Understanding Air France 447 by Bill Palmer Read Free Book Online Page A

Weather
    The crew was aware of the storm before they entered it, but probably not its severity. At 01:46, about 24 minutes before the pitot tubes clogged and the autopilot disconnected, First Officer Bonin dimmed the cockpit lights to see outside and noted that they were entering the cloud cover. At 01:50 the captain and First Officer Bonin discussed their desire to climb higher to get above some of the weather, but that the airplane was too heavy for the outside temperature to do so.
    At 01:51 the captain remarked, “All we needed was Mr. St. Elmo,” obviously referring to St. Elmo’s fire. Bonin said, “I don’t have the impression there was … much … storm … not much.”
    At 01:59 First Officer Robert returned to the cockpit from his rest break. First Officer Bonin briefed him on the weather saying, “Well the little bit of turbulence that you just saw, we should find the same ahead. We’re in the cloud cover unfortunately we can’t climb much for the moment because the temperature is falling much more slowly than forecast.”
    After the captain left, Bonin specifically mentioned the Inter Tropical Convergence Zone to First Officer Robert and the location where they would soon encounter it.
    At 02:06:05, four minutes before the autopilot disconnected, Bonin called the flight attendants and said, “in two minutes there, we ought to be in an area where it will start moving around a bit than now you’ll have to watch out.”
    But First Officer Bonin, who was the pilot in command at the time, apparently had no thought of deviating around the weather.
    At 02:08 First Officer Robert changed the gain on the radar to MAX. That will often significantly increase the displayed weather on the screen - both in quantity and intensity. It must have depicted parts of the storm not previously displayed or noticed. He suggested, “Do you maybe want to go to the left a bit? You can possibly go a bit to the left. I agree that we’re not in manual, eh? Well, you see at twenty with the …” Then “It’s me who just changed it to max.”
    They then turned 12° left.
    At 2:08:17 there was a change in the background noise of the precipitation striking the airplane. Shortly thereafter Bonin commented on a change in the cabin temperature. “Did you do something to the A/C?” He also noticed a smell, apparently concerned, “What’s that smell now?”
    Robert recognized the smell and answered, “It’s ozone, that’s it, we’re alright.” Then explained that ozone is, “the air with an electrical charge.”
    02:09:20 Robert commented, “It’s amazing how hot it is all of a sudden.” Twenty seconds later, the background noise changed and then intensified. The sound was identified by investigators as similar to the typical sound of ice crystals striking the airplane.
    The turbulence intensified and they slowed the aircraft from Mach .82 to the turbulence penetration speed of Mach .80, and the engine anti-ice was selected on. Then at 02:10:02 the autopilot disconnected and within 7 seconds the indicated airspeed fell from 274 knots to 55 knots.
    The discussion among the two first officers was ignored in the accident reports. However, it bares a striking resemblance to a first-hand account of a Northwest Airlines A330 pilot who encountered a loss of airspeed event in the South Pacific, also in the ITCZ 12 . The airplane’s air conditioning system, which extracts its air supply from air coming through the engines, became overwhelmed by the amount of water in the air. It is indicative of the conditions in the updraft they were flying through. The crew reported:
Outside air temperature was -50C SAT -21C TAT (you’re not supposed to get liquid water at these temps). We did.
As we were following other aircraft along our route. We approached a large area of rain below us. Tilting the weather radar down we could see the heavy rain below, displayed in red. At our altitude the radar indicated green or light precipitation, most