Beech 1900 Barbers Pole
Been wanting an answer to this question for some time.
The Beech 1900D has a Vmo of 248 KIAS from msl to 13200 feet. Above 13200 feet the Vmo decreases until 195 KIAS at 25000 feet. There is a corresponding barbers pole on the ASI which rests at 248 KIAS at msl and rotates anti-clockwise as the aircraft climbs.
The 1900 C model also has a barbers pole but its Vmo is fixed at 247 KIAS irrespective of altitude.
Why would these aircraft, which only cruise at around 230 - 250 KTAS, require a barbers pole? How could Mach crit be a problem at such low speeds?
Any input would be appreciated. Thanks.