Originally Posted by
CurtainTwitcher
There is a difference between the capabilities of the aircraft, the design of the approach and the FMC coding.
Yes, you are correct. My mistake, I hadn’t seen that approach chart.
I don’t know how it’s coded in the FMC, but the chart certainly makes it look like a dodgy approach. I am lucky enough to fly in a part of the world where almost every RNP or RNAV GNSS approach is coded to the runway, or at least very close to it in the case of GNSS.
This approach has an MDA of 420 feet at 2.2NM from the threshold. If you need to get to 420 feet to get visual, it won’t work on a 3 degree slope. You would have to fly it as a dive-and-drive, which is not a recommended procedure in my part of the world. Presumably the surrounding terrain coupled with LNAV GNSS design criteria makes it impossible to get any closer. Flying that approach in my airline would be done at 3 degrees, with autopilot off and flight directors cycled by the MAP (if visual). Not something you would do if you couldn’t clearly see the runway.
Even without RNP-AR (which I have no idea if this airline is certified for), Australia has implemented LNAV/VNAV GNSS criteria at many airports, which gets the aircraft quite a bit lower/closer sometimes, and sometimes even lower than RNP-AR 0.10 (which I can’t work out).
They are possibly lucky they hit the water. Otherwise they might have hit one of those hills.
Obviously the flight crew should not be fudging the visibily requirements of the approach (if indeed they were), but it would be interesting if procedure design and/or the cost of a better procedure design is a contributing factor. It also could be possible that the terrain would limit even GLS from getting any lower at DA, but at least GLS can remain coupled to the threshold, and could prevent this type of accident. I can’t believe how slowly the world is adopting GLS. The FAA has apparently delayed GLS adoption indefinitely. It seems to be very expensive, and I don’t understand why that needs to be the case.