They may as well have made the hull of the Titanic out of plate glass!
I remember once, friend Walt sent me a record of the temperatures and altitudes he wrote down from the passenger-provided air display monitor on a Boeing 757, as he flew from San Diego to Atlanta, and began descending over Mississippi, on October 7, 2006. Comparing his records with the Shelby, AL, National Weather Service sounding underway at nearly the same time, I realized Walt's records were complete junk - the temperature was much too high. The temperature monitor likely had iced over and was no longer functional, even on this normal, humdrum flight. At the time, Walt replied:
I knew it!!! Those bastards!!! When I flew over from Italy in June, at 39000 ft, the temperature was about -50 or -60 F the whole way. On this trip, they reported it at -30 to -35 F at 39K and 41K feet everywhere from CA to MS. If you can't trust data, what can you trust?I was mystified why icing may have occurred on this particular flight - perhaps water had somehow entered the device when the aircraft was on the tarmac in San Diego, or perhaps the aircraft had flown through rain clouds before rising to levels where the remnant water could freeze. It just illustrates how insidious ice can be. Granted, it is easier to ice up thermistors or thermocouples than pitot tubes, but still, icing is a chronic threat that has to be guarded against at every step!
How much more likely it is that icing will occur when flying right through powerful thunderstorms! As far as the thunderstorm was concerned, the Airbus aircraft was nothing but a giant hailstone, and a perfect icing target!
In addition, the aircraft was faced with a wall of thunderstorms (the Intertropical Convergence Zone near the equator can be like that at times) and there was no feasible way to fly around the wall without a huge detour - five hundred, or a thousand miles, perhaps. They had no fuel or time for such huge detours! The pilots thought they could fly high enough to avoid much of the turbulence and lightning and icing. Surely a modern aircraft should be sturdy enough to tackle such challenges as posed by thunderstorms. The pilots miscalculated. Their faith in technology was misplaced.
This manner of disaster will happen again, and again, and again, unless they get a handle on this! I just hope I'm not riding on any one of those fated aircraft!:
Air France flight 447 had been in the air for three hours and 40 minutes since taking off from Rio de Janeiro on the evening of May 31, 2009. Strong turbulence had been shaking the plane for half an hour, and all but the hardiest frequent flyers were awake.
Suddenly the gauge indicating the external temperature rose by several degrees, even though the plane was flying at an altitude of 11 kilometers (36,000 feet) and it hadn't got any warmer outside. The false reading was caused by thick ice crystals forming on the sensor on the outside of the plane. These crystals had the effect of insulating the detector. It now appears that this is when things started going disastrously wrong.
Flying through thunderclouds over the Atlantic, more and more ice was hurled at the aircraft. In the process, it knocked out other, far more important, sensors: the pencil-shaped airspeed gauges known as pitot tubes.
One alarm after another lit up the cockpit monitors. One after another, the autopilot, the automatic engine control system, and the flight computers shut themselves off. "It was like the plane was having a stroke," says Gérard Arnoux, the head of the French pilots union SPAF.
The final minutes of flight AF 447 had begun. Four minutes after the airspeed indicator failed, the plane plunged into the ocean, killing all 228 people on board.
...Over the course of several months of investigation, experts have gathered evidence that allows them to reconstruct with relative accuracy what happened on board during those last four minutes. It has also brought to light a safety flaw that affects all jet airplanes currently in service. "An accident like this could happen again at any time," Arnoux predicts.
...Captain Marc Dubois, 58, goes through the flight plan of AF 447: He enters a starting weight of 232.757 tons into the on-board computer, 243 kilograms less than the maximum permissible weight for the A330. As well as the passengers' luggage, the ground crews load 10 tons of freight into the cargo bay. Dubois has more than 70 tons of kerosene pumped into the fuel tanks. That sounds a lot more than it actually is, because the plane consumes up to 100 kilograms of kerosene every minute. The fuel reserves don't give much leeway.
It's only by means of a trick that the captain can even reach Paris without going under the legally required minimum reserves of kerosene that must still be in the plane's tanks upon arrival in the French capital. A loophole allows him to enter Bordeaux -- which lies several hundred kilometers closer than Paris -- as the fictitious destination for his fuel calculations.
"Major deviation would therefore no longer have been possible anymore," says Gerhard Hüttig, an Airbus pilot and professor at the Berlin Technical University's Aerospace Institute. If worse came to worst, the pilot would have to stop and refuel in Bordeaux, or maybe even in Lisbon. "But pilots are very reluctant to do something like that," Hüttig adds. After all, it makes the flight more expensive, causes delays and is frowned upon by airline bosses.
After takeoff, Dubois quickly takes the plane up to a cruising altitude of 35,000 feet (10.6 kilometers), an altitude known as "flight level 350." According to his kerosene calculations, he has to climb far further, to above 11 kilometers, where the thin air reduces his fuel consumption.
...It's hard to imagine a more precarious situation, even for pilots with nerves of steel: Flying through a violent thunderstorm that shakes the entire plane as the master warning lamp starts blinking on the instrument panel in front of you. An earsplitting alarm rings out, and a whole series of error messages suddenly flash up on the flight motor.
The crew immediately recognized that the three airspeed indicators all gave different readings. "A situation like that goes well a hundred times and badly once," says Arnoux, who flies an Airbus A320 himself.
The responsible pilot now had very little time to choose the correct flight angle and the correct engine thrust. This is the only way he could be certain to keep flying on a stable course and maintain steady airflow across the wings if he didn't know the plane's actual speed. The co-pilot must therefore look up the two safe values in a table in the relevant handbook -- at least that's the theory.
"In practice, the plane is shaken about so badly that you have difficulty finding the right page in the handbook, let alone being able to decipher what it says," says Arnoux. "In situations like that, mistakes are impossible to rule out."
