How Do Airports Prevent Aircraft Collisions?

DALLAS — In the world of commercial aviation, aircraft collisions are a serious concern. However, various measures are in place to prevent such accidents and ensure the safety of air travel. These strategies include:

1. Air Traffic Control (ATC): Air traffic control plays a crucial role in managing the flow of aircraft in and out of airports and ensuring safe separation between aircraft. ATC controllers communicate with pilots through radio communication, providing them with instructions on takeoff, landing, and taxiing. They also monitor for potential conflicts and issue alerts when necessary.
2. Pilot Responsibility: Pilots themselves have a significant responsibility to avoid collisions. They are required to follow all air and ground traffic control instructions and maintain situational awareness at all times. Pilots rely on a combination of visual cues and technology to navigate and avoid potential conflicts.
3. Technology: Technology plays a vital role in preventing aircraft collisions. Vehicles, radar systems, and collision avoidance systems are used to detect and track aircraft, providing pilots and air traffic controllers with real-time information about the position and movement of aircraft. These systems help identify potential conflicts and provide warnings to pilots to take necessary evasive actions.
4. Communication: Effective communication between air traffic controllers and pilots is crucial in preventing collisions. Miscommunication between ATCs and pilots can lead to near misses or collisions. Pilots must maintain clear and accurate communication with ATC and follow their instructions to ensure safe operations.
5. Situational Awareness: Pilots must maintain situational awareness at all times, both in the air and on the ground. This involves being aware of the position and movement of other aircraft, as well as potential hazards or obstacles. Pilots rely on visual cues, such as runway markings and signage, as well as technology, to maintain situational awareness and avoid conflicts.
6. Aircraft Marshaling: Aircraft marshaling is another strategy used to prevent collisions on the ground. Marshaling involves the use of hand signals by ground personnel to guide pilots during taxiing and parking. Clear and standardized hand signals help ensure the safe movement of aircraft on the ground and minimize the risk of collisions.

While rare, several factors can contribute to near misses or collisions at airports. These include increased miscommunication between ATC and pilots, a lack of situational awareness, a lack of trust in the cockpit, marshaling mishaps, and errors from collision avoidance systems.

Despite these challenges, it is important to note that air travel remains the safest mode of transportation. In the United States, for example, there has not been a fatal commercial plane crash since 2009, even though approximately 45,000 flights take off daily.

In the wake of the recent aircraft collision involving Japan Airlines (JL) Flight 516 at Tokyo International Airport (HND), we take a closer look at some of the aforementioned strategies in more detail.

Ground Operation Safety Measures

Pilots operating aircraft on the ground face various challenges due to restricted visibility from their cockpit windows. This limited view increases the risk of collisions with other aircraft, automobiles, airport infrastructure, and terminal buildings in the vicinity.

Swept Wing Growth

Aircraft wing tips and tails can extend significant distances from the nose during turns, a phenomenon known as 'Swept Wing Growth'. This increases the likelihood of a portion of the aircraft colliding with nearby objects, such as other aircraft or vehicles, when navigating through tight spaces.

Marshalling and Ground Personnel

In airports, aircraft carriers, or helipads, ground personnel known as marshals play a crucial role in assisting pilots during ground operations. Marshals communicate visually with pilots to facilitate various maneuvers, including turning, slowing down, stopping, starting, and shutting down engines.

Marshals guide aircraft safely and precisely to designated locations, such as parking gates after landing, maintenance hangars, or the runway. They position themselves prominently in front of the aircraft, ensuring visibility for the pilots. Marshals may also utilize follow-me cars to indicate directions to the pilots.

Lookout Personnel and Collision Prevention

To ensure adequate clearance between the aircraft and other objects, additional lookout personnel may be stationed at the wingtips or tail. These personnel work in coordination with the marshals to maintain a safe distance and prevent collisions during ground operations.

Ground Control Vehicles and Smart Systems

Ground controllers employ vehicles and smart systems to aid pilots visually during ground operations. These vehicles, such as follow-me cars, assist in guiding aircraft to their designated locations.

Smart systems, including advanced visual aids and technologies, are also utilized to enhance safety and situational awareness for both pilots and ground personnel.

Follow-Me Cars

Sometimes, marshals indicate directions to pilots by driving a "Follow-Me" car. This car is typically a yellow van or pickup truck with a checkerboard pattern. The marshal uses the car to guide the aircraft until they disembark and resume signaling.

However, it's important to note that the use of a "Follow-Me" car is not an industry standard and may vary among airports and operations.

