The New Reality

[JoeTomasone]

UDF mission last night...  Couldn't launch an aircraft for around 5 hours due to weather.   It finally launched and located the ELT waaaay outside where we concentrated the ground search.

Welcome to the new reality.

[PlaneFlyr]

That's nothing new.  The farthest away I've had a ground seach initiate from the actual ELT location was 43 miles.  (I'm sure others have had worse).

[JoeTomasone]

Yeah, I know it's nothing new (and isn't to me either, really), but it's tough to start a ground search intelligently when all the clues say "somewhere in the State".   

[Larry Mangum]

That brings back memories of chasing ELT's in Mass. It was not uncommon for the sarsat merges to place the elt's location 20 to 35 miles from where it was found.

[davidsinn]

That brings back memories of chasing ELT's in Mass. It was not uncommon for the sarsat merges to place the elt's location 20 to 35 miles from where it was found.

I'm curious why it was treated like a SARSAT merge? Florida is flat which means the ELT would be at a point that is visible to all 3 locations at once and that would be a huge roughly egg shaped area centered on the reports. You could somewhat safely rule out the gulf to the west but since there are no mountains to the east to block that it shouldn't have been ruled out. Basically we can't do squat without air support as you pointed out

it's tough to start a ground search intelligently when all the clues say "somewhere in the State".   

[Larry Mangum]

Because they were not SARSAT merges, they were airborne reports of a signal on 121.5 I am betting.  Since 121.5 is no longer being monitored the signal was not triangulated but rather simply airborne reports, with out bearings.

[JoeTomasone]

I'm curious why it was treated like a SARSAT merge? Florida is flat which means the ELT would be at a point that is visible to all 3 locations at once and that would be a huge roughly egg shaped area centered on the reports. You could somewhat safely rule out the gulf to the west but since there are no mountains to the east to block that it shouldn't have been ruled out. Basically we can't do squat without air support as you pointed out

it's tough to start a ground search intelligently when all the clues say "somewhere in the State".   

Lack of anything more constructive to do since the aircraft couldn't launch, basically.   We were hoping to get lucky and find that it was somewhere IVO the reports at one of the airports there.   

[Al Sayre]

Here's a useful piece of info if you are working with pireps. 

You can calculate the radio horizon of the reporting aircraft in statute miles by taking the square root of the AGL altitude in feet and multiplying that times 1.415 and then draw a circle of that radius from the point of the pirep. 

Example 1000 ft agl:  Sqrt(1000)x1.415 = 44.75 statute miles


if you have multiple pireps where the circles converge is where you start your search.

[davidsinn]

I'm curious why it was treated like a SARSAT merge? Florida is flat which means the ELT would be at a point that is visible to all 3 locations at once and that would be a huge roughly egg shaped area centered on the reports. You could somewhat safely rule out the gulf to the west but since there are no mountains to the east to block that it shouldn't have been ruled out. Basically we can't do squat without air support as you pointed out

it's tough to start a ground search intelligently when all the clues say "somewhere in the State".   

Lack of anything more constructive to do since the aircraft couldn't launch, basically.   We were hoping to get lucky and find that it was somewhere IVO the reports at one of the airports there.   

I can understand that. I just did a quick drawing in autocad and the LOS horizon at 5k is about 90miles out. At 3k it's around 70 miles out. So if you plotted those circles the area that is covered by all three would be your search area. That's an area bigger than most New England states. Eye balling the distances between reports gives me about 12000 square miles. Without an airplane up there's really no point in dispatching a ground team.

[TXCAP]

Al,

For the math challenged could you please explain the basis of the formula and the constant of 1.415?

Thanks

[Al Sayre]

It's based on the pythagorean theorum, from which we derive the distance formula (from algebra).  Basically knowing the height of 2 antennas and the curvature of the earth, you can determine the maximum line of sight distance between the two (radio horizon).  This assumes the first antenna is on the ground (0ft AGL), and simply accounts for the height AGL of the second (the airplane).  the 1.415 is the result of the gyrations after all the math to convert the results into statute miles.  If you prefer Nautical miles use 1.23

[Al Sayre]

I'm curious why it was treated like a SARSAT merge? Florida is flat which means the ELT would be at a point that is visible to all 3 locations at once and that would be a huge roughly egg shaped area centered on the reports. You could somewhat safely rule out the gulf to the west but since there are no mountains to the east to block that it shouldn't have been ruled out. Basically we can't do squat without air support as you pointed out

it's tough to start a ground search intelligently when all the clues say "somewhere in the State".   

