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testing a 406 mhz ELT

wireweinie

FOUNDER
Palmer, AK
We are all familiar (or should be) with FAR 91.207 (d) (1) through (4)

(d) Each emergency locator transmitter required by paragraph (a) of this section must be inspected within 12 calendar months after the last inspection for--

(1) Proper installation;
(2) Battery corrosion;
(3) Operation of the controls and crash sensor; and
(4) The presence of a sufficient signal radiated from its antenna.

(1) Proper installation is pretty straight forward. Is the unit installed as per the manufacturer's instructions. If you need the manual, most are available on line for free. The only thing I would caution is that the 'stiffness' requirements for the tray mount is more than what has been previously acceptable.
(2) Battery corrosion. Again, very straight forward. Evidence of water intrusion? Green or white crusty stuff growing? Especially from the units battery compartment.

Before we get to lines (3) and (4) look back at how we tested the 121.5 mhz ELT's. We took them out of the tray. smacked them and checked to see if the signal bled over onto an am radio next to the antenna. Reset, re install, and done. And it actually worked well! These older units used g-switches for activation. They tripped when an impact of a high enough amplitude was sensed from the front of the unit. As for the signal strength, if a 121.5 mhz signal can be heard on an am radio, when it its tuned off station, that signal will measure strong enough to pass a measured test.

Now for testing these parameters in a 406 mhz ELT.
(3) Operation of controls and crash sensors. The new ELT's use accelerometers, not g-switches as crash sensors. These are designed circuits, not a one off item. And they are designed to trip when they sense a rapid deceleration instead of a high amplitude impact. It means that you can hit it with your hand, a rubber hammer, or bang it on the bench and it won't set the unit off. To set it off, you need to hold the unit in both hands, the forward portion (the arrow) facing away. Without letting go, 'throw' the unit away from you and jerk it back quickly. That motion will trip the accelerometer(s). then reset the unit as per the manuals instructions. This will test the sensors and controls on the unit. The cockpit switch can be tested after the unit is re installed.
(4) The presence of a sufficient signal radiated from it's antenna. Power out. Remember checking for 121.5 mhz with the am radio? It doesn't work for 406 mhz. While a 406 ELT does piggyback a 121.5 mhz signal along with a 406 mhz signal, 406 will not bleed over onto an am radio. To high a freq and most 406 signals are a 'blip' about a second in duration, every 40 to 60 seconds.

This will make some customers howl. The only way to comply with line (4) is with a dedicated test set. This is the rundown on how it's done.

The unit can be tested in the aircraft or on the bench (preferred). On the aircraft, the test set is set up with it's own antenna. The ELT is removed from the tray and power is measured on 121.5 and 406 mhz while the sensors and controls are tested. Read the manual for your exact model. On the bench, the ELT is connected directly to the test set, through an attenuator. A big advantage is that the test may be conducted at any time without pinging the SAR guys. Once again the unit is tested as per the manual for that model.

With either method, signal strength (power out) is actually measured and the controls and sensors are tested. Signal strength is usually given in dbm. For example Artex requires 37 dbm, +/-2 for 406 mhz and 20 dbm minimum for 121.5 mhz. Also all country, hex I.D. and aircraft codes are verified. Without a test set none of these things are possible. Just bought an aircraft? What codes are programmed into the ELT? I've come across wrong country codes and wrong aircraft codes (wrong N numbers) for example. I've also come across units that tested for good power on 121.5 and low power on 406 mhz. And I have not found a manual yet that did not call out a test set/service for the annual inspections.

If the unit was tested on the bench, the antenna (and only the antenna) can be tested by the old am radio test. If you have already bench tested for good signal strength, then if 121.5 mhz goes out over the antenna, 406 mhz will also be good. The antenna is just a piece of wire, after all.

Self test functions tell such info as correct wiring and connections and if the battery has low voltage. But it will not tell you of correct signal strength or codes. If someone relies on the am radio test and self test functions they are not in compliance with 91.207 (d).

You may fire when ready, Gridley

Web

 
How about 406test.com or other testing websites? Do they meet the legal requirement for that portion of the test?
 
As I have a test set, I haven't used one of the online test sites. Anyone else used one? I have to assume that they would meet the requirements, but you know what they say when you 'assume' . . . .

Web
 
This has been an interesting thread. If I had easy enough access to an avionics shop and the test equipment such as Web's I would go there and derive great comfort from actual confirmation.

