What is the minimum floor of Class E airspace when tied to an airport with an approved IAP?

The minimum floor of Class E airspace associated with an airport that has an approved Instrument Approach Procedure (IAP) is set at 700 feet above ground level (AGL). This altitude provides a buffer zone that allows for safe and efficient operations of aircraft during approaches and departures while accommodating the transition from controlled to uncontrolled airspace. The 700 feet AGL base of Class E ensures that aircraft operating under instrument flight rules (IFR) are adequately separated from terrain and obstacles, providing a safety margin necessary for instrument approaches.

This regulatory stipulation is vital for maintaining safe operations in the vicinity of airports and is particularly important in areas where other airspace classifications could be present. The decision to have this specific altitude reflects the need for a designated space for aircraft transitioning from en route operations into the terminal airspace where more stringent flight rules apply.