CFM International (CFMI) is working on measures to enable high gross weight, CFM56-5B-powered Airbus A321s to meet Chapter 4 noise rules due to come into force in January 2006.
The General Electric/Snecma joint venture confirms that the most powerful version of the -5B, offered for the 91t and 93t maximum take off weight (MTOW) versions of the A321-200, falls short of the proposed "Chapter 3 minus 10dB" standard by 1-2dB. It is understood that it is the "sideline" noise category, one of three standard noise measurements, in which this version of the Airbus twinjet is deficient.
CFMI is thought to have identified four different ways of bridging the shortfall, and is now finalising which method is the best one to adopt. Although there are around 47 CFM56-powered A321-200s currently in service, not all aircraft are affected as the basic 89t MTOW version already meets the Chapter 4 standard. More recently delivered 91t and 93t MTOW aircraft will need modification.
"This is technically not very difficult to solve," says CFMI vice president commercial engines sales Jean-Pierre Cojan. "It is not finalised yet but it is typically going to be done with acoustic treatments. There is not going to be any turbomachinery redesign," he adds.
The changes are expected to be limited to nacelle improvements, plus the introduction of a "chevron" shaped primary exhaust nozzle, according to Cojan.
All International Aero Engines V2500-powered versions of the twinjet meet Chapter 4.
Source: Flight International
