SPOT Versus ELT Analysis (Long)

All,

Some of the recent RAS articles about SPOT got me thinking that this
is a nice device with some important safety features. I decided to do
a quick and dirty analysis of the benefits of the SPOT device versus
the various ELT/PLB devices. Both basically fulfill the same
function, which is to alert someone to come and get you out the jam
you managed to get yourself into.

Below is a comparison of the various attributes of the SPOT device
PLB’s. I’d enjoy any comments that you might have.

Disclaimer: I own an ACR MicroFix PLB.

Background – Many/most (all?) powered aircraft, and some non-powered
aircraft contain ELTs (Emergency Locator Transmitter). The simplest
form of an ELT sends out an emergency signal at a specific frequency
(121.6 Mhz). This emergency signal can be listened for with standard
aviation receivers and then tracked to its source. In the US this
function is often performed by the Civil Air Patrol. Newer ELTs
(operating at 406 Mhz) can transmit GPS location information via
satellites orbiting overhead. A US government agency (NOAA) is then
alerted to the emergency and provides the GPS coordinates to the
appropriate rescue personnel. PLB (Personal Locator Beacons) are
similar in function, using GPS and 406 Mhz, plus being more compact
than ELTs, and typically less expensive. SPOT devices are identical
in function to PLB’s except they are smaller & lighter and transmit
their emergency information via commercial (non-government) satellite
system.

Cost - The SPOT is about $150 while the smallest personal PLB (ACR
MicroFix or ResQFix) is $650. Advantage SPOT it would seem. However,
SPOT requires a $100/year subscription fee (PLB is free). This makes
the cost break even point of 5 years between SPOT and this particular
PLB.

NOTES on Cost: I simplified this analysis by assuming that the cost of
battery replacement and future retail price discounts would not be a
factor. SPOT’s lithium batteries are to be replaced yearly while the
ACR MicroFix’s battery every 5 years). If you want SPOTcasting
(continuous monitoring), there is an extra $50 per year charge (break
even at 3.3 years). PLB’s don’t have a SPOTcast-like monitoring
feature. Important: Spots are being handing out FREE at the 2008 EAA
Airventure (Oshkosh, WI) show from July 23 – Aug 8 (http://
www.airventure.org). However, you must immediately sign up for the
$150/year SPOTcasting plan and also be an EAA member. See
http://www.findmespot.com/eaa.aspx for details. This would equate to
a cost break even point of 4.33 years (ignoring EAA membership
costs). A final aspect of cost, which I have not included, deals with
the potential cost of the first responders (fire, police, rescue,
etc).

Ruggedness – My impression is that the PLB’s (and certainly ELT’s) are
build to a more stringent standard than the SPOT devices. But to be
honest, I haven't researched this too much. Comments?

Monitoring Agency - PLB’s are monitored 24x7 by a government agency
(in the US this is NOAA). SPOT is monitored 24x7 by a private
concern. Which group is more viable in the long term remains to be
seen.

Monitoring Satellites - PLB’s are using government based satellites.
SPOT uses a privately owned satellite system. Which one is built and
maintained better also remains to be seen.

Emergency Response - Does anyone know how fast the “typical” emergency
response would be from first signal activation to first deployment of
the local emergency personnel (obviously the time to final rescue
would differ enormously)? Is SPOT any better or any worse than NOAA
in the US? I do have to wonder if, in an emergency, whether the non-
governmental GEOS team which monitors the SPOT system will be able to
contact a (non-US) government agency as quickly and efficiently as the
government based NOAA organization. Does NOAA carry more weight to
get non-US emergency teams to answer the phone and come to your
rescue? See http://www.magazine.noaa.gov/stories/mag96.htm &
http://www.geosalliance.com/ for some details.

