Runway Incursion at Denver International Airport Involves Key Lime Air and Frontier Flights (N425MA)

Incident Overview and Initial Taxi Instructions On the morning of the incident, a runway incursion occurred at Denver International Airport (DEN) in Denver, Colorado, involving Key Lime Air (LYM) flight 4216, an SW4, and Frontier (FFT) flight 297, an A319. At 0725:00 MST, the DEN ground controller instructed LYM4216 to taxi to runway 34 via taxiways M and AA. The pilot of the SW4 reported that blowing snow reduced visibility and that snow on taxiway SC prevented him from seeing the centerline lighting. While attempting to locate the centerline, the pilot saw blue taxi lights, followed them, and turned onto runway 35L. ## Surface Detection and Pilot Realization According to recorded airport surface detection equipment (ASDE), LYM4216 entered runway 35L at taxiway M2 at 0727:06 MST. At 0728:10 MST, the ground controller asked the LYM4216 pilot for his location. The pilot advised he was abeam Signature. After the controller asked for his location, the pilot stated that he noticed he was on a runway. ## Frontier Approach and Near-Miss The First Officer of FFT297 reported that the crew was returning to Denver from St. Louis. Due to deteriorating weather in Denver, they prepared for a full instrument approach and were cleared to land on runway 35L by the tower. The First Officer stated they broke out of the clouds around 600 feet, with visibility conditions of 1/2 mile in blowing snow. Both crew members looked down the runway and verbally confirmed it was clear. They did not see the Key Lime Air aircraft until they were about 100 to 50 feet above the deck, at which point the aircraft was at least 2,000 feet down the runway. The First Officer attributed the obscured view to winds, prop wash from the aircraft, and blowing snow. He immediately commenced a go-around as soon as the aircraft was in sight. ## Collision Avoidance and Weather Conditions At 0728:17 MST, AMASS provided an aural and visual alert for an occupied runway. Four seconds later, the tower controller instructed FFT297 to go around. The aircraft missed colliding by approximately 50 feet. Weather at the time of the incident was 600 overcast, 1100 broken, visibility 1/2 mile, light snow, mist, wind 030 at 12, and runway visual range on runway 35L was 5,500 feet.