What happened
At 1826 EDT, an Israel Aircraft Industries Astra SPX, registered C-GSSS, was landing on Runway 05 at Toronto Pearson International Airport. The aircraft was carrying two crew members and four passengers. Upon touchdown, the aircraft experienced a severe nosewheel shimmu. During the landing roll, the steering system provided an uncommanded full-left input, causing the aircraft to veer sharply to the left.
The flight crew attempted to use differential braking and reverse thrust to maintain directional control, but the steering control became unresponsive to rightward inputs from the first officer. Consequently, the aircraft skidded off the north side of the runway, coming to rest in the infield between Runway 05 and taxiway Juliet. There were no fatalities or injuries resulting from the incident, though the aircraft sustained minor damage.
The investigation
Investigators examined the nose landing gear and discovered that the upper and lower attachment brackets for the steering assembly had failed near the aircraft bulkhead. The left steering actuator was found fully extended while the right was fully retracted, confirming the uncommanded left steering. The entire assembly had rotated and jammed against the right side of the nose landing gear bay.
Analysis of the fracture surfaces revealed that the top attachment bracket had suffered an old failure. Evidence such as polished surfaces, Skydrol contamination, and softened paint suggested the bracket had been failing or rubbing for some time. Fretting on the mating surfaces indicated that steering loads had been transferring to the lower brackets. The lower bracket ultimately suffered an overload failure during the landing shimmy.
Findings
- The primary cause of the incident was that the aircraft had likely been towed beyond its steering limits while the steering scissors were still connected at an earlier date, causing the initial fracture of the upper bracket.
- A nosewheel shimmy during the landing at Toronto Pearson placed excessive stress on the remaining lower attachment bracket, leading to its failure.
- The failure of the steering assembly rendered the steering tiller ineffective, causing the aircraft to become uncontrollable and exit the runway.
- There were no external visual indicators on the aircraft to inform ground personnel of the specific steering limits during towing.
Safety action
Following the investigation, several safety actions were implemented:
- The State of Israel's Civil Aviation Administration issued an Airworthiness Directive requiring inspections of the steering assembly brackets.
- Gulfstream Aerospace LP issued a mandatory Service Bulletin for inspections of the brackets and the nose-centering spring.
- The operator, Partner Jet, issued a memo reminding pilots to disconnect steering scissors after flight and to instruct ground handlers to do the same.
- Maintenance manuals were revised to explicitly caution that the scissors must be disconnected prior to towing to prevent damage to the steering system support brackets.