CAPFlyer wrote:
This is simply a "fudge factor" in case there is undetected low-level windshear. Gusty winds increase the chance of windshear, thus the full component add and you can have windshear with nearly any wind. Also, unless the headwind is over 10 knots, most pilots don't add anything because most of the time you fly VREF+5 anyway.
Chris, I have never heard of such a thing. If one is always tacking on 5kts on the approach speed, it is doing something that is unnecessary. That isn't what I would call good airmanship.
• You have to remember, the airspeed given in the POH is normally for the airplane at max gross weight. So if you are not compensating for reduced weight, you already have that "fudge factor" built in.
• From the Private Pilot ACS:
Maintain a stabilized approach and recommended airspeed, or in its absence, not more than 1.3 VSO, with wind gust factor applied +10/-5 knots . So, if one is within Private Pilot standards, that could put one 10 knots fast on final.
• Extra airspeed, along with poor flare technique, can lead to ballooning during the roundout - that could result in a hard landing.
• When carrying extra airspeed into the flare, the airplane will float until that speed bleeds off.
• If you touchdown with that extra airspeed
your roll-out distance ratio will increase by the square of the ratio of your actual touchdown speed over your normal touchdown speed. So if your touchdown speed should be 40kts, and you touchdown at 45kts - 45/40 is 1.13 so that is 13% faster than you need to be. Square that - and you will require 27% more runway to roll out.
When you do add a gust factor, the typical rule of thumb is 1/2 the gust. So if the winds are 10kts gusting to 20kts,
then you would add 5kts.
-Rob