VOLUME I Multinational Maritime Tactical Instructions and Procedures

(1) Friendly Air Tracks. The altitude of friendly aircraft can be reported using the words AN-
GELS (in thousands of feet; e.g., ANGELS 1 DECIMAL 5 is 1,500 feet) or HEIGHT (in feet, e.g.,
HEIGHT 400 is 400 feet) or using the International Civil Aeronautical Organization (ICAO) term
FLIGHT LEVEL (e.g., FLIGHT LEVEL 250 is 25,000 feet).
(2) Other Air Tracks. The altitude of other air tracks can be reported using the word ALTITUDE
(in hundreds of feet; e.g., ALTITUDE 151 is 15,100 feet) or using the ICAO term FLIGHT LEVEL.
NOTE
FLIGHT LEVEL is only to be used when altitude is reported by the aircraft (secondary surveillance
radar, IFF, or voice).
b. Depth. If an accurate depth of a submerged track cannot be determined, an estimated depth may
be reported using the appropriate APP 7/MPP 7 brevity code words (i.e., SHALLOW, DEEP), or if an
accurate depth can be determined, it may be reported as DEVILS (in tens of feet; e.g., DEVILS 30 is 300
feet).
NOTE
NATO publications are in the process of being amended to the following standard units of
measurement:
(1) Range — yards.
(2) Distance — nautical miles.
(3) Altitude — feet.
(4) Depth of all objects in water, including bottom depth and thermal features, in meters with
feet or fathoms (as appropriate) in brackets using conversion of 1 meter = 3.28 feet and rounded
off to the nearest meter when exact figures are required. When using only approximate figures
the conversion may be rounded off accordingly (e.g.: 250 fm should be rounded off to 450 m
rather than 457 m).
(5) Thickness of ice — centimeters and/or meters.
(6) Temperatures — degrees Celsius.
The standard units above are not to be confused with the code words RANGE and ALTI-
TUDE. For safety purposes during the transition period, the depth of all objects will be in
meters followed by feet or fathoms in brackets.
2109 CHECK-SUM DIGITS
MTP 1(D), Vol. I
a. To avoid confusion caused by error in transmission, check-sum digits may be used in structured
and free text messages, and where available in formatted messages for positions, courses, speeds, and
times. Check-sum digits may also be used for ranges, frequencies, etc.
b. To derive the check-sum digit, the numbers in the position, course, speed, or time are to be added
together and the total put after the appropriate element. Only the last figure of the summation is to be used;
that is, if the total comes to “19,” only the “9” is used.
2-7 CHANGE 1