Hi, Fraser.
I too am a bit fed up that your examiner has left you with little idea what you need to improve on for your next attempt. Can I ask, did you fail the whole test, or just one section, and if so what section was that?
I wish that people would refrain from using big aircraft terminology for light aircraft.
Vref, when applied to a PA28, is the speed you aim to cross 50 feet above the threshold, just before you close the throttle to land.
This speed will vary with the mass/config. The speed will increase with increased mass, but the speeds for MTOM are usually quoted, by the manufacturer, for full flap, flapless, and some intermediate flap setting.. The checklist your school provided should list these and other important speeds.
As the PIC, you may decide to vary the threshold speeds, depending on the conditions, but you must be aware that increasing the speed above those quoted by the manufacturer, will increase the landing distance given in the performance section of the POH/FM by an unknown amount.
Hope that helps a bit.
MJ
