What happened
On 8 November 1998, a Boeing 767-300, registration OE-LAU, was performing a scheduled refueling stop at Shannon Airport after a flight from Milan to Cuba. Following a standard landing on Runway 24, the aircraft failed to decelerate sufficiently to exit via Taxiway Alpha. Consequently, the crew had to proceed to the runway end turnaround area to perform a 180-degree turn and backtrack down the runway.
During this maneuver, Air Traffic Control (ATC) requested that the aircraft expedite its clearance to clear the runway for approaching traffic. As the pilot attempted a left-hand turn within the turnaround area, the aircraft failed to respond to steering inputs and began to skid. The aircraft eventually drifted off the paved surface, with the nose wheel traversing 18 meters of grass. There were no injuries to the 254 passengers or the crew, and the aircraft sustained no significant damage.
The investigation
The AAIU examined the surface conditions, aircraft mechanics, and operational procedures at Shannon Airport. Investigators found that while the aircraft's braking and anti-skid systems were functional, the right nose wheel tyre had a tread depth of only 0.2mm above the minimum limit, which reduced its resistance to aquaplaning.
Crucially, the investigation focused on the threshold markings (often called "piano keys") for the reciprocal Runway 06, which occupied the turnaround area. These markings had been heavily over-painted, creating a smooth, hard surface that lacked the texture of the surrounding runway. Furthermore, a recently applied thin-film coating had been applied inappropriately, and existing depressions in the old paint layers were retaining rainwater. This created a condition conducive to viscous aquaplaning.
Findings
- The aircraft entered the turn at a speed higher than the friction levels could safely support.
- The primary cause of the skid was the low friction of the threshold markings, which prevented effective steering and braking.
- The lack of centerline guidance in the turnaround area and the narrow dimensions of the turning area provided a very limited safety margin.
- The pilot was under operational pressure to expedite the runway clearance due to ATC requests.
- The accumulation of rainwater in surface depressions on the painted markings significantly contributed to the loss of control.