The horizon was dark when USAir Flight 1493 began its approach to Runway 24 Left at Los Angeles International on February 1, 1991, but visibility was 15 miles. The Boeing 737 was arriving from Columbus, Ohio, with 89 passengers, four flight attendants, and two pilots on board. At 5:59 p.m., the flight was cleared for a visual approach and, at 6:03, was advised to contact the tower upon reaching ROMEN, the outer marker for the Runway 24R ILS also used as an approach fix for 24L.
Skywest Flight 5569 was taxiing to Runway 24L for takeoff; the Fairchild Metro was bound for Palmdale, California, with 10 passengers and two pilots aboard. At 6:03, the Skywest flight made initial contact with the tower.
"Skywest ah five sixty nine at [intersection] forty-five, we'd like to go from here if we can."
"Skywest five sixty nine taxi up to and hold short of two four left," the tower controller replied, and SKW5569 acknowledged the hold-short order. (At LAX, tower operations are divided between the north and south runway complexes. The local controller responsible for Runway 24L was designated LC2.)
At 6:04:33, USA1493 checked in.
"USAir fourteen ninety three inside ROMEN." The transmission was not acknowledged by LC2. At 6:04:44, LC2 transmitted:
"Skywest five sixty nine taxi into position and hold runway two four left, traffic will cross downfield."
"Okay two four left position and hold, Skywest five sixty nine," was the last transmission received from the Metro.
The downfield traffic was a Wings West Metro waiting to cross the runway. The Wings West crew had unintentionally switched to the wrong frequency and did not receive clearance to cross until 6:05:16.
At 6:05:29, the 737 tried again. "USAir fourteen ninety three for the left side, two four left."
LC2 conducted other radio transmissions before, at 6:05:53, responding.
"USAir fourteen ninety three cleared to land runway two four left."
The captain's acknowledgment of the landing clearance was the last transmission recorded from the 737.
At 6:06:08 a second Wings West Metro advised LC2 it was ready for takeoff on Runway 24L, but LC2 could not find a flight progress strip for the airplane. LC2 queried the crew about their intended departure intersection and initiated a search for the missing flight progress strip.
The first officer of USA1493, who was flying the approach, later recalled hearing radio transmissions that included LC2 asking an airplane about its position on the ground. He did not recall hearing any hold or take-off clearances for any aircraft on 24L or 24R. He did not see any aircraft on the runway and did not recall any distractions during the approach. He stated that the 737 touched down about 1,500 feet from the threshold of the runway. As he was lowering the nose, he observed an airplane on the runway in front of him. He said the airplane had a position light and/ or a red light on its tail.
He recalled seeing his landing lights reflecting off the Metro's propellers.
At 6:07:04, an unidentified voice transmitted, "What the hell....
The collision occurred just as the 737's nosewheel touched down. The two airplanes — the Metro crushed beneath the left side of the 737 — slid down the runway, then off its left side, and eventually struck an unoccupied building. Fire spread quickly, accelerated in the cabin of the 737 by the release of oxygen from the flight crew oxygen system, which was damaged in the collision. Twenty passengers and two crewmembers — including the captain — aboard the 737 died, most due to smoke inhalation. Another passenger died a month later of burns. The 12 people aboard the Metro were killed. Both aircraft were destroyed.
The National Transportation Safety Board's finding of probable cause attributed responsibility for the accident to failures of FAA procedures, policies, and oversight that ultimately led to the failure of LC2 to maintain an awareness of the traffic situation. NTSB concluded that LC2 "forgot that she had placed SKW5569 into position for takeoff ... because of her preoccupation with another airplane." The board's investigation revealed that, six weeks prior to the accident, an evaluation of this controller's performance identified five deficiencies, including "a loss of awareness of aircraft separation" and "the misidentification of an aircraft by use of an incorrect call sign." The NTSB also concluded that glare from apron lights complicated the ability of tower personnel to distinguish aircraft on the runways and other airport traffic movement areas.
Pilots have little influence over what happens in a control tower. However, the NTSB raised safety issues that pilots can address, including aircraft exterior lighting and conspicuity and pilot situational awareness during takeoff and landing and operations on airport surfaces.
The accident report noted that "aircraft external lighting systems required for certification are intended primarily for in-flight conspicuity, rather than for conspicuity on airport surfaces; consequently the external lighting of SKW5569 tended to be indistinguishable from the runway lights when viewed from the cockpit of USA1493."
At the time of the accident, SKW5569 had only its navigation/position lights and red anticollision beacon illuminated. Skywest procedures called for turning on strobe, taxi, landing, and recognition lights after takeoff clearance had been received, and that clearance was never issued to SKW5569. Tests showed, however, that even with all lights operating, a Metro was not readily detectable either from the tower or from an aircraft on final approach.
The tests indicated that the likelihood of detecting an airplane on the runway when approaching from behind can be increased if the airplane on the ground is displaced from the runway centerline lighting by about 3 feet. This offset procedure, used in conjunction with strobes and other anticollision lighting, enhances the airplane's conspicuity.
The NTSB report also noted that "inherent in the 'see and avoid' concept to avoid collision is a need for pilots to be alert and vigilant in monitoring air traffic communications for situations that may lead to conflicts with other aircraft." This can be challenging. In the 3 minutes 43 seconds from the time the 737 came onto the LC2 frequency until the accident, more than 60 ATC communications took place. The LC2 controller missed some key transmissions, according to NTSB.
Granting the volume of radio traffic, each flight crew was in a position to be aware of the other from radio transmissions.
The Metro was on the LC2 frequency when the 737 checked in inside ROMEN. The 737 did not at first specify the runway on which it intended to land, and the Metro crew probably knew that ROMEN serves as an approach fix for both 24L and 24R. Subsequently, however, about 90 seconds before the accident, the 737 did identify the runway of intended landing. The 737 was on the frequency when the Metro was cleared to taxi into position and hold.
For a pilot on the ground waiting for a takeoff clearance, a call from an aircraft at or near the outer marker establishes a useful benchmark. Most outer markers are about 6 nm from the runway threshold. At an approach groundspeed of 120 knots, the aircraft at the marker will arrive at the runway in three minutes. Given the range of speeds over which approaching aircraft may operate, the window widens to two to four minutes. A pilot might reasonably question a "position and hold" clearance if he is aware of another aircraft inside the outer marker. A pilot would want to be particularly attentive if he knows that an approach fix serves more than one runway.
Likewise, aircraft on approach should be vigilant for "position and hold" clearances involving the runway they're headed for. Pilots on approach should also recognize that aircraft may be holding in position at places other than the approach end of the runway. At LAX, Taxiway 45 is 2,354 feet from the threshold of Runway 24L.
As a result of this accident, the FAA changed its procedures to prevent controllers from authorizing an aircraft to taxi into position and hold at an intersection between sunset and sunrise or at any time when the intersection is not visible from the tower.
The lessons for pilots are clear. First, maximize the conspicuity of your airplane by positioning it offset from runway centerline lighting and by using strobes and other lights to draw attention to yourself whenever you're on an active runway. Second, remain attentive for radio transmissions regarding the runway or taxiway you're using. Guard against complacency, and maintain a high degree of situational awareness at all times.
The NTSB is solely responsible for determining the probable causes of accidents, Information contained in this "By the Book" is derived from the NTSB aircraft accident/incident summary report.
