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What Is An ELT Signal?  
User currently offlineUAL747 From , joined Dec 1969, posts, RR:
Posted (4 years 3 months 2 weeks 1 day 9 hours ago) and read 10598 times:

I just flew from DEN to MCO today, and was listening to Channel 9. Several times during the flight, our pilot radioed center saying he was picking up a really strong ELT signal. One was when we were under Kansas City Center, the other was under Atlanta Center. When he reported it to ATL, center replied that she had gotten a lot of those reports today.

So what is an ELT, what makes it strong (or weak), and what does it have to do with my aircraft?

UAL

22 replies: All unread, jump to last
 
User currently offlinejetfuel From Australia, joined Jan 2005, 2227 posts, RR: 0
Reply 1, posted (4 years 3 months 2 weeks 1 day 9 hours ago) and read 10590 times:

Emergency Locator Transmitter.

It may have been activated accidentally, not uncommon



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User currently offlinemodesto2 From United States of America, joined Jul 2000, 2815 posts, RR: 5
Reply 2, posted (4 years 3 months 2 weeks 1 day 9 hours ago) and read 10569 times:

ELTs transmit a signal on "guard" frequency 121.5. When pilots tune this frequency on their VHF radios, they can hear an ELT signal if they're close enough. The strength of the signal is dependent upon distance, obstacles, etc... In a worst case scenario for example, a plane may have crashed, and the ELT would then emit a signal. Pilots who are tuned to the guard frequency would hear this signal and could help rescue crew triangulate the position of the beacon (and associated crash).

When I was flying with the airlines, air traffic controllers would occasionally ask us to tune 121.5 and listen for a possible signal.


User currently offlineJBirdAV8r From United States of America, joined Jun 2001, 4491 posts, RR: 21
Reply 3, posted (4 years 3 months 2 weeks 1 day 9 hours ago) and read 10559 times:

Many (most?) flight crews and ALL ground stations monitor the "guard" frequency, 121.5 MHz. It's pretty much the emergency frequency. It's mostly used to get in touch with aircraft that have missed a frequency change, warn aircraft of restricted airspace, etc.

It's also the channel where Emergency Locator Transmitters (ELT's) broadcast their emergency signal. Sounds like a siren. Some ground stations and search and rescue aircraft have direction finding equipment that can help them pinpoint the location of the signal.

An ELT can be activated accidentally (due to a hard landing or broken switch), accidentally switched on by the pilot, or in the event of an actual crash. Unfortunately, I've heard ELT's going off in all those cases.

Us "normal" guys can sometimes give the controllers a better idea of the transmitter's location. If it's weak and barely breaks squelch, then gets stronger and clearer, we know we're likely headed closer to it. If it's very strong, we might be on top of it--or very close by.

[Edited 2010-08-10 20:16:42]


I got my head checked--by a jumbo jet
User currently offlinealphaomega From United States of America, joined Aug 2005, 581 posts, RR: 0
Reply 4, posted (4 years 3 months 2 weeks 1 day 9 hours ago) and read 10559 times:

Basically an emergency locator beacon that is activated when an aircraft (usually small like Cessna 172) crashes (or is jolted hard), so it makes it easier for search and rescue crews to locate it. Most ELTs and EPIRBs (personal locators) transmit on 406 or 121.5 - 121.5 is monitored by most aircraft (also referred to as guard) which is why it is picked up by airliners or anyone else listening. Search and rescue teams and Civil Air Patrol (in the US) aircraft have direction finding equipment that can read the "strong" signal and direct them to the crashed aircraft.

Even more common, a student pilot will have a hard landing and forget to check the ELT is not transmitting after parking, and it is heard by a lot of people.

Maintenance hangars are also frequently at fault for errant ELTs.


User currently offlineCorey07850 From United States of America, joined Feb 2004, 2528 posts, RR: 5
Reply 5, posted (4 years 3 months 2 weeks 1 day 8 hours ago) and read 10511 times:

One fun task I had during my airport management internship was to locate the offending ELT going off at the airport I worked with. We would get a call from the tower saying they were picking up an ELT on the field and asked for us to check it out. What we would do is take a small handheld radio and tune it to our ground frequency of 121.9. After this we would take the radio and drive around the airport waiting for the sound of the ELT to bleed over on 121.9 (since the transmitter is so strong, when you get close enough you will pick it up). It's always fun to go up to a mx guy and tell them their ELT is going off. Even more fun was to turn the radio on with the ELT blasting when they didn't believe you

User currently offlineKELPkid From United States of America, joined Nov 2005, 6428 posts, RR: 3
Reply 6, posted (4 years 3 months 2 weeks 1 day 8 hours ago) and read 10491 times:

One little-known fact about ELT's:

Many amateur radio repeaters in the USA also monitor 121.5, and and ELT activation will be reported to all repeater users (I'm also a ham   ). 90% of the time, the activation was accidental, and had nothing to do with an aircraft accident.

