Germany's Der Spiegel has a detailed story about the last minutes of Air France Flight 447. Last June, en route from Rio to Paris, it crashed in the Atlantic, killing all 228 people aboard. Preliminary indications are that one factor was ice on the pitot tubes that control the airspeed indicators. Apparently nearly all jets in service have a potentially catastrophic flaw.
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).
Without an airspeed reading, everything else can fail--a situation French pilots' union head Gérard Arnoux likens to having a stroke. That's exactly what happened to Air France 447. In rapid succession, the plane lost everything--autopilot, computers and all--stalled, and fell into the ocean.
Most pilots usually don't train for a high-altitude failure of the airspeed indicator--and according to French pilots' union head Arnoux, there's not a whole lot they can do even when you are trained for it.
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."
Moreover, it can happen so fast that there's literally no time to prepare the passengers for emergency procedures. The BEA, the French equivalent of the NTSB, indicates that there was no evidence the passengers were briefed for an emergency landing. The flight attendants weren't in their seats, and the lifejackets weren't even touched. This may have been because the plane was falling at 95 mph--the same speed as a skydiver in free fall.
According to Der Spiegel, there have been at least 13 incidents involving pitot-tube icing on Boeing jets in the States. Boeing is currently doing a study on possible safety issues rising from ice getting on the tubes at high altitudes.
Still, it's staggering to notice that airspeed indicators are still being tested according to standards dating to the days when passenger planes were flown using propellers and turboprops. Hopefully it won't take another "tombstone" moment to do something about a serious flight safety issue.