Ric, on page 225 of your book you state that there was only a 10 to 20% chance of Lambrecht's search of spotting anyone on the ground. How is this calculated?
In
Finding Amelia, Chapter 22 "Banquo's Ghost" (page 225), I wrote:
"In 1937, the techniques and standards of aerial searching were in their infancy. According to present- day Civil Air Patrol Probability of Detection (POD) tables, the chance of Colorado’s planes locating the aircraft in the course of a single inspection of each island was on the order of 10 to 20 percent. In other words, if the Earhart plane was on one of the islands of the Phoenix Group, there is an 80 to 90 percent chance that Colorado’s search missed it."
Like everything else in the book, the source is cited. The statement is footnoted to:
"Civil Air Patrol, Mission Aircraft Reference Text, Chapter 9: “Search
Planning and Coverage,” section 9.2.1: “Probability of Detection Table,”
Civil Air Patrol."
The current on-line version is called
Mission Aircrew Reference Text The on-line manual is organized a bit differently than the cited text but the same information is there. It's pretty interesting to compare the current guidelines for organizing and conducting an aerial search to how the aerial search for Earhart was done.
I'd suggest starting with Section 9.2.2 Probability Areas. You'll see that the first thing you have to do is establish the LKP (Last Known Position). There's a list of primary factors used to establish the LKP:
• The aircraft disappearance point on radar.
(Yeah, right.)• The bearing or fix provided by other ground stations.
(The Pan Am and Coast Guard DF bearings on post-loss signals.)• Dead reckoning position based on the time of LKP.
(Dead reckoning down the LOP.)• Reports of sightings-either ground or air.
(None.)• Emergency locator transmitter (ELT) reports.
There are instances where the above information is not available to assist the planner. To establish a probable position in these instances, the planner must rely on less specific secondary sources of information including:
• Flight plan.
(Known.)• Weather information along the intended route or track.
(Sketchy at best.)• Proximity of airfields along route.
(No airfields, but the post-loss signals indicated that the plane landed some place so "Proximity of islands along route.")• Aircraft performance.
(Known.)• Pilot's previous flying record.
(Known.)• Radar coverage along the intended track.
(Dream on.)• Nature of terrain along the intended track.
(Known. Open ocean and coral atolls.)• Position and ground reports.
(Scant and ambiguous.)Section 9.2.3 covers Search Altitudes and Airspeeds. There are recommendations based upon the type of terrain:
- Open Flat
- Moderate Tree Cover and/or Hilly
- Heavy Tree Cover and/or Very Hilly
The manual gives this example:
"A red and white Cessna 172 has been reported missing and presumed down in eastern Arkansas, in open flat terrain. At the time of the search, flight visibility is forecast to be greater than 10 miles. The incident commander determines, based on available aircraft and crews, that the single probability of detection for this first search must be at least 50%."
Note that this is the estimated probability of seeing an airplane, not people, in flat, open terrain.
As shown in table 9-2 on page 156 of the manual, a big factor in the probability of finding what you're looking for is "track spacing." In other words, when you fly back and forth over your search area (aka "mowing the lawn"), how close together are your respective passes? Or, if you have multiple aircraft flying line-abreast, how far apart are they? The
Lexington used a plan that put aircraft line-abreast with a spacing of 2 miles between planes. We don't know what the Colorado planes did but there is no indication that they had any kind of plan. The CAP figures assume a search for an airplane. A ten to twenty percent chance of seeing people on the ground at Gardner in a single pass around the island is probably generous.