AACs - Part 1-26 - Airworthiness Articles
Part 1 - Airworthiness Articles
Electrical Load Analyses
Some concern has been expressed by various members of the industry about the validity of our requirements for an electrical load analysis for Certificate of Airworthiness issue. The purpose of this article is to explain the rationale for the requirement which is specified in CAO 100.2 paragraph 5.1(c)(VI).
The requirement to show that each aircraft has an adequate electrical system is not unique to Australia. The requirement is also valid regardless of the aircraft type and its intended operation. The basis for the requirement is that the design rules applicable to aircraft require that an adequate electrical system be provided. While the aircraft type will have been shown to have an adequate electrical system, there is no guarantee that each aircraft of the type will have the same electrical loads. In fact, the most common modifications include variations to the aircraft electrical loads.
We believe that the requirement for an adequate electrical system is valid. However, the method of demonstrating that the requirement is met may vary. In fact, we apply different rules to aircraft depending upon whether or not they are approved to operate in accordance with the Visual or Instrument Flight Rules.
For aircraft only permitted to operate in accordance with the Visual Flight Rules, it may be sufficient to show that the aircraft generating system capacity is adequate to provide for the installed loads. Since total loss of electrical power during flight conducted in accordance with the Visual Flight Rules is not a critical situation, that approach is generally considered adequate and no "analysis" would be required.
In the case of aircraft able to be operated IFR, merely showing that the generating system capacity is adequate is not sufficient.
Experience has shown that the loss of generated electrical power is not an improbable event, nor is it required to be for most aircraft. However, total loss of electrical power in Instrument Metereological Conditions can, depending on the particular aircraft avionics installation, be a catastrophic event. In the case of IFR aircraft, an electrical load analysis is required to show that the battery capacity is adequate. The consideration of adequacy is based on the ability of the battery to provide power for the electrical loads required for safe flight and landing for some "reasonable" period of time. The reasonable period has generally been accepted as the 20 or so minutes shown in the example at appendix 2 to CAO 108.32, with the loads also shown in that example.
We trust that this short article puts the matter of electrical load analyses into perspective. If further information is required your local Airworthiness officers should be able to provide assistance.