Coverage – While I bought my PLB specifically for soaring use, it has
been taken on trips to Borneo and Haiti (as a just-in-case tool). GPS
(based PLBs) have worldwide coverage. SPOT coverage misses some areas
of sub-Saharan Africa, India, Micronesia and the north and south
poles. While these are not exactly prime soaring locations, I bring
this up to make a level comparison. http://www.findmespot.com/ExploreSPOT/Coverage.aspx

Batteries – All these devices rely on batteries. The SPOT FAQ says
that a set of lithium AA batteries will last for one year (non-
SPOTcasting mode). A PLB’s battery is designed to last for ~5 years
between replacements. Because the lithium AA batteries are
approximately 5x the replacement cost of the specialized PLB’s
battery, this ends up being a wash. During emergency use the SPOT is
rated for 7 days (911 mode) while the MicroFix PLB is rated for 40
hours. This time difference is not as critical as it would seem as
long as both GEOS and NOAA get the all important GPS coordinates in
the first few minutes or hours. The critical element is, will the
batteries be fresh when needed? This points to SPOTcasting (battery
life is 14 days) users needing to be rather religious about replacing
their batteries often or risk having a dead unit on their hands when
the chips are down.

Size/Weight - SPOT (4.38 x 2.75 x 1.5 inches) is the same size as the
MicroFix (5.85 x 2.21 x 1.4 inches), 18 cubic inches in both cases.
However the SPOT is 36% lighter, 7.37 oz versus 10 oz, the difference
primarily due to the lithium batteries being used.

Triggering – Unlike ELT’s, both SPOT and PLB devices must be manually
triggered (in emergency use).

Antenna – The antenna on the SPOT is internal while the antenna on the
MicroFix PLB is external. In my experience, external antennas provide
better reception and transmission. However, I don’t know if this
makes a difference with these types of devices.

Conclusion – I think that there are two key points, and two lesser
points, that are important to be considered.

First, the lesser points of size and battery life. Both devices are
basically the same size and small enough to be easily carried. Will
either or both grow smaller as technology advances? Undoubtedly. As
to battery life the SPOT is the clear winner (emergency use only) but
as I stated before, I am unsure if this is truly a critical element in
the analysis.

Next, the primary point of cost and the combination of coverage/
response/monitoring.

Cost - everyone’s primary metric. Obviously, the initial outlay to
obtain a SPOT is much less (4x) than the MicroFix. However, as we all
know from life with cellular phones, service charges can quickly
invert this equation. I fully expect to keep my PLB for more than 5
years and I suspect the SPOT users feel the same about their device.
Crunching the numbers makes this a tie between the two devices.

Finally, let’s look at the trickier coverage/response/monitoring
analysis. I believe that it comes down to the organization behind the
device. At this point in time I am still leaning towards PLB’s as the
item of choice. My reason is that when the chips are down, I would
rather have the reliability, capabilities, contacts and dedication of
a government agency rather than a private enterprise.

My $0.02.

- John “67” DeRosa

Web Links
http://www.findmespot.com
http://www.adventuretrak.com
http://en.wikipedia.org/wiki/Emergen...or_Transmitter
http://www.acrelectronics.com/microfix/microfix.htm
SPOT use video at: http://www.youtube.com/watch?v=-q2um6vGERY

SPOT use video at: http://www.youtube.com/watch?v=-q2um6vGERY
SPOT commercial video at: http://www.findmespot.com/MediaCente...VideoTour.aspx
PLB use video at: http://youtube.com/watch?v=Y8yIXrRZ1DQ
PLB commercial videos at: http://youtube.com/watch?v=C8I5aK_5bZk and
http://youtube.com/watch?v=psel_NhpiUg

John:

Good analysis. I have a few additional thoughts based on limited use
of SPOT at SoaringNV here in Minden:

First, SPOT is a non-emergency tracker. One of our instructors
carries his personal SPOT on long XC flights and we can get his
current position (updated every 10 minutes or so) online. This means
we know if he is making normal progress or is spending a long time
somewhere looking for a thermal. It also lets us know if there's a
good chance he'll make it home without an aeroretrieve, so we can send
the tow pilot home early.

ELTs and PLBs don't offer this kind of capability. It's a
convenience, not an emergency consideration, but it is a
consideration.