Taxiway Lights

The taxiway lights also play a crucial role in guiding aircraft during taxiing operations. These lights are designed to turn green when a specific aircraft is granted taxi route clearance, and they turn red when no aircraft is authorized to taxi on that particular route.

For instance, a common callout might be "Singapore 875, taxi on the green, W7, NC, S3," with the keyword being "taxi on the green."

There are two main benefits to these bi-colored lights. Firstly, their dual-color configuration provides a secondary confirmation to pilots that they are indeed taxiing on the correct routing. This helps ensure accuracy and prevents any potential confusion.

Secondly, in addition to their signaling function, these lights serve as visual aids for pilots. With numerous taxiway lights in place, they assist in identifying the center of the taxiway. This helps pilots maintain proper alignment and ensures there is sufficient clearance between the aircraft's wingtips and the edges of the taxiway.

A-VDGS

At busier and more advanced airports, marshaller personnel are sometimes replaced on certain stands with a Visual Docking Guidance System (VDGS), which comes in various types.

Advanced Visual Docking Guidance Systems (A-VGDS) employ electronic displays to perform similar tasks as an AGNIS/PAPA installation but with greater accuracy. These systems may also offer protection against collisions with stationary objects.

To enhance safety, an infrared high-definition camera that scans for potential objects that could pose a risk to the aircraft monitors the entire area. The typical separation distance provided by A-VGDS ranges from 8 to 50 meters (26–164 ft). Additionally, A-VGDS systems incorporate a low-visibility feature, allowing aircraft to safely park even in extremely poor visibility conditions.

Emergency stop buttons are usually installed on stands and in the jetway/gate area of A-VDGS systems. When activated, these buttons instantly trigger the stop indication, providing an immediate means to halt any potential hazards.

Another example of a VDGS is the RLG GIS-206, which utilizes lasers to determine the aircraft's position. It then displays the remaining distance the aircraft needs to travel while providing azimuth guidance.

Anti-collision Lights

Anti-collision lights are an essential component installed on every aircraft to enhance visibility and prevent collisions. These lights serve to alert other pilots, ground personnel, and vehicles to the presence and position of an active aircraft.

Transport category aircraft typically incorporate two types of anti-collision lights: beacons and strobes. Beacons are characterized by a red flashing light, while strobes are synchronized flashing white lights. In many aircraft, there are two beacon lights, with one placed on top of the fuselage and another on the bottom. Strobe lights are typically positioned near the trailing edge of each wingtip and below the tail cone of the aircraft.

Aviation regulations mandate that an aircraft's anti-collision lights must be activated as soon as the engine is started for air navigation purposes. Additionally, as a safety measure, these lights must be turned on before starting an engine, moving a propeller, or activating a rotor.

To prevent collisions and mitigate risks such as ingestion by engine intake, jet blast, radar interference, and fire hazards, it is advised that anyone approaching an aircraft in operation maintains a safe distance of at least 10 meters and takes all necessary precautions.

Navigation Lights, Right-of-Way Rules

Navigation lights, also known as running or position lights, play a crucial role in preventing collisions by providing information about an aircraft's position, heading, and status. These lights assist other aircraft in understanding the orientation of the aircraft and determining the appropriate course of action.

Aircraft are equipped with three color-coded navigation lights: red, green, and white. The red navigation light is typically located on the left wingtip, while the green navigation light is placed on the right wingtip. The white navigation light is usually positioned as far back as possible on the tail or vertical stabilizer of the aircraft. These lights must be turned on from dusk until dawn, or as directed by government regulations.

To avoid potential disasters when aircraft are on a collision course, pilots utilize the right-of-way rules in conjunction with navigation lights. In a head-on situation where both aircraft see each other's green and red lights, neither aircraft has the right of way. In this case, pilots from both aircraft must immediately change course to the right to avoid a collision.

When aircraft are on a crossing course, the pilot in the aircraft on the left will observe the red navigation light of the other aircraft, while the pilot in the aircraft on the right will see the green navigation light. Regardless of their speed, the pilot on the left (seeing the red light) should give way by veering to the right, while the pilot on the right (seeing the green light) has the right of way and should maintain their course and speed.

In situations where a faster aircraft is approaching from behind and on a collision course with another aircraft, the pilots in the leading aircraft may not be aware of the impending danger, while those in the following aircraft can see it. In this overtaking scenario, the aircraft in front has the right of way, and its pilots should maintain their speed and heading. The pilots of the trailing aircraft intending to overtake must give way by veering to the right.

