Circular Letter
MSC/Circ.999

ADOPTION OF AMENDMENTS TO THE INTERNATIONAL AERONAUTICAL AND MARITIME SEARCH AND RESCUE (IAMSAR) MANUAL

(11.06.2001)

 

1. The Maritime Safety Committee (MSC), at its seventy-fourth session, 30 May to 8 June 2001, having been informed that the International Civil Aviation Organization had approved amendments to the IAMSAR Manual, as prepared by the Joint ICAO/IMO Working Group on Harmonization of Aeronautical and Maritime Search and Rescue and endorsed by the Sub-Committee on Radiocommunications, Search and Rescue at its fifth session (11 to 15 December 2000) adopted the annexed amendments in accordance with the procedure laid down in resolution A.894(21).

 

2. MSC 74 decided that the amendments should enter into force on 1 July 2002.

 

Annex.

SUMMARY OF AMENDMENTS TO THE IAMSAR MANUAL SEARCH PLANNING PROCEDURES.

 

The major changes being proposed involve the methods for estimating the drift and determining the optimal search area for search objects in the marine environment. Specifically, methods for dealing with search objects that tend to have leeway vectors diverging from the down wind direction to the right or left, have been added. An improved method for estimating the total probable drift error has been developed. Methods for optimally allocating effort to leeway divergence datums have also been added. New leeway data is proposed in the form of new graphs for leeway speed and values for leeway divergence angles and probable errors in leeway estimates. New sweep width tables and correction factors for aircraft searches are proposed to correct certain anomalies that have been observed when using the present values. Appendices K, L and N have the greatest volume of changes.

 

In addition to the changes just mentioned, a number of corrections are proposed. Most require only minor editing and many can be done with pen and ink if the cost of publishing corrected pages is considered prohibitive. However, most of these changes are also quite important if the reader is to gain a correct understanding of the material. The few remaining changes are generally minor grammatical corrections.

 

1. Several acronyms and terms associated with the proposed new methods are proposed for inclusion in the Abbreviations and Acronyms and Glossary sections.

 

2. A minimal number of changes are proposed for Chapter 4 to make the text and figures there consistent with the proposed new methods.

 

3. The Datum Worksheet and the worksheets supporting it have been modified to accommodate leeway divergence and the new method for estimating total probable drift error. A Leeway Worksheet was added. Appropriate modifications to all worksheet instructions are included.

 

4. The present Effort Allocation Worksheet for Optimal Search Around a Datum Point or Datum Line was divided approximately in half to form two separate worksheets a Total Available Search Effort Worksheet and a new Effort Allocation Worksheet for Optimal Search of Single Point, Leeway Divergence, and Line Datums. Between these two worksheets is a Widely Diverging Datums Worksheet. Use of this worksheet is needed only when the divergence distance between leeway divergence datums is large in comparison to the total probable error of position a situation that is expected to be relatively rare in practice. The new Effort Allocation Worksheet for Optimal Search of Single Point, Leeway Divergence, and Line Datums and corresponding instructions contain procedures for optimally allocating effort in situations involving leeway divergence as well as for single point and line datums. Procedures for extending line datums to account for probable position error around one or both end points and procedures for optimally allocating effort in these cases were added. The Total Available Search Effort Worksheet is consistent with the proposed replacement sweep width tables and correction factors.

 

5. Minor changes to other worksheets needed for correct referencing of the above worksheets are proposed. Some unrelated minor corrections are also proposed.

 

6. New leeway graphs and data based on the latest available experimental data and analyses are proposed as replacements for the present Figures N-2 and N-3.

 

7. New tables of sweep widths for helicopters and fixed wing aircraft are proposed. These are based on the latest sweep width experiments and data analysis. The proposed replacements for Tables N-5 and N-6 have meteorological visibility as an entering argument, making them more consistent with the other two sweep width tables. New weather correction factors (Table N-7) are proposed that is also based on the latest sweep width experiments. Since the need for a visibility correction factor has been eliminated, it is proposed that Table N-8 be replaced with a table of correction factors for search facility speed (velocity) that was also an outcome of the latest sweep width experiments and data analysis.

 

Annex.

AMENDMENTS TO THE IAMSAR MANUAL1.

______________

1 Contents and index for each volume should be checked and renumbered, if necessary.

 

Volume I.

 

In page 2-9, paragraph 2.7.2 last line after "... organizations" add:

 

", including support for specialized functions such as developing a search plan";

 

and after "other sources of data." add:

 

"Additional information may be found in paragraph 1.11 of Volume II, Mission Co-ordination."

 

Volume II.

Abbreviations and Acronyms

 

Page

Amendment

ix

 

 

 

 

 

 

 

X

 

 

 

xi

 

 

 

xii

 

xiii

 

 

 

 

 

xiv

Add: "ASW........................average surface wind"

 

Add: "ASWe.................average surface wind error"

 

Add: "ASWDVe..........drift velocity error due to ASWe"

 

Add: "DD.................(leeway) divergence distance"

 

Add: "DVe..................total drift velocity error"

 

Add: "fv....search facility velocity correction factor

 

Add: "Lb..............................datum base line"

 

Add: "LWe................................leeway error"

 

Add: "SCe...........................sea current error"

 

Add: "SR.............................separation ratio

 

Add: "TCe.........................tidal current error"

 

Add: "TWCe..................total water current error"

 

Add: "WCe..........................wind current error"

 

Add: "Za.............................available effort"

 

Add: "Zr..............................relative effort"

 

Add: "Zrc..................cumulative relative effort"

 

From "Zt" to "Zt, Zta"

 

Glossary.