Another aspect of ELT use (which does not, I don't think, apply to PLB
use) is that they are frequently triggered inadvertantly. I fly with
the local Civil Air Patrol, and I think more than half the alerts they
are called out on turn out to be to search for an ELT alarm that they
subsequently learn is in an aircraft sitting on an airport somewhere.
And this high incidence of false alarms brings to light how slow the
response actually is to a signal on 121.5. By the time the Sheriff or
CAP locates the triggered alarm it has often been alerting for a
number of hours. My understanding is that the NOAA satellite that
responds to 121.5 needs to get two signals from the same location
before it alerts, and this requires two passes of the satellite. This
might not be the case any longer, but I'm pretty sure it was when the
service was first put in place.

Finally, SPOT and PLBs both offer active alert capability, while ELTs
offer passive alert. I suppose this could be a consideration if you
are incapacitated upon reacing the ground -- maybe you couldn't push
the "help" button -- so you need to think about what you want to be
prepared for: letting people know you're ok, or letting the NOK know
where to find the remains. (Sorry for the gruesome touch.)

Fred

Hi Gang
Having used a Spot for some time now I agree that it is almost an
essential safety item for XC either in a glider or power plane. All
modern power planes require not only the use of an ELT but also that
the ELT can be operated from a control on the instrument panel or
equivalent so that if you are going to have an emergency landing you
can actuate the ELT before the landing and not rely on the G forces to
trigger it. I have this on my Jabiru J250 LSA. I also take and operate
my Spot on all flights whether in the LSA or in a glider. I set the
Spot to the tracking mode so that it sends out messages every 10
minutes. My wife and a couple of close friends have my Spot user name
and password so that they can either track a flight in real time or
bring up a flight later if they so wish.
I have not found any significant problems with the Spot system. It
works! If Steve Fossett had used a Spot he would have been found
(assuming he wanted to be found) and for its low cost, simplicity and
ruggedness I consider to be an
essential piece of safety equipment. I won't fly without it. Don't
procrastinate you pilots just go and buy one. Could be one of the best
investments you might ever make?
Dave

Has anyone heard of any prospect of an improved SPOT coming out.

My biggest hang up is I don't like replacing batteries and I would
want to use it in tracking mode. It would be Ideal if it had an
external Power option. I am sure I could jury rig something but it
would be nicer to have the external power for normal operation and
still have the batteries for emergency operation.

An external antenna option might be nice as well.

A display of your current postion might be of use as well but of
lesser concern to me.

Brian

On Jul 5, 5:49*pm, Brian wrote:
Has anyone heard of any prospect of an improved SPOT coming out.

My biggest hang up is I don't like replacing batteries and I would
want to use it in tracking mode.

I tested battery life earlier this year by leaving on in tracking mode
on the dash of my car, and restarting it every 18-24 hours to ensure
it was operating 24/7. Sometime around day 12, the power LED turned
RED, and the SPOT continued to operate just fine for several more
days. So this means at least 300 hours of CONTINUOUS live tracking.
That's pretty much a typical season for a fairly active pilot.

The local grocery store sells a 4 pack of the batteries for $12 or
so. I'm sure they can be found elsewhere for even less.

Why on earth would you want to complicate things and add an external
power cord??? ;-)

The only improvement that could come from SPOT is if the unit
transmitted a NEW position every minute instead of what it does
currently, which is the same position every 10 minutes.

Think about it, if a new position were transmitted every minute, and
if 90% were lost, that would still provide a position every 10
minutes.

The compelling reason to fly with SPOT is that it provides a
RELATIVELY failsafe crash location. If I'm incapacitated in a crash,
then the PLB is useless. If there's major damage to the airframe,
then the ELT is useless. The SPOT will give rescuers a 10 minute
search radius and a flight vector. Yes, I understand that sometimes
SPOT leaves holes of 2, 3 or even more intervals, and it's possible I
chose to reverse course immediately after the SPOT sends a position
report. But this still provides an excellent starting point for S&R.

-Tom

And I do have an ELT as well. And am installing a transponder
tomorrow. ATC radar history is yet another passive way to find a
downed aircraft, especially if used in conjunction with SPOT to
isolate the VFR target.

One problem with a transmit every minute, rather than 10 minutes, would be
that it would shorten battery life considerably. I am guessing it would
approximate 10% of the present battery life. The 300 hours of transmit
quoted would be reduced to 30 hours.

Also, with transmissions every minute, the processing through the satellite
might be overloaded with present equipment, which would require more money
to correct - hence higher user fees.

