flarepilot;
Re, "there...I've said it...any non precision apch in real conditions is more dangerous than a normal ILS apch."
It's a known fact of aviation and the accident statistics have proven it over and over. One can also see this occuring in FOQA data - non-precision approaches are generally less stabilized.
The great value in this thread has been the wide discussion between those who know their stuff, about RNAV/GNSS and LOC(BC) approach requirements, legalities, traps and techniques as well as personal experiences. Such a discussion cannot but help others who will inevitably face similar circumstances at some point in their career. If I'm somewhat confused by the mix of RNAV & LOC approach techniques and requirements then others must be as well.
One trap I can recall on the DC9 (which had only 1 DME and the 1:3 mental calculation to aid non-precision descents), is the use of DME which is not co-located with the threshold. We became very good and very fast at using the whiz-wheel* for timing and descent rates to MDA, (the +50ft. requirement is a relatively recent change, made ostensibly because pilots were being failed on their PPC/IFR rides for descending below the MDA on a go-around...)
I think this was a rushed, straight-in approach by a crew who quite possibly were at their circadian low point, into rolling, monotone terrain dimly lit only by twilight, a very challenging set of circumstances. As indicated on the chart, the ILS DME was 1.3nm beyond the threshold so part of the examination will take a look at this as part of investigating how the distance-vs.-altitude descent was calculated and handled.
*"whiz-wheel" - plastic, round slideruley thingy often found in the breast pocket of a pilot or less often in a "leather" pouch in a "brain bag" - the device was equipped with "analog scales" upon which could be done manual calculations of remarkable variation and accuracy. The "other side" of the device modelled "trignometric functions" for actual (real-time) wind "calculations" so that the pilot might track between points with some accuracy. One could find true airspeed, density altitude, do pressure-pattern flying and even find distance and track between two points of latitude and longituded when flying the Atlantic and Pacific, verifying what the Doppler and/or the Loran were telling the pilot. The device, manufactured by the historical map-maker Jeppesen and known as a "CR2" and for those who's eyes were challenged, the "CR3" were humourously known as "computers" at the time.
Last edited by PJ2; 5th Sep 2013 at 17:22.