Assuming zero wind, groundspeed (GS) equals true airspeed (TAS), which is indicated airspeed (IAS) corrected for density error, an increase of roughly 2% for each 1000 feet above sea level. The aerodynamic properties of aircraft relate to IAS. A typical approach IAS for a B737 (Vref + 5) is in the region of 130 knots. At 11,000 feet density error will be approx 22%, so the TAS (and zero wind GS) will be approx 160 kt.
If for some reason the approach is made with Flaps 15 (rather than 30 or 40) the Vref will be increased by approx 10 kt, as will therefore TAS and GS.
(Source: 'How Airliners Fly' by Julien Evans)
Last edited by Discorde; 2nd Apr 2017 at 11:10.