ARC weighs in on new weight-and-balance AC

 - October 4, 2007, 10:00 AM

An aviation rulemaking committee (ARC) that includes five representatives from the regional airline industry has submitted the final draft of a proposal to the FAA to revise the nine-year-old guidance for weight-and-balance procedures. Provoked by the January 2003 crash of an Air Midwest Beech 1900D in Charlotte, the March 27 recommendations would essentially rewrite Advisory Circular 120.27, the guidance most of the industry has followed since 1995 and an undeniable contributor to the crash that took the lives of 21 people.

Soon after Air Midwest Flight 5481 pitched up and rolled into a maintenance hangar on takeoff at Charlotte International Airport, the FAA ordered all 24 Part 121 regional airlines flying airplanes designed to carry between 10 and 19 passengers to collect weight samples over a three-day period. Another 10 airlines conducted much more elaborate appraisals of their own route structures, while industry commissioned at least another five weight surveys. The results almost uniformly showed that both passenger and baggage weights have grown well beyond the assumptions used until last year. As a result, the FAA issued a series of bulletins that in effect raised assumed passenger weight with carry-on baggage by 10 pounds and checked baggage by another five pounds.

After reviewing the bulletins, the ARC submitted suggestions of its own, including a proposal to re-validate average weight assumptions every two years to coincide with the release of the National Health and Nutrition Examination Survey (NHANES), conducted by the Centers for Disease Control. According to NHANES data, the incidence of overweight adults in the U.S. rose from 56 percent to 65 percent since the FAA last issued guidance on weight-and-balance assumptions, while the rate of obesity (defined as those carrying a body mass index of 30 or more) grew from 23 percent to more than 30 percent.

Not surprisingly, the FAA has already endorsed the committee’s proposal to review the data every two years; in fact, the ARC’s recommendations reflect close and frequent consultation with the agency. “Because the AC is an official document, [the FAA] felt it couldn’t do this any more–that is, provide these average weights that in effect it sanctions,” said RAA director of technical affairs Dave Lotterer. “So [the FAA] wanted to get out from under this [liability].”

According to the recommendations, if the NHANES data show a change in average weight of two percent, the airlines would have to revise their weight assumptions. “The weights are really quite high under this NHANES, particularly for women,” said Lotterer. “In fact, some airlines might think these assumptions are so high that they will elect to perform their own surveys, and they certainly have that option.”

Heavy Bag Program
Due for release for public comment in the coming weeks, the proposed AC would not only raise passenger weight assumptions by 10 pounds and the average for checked bags from 25 to 30 pounds; it would establish special rules for heavy-bag programs, which generally exist today purely as a means to ensure passengers pay extra for consuming a disproportionate share of the airplane’s weight limits with excessive baggage. Under the program, operators would assume an average weight of 60 pounds for any bag weighing between 50 and 100 pounds. Up until the Air Midwest crash, airlines typically assumed an average weight of 50 pounds for “heavy” items, even though most weighed more than that. As always, operators must classify any bag weighing more than 100 pounds as cargo and include its exact weight in the total.

To arrive at its heavy-bag estimates, the ARC compiled a database of 7,000 articles of checked luggage and other personal items. Of those, roughly 10 percent weighed between 50 and 92 pounds, while the remaining 90 percent averaged 28.7 pounds. As a result, the new guidance would leave a margin of 1.3 pounds for items weighing less than 50 pounds, enough to compensate for the slightly higher than 60-pound average observed for heavy bags.

Described by Lotterer as “very comprehensive,” the ARC proposal as a matter of course addresses center-of-gravity issues as well. The new procedures in effect establish more restrictive c-g envelopes for operators whose programs do not reflect a sufficiently rigorous standard of accuracy. “It basically constructs an artificial envelope based on what you’re doing within your system to raise the precision of your estimates,” said Lotterer. “For example, if you used actual bag weights in your totals, that would be good because your level of confidence is higher.”

The NTSB recently confirmed the long-held suspicion that weight- and-balance issues contributed to the crash of Flight 5481, and faulted the programs of both Air Midwest and the FAA. Using FAA-approved weight calculations, Air Midwest baggage handlers assumed they loaded the airplane to within 100 pounds of the airplane’s 17,000-pound mtow. However, subsequent findings showed the airplane’s center of gravity at 5.5 percent beyond the aft limit, suggesting an overweight baggage hold.
Depending on whether or not the FAA decides to order another round of revisions, the proposal could appear as an official bulletin based upon the AC draft within a year, said Lotterer. “The FAA is quite pleased with the results,” he added.