Saab Aircraft has made significant strides in increasing design weights on its 340B turboprop to accommodate customers affected by the US Federal Aviation Administration's revisions to passenger weights, says the firm's Americas customer service director Erik Harrweg.
Harrweg says Saab aims to raise the maximum take-off weight (MTOW) and the maximum zero fuel weight (MZFW) of the 340B by 454kg (1,000lb) - the conservative equivalent of about four passengers.
In its investigation into a January 2003 Air Midwest Beech 1900D crash at Charlotte Douglas airport, North Carolina, the US National Transportation Safety Board (NTSB) determined the probable cause was a loss of pitch control during take-off exacerbated by the aircraft's aft centre of gravity. The FAA in August issued an advisory circular (AC) to operators adding 4.54kg to the average assumed passenger weight of 82kg in the summer and 84kg in the winter.
This meant that some US customers using 34-seat Saab 340s, for example, had to remove a few seats in certain circumstances as a result of the revised averages.
A final order covering passenger and baggage average weight is expected to be released in June 2005. "The [AC] in June of 2005 will be clarifying certain things...but does not change the actual weight," says the FAA.
To mitigate the effect of the weight increases, Saab performed a comprehensive study to evaluate possible increases in the design weights of the 340B.
Harrweg says: "New certification regulations will be adopted requiring a change in stall definitions, gust load considerations and a re-analysis of the structural loads [and] aircraft performance."
He adds that some structural reinforcements of the 340B are expected, as is a modified stall warning computer. In addition, "there is very small risk for a new main wheel or nose landing gear cylinder", says Harrweg. Saab has determined that the maximum landing weight cannot be increased without introducing a new landing gear, which has been judged too expensive.
Harrweg calls the 340B modification "a huge undertaking" that requires a 21-month lead time "from the day we get a substantial order", which he hopes will be "between now and January".
MARY KIRBY / WASHINGTON DC
Source: Flight International
