.

121.5 and 243.0 transmissions are not monitored by satellite any more - hence the move to 406 beacons which are.

[evil7]

@EN48

Just to add - the Spidertrack system (for example) features an "SOS" button. Once this is used the position reports are send every 10 seconds!

So if one would have time enough to activate this feature I think you would more or less definately have the last position once the aircraft is down.

[John R81]

Crab


I get that. just don't understand 2 things


1. why I need it to fly around London (single engine machine so no commercial work over the sea) - a PLB should suffice, as it always did previously; and
2. Why locate it by the fuel cell, maximising the chance of it being destroyed just when you might want it to actually do something

[[email protected]]

John - I can't answer 2 but a PLB signal needs monitoring if it going to be of any use and 121.5 isn't monitored by satellite any more. It might still be monitored by ATC units but you would have to be line of sight of one to notice your beacon.

Without an alerting system, any beacon is useless.

[Non-PC Plod]

A PLB won't work unless you are able to activate it. An ELT will go off automatically if you crash

[John R81]

My PLB is 406mhz and 121.5 as you say.


Non-PC Plod - true sometimes; depends on the impact. But then an ELT sinks with the air frame whilst you float about waiting to be rescued.


Not going to solve this one. I am not a strong believer that all machines need to carry an ELT; I would prefer the option of ELT / PLB to suit the use of the machine. I can't have that as I don't write the law, hence ELT is fitted as mandated.

[[email protected]]

You could always carry a personal 406 mhz beacon as well.

[John R81]

Just back in from a day in the sky ..... and that's exactly what I do