What happened
On 20 January 2010, a Cessna 560 XLS, registration CS-DXR, was performing a ferry flight from Rotterdam to Amsterdam SchipHD. Upon landing on Runway 06, the crew attempted to decelerate the aircraft using the primary braking system. However, the foot pedals provided no braking effect, and cockpit warning lights for low brake pressure and anti-skid malfunction illuminated.
In an attempt to stop the aircraft, the crew activated the emergency brake system. This action caused the aircraft to veer sharply to the right, exiting the paved surface and traveling through the grass. The aircraft eventually came to a halt on Runway 18L-36R. The incident resulted in major aircraft damage, including a collapsed right main landing gear and damage to the wing surfaces, though there were no injuries to the two crew members.
The investigation
The Dutch Safety Board examined the aircraft, flight data from the QAR, and the physical wreckage. Investigators discovered a trail of hydraulic fluid on the runway and noted that an air traffic controller had observed a mist of fluid trailing behind the aircraft during taxiing.
Technical analysis of the left main landing gear revealed that a component known as a wheel insert had become loose. This looseness was traced back to a failed screw that had succumbed to fatigue. As the wheel rotated, the loose insert struck the brake cylinders, causing two of them to partially unscrew. This created a leak so significant that the primary hydraulic reservoir was emptied, rendering the primary braking system ineffective. Furthermore, because the leak persisted, the secondary emergency system also failed to generate sufficient pressure on the left side, leading to asymmetrical braking.
Findings
- The primary cause of the braking failure was an inadequate interference fit between the wheel insert and the mounting lugs.
- The dimensions of the inboard and outboard lugs on the left wheel did not meet manufacturer specifications, preventing a secure connection.
- This dimensional deviation caused the retaining screw to undergo cyclic loading, eventually leading to its fracture.
- The resulting lateral movement of the insert caused physical damage to the brake cylinders, which subsequently unscrewed and leaked hydraulic fluid.
- The loss of hydraulic pressure on the left side created asymmetrical braking forces, which the crew could not counteract with the rudder at low speeds.
Safety action
Following the investigation, the aircraft manufacturer and the brake manufacturer issued a Service Bulletin. This directive mandates that the dimensions of the inboard and outboard lugs, as well as the insert, must be inspected every time wheels are replaced. Any components found to be below the required thickness must be replaced to prevent similar failures.