EUROCAE ED-306 PDF

The scope of this document is to provide guidance to applicants to demonstrate compliance with the rotor burst protection requirement expressed by EASA Special Condition SC-VTOL.

This includes protection of aircraft from High-Energy fragments and evaluation of the effects of sustained imbalance condition.

Practical design precautions are presented to protect the aircraft from damage that can be caused by uncontained rotor fragments and reduce the residual risks to the level required by the safety objective of the certifying category.

It is worth noting that EASA SC.VTOL 2250(c) requires, for Category Enhanced, no catastrophic events to be generated by a single structural failure, and EASA MOC.VTOL 2240(d) makes it applicable to rotor burst events. This document clarifies how to comply with this requirement, highlighting the differences between a first fragment release and a second fragment release generated by a rotor-to-rotor impact.

Compliance to SC.VTOL 2240(d) is also required for Level 3 Basic Category VTOL aircraft, this is a minimisation of risk exercise. This document defines how to perform the analysis and minimise the risk posed by High Energy debris.

This includes:

• Evaluating the loss or malfunction of flight-critical components/systems and structure impacted by high-energy debris from a rotorburst, including other Lift/Thrust Units,

• Protecting the aircraft occupants who could be hit by the high-energy fragment,

• Assessing the imbalance effect, meaning effect of the loads and vibrations potentially generated by the rotorburst itself.

This document contains an acceptable means to comply with SC.VTOL requirements for Rotor Burst protection of Small-category VTOL Aircraft. It includes, when accepted by an aviation authority, the methodology and the acceptance criteria that may be used for assessing and minimising the risk. This includes different types of rotating elements, such as Lift/Thrust Rotors, electrical engine rotors and thermal engine rotating parts.

Hazards to the aircraft may be generated by the loss or the malfunction of components and Lift/Thrust Units impacted by the fragment, the loss of structural integrity, the loads and vibration generated by the loss of the rotating fragment and injury to the occupants.

The exercise will cover protection of the following:

• structural elements

• flight-critical components, including other LTUs and High-Energy Rotors

• pilot(s)

• passenger(s)

Main techniques proposed in this document to protect the aircraft from rotor burst fragments include:

• separating flight-critical components,

• isolating functions,

• incorporating redundant functions, and

• shielding and deflectors.

Rotor imbalance threat evaluation is also described to provide guidance to comply with EASA MOC VTOL.2240(d).

As stated above, the safety objective for Category Enhanced is different to that of the Category Basic. First issue of this document presents a guidance for Category Enhanced. A future revision will include a process dedicated to Category Basic. Placeholders are included within the text to give to the reader an idea of where specificities for Category Basic will be detailed.

This document also covers equipment High-Energy rotors, such as cooling fans. In this case, current CS27 Amdt. 9 guidance applies and are reported here for completeness. If the guidelines presented within this document have been followed, compliance to this requirement in the scope of this ED has been demonstrated for the considered components.

It should be noted that this document refers only to protection against Catastrophic failure conditions. This is in line with EASA’s MOC VTOL.2240(d) guidelines, which specifies that only Catastrophic events at aircraft level need to be considered in the analysis of this specific Particular Risk Analysis.

OUT OF SCOPE

The following topics are not in the scope of this document and are therefore not covered:

• Damage and hazard to third parties as a consequence of the rotorburst event,

• Methodology to demonstrate full containment of High-Energy Rotor fragments,

• Methodology to demonstrate fragment trajectory,

• Evaluation of the effects of degradation of Lift/Thrust Units on aircraft performance, handling qualities degradation and potential increased loading on aircraft,

• Details of the Safety Analysis to be performed to assign criticality to the failures (covered by ED-300),

• Containment and management of main battery fire following rotor burst damage.

• Shaft support structure and shaft bearing failure are out of the scope of this document. However, any imbalance generated may be considered following the approach outlined in CHAPTER 7.