What happened
On the afternoon of 27 June 2010, a Boeing 737-800 operated by Ryanair Ltd. was parked at Dublin Airport following a flight from Krakow. As passengers began exiting the aircraft through the rear door, the first three individuals stepped onto a mobile air stairs unit. During this process, the telescopic stairs partially collapsed, resulting in one serious injury to a passenger's leg as they became trapped in the shifting mechanism.
The investigation
The investigation focused on the mechanical integrity of the LTPS 2636 air stairs unit. Testing of the specific unit involved in the accident revealed that one of the two locking pawls, which are intended to secure the sliding section against arrestor blocks, was unserviceable. Furthermore, the malfunctioning pawl was found to be interfering with the movement of the remaining functional pawl.
Investigators discovered that the stairs could enter a "false lock" state. In this condition, the upper platform and the sliding step appear properly aligned, even though the locking mechanism is not fully engaged. While this unstable state could support a single person, the weight of three passengers caused the mechanism to fail. The sudden downward slide of the upper section, combined with the simultaneous movement of the next step, created a gap that trapped the passenger's limb.
Findings
- The primary cause of the collapse was a false locking configuration where the arrestor block rested on the leading edge of a single serviceable pawl rather than being fully secured.
- One locking pawl on the unit was unserviceable and unable to engage the arrestor blocks.
- The mechanical failure of the unserviceable pawl was actively obstructing the operation of the functional pawl.
- The design of the LTPS 2636 unit allowed for a state where the stairs appeared locked despite the mechanism being improperly engaged.
Safety action
Following the incident, several safety measures were implemented:
- Ryanair Ltd. committed to ensuring ground personnel visually verify and crosscheck the engagement of both pawls before every use, and updated training to help staff recognize improper engagement.
- Ryanair Ltd. also agreed to review maintenance procedures for air stairs.
- The manufacturer, TB Davies (UK) Limited, issued a Critical Customer Safety Bulletin to alert operators to the risk of false locks and assigned engineers to review the design of the LTPS 2636 units for potential modifications.