eVTOL Aircraft are essentially battery powered Electrical Vertical Take-Off and Landing aircraft.

Aimed at the Urban Air Mobility market, eVTOL aircraft aim to reduce traffic congestion by making airborne short-hop services achievable and affordable.  Particularly suited for air taxis and emergency response vehicles, an eVTOL is designed to allow quick access to areas at a much lower cost than a traditional helicopter.

These aircraft, which are currently in development, are designed to carry generally between 2 and 10 passengers, fly short routes within urban environments, provide quick turnarounds for arrivals and departures, and may even operate autonomously.

eVTOL aircraft differ from traditional aircraft and rotorcraft as they are powered by multiple battery driven rotorblades and offer vertical take-off and landing.  This does have an impact on safety, as during the take-off / landing phase, they will not have little (or no) forward momentum in order to generate lift; nor will they be able to use autorotation, which is used by helicopters to allow a controlled form of crash landing.

This exciting market has drawn attention from both traditional aircraft manufacturers, such as Boeing and Airbus, but also car manufacturers and the likes of Uber.

The emergence of eVTOLs could catalyze transformation across many different areas, with these being particularly pertinent:

• Air traffic management system: Developing and deploying a new, complete air traffic management system is expected to be key. This system must span airspace allocation and management as well as airworthiness certifications and pilot requirements for unmanned autonomous aerial systems. National governments need to work together as well as in conjunction with local councils to settle upon a common operating concept and establish a universal set of requirements that would allow eVTOLs to be widely deployed. This includes ensuring interoperability with existing air traffic management systems globally.
• Physical infrastructure: Significant capital is required to acquire the land/space necessary for building vertiports and other infrastructure components. Extending existing types of public/private partnerships or establishing new models will be needed  to secure adequate funding. Without this type of collaboration, infrastructure projects may not get off the ground, thus delaying, limiting, or entirely blocking the widescale deployment of eVTOLs.
• Aircraft development: Current helicopter developers and manufacturers  are at risk of being disrupted, with the implications being similar to those incurred by the automotive sector when new entrants used electrification and autonomous capabilities to re-envision the automobile. Parallels can also be drawn with taxi and rental car industries when technology companies used apps and geo-location capabilities to reimagine ride-sharing services.The future market for eVTOL aircraft manufactures could be substantial. For example, the estimated market size for the US alone is approximately $17 billion by 2040.

At present there is no specific certification and safety requirements for eVTOL aircraft.  As with any aircraft, before they can be used in public service, they will need an airworthiness certificate to show how they meet the relevent safety standards.

The European Union Aviation Safety Agency (EASA) has been working on the certification of such aircraft since 2018 and Active VTOL Crash Prevention Limited is part of the team formulating the EUROCAE/EASA safety standards for eVTOL aircraft with specific responsibility for drafting new standards for both eVTOL Active Safety Systems and for Stroking Crashworthy seats.

Taking accident data for helicopters as a starting point, the two highest causes of accidents are Loss of Control-Inflight and System (Powerplant) malfunction, with Low Altitude Operations and Collision cited as two additional causes for accidents.

Fixed-wing aircraft already deploy a parachute in an emergency; inflating and slowing the descent to provide an acceptable touchdown condition.  Over 500 lives have been saved worldwide to date by whole aircraft recovery systems and these are becoming more standard in the redundancy systems of many general aviation aircraft.

There are dangers inherent in the design and operation of eVTOL aircraft:

• eVTOL aircraft are designed to be flown at low altitude where the incidence of bird strike is higher due to the greater density of birds;
• the increased number of take-offs and landings will result in additional stress for pilots, airframes and engines alike – remembering that pilots will need to consider potential traffic, obstacles and wildlife in all 6 directions;
• the increase use of the eVTOL aircraft over towns and cities increases the risk to those on the ground as well as animals and property in the event of an emergency;
• electrical power trains and the lithium batteries used to power eVTOL aircraft are at greater risk of fire / explosion if an emergency landing has to be made or the aircraft strikes an obstacle;
• the lack of any (or minimal) forward momentum during the vertical take-off and landing phases means that there will be no normal lift under any wings; and no rotational effect which is used by helicopters to control emergency descents;
• eVTOL aircraft are likely to appeal to a wider audience than standard helicopters and light aircraft which means that safety features will need to deal with a much wider range of parameters such as weights, sizes and the excitement of passengers

 

As part of this, it has become apparent that current Emergency Descent Arrest Systems designed for fixed wing and rotary aircraft will not work when it comes to eVTOL aircraft and a new approach is required.

In particular, in the NASA Langley Research Center’s paper on “Challenges in Vehicle Safety and Occupant Protection for Autonomous electric Vertical Take-Off and Landing (eVTOL) Vehicles” by Justin Littell; the author concluded that a Ballistic Recovery System should be a required piece of equipment but notes that existing systems do not advertise operation below 400 feet.

There have been some improvements since that paper was written, with one Ballistic Recovery System claiming to work at heights of 100 feet and over.  However, this still leaves a safety gap should an emergency occur below that height. We have created our own white paper outlining the various Emergency Descent Arrest Systems which currently exist and how they can be applied to eVTOL aircraft.  This white paper was presented to EASA in February 2021.

Standard parachute / ballistic recovery systems are normally reliant on some forward momentum for proper and expedient deployment of the parachute – this is the reason why revovery parachutes are not found on helicopters.  The parachutes also take time to deploy and hence require sufficient lateral airspeed and altitude to allow them to work (for example, the Cirrus aircraft needs to be 920 feet in the air) – well above the ceiling for eVTOL aircraft.

This is where the AVCP Zero-Zero Safety System comes to the rescue.