Capt Blogs etc:
>>Satellites not in optimal positions.
The satellite constellation is fixed, while the Earth rotates inside it. Thus the number of satellites you can see, and the declination and azimuth of those satellites, will change during the day (and with your location). Some locations and times are better than others - especially if there is a satellite outage in your area.
>>Nav Performans Scales
>>and vertical profiles
Not fitted in our steam driven Boeing. But we do have the approaches in the FMC. Beginning to see the problem of the lack of regulatory oversight?
>>IRS backup.
Worse than useless. As I said before, our IRS fix can easily be a couple of miles away from the GPS fix, and the VOR/DME is not much better in mountainous terrain. So if you lose the GPS on the approach, and the FMC position reverts to IRS fix position, you get a rapid 2nm map-shift. Ok, so the nearest mountain peak is only a couple of nm away, and the autopilot is trying to recapture the new IRS trackline which is 2nm away - your move, as they say...
>>TCAS assisted incidents.
The Swiss collision would not have happened without TCAS. It was a total system usage error that had not been fully thought through and promulgated to all airlines and crews before the incident.
>>RAIM outages.
RAIM is real-time monitoring of the satellite constellation. You cannot determine RAIM outages by NOTAMS. Or are you telling me that the NOTAMS know exactly when the next satellite will be hit by some space debris, or lose its IRS stability system?
>>300ft per nm
Brilliant. The max altitude deviation on a 0.3 nm rnp approach is just 75ft, and the hills are all around you. Is that a satisfactory check? Do you really monitor ILS glideslope excursions by doing a 3x crosscheck?