About the ATCO´s role in this collision at LAX and various contributing factors, you can read here:
1. Who Was Executing What Tasks in the Tower?
The air traffic controllers at Los Angeles International Airport, LAX, were experiencing a usual shift with a typical amount of airliners landing and taking off from the airport on 1 February 1991. Outside, the weather provided good visibility. Night had fallen and strong lights lit the airport with its four runways.
Before we take a closer look at the roles of the six employees who controlled the air traffic at LAX that night, we will occupy ourselves with the flight progress strips briefly.
1.1. A Short Explanation of the Flight Progress Strips
When physical flight progress strips are used, one flight progress strip is printed for each arriving, departing, or passing aeroplane containing all the necessary information about the aircraft and the flight. The strip is inserted into a strip holder which is passed on to the air traffic control officer, ATCO, in charge.
The strips and the holders can come in different colours so that the ATCOs can distinguish them from one another more easily. The air traffic controllers have strip boards in front of them on which they arrange the progress strips in different areas which represent, for instance, the taxiways and the runways.
Moving the flight progress strips on the strip board with accuracy and efficiency is vital to prevent runway incursions.
1.2. The Air Traffic Controllers and Their Different Roles at LAX
In the tower at LAX , twelve storeys above the ground, in 1991, there was a clearance delivery controller who, in addition to highly responsible tasks, printed the flight progress strips and handed them to the other four controllers. There were two ground controllers who guided all kinds of traffic along the apron and the taxiways.
Two local controllers were responsible for the runways. That night, Robin Wascher was overseeing the two north runways at LAX, 24L and 24R. She had a considerable amount of progress strips on her strip board and had to take care of several planes simultaneously. One supervisor was also present in the tower and helped the ATCOs when needed.
2. LAX and Its Extremely Dense Air Traffic
Los Angeles International Airport is one of the busiest airports in the world. It has four runways, runway 24L and 24R to the north, and 25L and 25R to the south. Several taxiways cross these runways which renders following all ATC instructions during taxiing a challenge. The layout of LAX is depicted in the Aircraft Accident Report on page 2 (1).
In 1991, all four runways were used for take-offs and landings. Not only on the runways, but also in the air space around the airport, there can be a considerable amount of air traffic. Hence, the ATCOs have to pay close attention to separate the planes adequately at all times. Also the pilots need great situational awareness and have to scan the air space around them carefully in oder to land at LAX safely.
1 ) National Transportation Safety Board, NTSB: Aircraft Accident Report, Runway Collision of USAir Flight 1493, Boeing 737 and Skywest flight 5569, Fairchild Metroliner, Los Angeles International Airport, Los Angeles, California, Feburary 1, 1991. Adopted: October 22, 1991, Notation 5461A
3. USAir Flight 1493 Was Approaching LAX
USAir flight 1493 took initially off from Syracuse, New York, and was bound for San Francisco. Several stops were included in this route. The actual leg of the flight led from Columbus, Ohio, to Los Angeles, California. There were two pilots and four flight attendants along with 89 passengers on board the Boeing 737-300.
As USAir flight 1493 was nearing LAX, the pilots were asked to expedite their descend due to crossing traffic above them. After their final contact with the approach controller, they contacted the local controller, Robin Wascher, in the tower. The pilots did not receive an answer to their first radio call.
However, the contact to the local controller was absolutely necessary, as no flight crew is allowed to land without a landing clearance. The pilots of USAir flight 1493 obtained their clearance to land on runway 24L from Robin Wascher less than one minute before their touch-down. In aviation, this is called a short final.
4. Right After Touch-Down the Plane Burst Into Flames
When the pilots had just landed their Boeing 737 on runway 24L at 18:07 hrs (Pacific Standard Time), the aeroplane caught fire. It skidded further down the tarmac, veered off it and ultimately crashed into an unoccupied fire station.
In the tower, the air traffic controllers saw the burning airliner as it careened along the runway. The supervisor instantly rushed to alarm the fire brigade and rescue services using the red phone circuit.
4.1. A Plain Clothes Police Officer Helped Immediately
Rosa Reynoso, a plain clothes police officer at LAX sat in her car close to the crash site with a companion. She, as well, immediately grabbed her radio and sounded the alarm. She then left the car and rushed towards the plane in order to help those passengers, who had already managed to escape, to move away from it quickly. In an interview, she later recalled their injuries and burns, as well as the unbearable and dangerous heat (2).
2 ) Mayday - S09E04 - Cleared for Disaster (USAir Flight 1493 + Skywest Airlines Flight 5569), produced by Cineflix and originally aired in 2010, later made available on dailymotion.com
4.2. In the Burning Wreckage, a Propeller Was Found
As the rescue services tended to the victims and as fire fighters brought the post-crash fire under control, a propeller was found amidst the wreckage. It was the horrible hint to the fact that another aircraft had been involved in this accident. Rescue personnel called the air traffic controllers in the tower to let them know.
4.3. Which of the Aeroplanes Was Missing?
In the tower, the air traffic controllers had to find out what exactly had happend in the minutes before the crash. First and foremost, they had to identify the aeroplane which was also involved in the accident. At the same time, they still had to handle traffic, as planes were continuing to land at LAX.
