The Boeing 737 NG Prompted by the modern Airbus A320, in 1991 Boeing initiated development of an updated series of aircraft. After working with potential customers, the 737 Next Generation (NG) program was announced on November 17, 1993.  The 737NG encompasses the -600, -700, -800 and -900, and is to date the most significant upgrade of the airframe. The performance of the 737NG is essentially that of a new airplane, but important commonality is retained from previous 737. The wing was modified, increasing its area by 25% and span by 16 ft (4.88 m), which increased the total fuel capacity by 30%. New quieter more fuel-efficient CFM56-7B engines were used.^[6] These improvements combine to increase the 737's range by 900 nmi, now permitting transcontinental service. A flight test program was operated by 10 aircraft; 3 -600s, 4 -700s, and 3 -800s.In terms of the passenger cabin, the new style interior on the 737 Next Generation improved on the previous style interior used on the Boeing 757-200 and the Boeing 737 Classic by incorporating select features of the 777-style interior, most noticeably larger, more rounded overhead bins and curved ceiling panels. The interior of the 737 Next Generation also became the standard interior on the Boeing 757-300.The first NG to roll out was a -700, on December 8, 1996. This aircraft, the 2,843rd 737 built, first flew on February 9, 1997 with pilots Mike Hewett and Ken Higgins. The prototype -800 rolled out on June 30, 1997 and first flew on 31 July 1997, again with Hewett and Jim McRoberts. The smallest of the new variants, the -600 series, is identical in size to the -500 and was the last 737NG, launching in December 1997 with an initial flight occurring January 22, 1998; it was granted FAA certification on August 18, 1998. In 2004, Boeing offered a Short Field Performance package in response to the needs of Gol Transportes Aéreos, who frequently operate from restricted airports. The enhancements improve takeoff and landing performance. The optional package is available for the 737NG models and standard equipment for the 737-900ER.In July 2008, Boeing offered Messier-Bugatti's new carbon brakes for the Next-Gen 737s, which are intended to replace steel brakes and will reduce the weight of the brake package by 550-700 pounds (250-320 kilograms) depending on whether standard or high-capacity steel brakes were fitted. A weight reduction of 700 pounds on a Boeing 737-800 results in 0.5% reduction in fuel burn. Delta Air Lines received the first Next-Gen 737 model with this brake package, a 737-700, at the end of July 2008. On August 21, 2006, Sky News alleged that Boeing's Next Generation 737s built from 1994 to 2002 contained defective parts. The report stated that various parts of the airframe produced by Ducommun were found to be defective by Boeing employees but that Boeing refused to take action. Boeing said that the allegations were "without merit". Boeing has already hinted that a "clean sheet" replacement for the 737 (internally dubbed "Boeing Y1") could follow the Boeing 787.  Boeing is also considering putting new engines on the 737, to make the model stay competitive.Boeing is planning to increase monthly 737 production from 31.5 to 35 per month in 2002, and 38 per month in 2013.