For testing purposes, the rules are that it can be intentionally activated for 1 minute starting at 5 past the hour...



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineMarkHKG From United States of America, joined Dec 2005, 960 posts, RR: 2
Reply 7, posted (4 years 3 months 2 weeks 1 day 7 hours ago) and read 10472 times:

Just as an additional mention, if the ELT is equipped as a 406 MHz ELT, it will usually do two things:

- The 406 Mhz transmission is sent to a system of satellites out in space called the COSPAS-SARSAT system. Part of this system can figure out the general location by using "doppler shift" giving accuracy of up to 5 square kilometers. Some ELTs are equipped to also send out GPS location, which increases the location accuracy to mere meters. The transmission also sends out a code of numbers that helps rescue organizations determine who the ELT is registered to - helpful since an ELT signal could be from a ship's distress beacon, hiker personal locator beacon, etc.

- It will also emit a 121.5 Mhz "homing" signal for search and rescue teams to pinpoint the location once they arrive. This is what you hear on the 121.5 channel. A demo of the homing system (and figuring out where it is) can be seen here: http://www.youtube.com/watch?v=vO4b_UhM3Cw

- Military transmitters can emit a 243 Mhz homing signal



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User currently offlineBlueJuice From United States of America, joined Jun 2010, 250 posts, RR: 0
Reply 8, posted (4 years 3 months 2 weeks 1 day 7 hours ago) and read 10470 times:

ELTs can be tested during the first 5 minutes of each hour.

My CFI always told me to wait until 6 minutes after the hour to have an accident.  


User currently offlinebri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 9, posted (4 years 3 months 2 weeks 23 hours ago) and read 10368 times:

Since airliners cruise at such a high altitude, and VHF radios are line-of-sight, they can pick up ELTs over a huge area. Unfortunately, this doesn't do much to help ATC narrow down the specific location.

When I was training for my PPL, I was on a solo cross-country flight and receiving flight following from Denver Approach. As I got near one of my planned touch-and-go spots, GXY, the controller told me they had just heard a report of a crash in the area and asked if I would be willing to tune 121.5 and fly over the suspected location to listen for an ELT beacon. I skipped the touch-and-go and gladly obliged, spending about 20 minutes criss-crossing the position the controller gave me. I saw some smoke but it turned out to be a farmer burning weeds out of a ditch, and I never heard the ELT. Eventually I had to continue so my fuel planning worked out. I never heard if there was actually a crash or if it was located.

I also heard a student pilot on the radio one day who could barely hear ground control telling him to taxi into parking. When he would transmit, you could hear the characteristic "bwee bwee bwee" of his ELT going off. I'm guessing his last landing was not exactly a 10, but no one had ever taught him about an ELT (shame on his instructor I guess). He kept trying to shout into the mic to the controller, "we're having some trouble with the radios!" Someone must have clued him in because by the time he got back to the club's line it had stopped.



Position and hold
User currently offlineChese From United States of America, joined Sep 2006, 29 posts, RR: 0
Reply 10, posted (4 years 3 months 2 weeks 22 hours ago) and read 10351 times:

I have just a little to add on the ELT for those interested. FAR 91.207 covers ELTs and they have to be tested every year. We test that the G-switch in the unit works and that the pilot can operate it from the cockpit. The ELT itself is orange like the flight recorder and has its own battery. With the newer 406 ELTs we verify it transmits the extra information such as the HEX code and the actual tail number of the aircraft. Most ELTs that go off are probably tests that didn't manage to turn off the transmitter I bet.


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User currently offlinexero9 From Canada, joined Feb 2007, 155 posts, RR: 0
Reply 11, posted (4 years 3 months 2 weeks 19 hours ago) and read 10306 times:

Quoting MarkHKG (Reply 7):
For testing purposes, the rules are that it can be intentionally activated for 1 minute starting at 5 past the hour...

