190-01134-11
GMA 350/350c/350H/350Hc Installation Manual
Rev. J
Page 2-7
2.7 Installation Approval Considerations for Pressurized Aircraft
Antenna and cable installations on pressurized cabin aircraft require FAA approved installation design and
engineering substantiation data whenever such installations incorporate alteration (penetration) of the
cabin pressure vessel by connector holes and/or mounting arrangements.
For needed engineering support pertaining to the design and approval of such pressurized aircraft antenna
installations, it is recommended that the installer proceed according to any of the following listed
alternatives:
1. Obtain approved antenna installation design data from the aircraft manufacturer.
2. Obtain an FAA approved Supplemental Type Certificate (STC) pertaining to and valid for the sub-
ject antenna installation.
3. Contact the FAA Aircraft Certification Office in the appropriate Region and request
identification of FAA Designated Engineering Representatives (DERs) who are
authorized to prepare and approve the required antenna installation engineering data.
4. Locate an appropriate consultant FAA DER, by reviewing the “FAA Consultant DER
Directory”, which can be found at the FAA “Designee and Delegation” web page.
5. Contact an aviation industry organization such as the Aircraft Electronics Association and request
their assistance.
2.8 Electrical Noise
Because the audio panel is a point in the aircraft where signals from many pieces of equipment are brought
together, take care to minimize effects from coupled interference and ground loops.
Coupled interference can sneak into audio system interconnecting cables when they are routed near large
AC electric fields, AC voltage sources and pulse equipment (strobes, spark plugs, magnetos, EL displays,
CRTs, etc). Interference can also couple into audio system interconnecting cables by magnetic induction
when they are routed near large AC current-carrying conductors or switched DC equipment (heaters,
solenoids, fans, autopilot servos, etc).
Ground loops are created when there is more than one path in which return currents flow or when signal
returns share the same path as large currents from other equipment. These large currents create differences
in ground potential between the various equipment operating in the aircraft. These differences in potential
can produce an additive effect on audio panel input signals.
The audio panel may “see” the desired input signal plus an unwanted component injected by ground
differentials, a common cause of alternator-related noise. This is the main reason why all audio jacks
should be isolated from ground. Terminating audio shields just at one end eliminates another potential
ground loop injection point.
Single-point grounding cannot be overstressed for the various avionics producing and processing audio
signals. Single-point, in this context, means that the various pieces of equipment share a single common
ground connection back to the airframe. Good aircraft electrical/charging system ground bonding is also
important.
The wiring diagrams and accompanying notes in this manual should be followed closely to minimize noise
effects.