However, I checked and my local large avionics shop is booked out 5 mos, so I called the manufacturer. My unit has its own internal GPS (it's made by Emerging Lifesaving Technologies). It has a test function built into the remote switch, and includes a GNSS system test. According to the manufacturer, when tested properly and viewing the results, it is indeed both sending out its position and receiving confirmation from satellites. (That's a vast oversimplification of what I was told and may not be 100% accurate.) The upshot though, is that this particular unit self-tests for a ton of parameters and includes everything required by the FARs. Everything that is, except the accelerometer test, which you have to do physically. He did say that if you had the test equipment you would see the actual lat-lon of the unit itself, during a self-test.

The impression I am getting is that the manufacturer can design it's system to self-test whatever it wants. The question of #4 on the list of items required by FAR, apparently is answered in my unit's self-test. However, I think the only truly independent confirmation possible is to take it to an avionics shop and have it done.

According to the mfr of my unit, when self-testing it scrambles the Hex Code in some way so that the SAR authorities know it's only a test. Of course the problem with that is you don't get confirmation that it will transmit the real HEX code in an emergency.
 
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Items like codes transmitted and power out are tested or verified with an external test set. For instance table 6 in the ELT 345 manual shows a flash code that indicates battery use time in excess of 1 hour, battery voltage low, and battery memory error, but no flash codes for low power out. It also lists a flash code for 'missing data' such as no N number or ELT serial number, but it won't tell you which data is not programmed. The ME406 will flash a low power code but there is no spec listed as to just how low before it triggers the code.

I just read through the E.L.T. manual that you referred to for your unit. I found no flash code listed to show low power out. You might want to question the shop further to find out what they based their claim on.

Web
 
Thanks Web.

Also, I just called the contact number of the 406test website. They said its proprietary and in the case of aircraft, only works for Artex ELTs.
 
I assume we're talking about the ELT test during annual inspection here (and not a repair). I don't believe that a power test, bench or radiated. is required, or practical in most cases. The rules for testing a 406MHz unit are different, and accordingly, they have more comprehensive internal test modes.

While you can make a case that you learn something via bench testing, without testing with the installed antenna not much more is really learned.

A 406MHz radiated power test requires a shielded room (a typical hangar is not shielded enough, as several aircraft owners have found to their chagrin). This is different than the 121.5 MHz test, which allows transmission on the hour to 5 minutes after the hour. The differences are due to different treaties regulating transmissions on each frequency.

An annual test of a 406MHz unit requires following the manufacturers instructions, and making up new tests is not required, although I imagine test equipment vendors are happy to imply otherwise.

The following are excerpts from AIM Section 6-2-5, Emergency Locator Transmitter (ELT), dealing with testing, false alarms, and reporting.

Testing
1. ELTs should be tested in accordance with the manufacturer’s instructions. This should be done, preferably, in a shielded or screened room or specially designed test container to prevent the broadcast of signals, which could trigger a false alert.

2. When this cannot be done, aircraft operational testing is authorized as follows:
(a) Analog 121.5/243 MHz ELTs should only be tested during the first five minutes after any hour. If operational test must be made outside of this period, they should be coordinated with the nearest F A A Control T ower or Flight Service Station. Tests should be no longer than three audible weeps. If the antenna is removable, a dummy load should be substituted during test procedures.

(b) Digital 406 MHz ELTs should only be tested in accordance with the manufacturer’s instructions.

(c) Airborne test are not authorized.
----
Using the ACK E-04 as an example, manufacturer instructions for the ACK E-04 require an annual tests comprising:
a) the self test (the same one the owner performs by pushing the button on the remote panel) and
b) the g-switch test, which requires monitoring 121.5. (less than 30 sec, which prevents the 406MHz transmit burst)

There is no mention of a 406MHz radiated test or a bench test.
 
91.207 (d) (1) through (4) have NOT changed. And I didn't make it up. Line (4) specifically requires testing for "the presence of a sufficient signal radiated from it's antenna". Makes no difference if the signal is 121.5 or 406 mhz.

The ACK E0-4 manual does not address FAR requirements. They simply call out the self test as per section 9. Page 10 only states that the self test 'verifies that major ELT systems are functioning properly'. Page 15 gives the required power at a 50 ohm load (antenna or attenuator) should be 37.3 dbm at 406 mhz.

We can argue about how to test for power out but not whether the test is required. It's written right there in the regs.

