US ELT Installation

Thanks Jay, that's good news. I hope the other contests announce their
requirement well before the preferential entry deadline so that all
propspective contestants will have time to accommodate the rule, if
iimposed.

Jim

This has been an interesting thread. But there seems to be a
potentially major problem with ELTs that depend upon a cable and an
external antenna - they may not work after a crash!

First, consider the cable. I make my living using coaxial cables with
BNC (and other) types of connectors, and I can't count the times that
those connectors have failed. True, some were due to poor assembly, but
others (that had been tested after assembly) failed during non-abusive,
normal service. Considering the magnitude of the g-forces that could be
generated during a crash and the likely fragmentation of the fuselage,
how likely is it that the antenna will be electrically connected to the
ELT afterwards?

Second, consider the antenna. There was reference in this thread to a
whip antenna whose instructions specified that it needed to be mounted
within 20 degrees of vertical. There was also reference to mounting
antennas in carbon fiber gliders near the canopy or under a small
fiberglass area in the fuselage. How likely is it in these cases that a
wrecked glider will come to rest with the antenna properly oriented for
transmitting?

It seems strange to have the device itself meet a whole raft of specs
under a TSO (even going to the lengths of specifying the type of
battery) when after a crash the signal might not be able to leave the
ELT. Have the regulatory bodies (FAA, JAA, CAA, etc.) formally
considered this problem, or is it just left to the installer to assess
operational survival probabilities for the ELT system as a whole?

-John

Interstingly enough, they do seem to work pretty well after a crash. I
investigated a mid-air in 2004 (I'm a Fed, but normally assigned only
to air carrier ops) where one aircraft was cut in half ( a Cessna 210)
and the ELT was in the aft part of the fuselage - pretty well rolled up
in the tin - and the antenna rolled up in another part of the fuselage,
but the coax was still connected. The Thurston County Sherriff's Huey
had no trouble locating the aft fuselage pieces, the ELT was
transmitting clearly. The other Cessna was not so lucky, the antenna
was not connected - because the ELT had been removed. That aircraft
wasn't hard to find - it was in an open field.

All those specific requirements that we have to comply with are
required by the manufacturer to insure that the installation complies
with the TSO. Maybe not real world in the end, but they do seem to
work. From what I've seen and read, most ELT failures are due to dead
batteries or improper installation, or even missing! Note the rule
allows a required ELT to be removed for repair for I think 90 days,
with a log entry, etc.

I made the decision to install an ELT in my glider after reading all
the discussion, seems like a good idea and for $200 what the heck, why
not? This will be harder to do for others because they have to get
somebody to install it and/or sign it off, or they cannot find a good
place to locate one. My glider was easy with a large unused open space
to mount it, many gliders do not have this kind of open real estate
available.

Jim

Not sure that I follow you, Jim. You say "All those specific
requirements that we have to comply with are required by the
manufacturer to insure that the installation complies with the
TSO.....From what I've seen and read, most ELT failures are due to dead
batteries or improper installation, or even missing!"

Do ELT manufacturers specify how to mount the antenna and how to strain
relieve the cable to meet TSO requirements? From my reading, the choice
of antenna and the antenna mounting appears to be at the discretion of
the installer. You seem to confirm that when you say "most ELT
failures are due to ...improper installation...".

The example you gave of the Cessna 210 cut in two with the ELT still
working is remarkable, but that certainly wouldn't be typical. I've
seen a 70 pound instrument brought up short after an accidental 50 foot
drop to the end of a single RG-58 cable, and we found the electrical
connection still good afterwards. But I've also seen a two year old
circuit fail at a BNC connector when the attached coaxial cable was
gently moved sideways less than 3 inches. The point is that the
cable/connector interface is problematic, and is therefore a weak point
in what is arguably a critical system.

By the way, I sincerely hope you don't think I was criticizing you.
Your web site shows that your ELT is mounted in a very sound,
workmanlike manner. I was merely asking a rhetorical question as to
whether the regulating bodies had considered what appeared to be a weak
link in the ELT chain.

