Part 25 is a certification regulation, detailing the conditions that must be in effect during the certification process to make certain performance determinations. It in no way contains any regulation, nor does it infer such, that a pilot should operationally maintain any airspeed on final approach.
A pilot is not required to fly Vref, plus or minus Vref, or any other speed, by the regulation. Vref is typically 1.3 times the stalling speed in the landing configuration, or for other configurations, 1.3 times the stalling speed in that particular configuration. That assumes a level stall conducted at the rate of a 1 knot per minute speed decrease, power off.
Vref is different for each aircraft configuration, and each weight.
If you examine your landing performance data for your Ultra, you'll note that you are provided with the exact parameters used to make the landing distance determinations. If you wish that information to be accurate, then you must fly exactly in accordance to those parameters. A few degrees warmer ambient tempeature, a few pounds heavier, a different flap setting, your approach speed higher or lower, and the numbers are no longer accurate. Add to that slight variences in each airframe, bugs on the wing, etc...and the numbers change.
Whereas Part 25 certification for certain demonstration requires showing of a predicted Vref speed at 50 feet, do not assume this provides any requirement what so ever to you or I in operating the aircraft. None. I am not obligated nor required, to fly at Vref. I can fly above it, or below it. If I have gusty conditions, I'll had half the gust factor. If I have ice or am in icing conditions, I may add more speed...or less, depending on the runway condition. I may vary that speed for other traffic in the air or on the runway. I may elect to land with partial flaps or may have a system malfunction that requires it, and my reference speeds will change.
You can fly around all day at Vref, whatever you have determined it to be for your weight and configuration. Won't hurt a thing. But why would you?
Generally you don't want to be below Vref on the approach. So long as you can arrive at the runway without making excursions below Vref, you're okay.
A pilot is not required to fly Vref, plus or minus Vref, or any other speed, by the regulation. Vref is typically 1.3 times the stalling speed in the landing configuration, or for other configurations, 1.3 times the stalling speed in that particular configuration. That assumes a level stall conducted at the rate of a 1 knot per minute speed decrease, power off.
Vref is different for each aircraft configuration, and each weight.
If you examine your landing performance data for your Ultra, you'll note that you are provided with the exact parameters used to make the landing distance determinations. If you wish that information to be accurate, then you must fly exactly in accordance to those parameters. A few degrees warmer ambient tempeature, a few pounds heavier, a different flap setting, your approach speed higher or lower, and the numbers are no longer accurate. Add to that slight variences in each airframe, bugs on the wing, etc...and the numbers change.
Whereas Part 25 certification for certain demonstration requires showing of a predicted Vref speed at 50 feet, do not assume this provides any requirement what so ever to you or I in operating the aircraft. None. I am not obligated nor required, to fly at Vref. I can fly above it, or below it. If I have gusty conditions, I'll had half the gust factor. If I have ice or am in icing conditions, I may add more speed...or less, depending on the runway condition. I may vary that speed for other traffic in the air or on the runway. I may elect to land with partial flaps or may have a system malfunction that requires it, and my reference speeds will change.
You can fly around all day at Vref, whatever you have determined it to be for your weight and configuration. Won't hurt a thing. But why would you?
Generally you don't want to be below Vref on the approach. So long as you can arrive at the runway without making excursions below Vref, you're okay.