I thought it was within the first 5 minutes of the hour, and only for a maximum of 5 seconds? If what you said was true, then you can test it for 55 minutes out of every hour  


User currently offlineLarshjort From Denmark, joined Dec 2007, 1506 posts, RR: 0
Reply 12, posted (4 years 3 months 2 weeks 17 hours ago) and read 10277 times:

Quoting xero9 (Reply 11):
I thought it was within the first 5 minutes of the hour, and only for a maximum of 5 seconds? If what you said was true, then you can test it for 55 minutes out of every hour

AFAIK it is a maximum of three sweeps which is about 4-5 seconds.Once got a call from the tower who said they had a frenchman in the telephone asking if he could see the crashed aircraft. Yjat was during one of our first 406 mhz installations.

/Lars

[Edited 2010-08-11 12:12:22]


139, 306, 319, 320, 321, 332, 34A, AN2, AT4, AT5, AT7, 733, 735, 73G, 738, 739, 146, AR1, BH2, CN1, CR2, DH1, DH3, DH4,
User currently offlineetherealsky From United States of America, joined Apr 2010, 328 posts, RR: 0
Reply 13, posted (4 years 3 months 2 weeks 13 hours ago) and read 10220 times:

One of the disadvantages of the simple 121.5 MHz units becomes apparent in mountainous terrain. I've heard stories of rescuers out in the Rocky Mountains hearing ELTs loud and clear but being unable to locate crashes quickly because the signal just bounces back and forth off of the mountainsides, making it extremely tough to accurately triangulate down in the valleys - another good reason to file a flight plan while flying in the mountains.

Quoting alphaomega (Reply 4):
Even more common, a student pilot will have a hard landing and forget to check the ELT is not transmitting after parking, and it is heard by a lot of people

Yikes, how hard is 'hard' ? I've watched a Skyhawk landing in person (well, actually more like a series of 5 touch and go's in rapid succession) that caused a tailstrike and broke the bulb in the beacon light, and even that didn't set his ELT off. Maybe it's more common with planes with oleo strut main gear and not the springy Cessnas?

[Edited 2010-08-11 16:06:12]


"And that's why you always leave a note..."
User currently offlinexero9 From Canada, joined Feb 2007, 155 posts, RR: 0
Reply 14, posted (4 years 3 months 2 weeks 8 hours ago) and read 10148 times:

Quoting etherealsky (Reply 13):
Yikes, how hard is 'hard' ? I've watched a Skyhawk landing in person (well, actually more like a series of 5 touch and go's in rapid succession) that caused a tailstrike and broke the bulb in the beacon light, and even that didn't set his ELT off. Maybe it's more common with planes with oleo strut main gear and not the springy Cessnas?

From what I heard at my flight school, some time ago they had some pretty sensitive ELTs. They apparently would some times be set off during a bumpy landing. They've also apparently been replaced. I've had a couple hard landings, but didn't set it off.

One thing I wonder though, is if I'm doing say 5 circuits and I have a hard enough landing on my first go that it sets off the ELT, the checklist doesn't have me check it until I park the plane. I might be flying around for over an hour with the ELT going off! You'd think it would be part of the post-landing checklist.


User currently offlinebri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 15, posted (4 years 3 months 1 week 6 days 19 hours ago) and read 10061 times:

Quoting xero9 (Reply 14):
I might be flying around for over an hour with the ELT going off!

I've never had to test one because my club is rigorous about having maintenance done. But the one guy I saw who landed hard and had it going off could definitely hear it bleeding over into his comm radios. If you're doing TnGs, even at a non-towered airport, you're on the radio a lot (hopefully) so I would think you'd hear it.



Position and hold
User currently offlineN243NW From United States of America, joined Jul 2003, 1639 posts, RR: 20
Reply 16, posted (4 years 3 months 1 week 5 days 10 hours ago) and read 9950 times:

Quoting xero9 (Reply 14):
I might be flying around for over an hour with the ELT going off!

An hour for 5 circuits? You must fly a wide pattern 

I always flip from Ground to Guard/121.5 on Comm 2 for a couple seconds once I enter the non-movement area after landing, but you're right...if my first landing is a bone-jarrer (especially with the stiff oleo struts Piper uses), I may not find out until after all my pattern work's done.

One of my instructors suggests keeping ATIS and Guard switchable in Comm 2 (if you have one) and always having Comm 2 enabled at low volume during flight, so any ELT signal would be immediately apparent through the headset. And when you're approaching the airport, simply press the flip-flop button and you've got instant ATIS, then flip back to Guard once you're done copying.



