Certification Issues

Every new aircraft in every country must obtain a Certificate of Airworthiness (C of A) from their local Authorities. In the case of Horizon, we will start with the UK CAA who have very similar requirements to the US FAA and Europe’s EASA. The development of the first generations of EVTOL aircraft, including the Autocopter, would be covered initially by an Experimental Category C of A. It is likely that any new all-electric air vehicle you see flying today is flying under an Experimental Category. This Category is very flexible so it doesn’t prevent full developmental flying. But for the aircraft to be cleared to operate for hire or reward and be commercially viable, it must have a Public Transport C of A, the highest for a VTOL aircraft at the moment is Cat A, Performance Class 1. There is a large gap between the Experimental and Public Transport Categories. It is expected that some of the first generation of EVTOL aircraft will simply not make it.

A Public Transport C of A is the guarantee of safe, passenger carrying performance and is the reason why airline travel is as trusted as it is today. Every single component and whole systems are subject to the most thorough testing, ground and flight, for function, durability, failure modes and crash resistance over long periods. Only then will a C of A be awarded. During the life of the aircraft a continuous feedback of data from accidents and incidents ensures that such safety is given continuous updates in service. The consequences of a manufacturer getting it wrong can cause fatalities and place large costs and delays on a new aircraft design. The recent experience of Boeing with the 737 Max 8 is illustrative.

As we enter the “Green” era, the integrity of complex, high-power batteries, their structure, composition and distribution systems, and the choice to use multiple electric motors as the primary drive will be subject to focussed scrutiny; these are new and very different technologies being used in critical parts of the new EVTOL aircraft and will be treated with extreme caution by Airworthiness Authorities.

It is for these reasons that the design of the Autocopter uses basic systems and architecture with which Authorities will be familiar but has added other layers of safety reflecting the unique and high-risk area of low level, congested, poor weather operation which all small VTOL aircraft are designed to work in. Continuous use of the HUMS system in production aircraft will be used to help identify failure modes that for one reason or another may have escaped the general certification process, and ideally long before they become either critical or expensive. We believe this cautious approach for entry into a new industry dependent on novel technologies will reduce developmental and in-service risks for any investor. Horizon also will involve relevant Authorities from the start to ensure we’re all on the same page.

All aircraft designers, including those of the Autocopter and the battery-powered multi-props, will have to provide credible answers to at least the following main question examples:

Ones that will be asked of all ‘New Aircraft’ designers:

  • Fundamentally, what design configuration is being used here to apply for Cat A, Performance Class 1 certification?
  • Where is the aircraft’s evidence-based Failure Mode and Effects Analysis, or in the UK its Safety Case? One of the most important documents!
  • What is the aircraft’s crash resistance? In the UK, a new helicopter has to show that the people on board can survive largely unharmed by a drop from 50 feet to the ground.
  • Are there any potential common-cause failure modes of a safety critical kind we should be aware of, e.g. of connections between engines or batteries that might involve one ‘helping out’ another, but in actuality causing another?
  • How will the aircraft get safely to the ground if there is a major power or control failure that is either total or results in a substantially uncontrollable aircraft? Are there any modes where getting safely to the ground might be realistically impossible? What are they?
  • How does the aircraft’s design deal with a lightning strike?
  • How will the aircraft deal with a bird strike, primarily to the rotor/props and engines, radiators etc?
  • If the prop/rotor drive is electric, how will the system deal with the massive, almost instantaneous torque levels electric motors are able to produce?
  • Noise, pollution?
  • For the various applications, what are going to be the reserve fuel requirements for a diversion, return-to-base, go-around etc?
  • Does the aircraft have a HUMS or similar? There’s a lot to fail. Where is the evidence it works effectively? What data will be shown in the cockpit? Will any of the alarms have a ‘land as soon as possible’ connotation?

Questions that will be asked additionally of Battery-Powered Multi-Props designers:

  • How does the design deal with massive battery power, including reduced power output at low ambient temperature, the reduction in battery capacity caused by a re-charge and over-charge where there might be a fire concern?
  • How is the existence of a massive battery in the aircraft going to affect its crash resistance?
  • How many propeller failures can the vehicle sustain and continue safely?
  • How will this “graceful failure” be quantified if there are many units?
  • How susceptible will the aircraft be to serious failure-created lift asymmetry? How will it be contained?
  • If multiple units fail, will the power be automatically increased on the remaining units? How?
  • In a tilt-prop aircraft, if the pod rotation mechanism fails, or partially fails, what then? Can the vehicle continue using wing-borne lift only? Will it still be able to do a rolling landing?
  • Can electric power be spread safely without over-stress between the remaining units if some fail? How many?
  • Because of the big differences in design approaches, will each aircraft have to be separately certificated?

These are all serious questions and often very expensive to answer in an evidence-based way. Life testing of an engine is particularly expensive and comes under the name of the ‘Type Test’ – possibly 150 max power flight cycles of 1 hr duration with no deterioration.

There have only been two civilian multi-props flown in the UK and those are the Boeing BV234 (a civilian version of the Chinook) and the AgustaWestland AW609 (a smaller civilian version of the XV15). Today, its unlikely that either would receive certification, primarily because of the asymmetric lift issue when one propeller or main rotor fails because of an engine or transmission system failure.  As it did on the BV234 and has now seen the 609 struggling for 25 years to gain certification. That’s not to say that the current crop of battery-powered, multi-prop aircraft will suffer the same fate, but it does show the difficulties they face. And to be sure the current multi-props are dramatically different aircraft to the 234 and 609.

In this respect the Autocopter, being much more of a conventional helicopter with (a) a lift system that avoids any degree of asymmetry because its lift vector always acts within inches of the aircraft’s centre of gravity and (b) multiple engines, will be a much easier aircraft to certificate.

Horizon Helicopters Ltd, based on 30 years of experience, has done everything it possibly can in the Autocopter’s design to ensure its certification to Cat A, Performance Class 1. It is probable that we will be able to create a whole new Certification class when our potentially fully autonomous flight control and management systems are included.

Grandfather Rights – What Are They and What Do They Mean

When a Company with a history of building aircraft decides to build a new type or model, within the certification process it can claim benefit from what are called ‘Grandfather Rights’. As the certification process requires evidence of what the service life of a part such as transmission unit will be, and this is expensive to obtain for a new part, the benefit comes from being able to cut the certification-driven cost of design and development by maximising the reuse of a largely identical design or part from an older type. In practice, grandfather rights therefore also extend to the design technology used and the experience of those engineers involved.

The Horizon Partnership (see ‘About’), when it came to deciding how the Autocopter should be built, clearly could not call upon grandfather rights for anything in the aircraft, to the detriment of the investment bill and time-to-market. Its decision was then to recruit a body of specialist contractors that could at least bring in the design and development skills, technologies etc required of an aerospace project. Today, these contractors number in the region of 15, spread across the UK, EU and US. The Horizon Partnership expects the benefit to be a reduction in the development bill of around 20% and about the same for time-to-market. However, that bill started high because there were no rights to start with.