Boeing 737-300 accident at US, 1 Feb 1991

Accident narrative

On February 1, 1991, at 1807 Pacific standard time, USAir flight 1493, a Boeing 737-300, collided with Skywest flight 5569, a Fairchild Metroliner, while landing on runway 24 left at Los Angeles International Airport. The Metroliner was positioned on the same runway at intersection 45, awaiting clearance for takeoff. Both airplanes were destroyed. All 10 passengers and 2 crewmembers aboard the Metroliner, and 20 passengers and 2 crewmembers aboard the Boeing 737, were fatally injured.

### The flights

Skywest flight 5569 was an intended departure from Los Angeles to Palmdale, California. There were 10 passengers and 2 flight crewmembers on board.

USAir flight 1493 originated in Syracuse, New York, and was destined for San Francisco, California, with planned intermediate stops in Washington, D.C., Columbus, Ohio, and Los Angeles. There were 89 passengers, 4 flight attendants, and 2 flight crewmembers aboard for the Columbus to Los Angeles segment. The first officer was performing the flying duties.

### The sequence of events

Weather conditions were visual, with a scattered cloud cover at 30,000 feet and 15 miles visibility. Official sunset was at 1723.

Approaching the Los Angeles area, USAir 1493 was cleared for a visual approach to runway 24 left at 1759:06. The first officer recalled configuring the airplane for landing approximately 12 miles from the runway and confirming to the captain that he had the runway in sight.

Around 1758, Skywest 5569 began taxiing to runway 24 left for departure. At 1803:38, the Skywest flight initiated communication with the tower's local controller 2 (LC2), stating, "at forty five, we'd like to go from here if we can." The controller instructed the flight to taxi up to and hold short of runway 24 left.

At 1804:33, the USAir captain transmitted that the flight was inside the final approach fix. The tower communications transcript indicates the transmission was received, but it was not acknowledged by the controller.

At 1804:44, the controller instructed Skywest 5569 to "taxi into position and hold runway two four left, traffic will cross downfield." The Skywest crew acknowledged at 1804:49. This was their last recorded transmission.

The controller then attempted to clear another Metroliner, Wings West 5006, to cross runway 24 left. The Wings West crew had unintentionally departed the tower frequency, resulting in a delay. When they returned to the frequency, the controller cleared them to cross at 1805:16.

At 1805:29, the USAir captain transmitted a second radio call to the controller. At 1805:53, the controller cleared USAir 1493 to land on runway 24 left. The captain acknowledged.

The controller then communicated with other airplanes, including another Metroliner, Wings West 5072, which called ready for takeoff at 1806:08. The controller had no flight progress strip for this airplane and initiated a search for it. The strip was located at the clearance delivery position, misfiled as a yet to be delivered departure clearance.

The USAir first officer stated that he looked down the runway and saw the runway lights and overall landing environment, but did not see an airplane on the runway. He believed the airplane crossed the threshold at approximately 130 knots and landed about 1,500 feet from the approach end. He deployed the thrust reversers and slowly lowered the nose. While lowering the nose, he observed an airplane on the runway immediately in front of and below him. He stated there was insufficient time for evasive action. The collision occurred simultaneous to the Boeing 737's nose wheel contacting the runway.

After the collision, the two airplanes slid to the left side of the runway and into an unoccupied fire station.

### What the investigation found

The Metroliner was totally destroyed by the initial impact, dragging, and ground fire. The major portion of the airplane was crushed beneath the Boeing 737's left wing. The Boeing 737 was destroyed by the impact with the building and a resulting ground fire.

The Board found that the fire in the Boeing 737's forward cargo bay was accelerated by the release of oxygen from the crew oxygen cylinder, which was damaged in the initial collision. Thick black smoke filled the cabin within seconds. Evacuation took place through the forward right service door, the right rear service door, and both overwing exits. The forward left door was jammed shut, and the rear left door was opened but closed again by a flight attendant due to flames outside. Egress through the right overwing exit was hampered when a passenger froze and an altercation occurred between two other passengers. Ten passengers and one flight attendant were found in the aisle near the overwing exits, having succumbed to smoke inhalation.

The investigation determined that the local controller forgot that she had placed Skywest 5569 into position for takeoff. The Board believed that during her delayed communications with Wings West 5006, she became preoccupied. When Wings West 5072 called for takeoff, she was distracted by the search for its missing flight progress strip. As a result, she misidentified Wings West 5072, which was taxiing on a parallel taxiway, for the Skywest Metroliner. Believing the runway was clear, she issued the landing clearance to USAir 1493.

The Board found that Los Angeles Air Traffic Control procedures did not specify the use and handling of flight progress strips at the ground control position. This allowed aircraft to request intersection departures directly from the local controller, relieving the ground controller from coordinating and marking strips. The Board concluded that this local procedure removed vital redundancies required by the FAA's National Operational Position Standards, placing the full burden of tracking aircraft on the local controller's memory and visual observation.

The Airport Surface Detection Equipment (ASDE) radar indicator at the local controller's position was inoperative at the time of the accident. The Board noted the equipment had an extensive history of failure, though it was unable to determine if its use would have prevented the accident. The Board also noted that glare from apron lights on Terminal 2 impeded visual observation of the collision area from the tower.

A conspicuity exercise demonstrated that the Metroliner's white tail navigation light blended with the runway centerline lighting when viewed from behind. The airplane's red anticollision beacon was obstructed by the rudder cap, a design permitted by FAA regulations. The Board concluded that the external lighting of the Metroliner tended to be indistinguishable from the runway lights when viewed from the USAir cockpit.

Toxicological testing revealed the presence of phenobarbital in the USAir captain, which he had used for a gastrointestinal condition without reporting it to his aviation medical examiner. The Skywest first officer's tests showed substances found in over-the-counter medications. The Board concluded that the medications did not contribute to the accident, but indicated a less than complete appreciation of the potential dangers of unauthorized medication use.

### Probable cause

The National Transportation Safety Board determined that the probable cause of the accident was the failure of the Los Angeles Air Traffic Facility Management to implement procedures that provided redundancy comparable to the requirements contained in the National Operational Position Standards and the failure of the FAA Air Traffic Service to provide adequate policy direction and oversight to its air traffic control facility managers. These failures created an environment in the Los Angeles Air Traffic Control tower that ultimately led to the failure of the local controller 2 (LC2) to maintain an awareness of the traffic situation, culminating in the inappropriate clearances and subsequent collision of the USAir and Skywest aircraft. Contributing to the cause of the accident was the failure of the FAA to provide effective quality assurance of the ATC system.