400W Series Installation Manual Page 2-7190-00356-02 Rev. E2.5 Mounting ConsiderationsThe 400W Series unit is designed to mount in the avionics stack in the aircraft instrument panel withinview and reach of the pilot. The primary unit location should minimize pilot head movement whentransitioning between looking outside of the cockpit and viewing/operating the 400W Series unit. Thelocation should be such that the 400W Series unit is not blocked by the glare shield on top, or by thethrottles, control yoke, etc. on the bottom.For VFR-only installations, the 400W Series unit must be mounted in the aircraft manufacturer’sapproved location or other FAA approved location (see Figure 2-2). No CDI/HSI interface is requiredbut if provided, proper source selection annunciation must be used.In accordance with AC 20-138A, for IFR GPS installations the 400W Series unit must be mounted in theaircraft manufacturer’s approved location or other FAA approved location, and the required CDI/HSImust be mounted in the primary field of view. CDI/HSI navigation source selection annunciation must beon or near the affected display and any additional annunciations must be mounted within the normalfield-of-view.An FAA issue paper was written to clarify the TSO-C146a annunciation requirement of “on or near theaffected display”. This issue paper said, in order to preclude the need for external source selectionannunciations (i.e. using the annunciation within the 400W Series unit), the source selectionannunciation displayed on the 400W Series unit must be within 13.856 inches of pilot view centerline. Ifthe CDI is to the left or right of centerline, it must favor the same side as the 400W Series unit placement(i.e. typically the radio stack is on the right of the pilot’s view centerline, so the CDI should be on theright side of the basic primary flight instruments). A CDI/HSI with a built-in annunciation may also beused in lieu of a separate external annunciator to satisfy the source selection annunciation requirement.In addition, any required GPS navigation annunciations must be within 16.805 inches of the pilot viewcenterline. If the 400W Series unit display is within this area, then no external GPS navigationannunciations are required.The 400W Series unit, as a redundant or secondary TSO-C146a certified navigation device, may beinstalled outside the acceptable view parameters if the unit is used as a backup system. Example: To theright of a center radio stack, when two columns of avionics are available. This places the unit too farfrom the pilot’s normal scan. As such, IFR flights may not originate or be predicated on this unit unlessthe primary system has failed.2.5.1 Determination of Acceptable Field-of-ViewThe FAA has determined that the acceptable field-of-view for TSO C146a annunciations related tonavigation source selection is approximately ±30° horizontally from the center of the attitude indicator(or centerline of the pilot’s seat/yoke), and that the acceptable field-of-view for TSO C146aannunciations related to GPS navigation data is approximately ±35° horizontally from the center of theattitude indicator. These angles are based on the closest panel distance of 24 inches resulting in ameasured offset from the attitude indicator of 13.856 inches and 16.805 inches respectively.The acceptable vertical field-of-view includes the area from the top of the instrument panel to the portionof the instrument panel that is immediately below the basic ‘T’ instruments. An example of the viewingarea based on the attitude indicator in an aircraft with basic “T” instruments is depicted in Figure 2-2.For an IFR-approved GPS installation, the 400W Series unit must be located within the ±35° horizontalacceptable field-of-view or source selection and GPS annunciations are required to be installed. If the400W Series unit is installed between ±30° and ±35°, at a minimum, source selection annunciation mustbe installed. See Figure 2-3.
