Certification Guidelines for Multi-Prop and/or Battery-Powered Aircraft

In Europe, the EASA have issued a discussion document called: MAC-2-SC VTOL issue 1 with the latest addition in a series of 3, so far, dated 23 June 2021, the main purpose of which is to lay the ground work for guidelines that will cover the design and development of multi-rotor, battery powered VTOL aircraft.

The US certification guidelines for light helicopters are contained in document FAR Part 27 and that is what will govern certification of the gas turbine powered Autocopter. Horizon Helicopters is totally familiar with it.

However, the certification guidelines being used for the Joby aircraft come under the heading of FAR Part 23 with heavy exemptions, largely because that aircraft is being treated, for the time being, as a fixed-wing with the exceptional ability to also take off and land vertically.

However, there is no hiding the fact that one of the Joby’s main attributes is to perform as a de-facto helicopter and that its ability to survive a total loss of power at or near the hover will be a major issue. It’s therefore likely that the ultimate certification guidelines for the Joby will move to incorporate the Special Conditions VTOL (SC-VTOL) guidelines currently being agreed between FAA, CAA and EASA. One of many other failure conditions that will then have to be dealt with is the loss of one propeller blade and the fact that in a cascade fashion it could then take out all the other props. Here we see the Failure Mode and Effects Analysis coming into play. The EASA discussion document already lays out in its list of Means of Compliance (MOC) the basis of the guidelines and in which appear many of the questions listed in the main Certification page, e.g. how is the development of a significant amount of lift asymmetry handled.

Their efforts over the past few years indicate that the new category of small VTOL aircraft has been identified as a serious and international potential new business area, and offers huge investment opportunities, but also there is significant risk if the design architecture is wrong.

This new certification category is designed to encourage development and reflects the many and varied design approaches of the First Generation eVTOL aircraft currently in the design and experimental stage. So each new aircraft will be pioneering new and demanding, yet different, certification standards. This will challenge the authorities, particularly as multi-prop or tilt-prop battery powered aircraft have never been cleared for public transport before. There is no standard for comparison.

The Autocopter’s designers will have to be cognisant of these new guidelines in the regard to the battery-powered variant.  The Authorities are, for example, expressing considerable concerns about the safety of batteries and what will be required to offer the equivalent of a Cat A, Performance Class 1 classification.