Canadian investigators discovered damage that jammed the rudder mechanism of a Pilatus PC-24 which suffered control problems during climb en route to Kelowna.
The aircraft had taken off from Vancouver on 3 November last year.
It had been passing through 24,000ft, at 280kt, on its way to the cruise altitude of 27,000ft when the crew felt a “brief shudder” followed by a “loud bang”, states Transportation Safety Board of Canada in a newly-issued bulletin.
The executive jet yawed right and started accelerating as it pitched nose-down.
Its captain responded by reducing thrust on both engines and applying left rudder, while instructing the first officer to apply nose-left rudder trim in a bid to counter the yaw.
“Attempts to control the yaw with rudder trim were unsuccessful,” the safety board says.
Control of the jet was passed to the first officer and directional manoeuvring was achieved by reducing airspeed and using differential engine thrust. Both pilots applied left-rudder pedal pressure.
The crew declared an emergency and notified air traffic controllers of the problems, adding that the aircraft would be landing at Kelowna. It touched down without incident and neither the pilots nor the jet’s passenger was injured.
Inspection of the PC-24 found that the rudder mass balance weight arm had broken away, and lodged in a position that prevented full rudder movement.
The examination also revealed that rudder trim-tab control rods had separated aft of the rudder trim actuator.
Transportation Safety Board of Canada identifies the aircraft as C-FMHR, delivered in late 2020 to the Canadian beverage company Mark Anthony Group.
About six weeks after the incident the European Union Aviation Safety Agency issued an emergency directive for the PC-24, following determination that titanium bolts on the rudder trim-tab actuating rods are susceptible to unexpectedly high oscillating loads arising from aerodynamic forces.
EASA warned that the condition could lead to failure of the components and potential damage to the rudder and rudder trim-tab, with consequent reduction, or even loss, of control.
Pilatus issued a service bulletin with instructions to conduct one-time inspections and replace affected parts, pending development and certification of a new design.