How did the crew get to where they were at 0208?
0 h 30 mn The crew received information from the [AF] OCC on the presence of a convective zone linked to the ITCZ between SALPU and TASIL
1 h 35 mn 46 No response from AF 447 to ATLANTICO's request for the estimated time at TASIL
1 h 35 mn 49 Copilot’s ND scale changes from 320 NM to 160 NM.
[Between 1 h 35 mn 53 and 1 h 36 mn 14, ATLANTICO asked again three times for the estimated time at TASIL with no response from the crew.]
1 hr 50 mn 35 The radar display mode changes from WXR ONLY to WXR+TURB. The Captain’s ND scale changes from 160 NM to 40 NM.
[A little later [after changing the scale] he [the Captain] mentioned the appearance of Saint-Elmo’s fire and said that “it’s going to be turbulent” when he went to take a rest.]
2 hr 00 mn 17 Copilot’s ND scale changes from 160 NM to 80 NM.
2 hr 01 mn 46 Captain leaves the cockpit
2 hr 08 mn (approximately) The copilot in the left seat moved the weather radar gain control to maximum, after noticing that he was in calibrated mode.
2 hr 09 mn 53 Copilot’s ND scale changes from 80 NM to 40 NM.
"The signal corresponding to the “fasten seat belts” information was not heard on the recording."
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The following English translation appears to be an extract or summary of AF procedures on use of weather radar.
1.17.3.2.2 Instructions for use of weather radar
In cruise mode above 20,000 feet, a slight downwards adjustment of tilt, depending on the scale selected, is recommended so that the ground echoes only appear on the ND at the edge of the furthest distance circles. This method enables the simple and practical application of the height/tilt rule of equivalence providing the optimum tilt adjustment.
When pilots monitor the weather situation, gain can remain in CAL position. In the confirmed presence of storms and during their avoidance, a manual adjustment can be used for comparison with the CAL image.
A scale of 160 NM enables the change in the weather situation to be assessed and anticipate route changes. A scale of 80 NM is used for avoidance. Short scales must be periodically discontinued in order to observe distant weather conditions and to avoid an impasse amid the disturbances.
The shape of the echoes may alert the crew to the possible presence of hail. Zones of turbulence may be presented above a detected zone of precipitation.
Red or magenta zones as well as fringe-shape echoes must in this way be by-passed from windward by regularly adjusting the tilt and the range. The avoidance decision must be taken before the echoes are at 40 NM.
The operator recommends avoiding flying less than 5,000 ft above or below a storm cell. It provides a formula for pilots to estimate the separation height between the top of a detected cell and the airplane. This formula uses the distance and the tilt points from which the zone echo disappears. Above 23,000 ft, it is recommended to fly more than 20 NM from these zones. (Compensated by 50%, that is 30 NM for U- or finger-shape echoes or with scalloped edges (storms, presence of hail).
In CAL mode without adjusting tilt, the BEA report notes that ice crystals will be hard to detect. The report also notes that "An oceanic cumulonimbus reflects radar waves less than a continental cumulonimbus cloud of the same size and height."
The change in gain from CAL to MAX on the PNF display was not made until 0208. There was apparently no change in tilt over this period.