Use of Fast Charged Electric Ground Support Equipment
as a Means of Reducing Airport Emissions

This page updated November 23, 2005.

Electric Transportation Engineering Corporation

Demonstration of the Use of Fast Charged Electric Ground
Support Equipment as a Means of Reducing Airport Emissions

CARB Grant Number ICAT 99-4

The statements and conclusions in this Report are those of the grantee and not necessarily those of the California Air Resources Board. The mention of commercial products, their source or their use in connection with material reported herein is not to be construed as actual or implied endorsement of such products.

Project Summary
The project established a fleet of fast charged electric ground support equipment (GSE) for use by Southwest Airlines (SWA) at Sacramento International Airport (SMF). A fleet of twelve (12) electric baggage tractors utilized the fast charge energy delivery system (EDS) developed by Electric Transportation Engineering Corporation (ETEC). The Project was designed to fully integrate the electric GSE with SWA management systems, human resources and operating strategies. The participants in the Project believe that a full scale demonstration of fast charged electric GSE at SMF provides the tangible results necessary for airlines to accept the use of fast charged electric GSE, eliminating the need for the time and expense required for massive electrical infrastructure upgrades to support conventional electric GSE charging and accelerating the air quality benefits derived from the use of electric GSE.
During the course of the Project, an additional Task was added to procure a 13th bag tractor powered by an AC drive system (as different from the DC drives for the original 12 tractors) in addition to laboratory and field testing of sealed lead-acid, golf-cart style battery modules. This task was designed to demonstrate te performance of an optimized bag tractor battery with reduced cost and improved performance over existing sealed batteries used with electric GSE. The ETEC Energy Delivery System (EDS) is a fully integrated battery charging system specifically designed for airport ground support equipment. The EDS is contained in a single, temperature controlled enclosure that can be delivered, pre-assembled, to an installation site. Exterior color and finish may be selected to match the airport environment.
The EDS is equipped with four charge ports to which GSE vehicles can be connected for battery charging. The main EDS charger, rated at 33 kW, sequentially charges all GSE vehicles connected to an EDS port. That is, when it has completed the charge on one vehicle, it automatically sequences to the next vehicle until all connected vehicles have been charged. Equalization of batteries is an automatic function of the EDS. Equalization charging occurs automatically after the completion of rapid charging. Equalization frequencies and algorithms are designed to minimize cell grid corrosion, extending battery life. All EDS ports are capable of performing equalizing charges. Equalization is performed by a separate charger and may proceed concurrently with a equipment receiving a high power charge from the main charger on another charge port.
The EDS routinely charged a GSE vehicle discharged from one day of use in one hour or less. This rapid turnaround allowed multiple bag tractors to be effectively charged throughout the working day. The sequencing capability allowed bag tractors to be placed on the EDS at the end of the work day to be charged during the night, keeping the EDS working 24 hours per day. With the rapid energy delivery provided by the EDS, the total energy requirements of all 13 GSE vehicles at SMF was provided by the single EDS, rotating vehicles on and off of the EDS for charging throughout the day and night. By spreading the charging out over the entire 24-hour day, the peak electrical demand resulting from charging activity was significantly reduced over that of conventional chargers operating at SMF. This allows a significant savings in the cost of wire, circuit breakers, transformers and switchgear from that which would typically be required for conventional charging. The rapid turnaround also allowed vehicles to be on the tarmac working 23 out of 24 hours in the day, increasing vehicle availability and eliminating the need to have a charging space for each GSE vehicle.
The EDS utilized an access control system to prevent unauthorized use and to provide use records for fleet management. Using the access control system, the EDS is capable of recognizing various battery capacities, voltages and types (e.g., flooded vs. gel). This feature allowed a single EDS to be the energy supply device for multiple types of GSE vehicles and eliminating the need to install a new (and often different) charger each time a new electric vehicle was added to the GSE fleet. During the course of the project SWA added electric pushback tractors and an electric lavatory truck to the charger. Each of these vehicle types utilized a different battery which would normally have required separate chargers to be installed. The access control system also allows collection and storage of operating data by vehicle using the ETEC Management Information System.
The Management Information System collected and stored battery performance data each time a vehicle was charged. These data were remotely collected from the EDS using a master computer at the ETEC home office. Once collected the data was processed using algorithms created by ETEC to develop information characterizing the performance of the vehicle battery. This information was organized into a series of internet pages that could be accessed by password from the internet. Pages present data on both vehicles (individually and for an operating unit) as well as for chargers (individual, airport and system wide). The Management Information System was used by ETEC personnel to gather data concerning system operation and verify the operating performance of the charger and battery systems.
Southwest Airlines believes that the use of sealed batteries in airport environments is critical to personnel safety, environmental compliance and flexible operating strategies. The energy delivery system is particularly well suited to charging sealed batteries as it uses an extremely sophisticated algorithm to protect batteries from over-charge. However, protecting the batteries from over-discharge is not a function within the control of the charger. Over-discharge protection must be resident on the GSE vehicles. To assure that the sealed batteries used in this Project at SMF were not over-discharged a more accurate over-discharge protection device than is currently available for electric GSE was designed, constructed and installed on the initial 12 bag tractors. In addition, a training program was developed for GSE operators to describe how the fast charge energy delivery system is designed to operate and to stress the deleterious effects of over-discharging the batteries.
The project successfully demonstrated that electric ground support equipment can replace fossil-fueled equipment in normal operations at SMF. While the charger was initially seen by SMF as a large electric load, its effects on the supply grid's power quality was found to be minimal. Furthermore, the additional cost of electric energy required for the Project was far offset by the fossil-fuel cost savings, resulting in a net savings of $1,277 per year per bag tractor. The optimized battery pack demonstrated excellent performance and cycle life during the project and is projected to result in a 40 percent savings in initial battery cost. Finally, the elimination of fossil-fuel powered equipment at SMF resulted in a reduction in emitted pollutants, including 343 tons of CO, 16 tons of HC and 7.4 tons of NOx.
As a result of the successful demonstration of an integrated electric GSE solution at SMF, Southwest Airlines has replaced additional internal combustion equipment at SMF with battery-powered equipment. Furthermore, Southwest Airlines has installed an EDS system at the Ontario, California Airport. ETEC is now offering the EDS as a commercial product for the airline industry.

Funding Source

Funding Amount



  Electric Transportation Engineering Corporation


  Southwest Airlines


  Sacramento County Airport System


  Defense Advanced Research Projects Agency


  Sacramento Municipal Utility District


ICAT Funded Projects