Web
 
WW, you're making my point. Bench testing does not test for the presence of a radiated signal. Testing a burst transmitter for a radiated signal is difficult, and in the case of 406Mhz, requires a shielded test facility, which is impractical. I concede there is arguably differing guidance between the various publications, but your proposal doesn't fix the problem.

What does fix the problem is following the manufacturer's guidance for continue airworthiness, which is what 99% of the IAs are doing right now.
 
Stay with me here.
Bench testing the elt will verify power, codes, etc. Reinstall it and do the 121.5/am radio test. If the antenna then radiates enough power for the 121.5 test it's radiating well on the 406 mhz side also. The antenna will not radiate one freq without the other. It's a case of works/doesn't work. But if you don't some how verify the ELT before you reinstall it, you'll never know if the 406 side worked at all.
And you don't need to use a shielded room if you choose to test the system as installed on the aircraft. Set up your test set and wait until the top or bottom of the hour and test it like any other ELT.
The rules have not changed, only the frequency.

Web
 
So I am testing an Artex ME406, per their instructions I don't have to test the 406 part. Only way to test the 406 side is with some high dollar test equipment.I figure that is because 406 is not required in the US. I test the G-switch and it doesn't work. Call and leave message, no call back. Call this morning as soon as they open and I tell the guy what the problem is. he asks how I tested it and after I tell him he says ok $450 flat rate repair. Fill out all kinds of forms and waiting on an RMA.

The 406 self testing capabilities and the personal service from Emerging Lifesaving Technologies looks better and better to me.
 
And for a few bucks more than the flat repair fee you could buy a new ACK E04 that allows GPS enabling. Fixing that ME406 is throwing good money after bad. That isn't easy to say since I still have an ME-406 myself. It made sense when I bought it but it's not up to snuff with the current ELTs on the market.
 
And for a few bucks more than the flat repair fee you could buy a new ACK E04 that allows GPS enabling. Fixing that ME406 is throwing good money after bad. That isn't easy to say since I still have an ME-406 myself. It made sense when I bought it but it's not up to snuff with the current ELTs on the market.
I agree, only extra cost is the installation.
 
Ever since our last go around on this subject wireweinie I contacted the avionics people at my company because we have a fleet of Airbus aircraft with Kannad ELT's installed in them. They told me the Kannad procedures fully comply with the 91.207. The voltage test is the check for battery condition and corrosion and pressing the self test fully tests for radiated signal. This is because the self test checks both the 406 and 121.5 side. In effect, the self check looks to see if the 406 signal is correct and appropriate but it is stunted at the output jack, but by hearing the 121.5 signal you are assured of continuity all the way to the antenna. I was informed that the entire fleet is maintained in accordance with the Kannad SB, and while we posses a test cell it is only used for verification of repair and not for annual checks. We have about 300 of these units (and about 2000 406 elts). I am sure if it were not compliant the FAA would have been all over us.
 
FAA requirements are minimalist. Thy don't require checking the 406 side.

A. United States
1) In accordance with FAR Part 91, Subpart C, § 91.207 (d), the ELT must be inspected within 12 calendar months after the last inspection for:
a) Proper installation;
b) Battery corrosion;
c) Operation of controls and crash sensor; and
d) The presence of a sufficient signal radiated from its antenna.
2) All maintenance shall be performed in accordance with FAR Part 43, Appendix D, which requires the following inspections at each annual or 100-hour inspection:
a) ELT and mount for improper installation (see Figure 25 Velcro Strap Installation & Inspection on page 61);
b) Wiring and conduits for improper routing, insecure mounting, and obvious defects;
c) Bonding and shielding for improper installation and poor condition; and
d) Antenna, including trailing antenna, for poor condition, insecure mounting, and improper operation.

A. Checklist
1) Table 5 provides a list of the ELT inspection and testing requirements, a copy of which may be used as a checklist to verify inspection and test completion. The item numbers in the table correspond to the item identifiers for each task.
NOTE: Items 5a through 5h are mandatory requirements only in Canada, in addition to meeting the other inspection and test requirements listed in Table 5.
ITEM NO.
DESCRIPTION
BY
1
Coax Cable and Wiring Connections Inspection
2
ELT Mounting Tray and Hardware Inspection
3
ELT Battery Pack Inspection
4
G-Switch Functional Check
5a
121.5 MHz Frequency Measurement
5b
Audio Modulation Check
5c
121.5 MHz Power Output Measurement
5d
406 MHz Frequency Measurement
5e
406 MHz Power Output Measurement
5f
Current Draw Test
5g
Digital Message Verification
5h
ELT Reset Check

6
Installed Transmitter Test
7
Antenna Test
8
Inspection and Test Documentation
Table 5 ELT Inspection and Test Checklist
 
Ya'all do what you need to.

