Second Century

Reading time: 4 minutes

When looking at the news and social media we can all see that aviation is changing. Fortunately. Manufacturers show fancy designs of what aircraft will look like in the future. With wings blended into the rest of the airframe and many small engines. Which are mostly electrical. Many with multiple vertical stabilizers instead of the singular that we are used to. Also airports will look different. They will be equipped with futuristic looking vertiports to facilitate the autonomously flying Urban Aerial Vehicles.

To facilitate all these visual changes, things that you cannot see need to change as well. For example the flight rules that all flying objects must follow. During the first century of flight Visual Flight Rules (VFR) and Instrument Flight Rules (IFR) where created to safely facilitate the increase in air traffic and the operational possibilities of flying.

Now, on the brink of the second century of aviation, the existing rules of the air are not sufficient to facilitate future developments. To make new concepts like Regional Air Mobility (RAM) and Urban Air Mobility (UAM) work, we need a new concept for Air Traffic Management (ATM). Fortunately, the invisible world is about to change too.

The rules so far

As stated in the above, there are two types of flight rules at the moment: Visual Flight Rules (VFR) and Instrument Flight Rules (IFR).

Flying VFR means that the pilot is responsible for maintaining separation with other aircraft. The pilot has to be on a constant lookout for other traffic and must initiate manoeuvres to avoid collisions. Navigating during a VFR flight is done without the help of radio beacons on the ground. The pilot uses a map (digital or analog) and looks outside to navigate.

The advantage of VFR flying is the level of freedom you have to fly wherever you want. As long as you are not close to a busy airport, you can chose the heading, altitude and speed you fly at. This makes VFR-flying excellent for sightseeing, leisure trips and search & rescue missions.

The downside is that keeping separation from other aircraft and navigating by looking outside can only be done when the weather allows you too. This means that VFR flying can only be done in Visual Meteorological Conditions, or VMC. In short, this means during daylight, not many clouds, no flying above clouds and no heavy precipitation. All to make sure that you can see other traffic, the ground and the runway. So VFR provides great operational flexibility, but the conditions are not always suitable for VFR flying.

IFR is sometimes jokingly called “I Follow Routes” or “I Follow Rules”. It is funny, 'cuz it's true. IFR-flying requires the pilot to follow an earlier prepared flight plan. Based on flying from waypoint to waypoint via airways. Deviating from this plan can only be done when authorized by Air Traffic Control (ATC). It is also ATC that handles traffic separation.

The downside is that there is limited flexibility once the flight plan has been filed. Once you are in the air, ATC will guide you through the flight. The upside is that IFR flying can be done without any visual references (except for take-off and touch down). Flight instruments inside the aircraft are used to navigate based on navigation systems on the ground (for example ILS, VOR and DME) or in space (GNSS). Making it is possible to fly during Instrument Meteorological Conditions (IMC): at night and during bad weather (as long as the weather doesn't reduce the aircrafts ability to stay in the air safely). This means that IFR flying is ideal for flights that need to stick to a schedule. Whether it is day or night, sunny or cloudy. Or when you just don't want the changing weather conditions to negatively affect your flight.

It is up to the operator or the pilot to chose to fly VFR or IFR. Do they want flexibility or 24-hour access? You can change from IFR to VFR, or the other way round, during the flight using a “Y” or “Z” flight plan. However, you need to state that in advance and is rarely done. Other than that, it is one way or the other and there is nothing in between.

Modern problems require modern solutions

New developments in aviation are challenging the long established VFR/IFR status quo. To effectively facilitate operations like UAM and RAM, operators shouldn't have to chose between flexibility or accessibility.

For example: flying with a small VTOL-aircraft from JFK-airport to a vertiport in Manhattan, using visual references (so VFR), is much easier than via IFR routes. When taking off from JFK you can see Manhattan and fly there in a straight line. IFR airways are usually not as straightforward, especially on short routes. However, navigating via visual references is not possible during IMC.

Does that mean that UAM-operators will only be able to offer quick shuttle flights during daylight and beach weather?

Not if it's up to NASA.

David Wing and Ian M. Levitt, two researchers from NASA's Langley Research Center, are proposing an alternative: Digital Flight Rules (DFR).

They state that: “To meet the needs of operators in the 21st Century and beyond, the objective of new flight rules should be to provide to all participating vehicle operators safe and unfettered access to the airspace in VMC and IMC, without incurring the access and flexibility limitations inherent to VFR and IFR”

They continue that: “This will be accomplished in large part by putting more separation responsibility and trajectory management authority into the users’ hands”

Interesting here is using the word “user” instead of “pilot” or “air traffic controller”. People working in IT know that a user can be both a person or computer system. And that is exactly what is responsible for navigating and separation under Digital Flight Rules: an ecosystem of computers and humans.

Computers, both in the air as on the ground, that are constantly feeding each other with real-time airspace information. This information is used by pilots, remote vehicle operators or autonomously flying systems to make decisions regarding navigation and separation.

During an IFR-flight, air traffic controllers and pilots both have a partial view of how a flight is executed in an airspace. The pilot sees the detailed, but narrow, view of his or her flight on the cockpit systems and through the windows. While the controller has a broad, but vague, view of all the flights in the airspace.

When filing a DFR flight plan, an operator commits itself to the responsibility of aircraft separation (as with VFR) regardless of the meteorological conditions (as with IFR). The digital ecosystem will provide the operator with the information of both the pilot and the air traffic controller. Making it possible for the operator, whether on board or on the ground, to take this responsibility.

Wing and Levitt emphasize that DFR should not replace VFR or IFR. They state that both these existing flight rules have their upsides. The added value of DFR will be to combine the upsides of both flight rules and thereby mitigating the downsides for flight operations that require such conditions.

If you want to know more about NASA's proposal for Digital Flight Rules, I highly recommend reading the paper of David Wing and Ian Levitt. You can find it here:

New Flight Rules to Enable the Era of Aerial Mobility in the National Airspace System