 

Page Item

Amendment

xv

 

"Available effort (Za)

 

 

xvi

 

"Datum base line

 

 

 

 

 

 

 

xvi Datum marker buoy (DMB)

 

 

"Divergence Distance

 

Drift error (De)

 

 

Effort factor (fZ)

 

 

xvii Initial position error (X)

 

 

 

 

 

 

 

 

 

 

 

 

xviii

 

"Leeway Divergence Angle

 

 

 

 

 

 

 

 

xviii

 

"Leeway error (LWe)

 

 

xx Add:

 

"Sea current error (SCe)

Add:

 

The amount of effort available for assignment to a particular datum"

 

Add:

 

That portion of a datum line that is drawn between two specific locations, such as way points on a distressed or missing craft's intended track line. May be extended to form a datum line that accounts for the probable error(s) of one or both locations.

 

From "actual sea current" to "actual total water current"

 

Add:

 

Distance between the left and right leeway divergence datums."

 

From "Total drift error" to "Total probable drift error"

 

From "(1) For point datums" to "(1) For point and leeway divergence datums"

 

Replace definition with:

 

"The estimated probable error of the initial position(s) at the beginning of a drift interval. For the first drift interval, this will be the probable error of the initially reported or estimated position of the SAR incident. For subsequent drift intervals, it will be the total probable error of the previous datum position(s)."

 

Add:

 

The average angle between an object's direction of leeway and the down wind direction. Leeway may diverge to either the right or the left of the down wind direction. Current evidence indicates that object's with significant leeway divergence angles rarely jibe or tack down wind."

 

Add:

 

The probable error of the leeway estimate."

 

 

 

The probable error of the sea current estimate."

 

 

Page Item

Amendment

xxii

 

"Separation Ratio (SR)

 

 

 

 

xxiii

 

"Tidal current (TC)

 

 

Tidal current error (TCe)

 

 

Total drift error (De)

 

 

 

 

 

 

 

 

xxiii

 

"Total drift velocity error (DVe)

 

 

 

 

 

xxiii

 

"Total water current error (TWCe)

 

 

 

 

 

 

 

"Wind current error (WCe)

Add:

 

The ratio of the divergence distance (DD) between two leeway divergence datums to the total probable error of position (E). (SR = DD/E)"

 

Add:

 

Near-shore currents caused by the rise and fall of the tides.

 

The probable error of the tidal current estimate."

 

Replace definition with:

 

"Also total probable drift error. The total probable error in the datum position that is contributed by the total drift velocity error (DVe). De = DVe x t where t is the length of the drift interval in hours."

 

Add:

 

Also total probable drift velocity error. The total probable error of the total drift velocity based on the probable errors contributed by the probable errors in the average surface wind, leeway, and total water current."

 

Add:

 

Also total probable water current error. The total probable error of the total water current based on either (a) the probable error of the measured total water current or (b) the probable errors of the wind current, tidal or sea current, and any other current that contributed to the total water current."

 

Add:

 

The probable error of the wind current estimate."

 

Chapter 1.

 

Page 1-15, paragraph 1.11.1 add at the end of the paragraph:

 

"This is not true for software that directly addresses the search planning problem. Developing such software requires specialized expertise in computer modelling, the application of search theory and the application of environmental sciences such as meteorology and oceanography to SAR. Paragraph 1.11.9 lists some of the functional characteristics that should be considered for search planning software."

 

Page 1-16, add new paragraph:

 

"1.11.9 Computer-based Search Planning. The use of computers to support the search planning process is growing as it offers the SAR Co-ordinator greater flexibility to calculate a refined search area. Although there may be a tendency to computerise the manual method, computerising this overly simplified pencil-and-paper technique should be avoided. Computers make much more sophisticated techniques feasible, such as making the best use of increasingly available detailed environmental data for modelling and predicting drift, creating and testing various scenarios, integrating and evaluating the impact of late-arriving information, and simulating changes in the search object's status and type, etc. Perhaps most importantly, such models can produce optimal search plans that maximise the probability of success. SAR Co-ordinators are cautioned that they should be familiar with the basic theories of each Search Planning element to fully take advantage of the search planning software. SAR Co-ordinators are also reminded that computers are only devices that provide support; they cannot make important decisions and the quality of their outputs can only be as good as the quality of the inputs. Further information may be found in Appendix P of this publication."

 

Chapter 4.

 

Page

Section

Line

Amendment

4-1

 

Footnote

From "a geographic point, line or area" to "a geographic point (or set of points), line or area"

4-2

4.2.2

1-2

From "The many diverse criteria ... makes ..." to "The many diverse criteria ... make ..."

