British Airway visual approach standards
 

I was flying as pax on a BA flight into Nice a few days ago. We flew the Riviera approach to 04L. As we made the final right hand turn to intercept the runway axis, I could see from my window seat that we were low and glancing at the runway we had four reds on the PAPI.

I was a bit surprised as I thought an airline like BA would have fairly strict gate standards on even a visual approach. Do BA procedures allow an approach to continue on four reds?

Without being familiar with this specific approach or BAs operation, here are some general points of view:

If you can see the PAPIs from your passenger window, the aircraft is not yet lined up on the final approach track. It is customary to join this first laterally from the side, and then vertically from below. Ie; the aircraft will maintain present altitude until established on the final approach track. When the correct glide path is intercepted (ie two whites - two red), a descent is begun to maintain the glide path.

It is normal for airlines to have very specific criteria to continue approaches, also visual approaches. This may include minimum altitudes, and more importantly "gates": specified points or altitudes where certain conditions have to be met. Such a gate may be at i.e. 1000' or even 500', which is quite late in the approach.

Sounds like a completely safe and normal approach to me.

I know nothing of BA SOPs but would guess that they require stable approaches.
The Riviera approach (or VOR A as it now called) has a turn in at 3 miles from CGS VOR at a height of 1410 feet, as this is over the sea, it is probably not dangerous to be a little below the profile at that distance, after that you would not see the PAPIs from the side window. Also well done for seeing them out the passenger window as they are sometimes quite difficult to make out in bright sun light.

The standard descent profile from 2000', the MDA, to CGS 3d is 3 degrees. At CGS 3d, if you're on the correct inbound course, you are more than 3d from the PAPI which means it will always indicate low if you have flown the correct instrument approach profile. If you start the turn at CGS 3d and continue that descent profile you will be below the 3 degree approach that the PAPI indicates.

Also the PAPI is calibrated for CAT D aircraft.

Thank goodness somebody glanced at the runway! I normally put my paper down when the TERR ON ND shows all red but when 04L was closed I couldn't wait that long so had to rely on the pax shouting very loudly through the open cockpit door to remind me not to fly through the extended centreline for 04R.

Jesting aside and just out of curiosity, what did the flight crew say when you asked them this question after landing?

Interesting observations from Spandex and Fatflyer - whenever I have flown the approach myself I have always started a 3 degree descent at the MAP (D5 CGS at 2000') and (as Fatflyer points out) this means we make the D3 CGS turn with 2R2W on the PAPI at about 1400', and then continue on 3 degree down to the threshold.

But indeed as Spandex alludes, on looking at the card more carefully, I suppose that there is nothing to stop you descending to below 1400' before the turn, then making a level turn and intercepting the glide slope from underneath, which is what the BA flight did. It doesn't seem the smoothest or most stable option though, and quite a strange way to interpret the card.
http://img195.imageshack.us/img195/6130/niceze.jpg

Didn't think so... :D