Lack of anything more constructive to do since the aircraft couldn't launch, basically.   We were hoping to get lucky and find that it was somewhere IVO the reports at one of the airports there.   

I can understand that. I just did a quick drawing in autocad and the LOS horizon at 5k is about 90miles out. At 3k it's around 70 miles out. So if you plotted those circles the area that is covered by all three would be your search area. That's an area bigger than most New England states. Eye balling the distances between reports gives me about 12000 square miles. Without an airplane up there's really no point in dispatching a ground team.

That's why I dread searches that begin with airliner pireps...35K ft = a radius of 264.72 miles=search area of 220152 square miles

[N Harmon]

h = altitude in nm, calculated by taking altitude in ft and dividing by 6076.
r = radius of earth, approx 3440nm

d = sqrt ( ( r+h )^2 - r^2 )   = sqrt(2rh+h^2)      (Pythagorean therom)

To find the surface radius from ground point to radio horizon:

s = arcsin ( d / (r+h) ) * r         (in radians mode)

or

s = arcsin ( d / (r+h) ) * r * 180/pi    (in degrees mode)

For an aircraft at 1000ft AGL, the approximate radio horizon would be 33.6 nautical miles.

At FL350, that becomes almost 200nm.

Now, the real fun part is adding in fresnel zone clearance calculations.

[N Harmon]

That's why I dread searches that begin with airliner pireps...35K ft = a radius of 264.72 miles=search area of 220152 square miles

It really depends on the quality of the airliner pireps. If you're given a single point and an altitude then yeah, it's practically useless. But a point first heard, and a point last heard can really constrict that probability area.

[Al Sayre]

See, isn't 1.415 a whole lot simpler?   

[sardak]

Here are some theoretical/ideal detection ranges:
At 3,000 AGL
Visual
Calculated: 58 nautical miles (NM)
US SAR Manual/National SAR Supplement: 63 NM

Electronic (theoretical ELT detection range):
Canadian SAR Manual: 55 NM
CAP Pamphlet 2 "ELT-EPIRB Search": 30 NM
CAP NESA "Inflight Guide": 26 NM

At 5,000 AGL
Visual
Calculated: 75 NM
US SAR Manual/National SAR Supplement: 81 NM

Electronic (theoretical ELT detection range):
Canadian SAR Manual: 85 NM
CAP Pamphlet 2 "ELT-EPIRB Search": 36 NM
CAP NESA "Inflight Guide": 32 NM

Since it was added while I was typing, at 35,000 ft AGL:
Visual = 214 NM SAR manual, 199 NM calculated
ELT = 236 NM CAPP2, 232 NM NESA

I've attached a chart with all these curves from 0 to 40,000 ft AGL.
Remember that detection ranges are based on AGL, while aircraft altitudes are MSL.
AGL = MSL - surface elevation.

Mike

[Al Sayre]

That's why I dread searches that begin with airliner pireps...35K ft = a radius of 264.72 miles=search area of 220152 square miles

It really depends on the quality of the airliner pireps. If you're given a single point and an altitude then yeah, it's practically useless. But a point first heard, and a point last heard can really constrict that probability area.

Agreed, and there are other things you can do to narrow it down as well based on the terrain, known signal strength etc.  I believe in the KISS principal and using the formula I gave gives you a larger and more conservative search area that will be a maximum area that makes a good starting point if you are in a reasonably flat area.  Put the ELT half way up a 5000 ft peak in terrain that rapidly changes altitudes and the area really expands... Minimizing it is up to the IC.

[JoeTomasone]

That's why I dread searches that begin with airliner pireps...35K ft = a radius of 264.72 miles=search area of 220152 square miles

It really depends on the quality of the airliner pireps. If you're given a single point and an altitude then yeah, it's practically useless. But a point first heard, and a point last heard can really constrict that probability area.

...Which we never seem to get.   

Using the CAPP2 range estimates, the ELT was in the overlapping ranges - but just barely.



And we did search a good chunk of it.   

[SJFedor]

It's a shame you didn't get any reports out near the Lakeland area, or you woulda had it!

[RADIOMAN015]

UDF mission last night...  Couldn't launch an aircraft for around 5 hours due to weather.   It finally launched and located the ELT waaaay outside where we concentrated the ground search.

Welcome to the new reality.
[

Well s was it located on an airport  & if so where there any CAP members that lived right in the area that with a simple radio scanner could have heard the signal

Additionally Joe, are you in FL wing now using outside magnetic mount antenna on your vehicles attached to the DF equipment, especially during inclement weather?
RM

[JoeTomasone]

It's a shame you didn't get any reports out near the Lakeland area, or you woulda had it!

