wrote:

The origin of the timing table was not specifically referenced to ground
speed. In fact, the KISS concept in pre-GPS days favored simply applying IAS
on final, as in managing human factors and keeping the priority tasks at the
top of the list, so to speak. So, the discussion is not silly at all.


That may have been a simple way some pilots were taught to use it, but
the time/distance table is based on true speed, not indicated speed. If
the FAF to MAP distance is 5NM, the time shown under 60 kts will be 5:00
minutes. This requires 60 kts TAS to cover that 5 NM distance in 5
minutes. If you have a IAS of 60 and a TAS of only 30 based on
headwinds, then it will take you 10 minutes to get to the MAP. Of
course, using IAS, you're unlikely to overshoot the MAP as long as you
have a headwind, so you're safe in that respect, but then you might
start a missed approach turn too early, and fly into an area not
protected by TERPS obstacle assessment.

JPH