4-3

4.3.2

1

From "A datum may be a point, line or area." to "A datum may be a point (or set of points), line or area."

 

4.3.3

4

From "geometric figure covering" to "geometric figure or figures covering"

4-6

4.4.3(a)

4

From "be somewhat off the downwind direction" to "diverge to the left or the right of the downwind direction. (The average angle between the search object's leeway direction and the downwind direction is known as the leeway divergence angle.) Whether the craft's leeway will diverge to the left or the right is unknown. This uncertainty requires that both possibilities be considered."

4-6

4.4.3(a)

7

From "Leeway rates may be computed" to "Leeway rates and leeway directions may be computed"

 

 

8

From "procedures provided with the Datum Worksheet" to "procedures provided with the Leeway Worksheet"

4-7

4.4.4

13

From "Only those designed to move with the upper one or two metres of the ocean are useful for search planning purposes." to "Those that move with the upper one or two metres of the ocean measure total water current while those that are designed to move with deeper currents tend to measure only sea current."

4-8

4.4.6

1

From "the direction and rate of drift" to "the directions and rates of drift"

4-8

Figure 4-7

 

Replace Figure 4 -7 with the one shown below.

 

 

 

 

Page

Section

Line

Amendment

4-9

4.4.7(a)

1

From "Point Datums" to "Single Point and Leeway Divergence Datums"

4-9

4.4.7(a)

3

Add: "In a drift involving leeway, the first drift interval will produce two new datum points, one for each of the leeway vectors. Thereafter, it is assumed that the "left" datum will always use the leeway vector that is to the left of the down wind direction and the "right" datum will always use the leeway vector that is to the right of the down wind direction."

4-9

Figure 4-8

 

Replace Figure 4-8 with the one shown below.

 

 

 

 

Page

Section

Line

Amendment

4-10

4.4.8

1

From "the computed drift velocity and the resulting drift distance" to "the computed drift velocities and the resulting drift distances"

4-10

4.4.8(a)

1

From "a few types of craft" to "many types of craft"

 

 

2

From "Furthermore, most leeway studies have data only for light to moderate wind speeds. Estimates for higher" to "Furthermore, few leeway studies have data for high wind speeds. Therefore, estimates for high"

 

 

5

From "Some craft show a tendency to drift considerably off" to "Most craft show a tendency to have leeway off"

4-10

4.4.8(c)

all

Replace this entire paragraph with the following:

 

"The combined effects of the uncertainties in both environmental data and drift characteristics of the search object are taken into account by calculating the probable drift error rate (total probable drift velocity error) in knots. Multiplying the length of the drift interval in hours by this value gives the total probable drift position error (De). If uncertainty values are unavailable, a probable error rate of 0.3 knots is usually assumed for each component of the drift velocity. The greater the uncertainty about the object's drift characteristics or the winds and currents driving it, the greater the probable drift error rate estimate will be."

4-11

4.6.1

Effort Factor (fZ)

From "(1) For point datums" to "For single point and leeway divergence datums"

 

 

3

From "length of the line (L)" to "length of the datum line (L)"

Optimal Search Factor (fs) 3

4-17

4.6.9(b)

2

From "line (L)" to "datum line (L)"

4-18

4.6.11

Note 1

From "around datum points or along datum lines" to "for single point, leeway divergence and line datums"

4-18

4.6.12

last

From "(for line datums)" to "(for leeway divergence and line datums)"

 

 

Page

Section

Line

Proposed Change

4-19

4.6.14(b)

2

From "is as large, or larger than" to "is as large as, or larger than"

4-21

4.6.17

3

From "then the total POC for the two searches would be 75%" to "then the total POS for the two searches would be 75%"

 

 

Equation

From "+ ... + POCn" to "+ ... + POSn"

4-23

4.7.4(b)(2)

last

From "search is about 82%" to "search is about 87%"

4-23

4.7.4(c)

5

Add: "Probability maps are very useful when searching for stationary search objects even when the map probabilities must be updated by hand. Their use is always highly recommended for this type of search. However, when searching for moving objects, such as a boat or raft adrift on the ocean, maintaining probability maps by hand can prove to be very difficult. Updating of probability maps to account for both unsuccessful prior searching and increasingly uncertain search object drift is such a complex task that it is better left to computers programmed for the purpose."

4-24

4.7.5(b)(2)

8

From "the optimal search factor ... is 1.4" to "the optimal search factor ... is 1.5"

 

 

3rd equation

From "= 1.4 10 = 14 NM" to "= 1.5 10 = 15 NM"

 

 

4th equation

From "= 2 x 14 x 100 = 2800 NM2" to "= 2 x 15 x 100 = 3000 NM2"

 

 

next line

From "which is a 28 NM" to "which is a 30 NM"

 

 

5th

equation

From "4000/2800 = 1.4" to "4000/3000 = 1.33"

 

 

next line

From "the POD for this search is about 92%" to "the

 

 

 

POD for this search is about 74%"

4-26

4.7.6(d)

last sentence

From "a sweep width of 5.0 nautical miles" to "a

 

 

 

sweep width of 2.0 nautical miles"