I was recently asked to confirm that 5 knots is added to the Vref Speed on final approach when an unusual Vref is specified by the Non Normal Checklist. I eventually found a reference …
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Practices & Techniques : NNM Vref & Speed Additives
During training crew often ask if 5 knots is added when using a Vref speed specified by a NNM checklist (such as Vref30 + 30) as is normal practice during NM operations.
The FCTM is clear on this – 5 knots is added, as are corrections for steady/gusting headwinds during manual thrust or 10 knots for manual landings with auto throttle engaged in high or gusting wind conditions.