Mid-air collisions are an incredibly infrequent occurrence nowadays, thanks to extensive aviation safety legislation. These regulations enforce, among other things, minimum distances between aircraft under different conditions. However, what exactly do these regulations dictate?
Strict rules to ensure safety
Safety is at the heart of all aviation operations, regardless of the size or number of aircraft involved. Anything that takes to the skies, from single-engine turboprop aircraft to the Airbus A380 superjumbo, is bound by countless regulations designed to ensure the safety of everyone concerned.
The consequences of two or more aircraft colliding can be disastrous, whether in the air or on the ground. As such, this is an area in which regulations are particularly strongly enforced. The International Civil Aviation Organization (ICAO) is one body responsible for dictating such legislation.
Aircraft separation is the action taken by Air Traffic Control (ATC) and pilots to keep aircraft operating in a common area at a distance that minimizes the risk of a collision. It is classified into vertical and horizontal separation, while the latter includes longitudinal and lateral separation. We shall now examine the specifics of ICAO’s regulations concerning aircraft separation.
Vertical separation
Perhaps the most important sort of aircraft separation is vertical. It can be enforced both by Air Traffic Control and by aircraft’s Traffic Collision Avoidance Systems (TCAS). However, confusion between the two led to a midair collision over southern Germany in July 2002, resulting in the deaths of all 71 occupants of the two aircraft involved.
According to ICAO standards, the minimum vertical separation between aircraft under Instrument Flight Rules (IFR) depends on altitude. For aircraft flying below 29,000 (FL290), the minimum vertical separation is 1,000. Above this, aircraft are typically required to maintain a vertical distance of at least 2,000 ft.
However, some airspace is subject to Reduced Vertical Separation Minima (RVSM) to increase capacity at higher altitudes. Between FL290 and FL410, a distance of 1,000 ft is allowed between RVSM-approved aircraft. The Federal Aviation Administration (FAA) states that, alongside increased capacity, benefits include fuel savings and more optimum flight profiles.
Similarly, more significant separation vertical distances are sometimes specified in light of navigational challenges, bad weather, or special requests by pilots. During climbing or descent, an aircraft may be cleared to occupy a level previously occupied by another aircraft unless there is severe turbulence, both aircraft are entering the same holding pattern, or there is a significant difference in aircraft performance.
Lateral separation
When aircraft fly above the minimum vertical distance, horizontal separation can be reduced without risking collisions. Horizontal separation is categorized into two: lateral and longitudinal. Aircraft can achieve suitable lateral separation by the following means:
Position reports: These positively indicate that aircraft are flying over different geographic locations as determined visually or by use of a navigation aid.
Navigation aid: Ensuring that the paths the two aircraft in question are flying on are separated by a minimum angle, depending on the navigation aids used. Here are some examples:
- Very high frequency Omnidirectional Range (VOR): Both aircraft are on paths diverging by at least 15 degrees, and at least one aircraft is 15 NM (28 km) from the facility.
- Non-Directional Beacon (NDB): Both aircraft are on paths diverging by at least 30 degrees, with one at least 15 NM (28 km) from the NDB.
Longitudinal separation
Longitudinal separation is applied so that the distance between the estimated aircraft positions is never less than a specified amount. When two aircraft follow the same flight path, Air Traffic Control may ask their crews to make position reports upon reaching a particular area and compare the time between them.
This way, ATC can calculate the distance between the two and ask the aircraft to adjust their speed if necessary. Distance is maintained by ensuring that the trailing aircraft’s speed does not exceed that of the aircraft in front of it. Otherwise, reduced separation (below the specified minimum distance) may occur.
What could go wrong?
With approximately 100,000 flights operating daily, a lot of work must be done to avoid aircraft crossing paths. While mid-air collisions are almost unlikely, some near misses have occurred in recent years. In April, the loss of separation forced an American Airlines B737 MAX to perform a go around to avoid colliding with a JetBlue A220 at Charleston.
When aircraft fly too close to each other below the minimum separation distance, ATC will try every method at their disposal to obtain the required minimum separation with the least possible delay.
In certain situations, the distance between two aircraft can be reduced below the specified minimum. During an emergency, if it is impossible to maintain the applicable horizontal separation, aircraft may be cleared to fly at half the vertical separation, meaning two aircraft could be as little as 500ft apart. In this case, all crews involved must be notified.
Source: simpleflying.com