WHY ELECTRICAL LOAD ANALYSIS MATTERS

Electrical Load Analysis (ELA) is a record of the current state of an aircraft’s electrical loads – that is the individual and cumulative load an aircraft’s systems place on the aircraft’s power sources (including engines, Ram Air Turbine (RAT), Auxillary Power Unit (APU), generators, and batteries) under various phases of flight and operational conditions.

A current Electrical Load Analysis (ELA) is used to demonstrate compliance with CFR 25.1351, AC 43.13-1B and FAA (Federal Aviation Administration) Order 8300.16A for carriers who operate in or enter the US (and are therefore subject to FAA regulations). Similar compliance obligations are prescribed by EASA (European Aviation Safety Agency [1]), and various CASAs (Civil Aviation Safety Authorities[2]). The increasing complexity in aircraft electrical systems is expected to result in regulations becoming more widely adopted and more stringent with increased focus on the currency an aircraft’s Electrical Load Analysis and the detailed maintenance records to support it.
[1] EASA AMC 20-23    [2] Australia AC 21-38
In effect, the ELA confirms that an aircraft can operate safely, and that flight critical systems have been evaluated to perform during routine and extreme operating conditions

HOW DOES ELECTRICAL LOAD ANALYSIS IMPACT AN AIRCRAFT OPERATOR?

A ‘baseline ELA’, unique to each aircraft ‘fleet or sub fleet type’ is delivered by the Original Equipment Manufacturer (OEM) with each aircraft. Any modifications made to an aircraft during its operational life which result in changes to electrical loads require the operator to perform analysis as prescribed by the OEM, update and produce a current ELA. Operators must be capable of producing, upon demand, a copy of the current ELA.

Every change to an aircraft electrical loads requires a thorough analysis of the impact the configuration / component change / additional load will have on all systems as they flow up to the power source. Operators that outsource STC or OEM modifications to vendors can have the vendor revise the ELA but the operator always remains accountable.
An FAA audit will examine whether the ELA provided is current, accurate, and the loads are within the capacity tolerance of the generators that have been defined by the OEM

When aircraft are sold, transferred, leased, or returned to lessor’s the current ELA  must be provided as part of the aircraft’s Bill of Sale / records package.

The FAA / EASA or an FAA DER (Designated Engineering Representative) can, without notice, demand operators provide the current aircraft ELA and demonstrate its currency and  accuracy of the ELA maintenance process.

1. Variation in ELA format, structure, and calculations produced and required by OEMs between fleet types and between OEMs

Airbus, Boeing, Bombardier, Embraer, et al, each produce ELAs with different analyses and calculations for the thousands of electrical loads on each aircraft. Variation occurs between the OEMs, between fleet types and within subfleets. To illustrate: Using power factor (pf) as an example, Boeing uses pf for each component to detail the actual electrical efficiency of the loads being applied from each component / bus / transformer up to the generators. Alternatively, Airbus assumes the pf is always 1.0 and uses modes of operation to report unique electrical loads. With these and other variations, ELA maintenance demands specialist ELA knowledge.

2. Increasing aircraft and electrical system complexity

Mechanical systems, as the primary basis for aircraft operation are continuing to be replaced by Electrical Wiring Interconnect Systems (EWIS); the introduction of fly by wire flight controls on the Boeing 777, 787 and A320 etc., in place of mechanical controls being one example. The rate of change in the EWIS is accelerating with more advanced flight control systems, passenger comfort and passenger entertainment systems. Increased generator output is often a result of the increased demand e.g. A350 generators produce 230 VAC not the 115-120 VAC typical on many aircraft.

We chose the number of spreadsheet sheets/tabs required to represent an ELA at the bus, sub bus and component level as a proxy for the increasing aircraft electrical system complexity. When we compare eleven different aircraft delivered into service since 1988 we can see that aircraft electrical loads have become substantially more complicated. The effort required to maintain and support these systems is increasing, placing greater demands on the engineering teams to support a fleet of aircraft.

As electrical systems become more complex, more resources are required to support and maintain systems and ensure the ELA is at all times current.

3. Hard copy documentation still prevails

Purchased aircraft are often accompanied by hard copy ELAs. For example, Boeing provides only PDF versions of the ELA for its aircraft and used aircraft are almost always accompanied by PDF or hard copy ELA documentation. Vendors / MROs doing mods typically revise the operators ELA and provide it back in PDF format, or provide hard copy documents back  to the operator which are then used to update the ELA. Transformation from a hardcopy or PDF document into data is expensive, time consuming, and requires a robust quality assurance process.

 

THREE SOLUTIONS FOR ELA MAINTENANCE

 

1. Outsource – simple but not necessarily cost effective

Outsourcing all modifications delegates the effort to MROs and services firms with proven capabilities. For the airlines that use multiple mod vendors, especially STC mods, coordination between vendors can become an issue. The cost and effort for an MRO to revise a customers ELA can be material. Regardless, responsibility remains with the operator to verify the ELA .

2. Adopt the spreadsheet approach – ideal for some but complex, error prone and labor intensive

Using spreadsheets is a practical solution for operators with a single fleet type who do not modify the aircraft, or those with a large fleet with a dedicated Avionics team of Electrical Engineers. When an operator’s fleet includes hundreds of aircraft, control and accuracy of the data can be challenging. When an operators fleet includes multiple fleet types complexity multiplies the challenge. Spreadsheets, however well designed cannot validate and control for all types of errors that are made during ELA maintenance.

3. Use an industry solution – ideal for operators of any size

The ELA Manager, a software application developed by SeaTec in consultation with major   airline operators  consolidates, standardizes and simplifies the maintenance of ELAs for multiple OEMs, fleets, and configurations. It is the only software specifically designed for Electrical Load Analysis.

John Schramm

Managing Partner
Digital

Author