The Search Pattern Report (SPR) communicates a search pattern from the SAR Mission Coordinator (SMC) to a Search UNIT (SRU) (either to transmit a pattern for action or to cancel a pattern) or from a SRU to the SMC (reporting acceptance or completion). Search plan nomenclature is included for reference in Appendix 2 of this IDD.
Version 0:
This is an RTCM compliant update of the FID 2 message listed in the Oct 2014 EAIS IDD. The FID was changed to avoid confusion with ASMs used by the Saint Lawrence Seaway Corp.
The encrypted Message 8 isn’t implemented.
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Parameter |
# of Bits |
Description |
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Standard Message Header |
Message ID |
6 |
Identifier for Message 26; always 26. |
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Repeat Indicator |
2 |
Indicates how many times a message has been repeated. 0 – 3; 0 = default; 3 = do not repeat any more. Set to zero (default). |
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Source MMSI |
30 |
MMSI number of source station. Varies according to the transmitter ID. |
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Destination Indicator |
1 |
0 = Broadcast (no Destination ID field used) 1 = Addressed (Destination ID uses 30 data bits for MMSI) Set to 0, broadcast. |
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Binary Data Flag |
1 |
0 = unstructured binary data (no Application Identifier bits used); 1 = binary data coded as defined by using the16-bit Application identifier. Set to 1, structured. |
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Binary Data |
Designated Area Code |
10 |
Designated area code (DAC). This code is based on the maritime identification digits (MID). Set to 366. |
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Function Identifier |
6 |
Function identifier. Set to 13. |
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Encrypted Payload |
Version |
3 |
Sequential number used to indicate the message version in steps of 1. 0 = test message = default; 1 – 7 = message version. Set to zero. |
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Message Linkage ID |
10 |
Identifier for the SAR Pattern Report. This number uniquely identifies a search pattern sent from a given SMC (MMSI) and is used to connect additional information with the search. Source MMSI and this ID uniquely identify the event. Set to 1 - 1023 by message originator; 0 = not available. |
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Pattern Type |
3 |
Type of search pattern: 0 = Expanding Square (SS) = default; 1 = Sector (VS); 2 = Parallel Line (PS); 3 = Creeping Line (CS); 4 – 7 = reserved. |
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Search Pattern Status |
3 |
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Binary Data |
Encrypted Payload |
Reference Time |
UTC Day |
5 |
UTC Day 1 – 31; 0 = UTC day not available = default. |
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UTC Hour |
5 |
UTC Hour. 0 – 23; 24 = UTC hour not available = default; 25 - 31 = reserved. |
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UTC Min |
6 |
UTC Minute. 0 – 59; 60 = UTC minute not available = default; 61 - 63 (reserved for future use) |
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Action SRU MMSI |
30 |
MMSI of the Action SRU. This varies according to the MMSI of the desired unit. 0 = unknown = default; |
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Case ID Number |
30 |
Case ID. Maximum 5 characters 6-bit ASCII as defined in ITU 1371-5, Table 47. “@@@@@” = not available = default. If less than 5 characters, the remainder of the parameter should be filled with “@” characters (set bits to 0); but, not shown on the presentation. |
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Search Point |
Longitude |
25 |
Longitude in 1/1000 minute. (±180°) East = positive (as per 2’s complement); West = negative (as per 2’s complement); 181° = not available = default. |
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Latitude |
24 |
Latitude in 1/1000 minute (±90°) North = positive (as per 2’s complement); South = negative (as per 2’s complement); 91° = not available = default. |
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Initial Heading |
9 |
Direction of the first leg. 0 – 359 degrees; 360 = not specified = default; 361 – 510 = reserved; 511 = not to be used. |
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First Leg Length |
12 |
Length of the first leg (lengths of succeeding legs depend upon the type of pattern) in 0.1 NM increments. 0 = not specified = default; 0.1 – 400.0 NM; 4001-4094 = reserved; 4095 = not to be used. |
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No. of Legs |
10 |
Total number of legs (search and cross) to execute. 0 = not specified = default; 1 – 1000 legs; 1001-1022 = reserved; 1023 = not to be used. |
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Track Spacing |
9 |
Track spacing in 0.1 NM increments. 0 = not specified = default; 0.1 – 50.0 NM; 501 – 510 = reserved; 511 – not to be used. |
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First Turn Direction |
1 |
Direction of first turn. 0 = port; 1 = starboard = default. |
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Search Altitude |
7 |
Altitude for search pattern in 50 ft increments. 0 = sea level; 50 – 6000 ft; 121 = not specified = default; 122 – 127 = reserved. |
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Search Speed |
9 |
Speed to execute the search pattern in 1kt increments. 0 = not specified = default; 1 – 500 kts; 501 – 510 = reserved; 511 – not to be used. |
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Search Area Width |
11 |
Total width of search area in tenths of NM 0 = unknown = default; 0.1 – 200.0 NM; 2001-2047 reserved. |
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Search Area Length |
11 |
Total length of search area in tenths of NM 0 = unknown = default; 0.1 – 200.0 NM; 2001-2047 reserved. |
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Encryption Bit Padding |
33 |
Sufficient spare bits to ensure that the binary data is a multiple of 128 bits for block encryption (256). Set to 0. |
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Checksum |
16 |
16-bit CRC calculated as per EAIS Specification |
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Footer |
Spare |
4 |
Four extra bits added to ensure the message ends on a byte boundary. Set to zero. |
Communications State Selector |
1 |
0 = SOTDMA communication state follows 1 = ITDMA communication state follows |
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Communications State |
19 |
SOTDMA communication state (see ITU 1371-5 § 3.3.7.2.1, Annex 2), if communication state selector flag is set to 0, or ITDMA communication state (§ 3.3.7.3.2, Annex 2), if communication state selector flag is set to 1. |
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Total bits |
352 |
2 Slot Binary Message |
Figure 1: SAR Plan Message State Diagram
An expanding square search pattern uses the following parameters:
All turns are 90°, typically to starboard. Each even turn, increase the distance of the leg by 1 track space. See Figure 1 within Appendix 2 of this VDL. For this pattern track spacing and initial leg length are the same and both fields should be set to the same value.
A sector search pattern uses the following parameters:
All turns are 120° to starboard, and all legs are of equal length. The legs are the equal length segments (from CSP to radius of the circle). It takes 9 equal length legs to complete one VS pattern (less than 9 legs can be specified if the full pattern is not desired). After completing 9 equal length legs (back to the CSP) the pattern can be repeated with a new initial heading 30° to starboard of the initial. So if the number of legs specified is greater than 9, after 9 legs, rotate the pattern 30° to the right and continue. After 18 legs, rotate the pattern another 30° to the right. See Figure 2 within Appendix 2 of this VDL.
A parallel search pattern uses the following parameters:
All turns are 90° – 2 turns in same direction then switch direction. Cross leg lengths are equal to track spacing. Go leg length, turn go track space, turn same direction go leg length, turn opposite direction go track space, turn same, etc. See Figure 3 within Appendix 2 of this VDL.
The creeping line search is the same as the parallel search except that the search legs are oriented along the minor axis of the search area vice the major axis.