Line d) 'Presence of a sufficient signal radiated from it's antenna' is where I have issue. To me that means measuring power out. Not power on a circuit card assembly but on the output line, such as to an antenna or into a dummy load. And there is no line stating that this applies only to 121.5 mhz.

I'm happy for the companies that somehow got a fed to let them not strictly comply with this requirement. Especially since we all know that they couldn't possibly be wrong (sarcasm!!!). To me the FAR requirements trump even the manufacturer's requirements. Lines a) through d) are basic common sense checks of a safety item. My bottom line is that I would not send out an ELT to ANY of you without performing these checks to the best of my abilities.

I'm done and out.

Web
 
Not sure what the cost is for other test sets but I paid around $3K for mine. It's one I had worked with and is easy to use. Obviously individuals users are not going to shell out that kind of money. (i.e. I have a $600+ multi meter that I use on a daily basis, to make a living. Most will never have need of that). There is at least one company that offers a subscription to test 406 mhz beacons 'real world'. Not sure of the specific details but you turn on your ELT and they call or email you to let you know if the signal has correct power and codes.

Web

Ok. NOW I'm out! lol.
 
Web,
What GeeBee failed to mention is that he works for a Part 121 carrier. They are allowed to negotiate with the FAA for their own maintenance procedures which may differ from that which we are obligated to comply with. Just because it is in a 121 operators manual that it may be done in a certain manner does not mean that you and I may also perform the same procedure in our application.
 
Web,
What GeeBee failed to mention is that he works for a Part 121 carrier. They are allowed to negotiate with the FAA for their own maintenance procedures which may differ from that which we are obligated to comply with. Just because it is in a 121 operators manual that it may be done in a certain manner does not mean that you and I may also perform the same procedure in our application.

In all my years in Part 135 and Part 121 (about 46) I have never seen an operations specification written that allows an air carrier to perform LESS than is mandated by the manufacturer. They can negotiate different intervals of when to do it as long as it does not exceed the manufacturer's interval, but procedurally the inspection requirements are the same. In fact if your read the NTSB report of an MD-88 that had a fan disk explode and kill passengers in the cabin, the carrier was faulted for not going beyond the manufacturers requirements.

Tell you what guys. I know an FAA avionics inspector. I am now going to query him.
 
Just heard back. It is exactly what I thought. The TSO anticipated the inability to do a 406 transmission test without specialized equipment, thus the TSO required a reliable BITE to be built into the equipment. That is why, and again the manufacturers state explicitly that a chamber test is not required to comply with 91.207 for the 406 portion of the test. I was told, if you comply with the manufacturer's instructions for the annual check, you are in compliance and it was further pointed out to get the FAA TSO approval the manufacturer's instructions are part of the entire approval process. Thus at least on the unit I am familiar with, the Kannad a chamber test is not required.
 
To update this thread. Kannad just changed their procedures. You can no longer field open the unit. It must be performed by a Level 2 service center. This means to check the battery to begin with you must use an oscilloscope or voltmeter with hold function as you are no longer allowed to open the unit even for a corrosion inspection. So the easiest way IMO is to send it off to the Kannad approved shop. Because if it fails the voltage test, you are going to the approved shop anyway.
 
To update this thread. Kannad just changed their procedures. You can no longer field open the unit. It must be performed by a Level 2 service center. This means to check the battery to begin with you must use an oscilloscope or voltmeter with hold function as you are no longer allowed to open the unit even for a corrosion inspection. So the easiest way IMO is to send it off to the Kannad approved shop. Because if it fails the voltage test, you are going to the approved shop anyway.

sounds like a good reason not to buy that brand!
 
It would seem so on first blush. I have had however, such bad luck with cheaper units and this one has been rock solid. Sometimes, good quality just costs money and sometimes buying quality is cheaper in the long run.
 
I just push the button on my AK-04 ELT at the appropriate test time and I get an e-mail from RCC saying they got my test. Done.;-)
 
I missed this thread when it started. But at the IA renewals when 406's first started they where saying you just follow the manufactures instructions to do the test.
 
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