Originally Posted by
pineteam
Guys if it was a good idea to use GPS or IRS ground speed for unreliable airspeed it would already have been implemented in the unreliable airspeed procedure.
In my home base, it's common to have on final a tail wind of more than 20 kt around 2500 feet AGL and a headwind on landing... The wind speed and direction change dramatically.
GPS is a great tool, I used it as my primary nav instrument back in the days flying in the bush; But I would definitely not use it as a primary tool to recover from an unreliable airspeed.
Perfect.
2500 ft tailwind 20
airfiel wind headwind 20
So your landing GS will be 20 kts less than V Ref. Say VRef 100, then fly whole approach at 120 GS. Your IAS will be 140 at 2500 and 100 on landing. Just what you were looking for- no? A perfect touchdown speed. Not approx.
more commonly one has reducing headwind during final descent. Say 30 kts HW at 1000 ,and 5 kts at touchdown. VRef 100.
Fly whole approach at 105 kts. GS. You will land at EXACTLY 100 VRef!
this is precision flying- not guesswork. Clearly you use manufacturer Pitch/power tables too to give you a clue but then refine the outcome using GS.