Yeah, if there had been anything near Tampa Executive, Lakeland, OR Plant City, I would have checked them out (and I did go by Tampa International just to make sure).    Like I said -- the new reality.    Gotta consider even what seems most unlikely.

[JoeTomasone]

Well s was it located on an airport  & if so where there any CAP members that lived right in the area that with a simple radio scanner could have heard the signal

Additionally Joe, are you in FL wing now using outside magnetic mount antenna on your vehicles attached to the DF equipment, especially during inclement weather?
RM

It was indeed at an airport - in fact, the aircrew landed, found, and silenced it.    We wouldn't have alerted anyone near there because it didn't occur to any of us to check that airport being so outside the likeliest range of the pireps.   

And I have to be honest here, when we've had pireps in similar locations, the ELT has been in the area that we searched, so we did have a little bit of precedent to work with -- but it just goes to show that nothing is ever routine.

And yes, mag mount antenna on the vehicle feeding the Sniffer - but not during lightning.

[RiverAux]

Boy, thats a tough one to think about whether to send out a ground team on until aircraft are available.  On the one hand, you don't want to sit on your hands and do nothing, but on the other hand we all know that in the "old days" AFRCC would sit on ELT signals for 3-6 hours until even calling CAP. 

I expect I might spend an hour or so calling airports in that zone and asking them to check the frequency and after all those are done that can be, then send a ground team to check any other likely spots.  Might even consider asking the local cops to check some of the non-attended airports just to make sure there aren't any obvious crashes even if they can't check 121.5.  All the while asking traffic control to keep soliciting reports from the big boys. 

Of course all I'm thinking is that this is actually a really SMALL search area for this consideration.  The more likely scenario could be a search area over a quarter of the state. 

[RiverAux]

By the way, are those detection ranges cited earlier based on modern equipment or are they something that was done with earlier models?  If so, is that likely to make a difference? 

[SarDragon]

They are based primarily on line-of-sight calculations, and are maximums at best. They are not equipment related.

[JoeTomasone]

I expect I might spend an hour or so calling airports in that zone and asking them to check the frequency and after all those are done that can be, then send a ground team to check any other likely spots.

The major issues with that approach here in FL are:

1.  We have a bajillion airports, airparks, and Goober-owned grass/dirt strips here.   Many are not staffed at night (or have no tower at all).   

2.  We have called towers who insist that there's no ELT going off.   We roll anyway, and it's as plain as the nose on your face.  And let's not get into carrier-only.

Might even consider asking the local cops to check some of the non-attended airports just to make sure there aren't any obvious crashes even if they can't check 121.5.

Again, a pretty monumental task across several agencies (County, City, Local). 

  All the while asking traffic control to keep soliciting reports from the big boys. 

I've made the suggestion, but I suspect that the FAA folks are not used to being ELT data-gatherers and may be non-plussed at being asked to solicit reports.   Remains to be seen, I guess.  Surely AFRCC is not asking them to do so.

Of course all I'm thinking is that this is actually a really SMALL search area for this consideration.  The more likely scenario could be a search area over a quarter of the state.

Absolutely, which makes getting a GT on standby interesting as well.    Who and where do you call?

[es_g0d]

I'd like to thank everyone for an excellent professional discussion, and then throw something out there.

Using an older program called FalconView, part of the PFPS (portable flight planning software) suite, I can make a "shadow" of line-of-sight.  This originally being a combat aviation program, the intent was to plot where threat radar would be obscured by terrain.  I've plotted SARSAT hits with it, and it fairly closely replicates where you can receive the ELT in an aircraft.

What I'm saying is that line-of-sight goes both ways.  Plotting a circle assumes that you have perfectly flat terrain in all directions.  If I were to plot several airborne ELT reports with an "antenna height" equal to the AGL altitude of the reporting aircraft, the intersecting region should contain the ELT.

And here's the question.  I cannot easily nor broadly distribute FalconView / PFPS to avail this tool.  Is there a tool or tools that use a real-world terrain database to plot multiple line-of-sight "shadows"?  It must be readily available either by download or in an online applet.

I will endeavor for a new generation of GridFinder(tm) to incorporate multiple airborne reports and port that to such other software.  Similarly, I'm probably going to be using some of the math shown on this thread for an informational page on the CAP-ES.net website. 

Good work, all ... so who knows of a program???

