Airbus has submitted a US patent application for an independent means of monitoring an aircraft's pressure-based airspeed measurement for errors.
While the process is mainly geared at determining pitot system errors on the takeoff roll, giving pilots the ability to abort a takeoff before flight speeds are attained, Airbus in the 3 December filing also notes that "failure to detect these erroneous measurements can have unfortunate consequences during flight".
Airspeed data has been a key focus in the unexplained crash of an Air France Airbus A330 off the coast of Brazil on 1 June. According to French investigators, 10 of the 24 automated messages transmitted by the aircraft in its final 5min of communication have been attributed to an inconsistency of speed measurements.
Both Europe and the US have issued airworthiness directives on certain Thales-built pitot tubes that are used on the A330 and A340 in the aftermath of the crash. "Depending on the prevailing airplane altitude and weather, this condition, if not corrected, could result in reduced control of the airplane," said the FAA in its 3 September mandate.
Pitot tubes, also known as pitot sondes, provide air pressure data used for to compute airspeed. Investigators have not tied potential problems with the devices to the Air France disaster at this point however.
Airbus in its patent application notes that "pitot sondes are easily blocked by dust, insects or any other matter foreign thereto. An error in speed measurement results therefrom. This type of error can have catastrophic consequences if it is not detected".
Of particular concern to the airframer is warning pilots of an airspeed inaccuracy while the aircraft remains on the ground during the critical takeoff phase, though the technology would also aid crews in understanding related anomalies in cruise.
The proposed airspeed monitoring system would compare changes in measured airspeed over a short period of time with changes in ground speed as computed by the accelerometers and gyros in the aircraft's air data and inertial reference unit (ADIRU). Airbus says the ADIRU has a "storage zone" available where the computations can be performed.
While airspeed and ground speed can not be compared directly, Airbus notes that over a "very short period", normally significant factors like wind speed, changes in altitude, air temperature and angle of attack will be negligible, allowing for a direct comparison of changes in speed rather than speed itself.
Once the speed differences exceed a pre-set threshold, the ADIRU system would alert the pilots with visual and/or aural warnings.
Source: Air Transport Intelligence news