Aerospace experts have long known how dangerous it can be if the airspeed indicators fail because the pitot tubes ice up. In 1998, for example, a Lufthansa Airbus circling over Frankfurt Airport lost its airspeed indicator, and a potential tragedy was only averted when the ice melted as the plane descended. At the time, German air accident investigators at the German Federal Bureau of Aircraft Accident Investigation (BFU) in Braunschweig demanded that the specifications of the pitot tubes be changed to enable "unrestricted flight in severely icy conditions."
As early as 2005, the French aerospace company Thales, which manufactures the pitot tubes used on flight AF 447, set up a project group called Adeline to search for new technical solutions to the problem. According to a Thales document, loss of the airspeed indicators "could cause aircraft crashes, especially in cases in which the sensors ice up."
Aircraft manufacturer Airbus was well aware of the shortcomings of the Thales pitot tubes. An internal list kept by the airline manufacturer shows there were nine incidents involving them between May and October 2008 alone.
More than two months before the Air France crash, the issue had been raised at a meeting between Airbus and the European Aviation Safety Agency. However, the EASA decided against banning the particularly error-prone pitot tubes made by Thales.
In fact, the problem with the airspeed indicators lies far deeper. To this day, the relevant licensing bodies still only test pitot tubes down to temperatures of minus 40 degrees Celsius (minus 40 degrees Fahrenheit) and an altitude of about 9,000 meters (30,000 feet). These completely antiquated specifications date back to 1947 -- before the introduction of jet planes.
What's more, most of the incidents of recent years, including that involving the ill-fated flight AF 447, occurred at altitudes above 10,000 meters (33,000 feet).
Did the pilots on flight AF 447 know about the airspeed indicator failures experienced by colleagues on nine other aircraft belonging to their own airline? Air France had indeed distributed a note about this to all its pilots, albeit as part of several hundred pages of information that pilots find in their inbox every week. One thing is certain: The pilots on flight AF 447 had never trained in a flight simulator for a high-altitude breakdown of the airspeed indicator.
The situation in the cockpit was made even more difficult by the fact that the flight computer of the A330 put itself into a kind of emergency program. The plane's digital brain usually supervises all activity by its pilots -- at least, as long as its sensors provide reliable data. Without a speed reading, the computer more or -less throws in the towel, which doesn't make things easier for the pilots.
"The controls suddenly feel completely different to the pilot," says flight expert Hüttig. The sheer complexity of the Airbus' systems makes it difficult to control in critical phases of the flight. It would be easier for pilots if they could simply switch the computer off in critical situations, as is possible on Boeing planes.
Pitot tubes sometimes also fail on Boeing aircraft. When SPIEGEL contacted the American Federal Aviation Administration, the body which oversees civilian flight in the US, the FAA confirmed that there had been eight such incidents on a Boeing 777, three on a 767, and one each on a 757 and a Jumbo. Boeing is currently conducting a study on the safety effects of "high-altitude pitot icing on all models in its product line," says FAA spokeswoman Alison Duquette. The FAA did not, however, identify "any safety issues arising" during these incidents.
Could it therefore be that the flight computer, which is hard to manage in emergencies, actually contributed to the loss of control by the Airbus pilots? Air-safety experts Hüttig and Arnoux are demanding an immediate investigation into how the Airbus system reacts to a failure of its airspeed sensors.
...Not long after the airspeed indicator failed, the plane went out of control and stalled. Presumably the airflow over the wings failed to provide lift. Arnoux, from the pilots' union, estimates that the plane fell toward the sea at about 42 meters per second (95 mph) -- almost the same speed as a freefalling parachutist.
Arnoux's version of events is based in part on the timing of a transmitted error message about the equalization of pressure between the cabin and the outside of the plane, which usually happens at 2,000 meters (7,000 feet) above sea level. Had the airplane nosedived, this alarm would have been triggered earlier. "It takes almost exactly four minutes to freefall from cruising altitude to sea level," Arnoux says.
...According to this scenario, the pilots would have been forced to watch helplessly as their plane lost its lift. That theory is supported by the fact that the airplane remained intact to the very end. Given all the turbulence, it is therefore possible that the passengers remained oblivious to what was happening. After all, the oxygen masks that have been recovered had not dropped down from the ceiling because of a loss of pressure. What's more, the stewardesses weren't sitting on their emergency seats, and the lifejackets remained untouched. "There is no evidence whatsoever that the passengers in the cabin had been prepared for an emergency landing," says BEA boss Jean-Paul Troadec.
Two seemingly insignificant lines from the warning reports transmitted by the aircraft show how desperately the pilots fought to keep control. They read "F/CTL PRIM 1 FAULT" and "F/CTL SEC 1 FAULT".
This somewhat cryptic shorthand suggest the pilots tried desperately to restart the flight computer. "It's like trying to turn your car engine off and then on again while driving along the motorway at night at 180 kilometers an hour (110mph)," says Arnoux.
The attempt to resuscitate the on-board computer proved unsuccessful. For the last 600 meters (2,000 feet) before impact, the pilots' efforts would have been accompanied by the chilling calls of an automated male voice: "Terrain! Terrain! Pull up! Pull up!"
More than 200 tons of metal, plastic, kerosene and human bodies smashed into the sea. The sheer force of the impact is described in the forensic report, which lists in graphic detail how lungs were torn apart and bones were shredded end to end. Some of the passengers were sliced in half by their seatbelt.
...For several years now, Airbus has offered its customers a special safety program - called "Buss" -- at a cost of €300,000 per aircraft. If the airspeed indicator fails, this software shows pilots the angle at which they must point the plane.
Up to now, Air France has chosen not to invest in this optional extra for its fleet.
