Spam Up. IIRC not all versions of ‘HS 125’ (if any) use the standard margins for calculating approach speed; thus you should follow what is written in the ‘particular’ aircraft’s manuals.
Normally the reference approach speed (Vref) is 1.3 stall speed (Vs), and most aircraft are certificated for a landing at or about 93% of Vref, often rounded to a training recommending to touchdown at Vref-7kts. However, as the 125 originated under UK BCARs many years ago, it claimed grandfather rights to maintain the benefits of reduced landing distance from a better (slower?) approach speed. A different FAA certification was used for the original ‘Hawker’ aircraft, circ 125-400, thus giving another set of figures; notably (to the angst of the Hatfield designers) a ‘lower’ FAR part 23 cert standard.
Later UK build and certified 125s may have compromised slightly in either using revised UK requirements, or moving toward the JAR 25 standard, but, not as I recall, ever having a JAR certification.
Most certifications normally account for an abuse approach and landing from Vref-5 at the threshold with a correspondingly lower touchdown speed – tail strike limit.
In addition to the old regulations being applied to later variants of the 125 (at least the 800?), there may have been other differences between the ‘A’ (USA and FAA cert) and the ‘B’ (rest of the world, UK cert) markets (N.B. there were some FAA certs in ‘the rest of the world’ so check the manuals and who owned the aircraft originally/previously). The AFM should reflect these differences, which might also include Vmo / Mmo.
There may be a reference in the aircraft documentation to the certification standard, i.e. UK BCARs (old), UK – becoming JAR, or FAA. When the basis of certification has been established, you can then check the speed margins for approach and landing from the appropriate regulations;- of course follow the advice in your ‘particular’ aircraft manual might be quicker.
The 125 also has a particular characteristic when landing with full flap, in that the ground effect can feel like sitting on a bubble of air, which cushions the landing. This depends on landing at the ‘correct’ speed and ‘holding off’ at relatively low height (1-2 ft?); if the aircraft is too high or held off too long with speed falling, the bubble can burst resulting in a ‘stiff’ landing. The trick is to ‘burst the bubble’ at touchdown.