of them (fleet number AP144, AP159) are the world's first two transit buses to be equipped with six-speed automatic transmission. The transmission is a modified ZF Ecomat 6HP602C. They were the test buses of Eco-driveline (with large differential gear ratio, engine with high low-end torque and six-speed automatic gearbox). Withdrawal of the first batch of Neoplan Centroliners started in 2016. The last were retired in 2018. In May 2003, KMB received a NEOMAN Centroliner N4426/3 (APM1) with MAN ND313F chassis and straight staircase. The width of the bus has increased from to , and is equipped with MAN D2866 LUH-24 straight six engine, four-speed Voith DIWA864.3E transmission, and ventilated disc brakes on all wheels. The bus was painted in gold with dark brown skirt, which is the standard livery for other straight-staircase low-floor buses such as TransBus Enviro500 and Wright-bodied Volvo Super Olympian. It was registered in October 2003. It has been criticised for its frequent breakdowns and extra difficulty in maintenance and so it has remained as a reserve bus since it entered service. This bus remained unique in KMB fleet and was retired on 16 January 2019. New World First Bus After KMB put its first 20 Centroliners into service, NWFB announced the order of 30 Neoplan Centroliner N4426/3s in October 1999. They were delivered in 2000 and entered service in 2000/2001. Since 2004, a number of these buses have been suspended from service. Some believe that it is caused by the difficulty in maintenance by NWFB, or due to the fleet quota limit set by the Transport Department of Hong Kong. However, the actual reason is not clearly known. All of them have been put back into the fleet. The last Neoplan Centroliner in NWFB (Fleet numbers 6024, 6027, 6030) was retired in February 2019, indicating that there are no more Neoplan Centroliners in franchised service. Sun Bus Sun Bus acquired two Neoplan Centroliners (formerly AP144, 146) from Kowloon Motor Bus, so that they could provide high capacity non-franchised private hire vehicles. They first appeared as a shuttle for tourists from the Kai Tak Cruise Terminal in a KMB gold livery with no logo. In December 2019, former AP146 toppled to its side on the roof of KMB's Lai Chi Kok depot. The bus was repaired and was put back into service two months later. The bus later retired in mid-2020. Premature withdrawal One Kowloon Motor Bus-owned