-John

John,

The ELT installation manual contains all of the specific requirements
that must be met to comply with the TSO. In other words, the TSO covers
not only the unit, but also the installation. For example, the
Ameriking ELT has a remote unit that appears to be optional because
there exist the same control switches on the unit. In fact, the remote
unit is not optional and must be installed in order to comply with the
TSO. Not installing the remote does not make your glider unairworthy,
it simply means the installation does not meet the TSO requirements.

If the ELT was installed in an airplane that requires a TSO'd ELT by
Part 91, then the installation must be exactly in accordance with the
manual, thereby exactly in accordance with the TSO. The Ameriking unit
must have the Ameriking antenna installed (in accordance with the
instructions in the manual) to meet the TSO.Everything is specified in
the manual, from the mounting position and alignment right down to the
D cell part number.

I decided that I wanted to do a "legal" installation - per the manual,
after all, I do need to set a good example ;-). But other folks may
decide they just want to meet the minimum requirement - the SSA rule. I
really don't care and certainly no offense taken on my part, I'm my own
worst enemy with the keyboard.

I don't disagree that the coax is a weak link, as is the antenna
location, but they sure seem to work even when damaged. I suspect the
transmitted range of an antenna wrapped in aluminum or broken is much
lower than one sticking straight up out of the trees. I can imagine
some of the airplanes crash with the ELT antenna on the bottom with the
remains of a twin Beech on top, not sure how well they work like that
-, but it would be difficult to engineer a simple installation that
would provide maximum transmitting power even when rolled into a ball
or subjected to the typical post crash fire. ELT's were certainly not
designed with gliders in mind and vice versa.

Jim

Jim,

Thanks! I've never seen the manual for an ELT, so your detailed reply
was very instructive.

I wonder if during the design process engineers ever considered the use
of an integral antenna for ELTs, which would take over transmitting
duties if the main external antenna were damaged or destroyed? Probably
not, since most ELT installations would be in metal aircraft, and as
you point out they could wind up inside a metal ball post-crash.

It's comforting to hear that ELTs seem to work even when damaged.
Guess I'm just making a problem where none exists.

-John

jcarlyle wrote:

First, consider the cable. I make my living using coaxial cables with
BNC (and other) types of connectors, and I can't count the times that
those connectors have failed. True, some were due to poor assembly, but
others (that had been tested after assembly) failed during non-abusive,
normal service.

Having made up, though not professionally, a few BNC terminated co-ax
cables I'd emphatically agree about some connectors being the weak link:
especially the solderless, no-crimp twist-on BNC connectors. I mean the
type where the centre wire is just pushed into the centre pin and the
ground is a knurled cylinder that you're expected to ram between the
braided shield and the insulation.

I've had uniformly bad results with these connectors and, as the
connector can be easily pulled off the cable, they're probably wildly
unsuitable for an ELT antenna cable.

I will go out of my way to find a soldered-on BNC connector: I've not
tried crimp-on types.


--
martin@ | Martin Gregorie
gregorie. |
org | Zappa fan & glider pilot

Martin,

You're absolutely correct - the push on BNC connectors are junk,
pure and simple. Their only claim to fame is that they will get you
working, right now - but they won't stay working for long! The
crimp-on BNC connectors are just slightly better, even if you invest
big bucks in the special crimping tool. They work for a bit, but they
just won't stand up to normal usage.

The best BNC connector is definitely the one with the soldered center
conductor, with the braid held solidly inside the body by a ferrule
locked by a nut, and a vinyl strain relief over the body of the
connector. They're not easy to make, though, even with lots of
practice. They usually fail because either the center conductor strands
or the shield braid get nicked slightly during assembly. Another
failure is due to corrosion of the braid or the center conductor.
Neither of these failure modes can easily be found in the field, until
things suddenly stop working.

You can see why I was concerned with the possibility of an ELT failing
suddenly when it was most needed.

-John