The external antenna would reduce reliability considerably, and may not gain
much. The exposure to a satellite from a sailplane would be very high, so
the most reliable and simplest antenna should work well.

Colin Lamb

snip

I tested battery life earlier this year by leaving on in tracking mode
on the dash of my car, and restarting it every 18-24 hours to ensure
it was operating 24/7. Sometime around day 12, the power LED turned
RED, and the SPOT continued to operate just fine for several more
days. So this means at least 300 hours of CONTINUOUS live tracking.
That's pretty much a typical season for a fairly active pilot.

The local grocery store sells a 4 pack of the batteries for $12 or
so. I'm sure they can be found elsewhere for even less.

Why on earth would you want to complicate things and add an external
power cord??? ;-)
snip

I didn't realize the battery life was this good. Replacing the battery
once per year would be ok.
Does it auto power off after a period of time? Especially if it can't
get a GPS fix like when the glider is in the trailer.. I can certainly
see me leaving it on and having dead batteries when I go to fly. Or
course I do always have spare batteries.

If it did have an external power supply it would be nice if it could
automatically power up to track mode when power is applied, One less
thing to remember to turn on.
It could possibly even be programmed to send a position when power is
turned off. LIke an external OK or Help button.

I like things that stay in the glider and I don't have to mess with
them until I need them.

More batteries I don't need. I already have a 9V in my B40 and 9V in
my EW FR 4 AA in my GPS, a watch battery and lithium battery in my
PDA. All are connected to my aircraft power supply.

Thanks for the info,

Brian

"Does NOAA carry more weight to get non-US emergency teams to answer the
phone and come to your
rescue?"

I doubt it. Search and Rescue is activated by the sheriff in most states
and they will respond as soon as practicable under the circumstances. The
key is the report and certainty of what has happened. The 121.5 MHz ELTs
can take a fairly long time to locate, and the satellite positions may not
be accurate. We have been sent out on searches from reports from the
satellites and learned they were off by 20 miles or more. We have had to
get close enough with ground vehicles to pick up the signal. Change to the
higher frequency will substantially improve the original report. CAP may be
activated sooner by a government organization, though, since it is
quasi-governmental. SAR groups like accurate information and it does not
matter where it comes from.

As to activation times, it all depends. Depending upon the information and
when it is received, CAP and SAR might not begin the search undil the
following morning - especially if the report is filed late in the afternoon.
It takes time to plan the search. Often, there is a "hasty" search where a
quick serach is made using such techniques as going to hilltops and trying
to receive the signal with gain antennas and driving around in automobiles
in possible areas with direction finding equipment.

I have been to many crashes where the ELT was destroyed, so it was not
useful. That would be a big advantage for SPOT, since you would be leaving
bread crumbs - not only of your trail but also your direction and speed.
That history would be invaluable. It is really difficult to look for a
downed aircraft when you are not sure what state they are in..

Colin Lamb

The problem I have with this is it is a false paradox, you don't need
to choose between a PLB/ELT or a SPOT. Especially since a SPOT is
cheap enough (think the cost of a few tows, a long aeroretrieve, a lot
cheaper than annual glider insurance... and so on) let alone the worry
of friends and relatives or the hassle of people trying to find you if
you land out etc.

I've used a spot for about 9 months now, from when they first became
available. There are quite a few people I fly with now who also use a
SPOT, universally the interest in them is for tracking (aka
SPOTcasting). This allows just tracking people out of interest,
facilitating easier aero and ground retrieves and hopefully being able
to find somebody in a crash or similar should the SPOT still be
transmitting after the crash or at least being able to have a good
last know location (and likely some direction intelligence) if the
SPOT is not transmitting after a crash.

I've also flown with a PLB on my parachute harness for several years.
My sentiment is that if I'm in serious trouble then I do want a full
PLB with 121.5 MHz homing beacon etc. for local SAR resources to find
me with. Also since for best GPS reception and GlobalStar transmission
the SPOT unit is sitting on the canopy rail on my glider and I have
the PLB on my parachute harness so it goes with me in case of a bail
out.