When the air traffic contollers assessed the flight progress strips and talked to the departure controller, they found out that a commuter plane, Skywest flight 5569, was missing. This flight to Palmdale, California, should have been conducted by two pilots and carried ten passengers. Their plane was a Fairchild Metroliner.
5. The Investigation at the Crash Site at LAX
The main purpose of the investigation was to answer the following two questions:
1. What caused the accident?
2. Why did so many people die in the burning wreckage?
5.1. The Crash Site Next to the Runway
As the tarmac was strewn with parts of the Metroliner after the crash, both the northern runways at LAX had to remain closed during the first days of the investigation. Travellers experienced a chaos, which increased the pressure on the investigators. In addition, fuel had to be removed from the Boeing 737, which took one entire day.
As you know, pressure is one member of the so-called "Dirty Dozen", a well-known compilation of human factors. In spite of the pressure, the NTSB members had to work fast, yet precisely so that the airport could be fully reopened quickly.
Not only the destroyed aeroplanes were examined, but also the marks that they had left on the tarmac and the adjacent ground.
5.2. Why Could so Many People Not Escape the Plane After the Accident?
The cabin filled with thick and toxic smoke quickly, and some passengers seemed to have collapsed whilst they were waiting to exit the plane. In addition, the emergency exit over the right wing was opened with a delay for several reasons. A passenger sat in the seat next to it and was "frozen" as she later said. Two male passengers were involved in a subsequent altercation. Lastly, part of a seat blocked the exit (Aircraft Accident Report, page 65).
In total, 20 of the passengers, one flight attendant and the captain died in the Boeing 737. Two passengers succumbed to their thermal burns a few days and 31 days after the crash, respectively (Aircraft Accident Report, page 30). All twelve occupants of the Metroliner were killed in the accident.
5.3. What Had Gone Wrong in the LAX Tower?
The important question was:
Which of the two planes was cleared to use runway 24L?
To learn more about this, the NTSB investigators climbed the stairs leading to the top of the tower at LAX and collected the ATC tapes. They also looked into the ATC procedures which were in place at that time.
5.4. There Was Only One CVR
Both flight data recorders, FDRs, were recovered. In 1991, commuter planes were not required to be equipped with a cockpit voice recorder, CVR. It was a setback when the investigators learned that they had only one CVR for their further analyses.
6. The Communications Between ATC and the Pilots
For their analysis of the communications between ATC and the cockpit crews, the investigators could only use the CVR from the Boeing 737 and the ATC tapes. They listened to the recordings carefully, whilst they reconstructed what aeroplane was in what position at what point in time.
6.1. Skywest Flight 5569 Followed the ATC Instructions
Skywest flight 5569 was cleared to taxi to runway 24L and hold short of intersection 45, because another plane, Wings West flight 5006, had requested permission to cross runway 24L. In addition, the pilots had to wait for their take-off clearance. As the investigators listened to the ATC tapes, they could hear that the crew of Skywest flight 5569 had followed all the instructions perfectly.
6.2. Wings West Flight 5006 Had Lost Contact With Robin Wascher
Wings West flight 5006 had landed on runway 24R and asked for permission to cross 24L in order to taxi to its final position at the gate. When Wascher was ready to cross this aircraft, the crew had unintentionally switched their frequency. The investigators learned that it took Wascher some time and several attempts to reestablish contact with Wings West flight 5006.
6.3. There Was Yet Another Plane Under Wascher´s Control
The crew of Wings West flight 5072 contacted Wascher to let her know that they were ready for take-off. This happened less than one minute before the landing of USAir flight 1493. As the investigators listened to this part of the communications, they realised that Wascher did not recognise this aircaft.
They summoned her to hear from her, what had happened. She told the NTSB professionals that she could not find a progress strip for that flight and asked her supervisor for help, who handed her the respective strip.
6.4. USAir 1493 Contacted the Tower at LAX More Than Once
When the crew of USAir flight 1493 contacted Robin Wascher the first time, they did not receive an answer, because she was occupied with the other aeroplanes. As we have already seen in subchapter 3, this resulted in a short final, which means that the crew of USAir flight 1493 obtained its landing clearance when it was less than one minute from touch-down.
Taken together, the investigators learned from the CVR and the ATC tapes that Robin Wascher did not recognise Wings West flight 5072. Furthermore, she had cleared both the Skywest flight 5569 and the USAir flight 1493 to use runway 24L.
7. What Did the ATCO Experience Before the Crash in Terms of CRM?
We have seen that the meticulous work with the tapes and the respective positions of the planes had already revealed the cause of the crash. Now, the investigators had to answer the following question:
Why had the air traffic controller forgotten that Skywest flight 5569 was already sitting on runway 24L when she cleared USAir flight 1493 to land on the same runway?
When Wings West flight 5006 had lost contact with her, Wascher had to spend precious minutes to solve this problem. When the pilots of Wings West flight 5072 radioed her to tell her that they were ready for take-off, she had to solve another problem, because the flight progress strip had not been handed to her yet.
