Automated Weight and Balance System Could Enhance Safety

Air Safety Week, June 22, 1998

A new product is in the works that could resolve the uncertainty

surrounding weight and balance calculations. With more accurate

measurements, operators could realize heavier payloads, improved

safety margins and measurable cost savings.

The NTSB's recent findings on the crash last year of a Fine Air

DC-8 cargo jet included this pointed observation: "If the flightcrew

had had an independent method for verifying the accident airplane's

actual weight and balance and gross weight in the cockpit, it might

have alerted them to the loading anomalies, and might have prevented

the accident."

Trinity Airweighs of Dallas, Texas, has developed just such a

device. It has received a supplemental type certificate from the FAA

for installation in the Saab A340, and the company is planning tests

for the 737 or the MD-80 by the end of this year, pursuant to

certification. The system's components weigh less than 50 lbs. and fit

in a flight kit bag.

Presently, aircraft weight and center of gravity (CG) are based

on a mix of historically-based averages and actual weights of

passengers, baggage and cargo. "Our system calculates actual weight to

an accuracy of less than one percent," said company spokesman Ed

Martelle. It determines center of gravity to within three-quarters of

an inch. To put that accuracy in context, the center of gravity

envelope for the 737-400 is 34 inches.

The system uses isolation metering cylinders in the landing gear

and an onboard computer to measure the actual weight supported by each

landing gear strut. From that data, the computer determines the

aircraft's weight and center of gravity. A cockpit display of six

lights warns if the aircraft is out of CG limits. The two end lights

are red, representing out-of-the-envelope loading, and the four lights

in between are green. Ideally, the aircraft will be loaded such that

the green light at or near the aft CG limit illuminates. Such loading

minimizes trim, reducing fuel-consuming drag.

Martelle claims, "With this system, you can load to the safe

maximum for the aircraft."

He estimates that if the system were installed on the more than

3,000 large jets operated by major U.S. carriers, they would save

about $130 million out of a $6 billion annual fuel bill.

The system is not yet in production. It takes about 1,000 loads

to calibrate the computer, therefore the effort to achieve

supplemental type certification is not trivial. >> Martelle, tel.

972/501-0400 <<