FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 11. Aircraft Electrical Systems | 4. Inspection of Circuit-Protection Devices | 11-53. Switches
AC 43.13-1B CHG 1
9/27/01
(2) Typical low-level load devices have
a voltage of less than 0.5 volts and a continu-
ous current of less than 0.5 amps. A suitable
method of rating switches for use on logic load
devices is specified in ANSI/EIA 5200000.
h. Shock and Vibration.
(1) Electromechanical switches (toggle
switches) are most susceptible to shock and
vibration in the plane that is parallel to contact
motion. Under these conditions the switch
contacts may momentarily separate.
ANSI/EIA 5200000 specifies that contact
separations greater than 10 microseconds and
that closing of open contacts in excess of
1 microsecond are failures. Repeated contact
separations during high levels of vibration or
shock may cause excessive electrical degrada-
tion of the contacts. These separations can
also cause false signals to be registered by
electronic data processors without proper buff-
ering.
(2) Although proximity switches do not
have moving parts, the reliability of the inter-
nal electronic parts of the switch may be re-
duced. Reliability and mean time between-
failure (MTBF) calculations should reflect the
applicable environment. Note that the mount-
ing of both the proximity sensor and its target
must be rigid enough to withstand shock or vi-
bration to avoid creating false responses.
i. Electromagnetic/Radio Frequency In-
terference (EMI/RFI).
(1) DC operated electromechanical
switches are usually not susceptible to
EMI/RFI. Proximity switches are susceptible
to an EMI/RFI environment and must be
evaluated in the application. Twisting lead
wires, metal overbraids, lead wire routing, and
the design of the proximity switch can mini-
mize susceptibility.
(2) The arcing of electromechanical
switch contacts generates short duration
EMI/RFI when controlling highly inductive
electrical loads. Twisting lead wires, metal
overbraids, and lead wire routing can reduce or
eliminate generation problems when dealing
with arcing loads. Proximity sensors generally
use a relatively low-energy electromagnetic
field to sense the target. Adequate spacing is
required to prevent interference between adja-
cent proximity sensors or other devices sus-
ceptible to EMI/RFI. Refer to manufacturer’s
instructions.
b. Temperature.
(1) Electromechanical switches can
withstand wide temperature ranges and rapid
gradient shifts without damage. Most aircraft
switches operate between -55 °C and 85 °C
with designs available from -185 °C to 260 °C
or more. Higher temperatures require more
exotic materials, which can increase costs and
limit life. It should be noted that o-ring seals
and elastomer boot seals tend to stiffen in ex-
treme cold. This can increase operating forces
and reduce release forces or stop the switch
from releasing.
(2) Proximity sensors are normally de-
signed for environments from -55 °C to
125 °C. During temperature excursions, the
operating and release points may shift from
5 percent to 10 percent. Reliability of the
proximity sensor will typically be highest at
room temperature. The reliability and MTBF
estimates should be reduced for use under high
temperatures or high thermal gradients.
c. Sealing.
NOTE: The materials used for sealing
(o-rings, potting materials, etc.)
should be compatible with any air-
craft fluids to which the switch may be
exposed.
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