The precious resource time was consumed in both cases. In addition, the workload grew and became more difficult to manage.
We may also assume that the lost radio connection and the missing flight progress strip increased the pressure and caused distractions. These may ultimately have impaired Wascher´s concentration and her situational awareness.
In the following subchapters, we will explore the factors which contributed to her human error. Furthermore, we will establish the chain of events.
8. Contributing Factors at LAX
After the thorough examination of the communications, the NTSB professionals went back to LAX to investigate the conditions at this airport and especially in the tower more extensively.
8.1. Why Could the Air Traffic Controller Not See the Metroliner?
When an NTSB employee sat down in the local controller´s seat, it was confirmed that a light pole and its glaring light obstructed the air traffic controller´s view of parts of the northern runways. Therefore, also Robin Wascher had difficulties to see the Metroliner taxiing out to the runway.
8.2. The Ground Radar at LAX Was out of Service - Again
The ground radar at LAX had been malfunctioning for some time before the crash and should have been replaced earlier. The antenna of that radar was moved by a system made of ring gears and spur gears, which wore off over time.
These parts were not readily available on the market and had to be made individually. Therefore, the ground radar system at LAX was constantly in and out of service. Airport officials had already asked the Federal Aviation Administration, FAA, to prioritise this serious problem.
When the accident happened, the ground radar was out of service. Hence, Robin Wascher did not have it at her disposal to see where the planes were and could not cross-check the position of the Metroliner. Another chance to detect her error was missed.
8.3. The Tower at LAX Was Understaffed
LAX had been known before the accident on 1 February 1991 as one of the airports with the most runway incursions in the USA. Seven months before the crash, an Airbus was waiting on the runway for its take-off when a landing DC-10 flew over it closely.
Following that incident, air traffic controllers at LAX informed the FAA about their staff shortage and clearly pointed out their concerns that a catastrophe might happen if these difficulties were left unaddressed.
8.4. Why Could the Pilots in the Boeing 737 Not See the Metroliner?
Pilots should not only observe the air space around them carefully as we said earlier. They should also scan the runway, on which they are going to land, for any objects that should not be there. This raises the question why the pilots of USAir flight 1493 could not see the Metroliner sitting on the tarmac.
The NTSB professionals flew the same approach as the Boeing 737 did and placed a Metroliner on the runway at night. On this aircraft, the same lights were switched on as there were on the plane, which was involved in the accident (in 1991, not all aircraft lights had to be switched on before take-off). Due to the many lights that illuminated the runway, the investigators could not distinguish the lights of the Metroliner from those on the ground. Hence, the aeroplane was invisible to them.
9. The Chain of Events That Led to the Collision
In the compilation below, you can see the links of the chain of events, which led to the collision on the runway at LAX in 1991.
10. Improvements Could Initially Not Stop Runway Incursions at LAX
In addition to the improvements mentioned below, the NTSB made more recommendations in its Aircraft Accident Report in order to enhance the safety at airports.
10.1. A New Tower Was Built at LAX and a New Surface Radar Was Mounted
A larger tower was built at LAX in 1996, overseeing the entire airport. It is sixteen storeys higher than the old one. In addition, a new ground radar system was finally installed. Now, all aircraft, which are displayed on the radar screens, have tags that clearly identify them.
10.2. The Local Controllers´ Workload Was Reduced After the Accident
After the accident, the handling of the flight progress strips has been changed. Ground controllers organised them before they were handed to the local controller in charge. This not only reduced the local controllers´ workload, but also introduced an extra set of eyes to detect potential errors.
10.3. Still too Many Runway Incursions at LAX
However, these improvements could initially not reduce the number of runway incursions at LAX. Rather, the rate increased in the years following the accident (Wes Timmons, National Director of Runway Safety, FAA, 2). What might the reasons be?
As we said in subchapter 2, LAX is one of the busiest airports in the world. The dense traffic should also be seen in the light of the fact that LAX has two sets of parallel runways. This, in turn, means that the inner runway must be crossed after landing on one of the outer ones in order to reach the terminals. The available taxiways cross the runways at many intersections.
10.4. Runway Status Lights, RWSL, Were Installed at LAX in 2009
The runway status lights are a fully automatic system which operates independently of ATC. It consists of the following three components:
- Runway Entrance Lights, REL: incorporated along the centreline of taxiways which lead to the entrance of a runway
- Take Off Hold Lights, THL: integrated in the runway departure area
- Runway Intersection Lights, RIL: they are installed at the crossing of two runways
The RWSL turn red if the respective runway is going to be used for high-speed traffic and are triggered by aeroplanes which are going to take off from or land on that runway.
In remembrance of the 36 victims of the flights Skywest 5569 and USAir 1493, which collided on the runway at LAX on 1 February 1991
11. In the Next Article: All About Runway Incursions
What types of errors can result in runway incursions? What can every single professional at the airport, but also in the air, do in order to prevent such an incursion and a potential accident? We will look at contributing factors, CRM prinicples, and technical aids which help to enhance the safety especially at busy airports. What do we learn from this for our own work?
Author: Eva-Maria Schottdorf
Date: April 24th, 2024
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