MIL-PRF-38135C(USAF)
maintainability, item identification, pointer, limitation of pointer movement, pointer zero position,
lighting, Interchangeability, and dimensions.
4.6.2 Fungus. The indicator, including applicable external connectors, shall be subjected to the
fungus test in RTCA/DO-160. The indicator shall then be subjected to the individual tests.
4.6.3 Salt fog. The indicator shall be subjected to the salt fog test in accordance with ASTM
B117 for 50 hours. The indicator shall then be subjected to the individual tests.
4.6.4 Scale error. The indicator shall be subjected to the pressures specified in table II, first with
increasing pressure, then with decreasing pressure. For increasing pressure, the pressure shall be
brought up to but not exceed the pressure required to give the desired reading and for decreasing
pressure, the pressure shall be brought down to but not below the pressure required to give the
desired reading. At each test point, the scale errors shall be within the tolerance in table II.
4.6.5 Friction error. The indicator shall be tested for friction at the 60, 100, 150, 200, 300, 400,
500, 600, 700, and 800-knot indications. The pressure shall be increased to bring the pointer to
the approximate desired reading and held constant while two readings are taken, the first before
the indicator is tapped, the second after the indicator is tapped. The difference between the two
readings shall be within the tolerances in table III. The pointer shall move smoothly while the
pressure is varied uniformly without vibrating the indicator.
4.6.6 Position error. Power and pressure shall be applied to the indicator. The indicator shall be
tested for position error at 60, 100, 150,. 200, 300, 400, 500, 600, 700, and 800 knot indications.
The pressure shall be increased to bring the indicator to the desired reading in the horizontal
position, and then again in the vertical position. The difference in reading at each test point shall
be within the tolerance in table III.
4.6.7 Reliability. The manufacturer shall demonstrate an MTBF of 1,200 hours with a confidence
of 0.90 and discrimination ratio of 2.
4.6.8 Overpressure. The indicator shall be subjected to a pressure of 10 inches of water at the
static connection and 73 inches of Hg at the pitot connection for 10 minutes. Five minutes after
the removal of the pressure, the indicator shall be subjected to the scale error test. The errors at
the test points shall be less than ±5 knots.
4.6.9 Magnetic effect. The indicator shall be held in various positions with its nearest part five
inches from the center of a short-bar magnetic compass with any compensator magnets removed.
The compass shall be in a uniform magnetic field having a horizontal intensity between 0.17 and
0.19 oersted. The maximum deflection shall not exceed 1 degree.
4.6.10 Case leakage. The pitot and static pressure connections of the indicator shall be
connected to the same mercury manometer, or equivalent, and a source of vacuum and pressure.
A vacuum of 25 inches Hg shall be applied to the pitot and static connections of the indicator.
With the source connections closed off at the indicator for 1 minute, the pressure in the case shall
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