190-00734-17
GTX 335 w/GPS Installation Guidance
Rev. 1
Page 3-22
3.16.3 Electrical Load is Increased After Modification
If it is found that the electrical load has increased, then a complete electrical load analysis must be done to
show that the capacity of the alternator/generator is sufficient for the electrical load. For guidance on
preparing an ELA, refer to ASTM F 2490-05, Standard Guide for Aircraft Electrical Load and Power
Source Capacity Analysis. Alternatively, the loads under different operating conditions can be measured.
Refer to section 3.16.4 for more information.
3.16.4 Performing an Electrical Load Analysis by Measurement
This section describes how to do an ELA for a single alternator/single battery electrical system. This
should be modified accordingly for aircraft with multiple batteries or alternators. For Commuter Category
aircraft, the electrical load analysis cannot be conducted by measurement. Refer to section 3.16.3 for
details. It must be shown that the maximum electrical demand for each alternator does not exceed 80% of
the alternator data plate rating.
Section Definitions
•
Normal operation: the primary electrical power generating system is operating normally.
•
Emergency operation: the primary electrical power generating system is inoperative.
If the installation of the GTX increases the overall load, an electrical load analysis must be done. Because
of the age of some equipment, there is not always sufficient information about the current draw of this
equipment. One permitted method of doing an electrical load analysis is to determine the electrical loads
by measurement. The measurements must account for loads applied to the electrical system in probable
combinations and durations for aircraft operation.
An in-circuit or clamp-on, calibrated ammeter with 0.5 A or better precision can be used for current
measurement. Record the continuous (data plate/nameplate) rate for the alternator and battery.
CAUTION
To avoid damage to equipment, make sure the ammeter can handle the anticipated load.
CAUTION
The Pitot heat should only be switched on long enough to take the current measurement
and then switched off. The Pitot probe can get hot so care should be exercised to avoid
burns or damaging the unit.
1. Use the blank electrical load tabulation form provided in figure 3-9 to compile a list of electrical
loads on the aircraft (generally, this is a list of circuit breakers and circuit breaker switches). Refer
to the example in figure 3-10.
2. Identify whether each load is continuous (e.g., GPS) or intermittent (e.g., stall warning horn,
landing gear).
3. Use the worst-case flight condition to identify whether each load is used in phase of flight for
normal operation. If some loads are mutually exclusive and will not be energized simultaneously
(e.g., Pitot heat and air conditioning), use only those loads for the worst-case condition.