[SarDragon]

I saw some CAWG repeater maps with that kind of graphic info, but don't who made them, or what program was used.

[JoeTomasone]

If I were to plot several airborne ELT reports with an "antenna height" equal to the AGL altitude of the reporting aircraft, the intersecting region should contain the ELT.

Fair enough, but when that's 30 sq. miles (as it was, roughly, last night), you're back in the same soup.   I can pick up an ELT at an average of 3 miles from my vehicle with an airband omni antenna on the roof, but that's not a great chunk of real estate and cannot be counted on.   I have had ELTs that were unreadable until I was 1/4 mile away.  And we're talking FL here -- flat as a pancake.

However, this does bring up an interesting possibility - checking out the height of the local office buildings in downtown Tampa and seeing what kind of footprint they might provide.   Not as good as an aircraft, but far quicker and cheaper if the proper arrangements are made in advance.

[RiverAux]

Joe, wasn't critisizing your approaching, just thinking about how I would do it in my area. 

[wuzafuzz]

I'd like to thank everyone for an excellent professional discussion, and then throw something out there.

Using an older program called FalconView, part of the PFPS (portable flight planning software) suite, I can make a "shadow" of line-of-sight.  This originally being a combat aviation program, the intent was to plot where threat radar would be obscured by terrain.  I've plotted SARSAT hits with it, and it fairly closely replicates where you can receive the ELT in an aircraft.

What I'm saying is that line-of-sight goes both ways.  Plotting a circle assumes that you have perfectly flat terrain in all directions.  If I were to plot several airborne ELT reports with an "antenna height" equal to the AGL altitude of the reporting aircraft, the intersecting region should contain the ELT.

And here's the question.  I cannot easily nor broadly distribute FalconView / PFPS to avail this tool.  Is there a tool or tools that use a real-world terrain database to plot multiple line-of-sight "shadows"?  It must be readily available either by download or in an online applet.

I will endeavor for a new generation of GridFinder(tm) to incorporate multiple airborne reports and port that to such other software.  Similarly, I'm probably going to be using some of the math shown on this thread for an informational page on the CAP-ES.net website. 

Good work, all ... so who knows of a program???

I've heard of people using RadioMobile for this kind of work.  It's free, but doesn't work on my Mac.
http://www.cplus.org/rmw/english1.html

[sardak]

They are based primarily on line-of-sight calculations, and are maximums at best. They are not equipment related.

The low altitude end (below 10k ft) of the CAPP 2 curve in the attachment to my earlier message is based on actual testing (see the first and last paragraphs on page 26 of CAPP 2). The NESA curve at the low end is shaped much as the CAPP 2 curve with some offset, so the two are somehow related. I asked a NESA source and NHQ about it and was told "they'd look into it." The two visual range curves are based on the formulas posted earlier. The Canadian curve is, well, interesting. I've attached a chart of the low-level curves.

Here is a plot of multiple PIREPs on an actual mission. Less than helpful was the fact that all three PIREPs were close together and almost in a straight line. Two were at 36,000 ft and one at 19,000 ft. Finding the beacon near the center of the circles didn't give much support to the technique of looking for the overlapping areas. The effects of terrain are obvious.

The computer generated visual coverage of one PIREP is shaded yellow and another light blue. The overlap area is green (yellow+blue). The third PIREP (magenta center) has gray coverage. If you look hard, there are light and dark shades of yellow, green and blue. The dark areas being the overlap of the gray coverage.  Again the rings are from the curves. The image size is reduced, so go to the image source for the full size version, which is more readable.


This plot is made using "Radio Mobile Deluxe" which is free. It was written by a ham using radio propagation code developed by our buddies at NTIA. Use of the software is not for the faint of heart.
Here is the Radio Mobile Deluxe homepage but a better page that has tutorials and a self extracting installation version is here.

After the beacon was found, I plotted the reception pattern for a receiver at 11,300 AGL, the same as the lowest PIREP. The reception pattern can't be plotted until the transmitter location is known, so visual range and the curves are the only technique available when looking for the beacon.

Mike

[BillB]

There is NO inclement weather in Florida.

[bosshawk]

If you guys think that you had a hard time finding the thing in Florida, on flat land, try chasing one in California with 14,000 peaks.  I chased one all day in a 182 that AFRCC said was plotting on the coast near Monterrey.  I finally found it at Mariposa, which is where I currently live, after flying about four hours.  The XXXXXX thing was bouncing off the hills and mts and was about 150 miles from the original merge: and that was with satellite hits.