MONTREAL—Canadian investigators are “concerned” about safety risks stemming from nose-wheel steering assemblies in some Boeing aircraft.
According to the Transportation Safety Board of Canada (TSB), an investigation into the November 2010 runway overrun of a Boeing Co. 737-800 in Montreal was caused by an “un-commanded veer” in the steering assembly—one of 12 reported instances worldwide involving Boeing aircraft over the past 21 years.
The TSB investigation probed the incident involving a Montreal-bound American Airlines flight from Dallas, where the Boeing aircraft left the runway at Pierre Elliott Trudeau International Airport Nov. 30, 2010.
With 113 passengers and crew aboard, the aircraft landed normally on a wet runway in a crosswind, according to the independent government agency.
“As the aircraft was slowing down, it veered, un-commanded by the crew, towards the left side of the runway,” the TSB said in a release.
The captain, who was in control of the aircraft at the time, attempted to use the rudder and nose wheel steering tiller to steer the aircraft back to the runway centerline.
Although the aircraft heading started to return back towards the runway heading, the agency said the aircraft continued to travel towards the left and exited the runway surface.
There were no injuries and damage to the aircraft was minor.
Investigators found that the un-commanded veer “was likely due to a jam in the nose wheel steering system.”
They didn’t find any anomalies with the nose gear wheel system, meaning the jam likely cleared up.
According to the TSB, the flight crew did not receive any indication that a problem existed with the nose gear steering system, nor is there any written procedure to manage a nose wheel steering problem of this kind.
The aircraft’s flight data recorder (FDR) does not record parameters from the nose wheel steering system, making it difficult to determine when and how problems with nose wheel steering occur.
There have been 11 similar occurrences reported involving various Boeing aircraft types in the past 21 years throughout the world, the TSB claims.
The cause of these un-commanded nose wheel steering occurrences remains uncertain, despite post-event examinations and other efforts to analyze them.
The TSB also said “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.”
With the cause still uncertain and little “being done to better understand the problem,” the TSB is concerned that a risk for runway excursions to occur still exists.
Whether the nose-wheel steering assembly was manufactured by Boeing or third-party contractor wasn’t immediately available.
The TSB did not say what Boeing models made up the other 11 similar incidents.