What happened
On September 3, 1998, a Mitsubishi MU-2B-35, registration N8484T, was performing an instrument flight rules (IFR) mission at Marinevliegkamp De Kooy in Den Helder. During the landing phase on runway 22, the aircraft encountered heavy rainfall and significant standing water on the runway surface. The pilot touched down approximately halfway down the runway, which significantly reduced the available stopping distance.
Despite applying full reverse pitch and braking, the aircraft could not decelerate sufficiently. The aircraft eventually drifted off the runway and tilted to the right, causing the right wingtip and part of the stabilizer to strike the ground. The crew, consisting of a pilot and a co-pilot, escaped the aircraft without injury.
The investigation
The investigation by the Dutch Safety Board examined the aircraft's performance, the runway conditions, and the actions of both the flight crew and air traffic control. Investigators found that the runway was in a "contaminated" state, with standing water exceeding 3 mm, rather than simply being a "wet" runway.
Technical analysis of the braking system showed no mechanical failures, but noted that the aircraft lacked an anti-lock braking system. The investigation also identified that the tires had low tread depth, which contributed to the occurrence of both standard aquaplaning and "reverted rubber" aquaplaning. Furthermore, the investigation scrutinized the approach speed, noting that the crew utilized a speed of approximately 115 KIAS, which was higher than the 101 KIAS recommended by the aircraft flight manual for that configuration.
Findings
Several contributing factors led to the runway excursion:
- The pilot landed too far down the runway, effectively halving the available landing distance.
- The pilot utilized an incorrect braking technique by applying full pressure to the brake pedals, which caused the wheels to lock up.
- The runway was contaminated with significant amounts of standing water, leading to aquaplaning.
- The approach speed was higher than necessary for the specific runway conditions.
- Air traffic control provided information regarding the rain but failed to report the specific contaminated condition of the runway, which deviated from ICAO guidelines.
Safety action
Following the investigation, safety recommendations were directed at the operator, Skyline Aviation. The recommendations emphasized the need to critically evaluate landing configurations, speeds, and techniques when operating on short or contaminated runways. Specifically, the operator was advised to weigh the use of single-engine approach speeds against the available landing distance and to implement clearer procedures for landing on wet or contaminated surfaces.