ELT on Expermentals

[Danzer1]

I should also add, even if a commercial airliner had an operational 121.5 receiver, most fly between 30-40k feet. So unless they flew directly overhead, they would likely be out of range of a 121.5 transmitters range (approx 6 miles on a good day).

Also should add, there are many ground based devices that give off random 121.5MHz signals - like microwave towers - so many "false alarms" resulting in many being ignored altogether until a plane is reported missing! The main reason for switching to the better 406's.

As a side note, the USCG did not give watercraft a choice - 406's are mandatory for seagoing vessels.

[Timberwolf]

Danzer,

You are way off on how radio transmitters work. All military aircraft are still required to monitor 121.5 and your theory on the 40K thing for airliners is false. If that were the case, satellites would never have been able to monitor 121.5. I don't disagree that 406mhz transmitters are the way to go, but please don't spread trash on a subject you have little knowledge about.

[Renard]

Commercial airlines aircraft usually have two vhf transceivers. One is used for ATC communications and the other monitors ARINC (Aeronautical Radio) which is a private company that connects the individual company with the aircraft) 121.5 is simply not monitored.

[jrevens]

Someone correct me if I'm wrong, but I believe I read that you must use a 406 unit on a new installation. If your aircraft was previously legally airworthy with 121.5, then you can still replace it with a new 121.5 unit, for now. This is in the USA of course.
Also, if your aircraft is a single place machine, you don't need an ELT. That's how it used to be anyway.

[Danzer1]

You are way off on how radio transmitters work. All military aircraft are still required to monitor 121.5 and your theory on the 40K thing for airliners is false. If that were the case, satellites would never have been able to monitor 121.5. I don't disagree that 406mhz transmitters are the way to go, but please don't spread trash on a subject you have little knowledge about.

Really? All 121.5 elt's transmit at between 75 and 100 milliwatts. All 406's transmit at 5 watts - 50 times the power and a hell of a lot more range. Most consider 100 milliwatts to be good for voice clarity at a 1/4 mile at the most. Aircraft at 30-40k feet would have to discern the (weak) tone from other background noise and clutter, and that has been determined to be difficult at best at that altitude. The satellites receivers were designed to pick out the (weak) tone and send it's location back to a ground station. There was over a 90% failure rate (false alarms) due primarily to not being able to discern an emergency tone from clutter/other noise - the main reason they stopped bothering to monitor it!

One of the problems with 121.5's was the satellite had to be very near overhead (and line of sight) to pick up a signal and then forward it to a ground station, hence coverage of only 60% of the earth at any one time and also why it could take up to 6 hours for a signal verification.

121.5 and 243.0 are still "guard" channels and are primarily monitored for VOICE emergency communications (usually transmitted at 5 watts or higher) - not elt's at 100 milliwatts or lower. Ask any SAR agency if they will deploy based on any single 121.5 signal tone. Also ask anyone the effective range (discerned identification of signal or voice) of a 100 milliwatt transmission. Go ahead ask and then get back to us without the snide commentary please.

[Danzer1]

John,

Someone correct me if I'm wrong, but I believe I read that you must use a 406 unit on a new installation. If your aircraft was previously legally airworthy with 121.5, then you can still replace it with a new 121.5 unit, for now. This is in the USA of course.
Also, if your aircraft is a single place machine, you don't need an ELT. That's how it used to be anyway.

Kind of, sort of, but not quite: The FCC's 3rd attempt at an NPRM is in the works and could be made a rule at any time - comments closed last March. If and when passed, it calls for

1, The FCC to stop certifying new 121.5 ELT's immediately (the FAA has already stopped, so that's a mute point).

2, The cease of import of 121.5 ELT's immediately.

3, The stop of sale of all 121.5 ELT's a year after passage of the rule.

4, The transition to a 406 ELT within 8 years of passage of the rule.

So (if and when passed) you'd have a hard time getting a 121.5 and you'd have to have a 406 anyway in no more than 8 years.

No mention if the current NPRM version still exempts single seat aircraft (as is current).

[Peteohms]

"The most common exceptions to the ELT requirements are for aircraft used in training within a 50-mile radius of their base of operations, aircraft used in aerial application (crop-dusters) and aircraft undergoing certification testing. Additionally, an exception is made for operation of an aircraft while the ELT..."

Read more : http://www.ehow.com/list_6021654_air...uirements.html

[Dorsal]

All 406's transmit at 5 watts - 50 times the power and a hell of a lot more range.

Just as a point of reference (my RF is a little rusty but I believe the following to be correct);

Range gets worse at higher frequencies 20log(f2/f1) so 406 MHZ has ~ 1/10 the range at the same power as 121.5 MHZ. Power increases range with the following relationship 10log(p2/p1) so 5 Watts @ 406 MHZ has a little more than twice the range of 100 milliwatts @ 121.5 MHZ (this does not take into account differences in antenna gain).

Other than that I agree with your sentiments on 406 and will eventually change over. The only reason I haven't yet is, like John P, my 121.5 was free and I don't fly over any particularly remote areas.

[bbryan]

Guess I'll be going with the 406 on a new built. At the speed this project has been going the 121.5 will be history. The knowledge share is fantastic. There are some smart folks out there.

[jtpitkin06]

Commercial airlines aircraft usually have two vhf transceivers. One is used for ATC communications and the other monitors ARINC (Aeronautical Radio) which is a private company that connects the individual company with the aircraft) 121.5 is simply not monitored.

I flew the last 23 of my 38 year career with AA. #2 com was used for clearance delivery, ATIS and ramp control when on the ground. In the air it was almost always monitoring on 121.5. There was no need to monitor ARINC frequencies as the ACARS would do that for you on a third VHF receiver or you would get the call via SATCOM. ARINC voice is rarely used when in domestic airspace because the ACARS spits out a paper message or displays it on the FMC.

Center would often ask if we could hear an ELT. If present, we could hear it for 100 miles or more by adjusting the squelch. So airlines do, in fact, listen to 121.5 and can pick up the signal for much further than a few miles. The airlines monitor not just for ELT's, but for voice calls as well. If someone makes an emergency voice call on 121.5 it may be the only signal received. We've already proven that both 121.5 and 406 beacons, as good as they are, don't always activate.

While 121.5 ELT's have limitations they can be picked up by almost any GA aircraft with a VHF radio. None of the radios installed in airliners or my personal aircraft receive 406 MHz. We rely on satellites to do that. Hmmm... how dependable is my satellite TV or internet when it rains?.

So, what do I have in my Kitfox and Cardinal? I have 121.5 ELT's. Why did I put a 121.5 in the Kitfox? Because it was free from someone upgrading their C210. When the current batteries go out of date, I'll probably put the money toward a new 406 as it is obviously a better unit for locating a downed aircraft. As a bonus, the 406 uses D cells which are a whole lot cheaper than the proprietary battery packs. It might take five or six cycles, but the 406 will eventually pay for itself in battery costs.

I would like to add the following suggestions.

1. If you are flying about and not using your radio, don't just turn down the volume... tune it to 121.5 and monitor.

2. If you are going down, broadcast on 121.5 and give your position several times. If you get contact with someone, stay with them. If no contact and/or just before touchdown, activate the ELT with the remote switch. Don't count on that G switch in the orange box to do it for you.

3. If you hear a distress call on 121.5 and either ATC or FSS does not respond, relay the information to ATC.

4. Remember, you do not have to be on fire to use 121.5. If you lose contact with ATC and can't find a working frequency, try 121.5. Some ATC or FSS will probably answer and get you on the correct freq. No fault, no foul.

John Pitkin
Greenville, TX