US investigators are examining landing distance calculations as they try to determine why a Honda Aircraft HA-420 overran a wet Oregon runway before coming to rest submerged in water.
All five occupants survived, although one of the four passengers suffered serious injuries during the 7 April landing accident, in early-morning darkness, at Southwest Oregon regional airport.
The pilot had calculated the required landing distance for runway 5 using the flight-management system, which gave a figure of around 4,200ft.
Runway 5 has an available landing distance of 5,320ft although a displaced opposite-direction threshold provides a further 660ft, and a 340ft overrun area lies beyond that.
According to the US National Transportation Safety Board, the jet’s flight-management system software had been upgraded to reflect revised wet runway performance in an aircraft flight manual supplement.
The safety board says a calculation from the supplement returned a required landing distance of 5,910ft, with an approach reference speed of 111kt.
Analysis of the landing shows the HA-420 crossed the runway 5 threshold at 117-118kt, slightly above the pilot’s calculated reference speed of 113kt owing to a crosswind.
Although the pilot “did not specifically observe standing water”, he was aware of recent heavy rainfall, says the safety board in preliminary findings.
The jet touched down about 1,000ft from the approach end, near the aiming-point markings.
It was not fitted with spoilers or thrust-reversers. Initial braking “felt normal”, according to the safety board, and the pilot believed the aircraft would decelerate sufficiently to exit at taxiway B – about 3,900ft from the threshold.
“As the airplane continued the landing roll and was about halfway down the runway, the braking was seemingly ineffective, though there were no warnings or messages,” the safety board add.
The pilot and a passenger sitting in the right-hand seat applied maximum brake pressure, but the aircraft did not respond.
As the HA-420 approached the localiser antenna at the runway end, the pilot steered to the right to avoid a collision. The jet overran through grass and mud, descending a 15ft embankment into the water which lay 100ft beyond the runway safety area.
The speedbrake was deployed during the landing but the emergency braking system was not used.
“Visual examination of the runway surface revealed no evidence of skid marks or indications of the anti-skid braking system operating,” the safety board says. “Light tyre tracks were observed on the overrun area and through the grass with no indication of braking.”
The flight had been similar to the previous flights, it adds, aside from a slightly higher ground speed at touchdown.
Initial examination of the wheels and braking system revealed no evidence of failures, excessive wear, or malfunctions. Components have been removed from the airframe for further testing.
