US Federal Aviation Administration orders replacement of airspeed sensors in Airbus A330, A340 planes

The United States Federal Aviation Administration (FAA) has ordered US-based airlines to replace airspeed indicators in some Airbus aircraft following suspicions that the devices might have had a role in the crash of Air France Flight 447 in the Atlantic Ocean on June 1, 2009, in which all 228 people on board perished.

Investigators in France have pointed out the possibility that the airspeed sensors of the Flight 447 “iced over” and sent false speed information to the computers as the aircraft ran into a thunderstorm while it was flying at an altitude of around 35,000 feet.

The Airbus A330 disappeared over the Atlantic Ocean while it was flying from Rio de Janeiro to Paris. The airspeed probes in question are built by the France-based company Thales SA.

In a notice published in the Federal Register, the  Federal Aviation Administration said that all United States-based Airbus A330 and Airbus A340 planes must replace, within 120 days, on each plane at least 2 of the 3 speed sensors made by the electronics major Thales.

The FAA-approved replacements have been manufactured by Goodrich Corporation, based in North Carolina, the United States.

The FAA’s order is applicable to 43 Airbus A330 aircraft registered in the United States – 32 of them operated by Northwest Airlines (now a part of Delta Air Lines), and the rest 11 planes operated by US Airways. There are no Airbus A340 aircraft registered in the United States.

In a press release, the FAA said that its order was based on “numerous reports” that the airspeed sensors, or the Pitot tubes, can get blocked at high altitudes in stormy weather, leading to either a loss of information on airspeed or inexact information on airspeed.

According to the FAA, Northwest Airlines and US Airways have already replaced their older Pitot tubes, made by Thales, with new models, and US Airways has installed speed indicators, manufactured by Goodrich Goodrich Corporation, to replace the Thales-made devices.

Delta Airlines said in a statement that the carrier is “working with Airbus Industries and Goodrich Corporation” in order to meet the replacement deadline set by the Federal Aviation Administration.

The Pitot tube works this way: while the speedometer of a land-vehicle uses the rotation of tyre to calculate speed, the Pitot tube in an aircraft measures the changing air pressure.

Computers interpret the information given by the Pitot tube as speed. In effect, while a car with a wrecked speedometer is mainly an inconvenience and not a hazard, an inactive Pitot tube can cause accidents since most airplane-control systems depend on accurate airspeed information for proper functioning.

According to aviation safety experts, in Airbus aircraft – which are highly automated – recent incidents have shown that either the absence of data on airspeed or inexact data could result in potentially hazardous events such as the shutdown of the autopilot and of the automatic power system.

A stalled Pitot tube can also lead to the aircraft’s  computers shifting to “alternate law” – that is, a situation in which nearly the total  control of the plane’s systems have to be taken care of by the  pilot.

An abrupt reversion to alternate law, or a totally manual flight, is usually resorted to as a last-ditch attempt to give the pilot an opportunity to save an aircraft in dire trouble, say safety experts.