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