What happened
The crew of US Air Flight 499 elected to land on Runway 24 after their planned Instrument Landing System approach to Runway 6 was cancelled due to insufficient visibility. The reported runway visual range was only 2,800 feet, which fell short of the required minimum of 4,000 feet for that runway. However, a visibility of one-half mile was deemed sufficient for Runway 24.
The approach was conducted with approximately a quartering tailwind and an airspeed roughly 10 knots above Vref. Operations manuals prohibited tailwind landings on Runway 24 under wet or slippery conditions. The reported runway braking action was fair to poor. Additionally, the pilot's handbook cautioned crews to monitor spoilers during landings on slippery runways because automatic deployment relies on wheel spin-up or nose wheel contact.
Upon landing, the aircraft touched down approximately 1,800 to 2,000 feet beyond the displaced threshold of the snow-covered runway. Although the spoilers were armed, they failed to deploy automatically. The captain manually deployed them and lowered the nose of the aircraft. He then activated reverse thrust and applied the brakes.
Despite these efforts, the brakes proved ineffective. The aircraft continued past the end of the runway, ran over a runway end identification light, struck a fence, and came to rest straddling a road.
Findings
Contributing factors included the decision to land on a slippery runway with a tailwind despite operational prohibitions, the failure of the automatic spoiler deployment system, and the resulting loss of braking effectiveness that led to the runway overrun.