Surely a programming and database update would resolve the hardware issues in any IFR TSO compliant GPS?
It would then simply be a case of a comprehensive reissue of the required IAL plates sans the Foxtrot waypoint.
The one step of removing the Foxtrot waypoint would bring GPS NPA approaches in line with every other IAL procedure...all of which, in the final descent phase, are referenced to a single point in space, a MAP.
For a GPS which is positioned within the radio stack a remote reading display would be required,
as is the case now. The GPS signal is coupled to the HSI/CDI,
as is now the case, and above the ADI is a small display with waypoint name and distance to it,
as is now the case. On the approach plate would be a table with distance/altitude
AND a profile which represents that table. For instance the profile may be
3xGPS distance + 100'= profile altitude.
The PIC has now all the information required to fly a safe final approach...he tracks the CDI the way he would for an ILS, either manually or coupled, and simply looks at the distance to the named MAPt in the window a few cm above his ADI as says to himself
"3x6+100' = 1900'...on profile".
3x5+100=1600'..50' high (adjust ROD slightly)
3x4+100=1300'...on profile (adjust ROD slightly)
3x3=1000' on profile, gear down.
3x2=700'..approaching minima.
3x1=400' level..MAPt, not visual going around.
And his/her eyes never leave the instruments until he/she looks for visual reference, his scan and SA are maintained.
As it currently stands he is required to be looking at the chart constantly and comparing his altitude and distance from 'a' waypoint..."Hmm 3 miles from F waypoint (which is probably 8nm from the MAPt waypoint) and I should be..where isn it...ok 2500'..ok now 1nm I should be 1800'...now 4nm from the next waypoint I should be..umm...oh 1300'."
In the first example the PIC
has no requirement to reference the approach plate at all after briefing and setting up the navaids in the cruise. The way it is at present he must constantly reference the approach plate, during the most critical phase of flight, to have
any chance of
remaining situationally aware...when he should just be
flying the aeroplane.