(Canadian OH&S News)
The Transportation Safety Board of Canada (TSB) said that it is concerned that runway overruns may continue if no more is done to understand the issue of uncommanded nose wheel steering events on Boeing aircraft.
The announcement follows the release of a TSB investigation report into a Nov. 30, 2010 incident involving an American Airlines Boeing 737-800 at the Montreal-Pierre Elliott Trudeau International Airport. That day, an aircraft on flight into Montreal from Dallas landed normally on a wet runway, but as it was slowing down, it veered, uncommanded by the crew, towards the left side of the runway, said the TSB report, released on Nov. 5.
Even though the captain managed to steer the plane partially back to the runway centre line, it continued to travel left and exited the runway surface. There were no injuries and damage to the aircraft was minor.
Investigators found that the uncommanded veer was likely due to a jam in the nose wheel steering system, but they did not find any anomalies with the system, “as the jam likely cleared up.” The report noted that there are no written procedures to manage a problem of this kind and the aircraft’s flight data recorder does not record parameters from the nose wheel steering system, making it difficult to determine when and how problems with nose wheel steering occur.
In the past 21 years, there have been 11 similar occurrences around the globe involving various Boeing aircraft types, the TSB said in a statement. “The cause of these uncommanded nose wheel steering occurrences remains uncertain, despite post-event examinations and other efforts to analyze them,” the statement read. “The manufacturer’s safety review process has deemed these occurrences to be an acceptable risk given their remoteness, and the manufacturer has not taken further action to correct them. As their cause is uncertain and because little is being done to better understand the problem, the [TSB] is concerned that there remains a risk for runway excursions to occur.”
Following the incident, American Airlines now discusses this occurrence as part of recurrent training for its flight crews to raise awareness of the possibility of such an event, the TSB reported.