Originally Posted by
Dick Smith
When carrying out the Bankstown RNP RWY 11C approach from the RAKSO IAF with a Garmin G1000 equipped aircraft while coupled to the autopilot, strange things happen. Fly over RAKSO at 3,700 feet and the Garmin unit doesn’t start descending to the 2,500’ SBKWI IF until there is a 3˚ approach angle. This would put the aircraft into the 2,500’ step.
In fact, if you look at the approach plate, it shows the descent should start at RAKSO from 3,700’, then go at a constant angle to WI at 2,500’. Once again, that means that the aircraft will clip the 2,500’ 20 DME Sydney Class C step. In effect, it means that the expensive and safer autopilot coupled system can not be used in this case.
Does anyone have an answer to this as to why the Garmin approach doesn't actually follow what is required in practice?
The chart is a LNAV chart, i.e. 2D, there is no descent angle coded in database. What annunciation did you have on the HSI, LNAV or LNAV+V ?
The initial segment from RAKSO to WI is actually from the Westmead Hospital RNP 052 chart, that charts has crossing WI at 2700 (it’s steeper at 3.07 degree). To fly the BWU approach at near 3 degree all the way, cross RAKSO at 6700 ft (13.3 nmx318 ft/nm +2500), cross 6.5 WI at 4600 (6.5x318+2500), that is the 2500 ft SY step, cross WI at 2500.