Fly with 1/2 a dot fly down indication?
Fascinating video. I note the YouTube version is edited to fit the permissable download time, and the person who posted it admits to editing out a lot of the technical lessons learned in terms of the technology.
So if this has been suggested before, I apologise.
It occurs to me, that a modification of the intercept procedure would eliminate the possibility of this particular error. Before anyone jumps down my throat, I am NOT advocating this should be done outside SOPs, but only that we consider this as a rhetorical suggestion.
A normal GS provides a beam width of 1.4 degrees. 0.7 degrees above and below the GS, i.e. Full Scale Deflection of the GS indicator represents 0.7 degrees. Most HSIs show 2 dots above and 2 dots below the GS. Each dot represents 0.35 degrees and 1/2 a dot would represent 0.17 degrees. At a range of 1 mile this equates to around 17 feet and at 1/2 a mile, approximately 8 feet.
It seems to me, therefore, that pilots would be advised to fly the entire procedure with a 1/2 dot fly down indication. (Or recalibrate the display so that glideslope intercept occurs 0.17 degrees ABOVE the actual glideslope.)
This would mean that (especially) the Autopilot would continue to fly straight and level on the localiser until a 1/2 dot fly down indication is achieved. As we have seen this will have an insignificant effect on the profile or performance, but it WOULD provide an airborne failure indication of the GS lobe transmitter.
If no fly down indication is forthcoming, the aircraft would continue to fly straight and level and the autopilot would not commence the GS descent profile. It would then quickly become obvious that the aircraft had flown through the glideslope without descending - upon which a missed approach procedure can be commenced safely and without any particular hurry.
Just a thought.
Regards,
LD Max