What happened
In mid-January 1996, two separate runway excursion incidents occurred involving identical aircraft types. The first event took place on Friday, 12 January, involving the ZK-POB, a Metroliner. The second event occurred several days later, on Thursday, 18 January, involving the ZK-SDA, also a Metroliner.
In both instances, the aircraft veered from the runway during the landing roll. During these operations, the pilot flying engaged the nosewheel steering system, which led to the loss of directional control on the runway. Neither incident resulted in no injuries, and the physical damage sustained by both aircraft was categorized as minor.
The investigation
An investigation into these two events established a pattern regarding the use of aircraft systems during landing. Investigators examined the mechanical state of the nosewheel steering systems and the decision-making processes of the flight crews. The inquiry focused on why the steering was engaged during the landing phase and how the mechanical failures were managed.
Findings
The investigation identified two primary drivers for these excursions. First, a malfunction of the nosewheel steering system was present. Second, the pilots continued to use the aircraft system despite it being unserviceable. This perseverance with a faulty system contributed directly to the loss of control on the runway.
Safety action
Following the investigation, two specific safety concerns were addressed. There was a noted lack of clear instructions provided to pilots regarding the proper control of the aircraft during the landing roll. Additionally, investigators identified a risk that the nosewheel steering system amplifier could fail without being detected by the crew. Consequently, safety recommendations were issued to address both the lack of procedural clarity and the need for better detection of system failures.