B-52s don't take off. They scare the ground away.
User currently offlinexero9 From Canada, joined Feb 2007, 155 posts, RR: 0
Reply 17, posted (4 years 3 months 1 week 4 days 18 hours ago) and read 9886 times:

Quoting bri2k1 (Reply 15):
I've never had to test one because my club is rigorous about having maintenance done. But the one guy I saw who landed hard and had it going off could definitely hear it bleeding over into his comm radios. If you're doing TnGs, even at a non-towered airport, you're on the radio a lot (hopefully) so I would think you'd hear it.

Interesting, I've never heard one go off so I didn't realize it would bleed off in to the neighboring frequencies. Makes sense though.

Quoting N243NW (Reply 16):
An hour for 5 circuits? You must fly a wide pattern

Haha, no not incredible wide :P The airport I fly at is quite busy though, so you waste a lot of time on the ground. A couple of days ago I did 2 take offs and landing with an aborted approach, and it was close to 50 minutes. The queue to take off was consistently 5-6 planes  


User currently offlineN243NW From United States of America, joined Jul 2003, 1639 posts, RR: 20
Reply 18, posted (4 years 3 months 1 week 4 days 9 hours ago) and read 9820 times:

Quoting xero9 (Reply 17):
Interesting, I've never heard one go off so I didn't realize it would bleed off in to the neighboring frequencies. Makes sense though.

It's especially easy to hear if you're using an old or inexpensive radio system. Heck, I went flying with my friend a couple months ago in his 1982 Cessna and we were able to hear the local Top 40 radio station bleeding over into his nav radio when he set it to 108.0.



B-52s don't take off. They scare the ground away.
User currently offlineHAWK21M From India, joined Jan 2001, 31702 posts, RR: 56
Reply 19, posted (4 years 3 months 1 week 3 days 4 hours ago) and read 9734 times:

Heard a Test to the ELT need to be performed 5 mins to the Hour,unless specific permission is obtained from ATC for the test at other times.
Can Anyone clarify.
regds
MEL.



Think of the brighter side!
User currently offlinebri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 20, posted (4 years 3 months 1 week 2 days 22 hours ago) and read 9703 times:

Quoting HAWK21M (Reply 19):

Well MEL, "out here" as you might say, in the US, it's the first 5 minutes of any hour. That is, between 12:00 and 12:05, or 1:00 and 1:05, etc. No more than three sweeps should be performed during the test. Testing other times is permitted after prior coordination with the local ATC facility or FSS.

FAR 91.207 describes the requirements of how often to test and replace an ELT, but doesn't specifically refer to the "first 5 minutes" thing. Maybe that's just an AIM issue? I don't have the book in front of me to provide the reference.

I did learn that most ELTs require a 9G impact to trigger when armed for normal operation. 9G's! There's a formula to calculate the necessary vertical speed to produce 9 G's based on the time of deceleration (how springy the gear is) and the weight of the plane, but suffice it to say it's a lot!



Position and hold
User currently offlineAirstairFear From United States of America, joined Nov 2009, 82 posts, RR: 0
Reply 21, posted (4 years 3 months 1 week 2 days 20 hours ago) and read 9677 times:

Quoting bri2k1 (Reply 20):

FAR 91.207 describes the requirements of how often to test and replace an ELT, but doesn't specifically refer to the "first 5 minutes" thing. Maybe that's just an AIM issue? I don't have the book in front of me to provide the reference.

Yeah I can't find it either. But it's on the written test; good enough for me.

And since it hasn't been mentioned yet: No matter how good of an idea it may seem, you may not test ELTs in flight regardless of the time of day.



CAM-1: Aw #. We're gonna hit houses dude.
User currently offlineLarshjort From Denmark, joined Dec 2007, 1506 posts, RR: 0
Reply 22, posted (4 years 3 months 1 week 2 days 16 hours ago) and read 9636 times:

What is the rules regarding installation of ELT's in GA aircraft around the world? In Denmark it is mandatory to have either a handheld or a fixed 406 mhz unit in the aircraft, except for LSA/ultralight.

/Lars



139, 306, 319, 320, 321, 332, 34A, AN2, AT4, AT5, AT7, 733, 735, 73G, 738, 739, 146, AR1, BH2, CN1, CR2, DH1, DH3, DH4,
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