GPWS

A ground proximity warning system (GPWS) is a crucial system utilized to alert pilots when an aircraft is in immediate danger of colliding with the ground or other obstacles. This system provides advisory alerts and mandatory response warnings to the flight crew when the aircraft approaches the terrain, prompting the crew to initiate a terrain avoidance maneuver by increasing engine thrust and ascending away from the potential hazard.

The GPWS tracks patterns in radar (radio) altimeter readings of the aircraft within a range of 50 to 2450 feet above the ground. If the system detects that the aircraft is in a configuration that could lead to a collision with the terrain or an obstruction, it provides visual and audible alerts to the crew.

An advanced version of the GPWS, known as the Enhanced Ground Proximity Warning System (EGPWS) or Terrain Awareness Warning System (TAWS), offers additional capabilities.

The EGPWS utilizes a combination of radio altimeter and GPS technology to accurately determine the height of the ground directly ahead of the aircraft. By comparing the aircraft's current GPS location with a global digital terrain database, the system can precisely assess its proximity to the Earth's surface.

In the cockpit, the terrain display provides pilots with visual orientation to nearby high and low regions, assisting them in making informed decisions to prevent collisions with terrain or objects.

Vx Airspeed

During airplane operations, Vx refers to the airspeed that provides the best angle of climb. It is specifically used during the initial climb after takeoff to safely clear obstructions such as trees, buildings, and hills that are located near the end of a short runway.

Flying at the Vx airspeed allows the aircraft to climb to higher altitudes while covering the minimum horizontal distance, effectively avoiding collisions with obstructions.

Various factors can influence the specific Vx airspeed; it can vary depending on the type and model of the aircraft. These factors include the aircraft's weight, altitude, temperature, air density, wind conditions, and the configuration of the landing gear and flaps.

As altitude, aircraft weight, and temperature increase, more engine thrust is required, resulting in a decrease in the angle of climb and an increase in the Vx airspeed. Conversely, a tailwind decreases the climb angle since it increases the ground speed and horizontal distance covered by the aircraft. On the other hand, a headwind increases the climb angle as it reduces the horizontal distance traveled by the aircraft.

ATC Communications

To maintain a safe and efficient flow of air traffic, pilots and air traffic controllers (ATC) engage in continuous communication using radio frequencies or light signals throughout all phases of flight, including preflight, takeoff, departure, en route, descent, approach, and landing.

Air Traffic Control communications encompass the specific radio frequencies and phraseology employed by air traffic controllers to communicate with pilots. These communications play a vital role in ensuring the safety and effectiveness of air traffic movements. ATC communications provide pilots with crucial information regarding potential traffic conflicts, weather conditions, and airport operations.

ATC utilizes a comprehensive network of computer systems, radars, VHF and HF radios, and reference materials to facilitate communication with pilots. Their responsibilities include directing and separating departing and arriving aircraft on active runways, as well as coordinating the movement of aircraft within the maneuvering area to prevent collisions with other aircraft or airport infrastructure.

Maintaining accurate use of standardized phraseology and clear communication between ATC and pilots is paramount to aviation safety. In addition, advancements in technology, such as automatic speech recognition (ASR), are being utilized to transcribe the communications between air traffic controllers and pilots.

Conclusion

The examples mentioned above are just a few of the measures taken in commercial aviation to prevent catastrophic incidents involving aircraft and obstacle collisions at or near airports. However, safety in aviation is an ongoing, iterative process that continuously strives to enhance safety standards.

The National Transportation Safety Board (NTSB) is actively investigating six recent close calls that have occurred since the beginning of 2023. Officials have urged Congress to increase the budget of the Federal Aviation Administration (FAA) to enhance training, technology, and available resources.

In a recent safety summit, a panel of experts from the aviation industry came together to analyze the commonalities among these close calls and gain insights into the underlying factors contributing to these incidents. During the summit, FAA Administrator Billy Nolen and Secretary of Transportation Pete Buttigieg acknowledged an observed "uptick" in close calls during 2023.

We invite you to share your thoughts on other factors that contribute to the prevention of aircraft collisions on the ground, as well as any obstacles that may hinder the safe movement of aircraft at airports. Feel free to leave your comments and engage with us on our social media channels.

Featured image: Japan Airlines Airbus A350-941 JA13XJ at HND on April 30, 2022. Photo: Steven Byles, CC BY-SA 2.0

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