Installation Instructions

190-01007-A3 GTN 6XX/7XX AML STC Installation Manual
Rev. 4 Page 3-37
3.7.2 Aircraft without Existing Electrical Load Analysis
Prior to undertaking a complete electrical load analysis, the net change to the electrical load resulting
from the GTN installation should be determined (refer to Figure 3-14 for a sample calculation). The
results of this analysis will determine how to proceed further.
Items removed from aircraft: Electrical Load (A) [1] Comment
GNS 530W (Main Connector)
1.4 A
GNS 530W (Com Connector)
0.015 A
Used non-transmitting
current draw
GNS 530W (NAV Connector)
0.5 A
PMA 7000M
2.5 A
Subtotal:
4.415 A
Items added to aircraft: Electrical Load (A)
[1] [2]
Comment
GTN 750 (Main Connector)
1.2 A
GTN 750 (Com Connector)
0.21 A
Used non-transmitting
current draw
GTN 750 (NAV Connector)
0.3 A
GMA 35
0.40 A
Subtotal:
1.91 A
Net Change in Bus Load:
-2.305 A [3]
[1] Use typical current draw when performing this calculation
[2] Use 28V current draw values for this calculation
[3] To obtain the Net Change in bus load, subtract the ‘Items Removed’
subtotal from the ‘Items Added’ subtotal.
Figure 3-14. Sample Net Electrical Load Change Calculation
3.7.2.1 Electrical Load is Reduced Following Modification
In many instances when older systems are replaced with newer equipment, the electrical load presented to
the power system may be reduced. If the overall load on the electrical system is reduced as a result of the
GTN installation (as shown in the previous example), no further analysis is required. This assumes that
the electrical system was within all limits prior to the GTN/GMA 35 installation. The amended electrical
load calculation should be added to the aircraft permanent records to document the electrical load
reduction.
3.7.2.2 Electrical Load is Increased Following Modification
If it is determined that the electrical load has increased, a complete electrical load analysis must be
performed to show that the capacity of the alternator/generator and battery are sufficient for the additional
electrical load. For guidance on preparing an ELA, refer to ASTM F2490-05: Standard Guide for Aircraft
Electrical Load and Power Source Capacity Analysis.
Alternatively, the loads under various operating conditions may be measured, as described in
Section 3.7.3.