Special manufacturer's symbols may be assigned
when two manufacturers are jointly producing an
engine. In these instances, the manufacturer's symbol is
one letter from each of the manufacturers' symbols.
The third part of the designation is a dash and a
number indicating the model number.
! Navy numbers begin with 2, and they continue
with consecutive even numbers. All even
model numbers are assigned to engines
approved by the Naval Air Systems Command.
! Air Force numbers begin with 1 and continue
with consecutive odd numbers.
Each engine design has only one type and model
designation for both the Air Force and Navy. For
example, the Navy may wish to use an engine that has
Air Force-approved type and model numbers. The
Navy may use those numbers without change, provided
there are no engine changes. If the Air Force wants to
use a Navy-approved type engine, but requires minor
engine production changes, the Air Force must use the
Navy type designation. The Air Force then assigns its
own model designation (which begins with the number
1 and progresses with consecutive odd numbers) to the
modified engine, regardless of the Navy model number.
This model number is actually a modification number.
It tells which service made the last production change
to the engine for a particular aircraft application.
The letter X or Y preceding the basic designation
signifies a special designation.
The prefix letter X is a basic engine designation
signifying the experimental and service test of a
particular engine. This prefix letter is removed after
tests prove the engine can perform as it should under all
The prefix letter Y indicates a Restricted Service
designation. It indicates that the engine will not, or is
not expected to, perform satisfactorily under all
operating conditions. It is applied to an engine with a
specific function or that has completed a 150-hour
qualification test only. Upon satisfactorily completing
the qualification testing, the Y designation is dropped.
The engine is then approved for installation in a
The following is an example of a complete ANA
Bulletin No. 306M engine designation number:
! 56Navy developed
! 14Navy model
The ANA Bulletin No. 306M designation system is
effective until each engine manufactured before the
introduction of MIL-STD-1812 is modified or deleted
MIL-STD-1812 DESIGNATION SYSTEM
This engine designation system is made up of
three-digit numerals and model numbers. It is used on
all newly developed gas turbine engines. Existing
engines receive a new three-digit model number
configuration or design. In most instances the old
MIL-STD-1812 engine designation system applies to
all the armed servicesAir Force, Navy, and the Army.
The complete designation system has three
partsthe type indicator, the manufacturer's indicator,
and the model indicator. Special designations in this
system are the same as those discussed under the ANA
Bulletin No. 306M system (X or Y preceding the basic
The first part is the type indicator. It consists of the
type letter symbol and the type numeral. Letter type
symbols are shown in table 6-3:
Table 6-3.Engine Type Indicator