But anyhow a couple of corrections to the original post -

ELTs and PLBs transmit a homing beacon on 121.5 MHz (not 121.6 which I
assume was a typo - although you'll see 121.6 MHz mentioned as a test
frequency by ELT/PLB manufactures their distress beacon is always on
121.5Mhz).

Comparing internal antennas on SPOT vs. external anennas on PLBs or
ELTs is nonsensical. The beacon anennas on PLBs and ELTs have to be
large becasue of the 121.5MHz beacon frequency. All current PLBs with
GPS use a planar GPS antenna (GPS is ~1.5 GHz), SPOT uses a similar
GPS antenna. The GloabalStar L-band antenna in SPOT operates on a
similar frequency to GPS and uses the same planar antenna technology.
The antenna are different because they operate on significantly
different frequencies. PLBs and SPOT use planar and not helical coil
antennas (which would also work at these frequencies) for various
technical reasons and practical ones including compactness and
robustness.

The 1 year life for SPOT batteries vs. a shelf life for PLB batteries
also is not a valid comparison. SPOT claims a ”Powered On unused”
battery life of one year. That means the unit is turned on by the user
but not sending any messages. SPOT claims that batteries installed but
with the device turned off the batteries will “last several
years” (see the SPOT User's Manual) . The Energizer e2 Lithium (non-
rechargeable Li-FeS2) batteries SPOT uses have shelf lives of more
than a decade and are the same basic chemistry as the batteries used
in the best PLBs and ELTs. PLB battery packs however are larger than
SPOT because a PLB draws more power than SPOT does in any of it's
operational modes. The sealing and construction of battery packs for
PLBs is more impressive than for a SPOT messenger, but the battery
compartment seals and construction on SPOT appear more than adequate
for our uses. SPOT messengers seem to give ample warning of battery
exhaustion, and it is easy to carry a spare set of batteries and
replace them if needed (tool less access to a well built, sealed
battery compartment). I'd actually be more worried about PLB
batteries because people don't test their PLB, so how confident should
they be that the actual device really will work if needed and the
batteries really are OK?). Bottom line is that batteries and SPOT just
do not seem to be an issue.

Not all 406MHz ELTs or PLBs transmit a GPS location. If I was buying a
PLB today I'd only look for one with a GPS and I'd look for one with
the longest battery life (I care about the built in 121.5 MHz homing
beacon lasting as long as possible so the local SAR organization can
home my location if needed). Effectively all current 406 MHz ELTs that
you would install in a glider do not encode a GPS location.

---------------------

While the SPOT service may be a black box in terms of how things
operate, ELTs and PLBs are not themselves magical devices and knowing
how they work in some detail might help in emergencies, so at the risk
of drifting off topic and getting boringly long...

A common misconception about 406MHz devices is they just transmit on
406Mhz - all of these also transmit a 121.5MHz homing beacon. PLBs
typically put out a less powerful 121.5Mhz beacon than an ELT and (in
the USA) also encode a morse code "P" (dit dah dah dit) about every 50
seconds on the beacon to signify it is a PLB. So if you suspect
somebody is missing and may have activated a PLB listen for their
121.5Mhz beacon just like you would with an ELT. This is also the
reason that 406 MHz ELTs and PLBs have long antennas - they are sized
for the 121.5 Mhz signal (some high end ELTs likely intended more for
corporate/jet aircraft do have separate 406 MHz and 121.5 MHz
antennas).

121.5 MHz ELT beacons can be Doppler located by low earth orbiting
(LEOSAR) satellites within the COSPAS-SARSAT network. It takes several
satellite passes to determine the approximate position and due to how
this is done at 121.5Mhz and the poor frequency stability specs or
these ELTS you end up with something like typically 4 hours needed for
a final position estimate and a position uncertainty of something like
up to 15 nautical miles (over 100k acres to search). It is this COSPAS-
SARSAT monitoring of 121.5MHz beacons that is going away in Febuary
2009. But airlines will still monitor 121.5 MHz, SAR organizatons like
CAP and the Coast Guard will still be able to DF/home on them etc.

