Gary, I think Andrew has done a great job of summarizing some of his experiences in SAR work, but let me, as an old Army pilot who spent more than 700 hours flying at low levels, usually less than 100 feet, in support of ground troops in Viet Nam put in my 2 cents worth. I also disagree with your pronouncements about how easily people on the ground can be detected. I have over flown friendly troops on the ground for hours at a time and we, my crew and I plus a second ship that was part of our team, frequently only got fleeting glimpses of them when they were in moderate cover and we basically knew where they were.
That's because you were flying too low. Look at the POD tables and you will see that the POD improves with higher altitudes and the lowest tabulated altitude is 500 feet and the highest listed altitude is 1,000 feet so at 100 feet or less you can expect the POD to be really bad. The marine search tables include altitudes all the way up to 3,000 feet and the POD for marine searches also increases with altitude. Oh, I just thought of this. The assertion that the bird activity caused the search to be flown at a higher altitude and that this caused the search to be less effective is proven wrong by the POD table since the POD increases with altitude, it does not decrease. (BTW, I've done a bit of flying myself.)
Gary, I usually have a lot of respect for your posts but in this case you have, in my opinion, stepped on it so to speak.
First of all, almost all of the Army close air support in Viet Nam was flown at very low altitudes until the Cobra helicopter came along. Although the cobra was normally flown at a higher altitude, usually 1500' or a little higher, in most cases he relied on a scout helicopter down on the deck , in many cases hovering right above the vegetation, to locate targets and mark them with smoke. Only rarely did the Cobra crew actually see what they were shooting at.
In the part of the country that I flew in your chances of survival decreased rapidly in the altitudes from 100' to 300' and then progressively got a little better up to 1500' which we considered to be fairly safe unless there were .51cal machine guns in the area. Army aircrews became very proficient in "scouting" operations at altitudes of 100' and below and received many hours of supervised practice before they were released to preform on their own. I personally had hundreds of hours of experience in this environment and yet you, apparently, pass that off as anecdotal and not worthy on consideration. I find this to be highly offensive. On the other hand you claim to have (expert?) experience, you don't mention how much, as an observer in a Huey that is credible. I am sure you have done a bit of flying yourself but how much of it was directly related to the questions here?
I guess that my whole point is that, in the eyes of one who has been there done that, your charts don't impress me much when it comes to finding people. Finding equipment yes, finding people no.
The Navy "Seawolf" pilots who flew Huey helicopters in the most southern parts of Viet Nam, where most of my experience was, used much the same tactics that the Army did.
By the way, US Air Force Pilots when in this area, with the exception of FACS (forward air controllers), rarely got below 5000' except when they were on takeoff/landing or cruising along at 400kts or more. The fighter pilots had to rely on the FACS to mark their targets with smoke before a strike and complete a BDA (bomb damage assessment) after the strike. On rare occcasions the troops on the ground surveyed the strike area to complete the damage assessment.
I think we are talking apples and oranges. In the past you have said that it was hard to spot people on the ground when you were flying at 100 feet or less and at high speed. I pointed out that this is not the best way to spot people because you were well below the optimum altitude. FM 20-150, the National Search And Rescue Manual, has this to say about that:
"Search Altitude. As altitude decreases, the search target passes more rapidly through the field of vision because of the angular acceleration. This effect is most pronounced below 500 feet."
And:
"Search Speed. At low altitudes, higher speed causes a blurring of targets at close ranges and decreases exposure time to the scanner."
Normal search and rescue does not contemplate having to dodge ground fire but you faced a much different set of priorities in Viet Nam. You had to choose between flying high and slow where searching is most effective or flying low and fast to minimize your exposure to Dushkas. But flying low and fast, so that the enemy only gets a fleeting chance to see you (ideally you would be past them before they even knew you were there), also means that you only had a fleeting chance to observe people on the ground, the line of sight works both ways. I don't know why you were offended, I certainly did not mean to be at all critical of your experience and knowledge about your operations in Army Aviation. But it is your personal experience in a very different environment than that encountered in peacetime search and rescue. I did not draft the National Search and Rescue Manual, FM 20-150, so they are not "my charts" that you are not impressed with. The manual was drafted by experts in that field and they recommend higher altitudes for searching in a peacetime environment and the PODs that they came up with is for that environment and is based on their studies and history of such operations. Don't blame, I'm just the messenger.
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Your post reminded me of a story told to me by my boss at the ferry company, he had ferried many O-2s to Viet Nam. He said that on his first arrival into Viet Nam he tuned in the ATIS (for non-pilots, the constantly broadcast prerecorded weather information at airports.)
"THIS IS DA NANG INFORMATION CHARLIE.
THE ZERO EIGHT FIVE ZERO ZULU WEATHER
SKY CLEAR, VISIBILITY ONE ZERO
WIND THREE TWO ZERO AT ONE FIVE
TEMPERATURE TWO SIX, DEW POINT ONE SIX
ALTIMETER TWO NINER NINER TWO
LANDING AND DEPARTING RUNWAY THREE FIVE
GROUND FIRE, LIGHT TO MODERATE"
gl