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

likely ice crystals we thought.
Entering the cloud tops we experienced just light to moderate turbulence. (The winds were around 30 kts at altitude.) After about 15 sec. we encountered moderate rain. We thought it odd to have rain streaming up the windshield at this altitude and the sound of the plane getting pelted like an aluminum garage door. It got very warm and humid in the cockpit all of a sudden.
Five seconds later the captain’s, first officer’s, and standby airspeed indicators rolled back to 60 kts. The auto pilot and auto throttles disengaged. The Master Warning and Master Caution flashed, and the sounds of chirps and clicks letting us know these things were happening.
The Capt. hand flew the plane on the shortest vector out of the rain. The airspeed indicators briefly came back but failed again. The failure lasted for THREE minutes. We flew the recommended 83% N 1 power setting. When the airspeed indicators came back. We were within 5 knots of our desired speed. Everything returned to normal except for the computer logic controlling the plane. (We were in alternate law for the rest of the flight.)
We had good conditions for the failure; daylight, we were rested, relatively small area, and light turbulence. I think it could have been much worse. The captain did a great job flying and staying cool. We did our procedures called dispatch and maintenance on the SAT COM and landed in Narita. That's it.
    The Air France 447 investigation concluded that ice crystals had clogged the pitot tubes. But the similarity in sounds between and interior air conditioning effects between the above account and AF447 indicates that water ingestion should not be completely discounted.
    Alternate law is locked in for the remainder of the flight, and the autopilot cannot be engaged, in cases where the airspeed does not return to within 50 knots of the original airspeed within about 10 seconds.
    On February 2, 2013, an Etihad Airways A340-600 experienced an unreliable airspeed incident en route from Abu Dhabi, UAE to Melbourne, Australia. The incident’s preliminary report 13 states:
While cruising at FL350, just leaving Colombo FIR and entering Melbourne FIR, the Aircraft encountered moderate to heavy turbulence and experienced significant airspeed oscillations on the captain’s and standby indicators. The autopilot, autothrust and flight directors were disconnected automatically. The aircraft’s flight control law changed from Normal to Alternate Law, which caused the loss of some of the flight mode and flight envelope protections. The change from Normal to Alternate Law occurred twice, thereafter the Alternate Law stayed until the end of the flight. Auto-thrust and flight directors were successfully re-engaged, however, both autopilots (autopilot 1 and 2) could not be re-engaged thus the Aircraft was controlled manually until its landing.
    Weather Radar
    All of these affected flights had operating weather radar, but interpretation of weather radar requires skill, experience, and understanding of the principles involved. It is not unlike a doctor reading an x-ray. We can all find the bone on an x-ray, but it takes training and experience to discern meaning from the subtle shadows and gradients. Airborne weather radar is much the same. The radar control allows the pilot to adjust the tilt of the radar beam, the sensitivity of the receiver (gain), and the range and brightness of the display. The colors and shapes have to be interpreted. Unfortunately the pilot does not have the option to call in a radiologist.
    Pilots rely on weather radar to navigate around storms. The objective is to avoid dangerous turbulence. Radar does not directly indicate turbulence. But operating and interpreting it correctly can indicate conditions where varying degrees of turbulence are likely to be.
    Radar sends out pulses of radio waves and then listens for those waves to bound back off of water droplets about the size of a raindrop.
    Heavy concentrations of