Final answer:
The minimum speed during radar vectoring for a propeller aircraft when less than 20nm from the destination airport depends on various factors such as aircraft type and operational requirements. As a general guideline, it is usually higher than the normal approach speed.
Step-by-step explanation:
In radar vectoring, the minimum speed that a propeller aircraft can be assigned when less than 20nm from the destination airport depends on the specific instructions provided by air traffic control (ATC) and the operational requirements of the airport. However, as a general guideline, the minimum speed during radar vectoring is usually higher than the normal approach speed, which is typically around 1.3 times the stall speed.
For example, let's say that the stall speed of a propeller aircraft is 60 knots. In this case, the minimum speed during radar vectoring could be around 1.3 times the stall speed, which would be approximately 78 knots.
It's important to note that the minimum speed can vary based on factors such as aircraft type, weather conditions, air traffic congestion, and airport procedures. Therefore, it's always best to follow the specific instructions provided by ATC in each situation.