In article ,
(Snowbird) wrote:
I don't know about a Skyhawk, but FWIW, our former home airport
used to have only 1 ILS, to Rwy 8 which meant if low wx combined with
wind, one might be landing with a tailwind (prevailing winds from
west in these parts). As a training exercise, one time I kept my
speed up to 90 kts over the threshold. I didn't run off the runway,
but I was durn close to my "go around!" point before my plane
decided to quit flying and settle down. I definately landed on
the last 3rd of a 6,500 ft runway. Dunno what the tailwind was --
nothing too startling (10-12 kts?)

As you discovered, a 10-12 knot tailwind is indeed pretty startling.
Most people don't realize just how much effect a relatively small
tailwind has.

I happen to have a Beech S35 POH handy here. For some mumble
combination of weight, temperature, and altitude, the distance over a 50
foot obstacle goes up from 900 to 1400 feet with a 10 kt tailwind. The
graph doesn't go beyond a 10 kt tailwind; I can only assume Beech
figured nobody would want to try a landing with any more :-)

By eye, it looks like the tailwind guide line goes up at about 2-3 times
the slope of the headwind guide line (there's nothing about the shape or
slope of those curves which is model specific).

For linear (de-)acceleration, the distance used goes up by the square of
the ground speed. You normally cross the threshold at maybe 70 kts in a
typical spam can. Crank that up to 90 at the end of an ILS, and you're
using 65% more runway. Add a 10 kt tailwind, and you're using 105% more.

The chart doesn't say anything about how much to increase the distance
by on a wet runway. Or because (as others have pointed out), it's night
and your visual cues suck so your landing isn't as good as it could be.