The 406 MHz ELT/PLB beacons transmit a much more stable signal, and
the signals are handled by the LEOSAR satellites differently and a fix
can be determined within about an hour to within a few miles
uncertainty, say typically less than a 1,000 acres to search. The 406
Mhz signal is transmitted in pulses roughly every 100 seconds, the
higher power during the pulse, the improved frequency stability specs
and different signal handling in the satellites allow this faster and
more precise Doppler location.

Now if the 406 MHz ELT (most glider ones won't today) or PLB (try to
buy one with GPS) also optionally encode GPS coordinates in the 406
MHz signal then the geostationary (GEOSAR) COSPAS-SARSAT satellites
can relay the location very accurately within a few minutes of
activating the ELT/PLB - it may take several minutes (up to 10 minutes
on older units) for the GPS unit in the PLB/ELT to obtain a cold GPS
fix.

The other thing the GEOSAR satellites always do is pick up a 406 MHz
ELT/PLB signal almost instantly and that allows the coordination/SAR
organizations to identity through the digital serial number who the
beacon is registered to. The SAR coordinators can attempt to contact
the owner or emergency contacts and quickly try to determine if this
is a real emergency or not. That's a big problem with 121.5 MHz ELTs,
there are just a huge number of false alarms. BTW there is a
significant fraction fo false alarms with 406MHz beacons, I don't have
the numbers handy, but the ability to identify the owner an contact
them helps quickly resolve those. Many of those false alarms have
historically come from 406 MHz marine beacons accidentally triggered
during testing/inspection (I believe due to having to remove units
from their shipboard mounts to read labels and thereby accidentally
activating it - a pretty amusing design mistake).

If the GPS enabled ELTs or PLBs can't get a GPS fix then they revert
and behave like a non-GPS unit. Just let it sit there and be Doppler
located in case there is a problem with the GPS (know what any GPS
status LEDs on the device mean), also you can verify the 121.5Mhz
beacon is working by listening with the glider VHF radio (or the
backup handheld you carry in your survival kit). The GPS enabled ELTs
and PLBs are not designed to provide continuous position tracking, in
fact they specifically avoid this for signal qualiy reasons so thigns
like obtain a location fix and continue to transmit that location for
a while. The exact behavior will depend on what spec the device is
complaint with but it may fix obtain a GPS fix and transmit that
location in every 406 Mhz pulse for 20 minutes or so or longer. So you
could imagine corner cases where this could create some problems (like
ideas people might have for trying to trip a PLB in flight if they
think they are in trouble then managing to flying some way before
crashing...) - but that hopefully should be rare wacky stuff and
ultimately that last location stuff can often be helped by SAR using
the 121.5Mhz homing beacon.

BTW a SPOT messenger that can't receive a GPS signal will transmit the
unit ID information and "911" or "Help" message type (but apparently
not an OK or SPOTcast message?) without the GPS coordinates and so the
same thing can apply there with people at least able to try to contact
the messenger owner or emergency contacts. Like many PLBs the SPOT
messenger also shows via LEDs wether it has a GPS fix or not.

----------------

SPOT is a tremendous tool for tracking gliders, it is the only
practical technology that I can think of that can do this. Like all
technology it is not goign to wakr always, but my experience with it
has been very impressive. It provides "I'm OK" or "I've landed out and
need a retrieve" type messages. The only other technology that has
anything as broad coverage and reliable as this would be an Iridium
satelite phone where you can call your crew once on the ground
(practically impossible in flight becasue of the large fold out
antenna--unless you have an external Iridium antenna installed on the
glider). There is a big piece of mind as well in flying with a SPOT
with tracking and knowing people have been able to watch your tracks –
which is my experience so far. Yes there are times when people have
seen problems with this - it would be useful to know if this was
really just the shared pages, whether it affects the private account
pages as well or whether position reports were really never received.

SPOT is so convenient for tracking for lots of reasons and is such low
cost that people should just get one, if you also fly in desolate
areas (most pilots I know do), fly by yourself a lot, etc. want a back-
up for real emergencies then I would also carry a PLB on your
parachute harness as well. If I have no interest in tracking or non-
emergency retrieve messages etc. and only wanted a distress beacon
then I'd buy a PLB - but I don't know of any glider pilot who want a
SPOT to use just as a distress beacon (i.e. in "911" mode).

Darryl