MOC VTOL.2000 Applicability and definitions

1.      General considerations

When this document quotes CS-27, CS-29, CS-23 or CS-25 paragraphs, unless otherwise indicated, the terms referring to aeroplanes, rotorcraft and their architecture should be replaced by those corresponding to VTOL capable aircraft and their architecture.

Unless otherwise specified, the following replacements should be assumed:

(a)      “Rotorcraft” or “aeroplane” should be replaced by “VTOL capable aircraft”

(b)     “Engine”, “Turbine”, “Powerplant” and “Rotor” should be replaced by “Lift/thrust system”

(c)      "Autorotation” should be replaced by “Controlled Emergency Landing”

(d)     “Fuel” should be replaced by “Energy”

(e)     “Fuel tank” should be replaced by “Energy storage device”

VTOL capable aircraft present an intrinsic capability to take-off and land vertically. Some VTOL capable aircraft may additionally be able to take-off or land as conventional aeroplanes, accelerating and/or decelerating on a runway. This mode of operation as conventional aeroplanes, also named CTOL or “conventional take-off and landing”, is also specifically addressed, when relevant, in the Means of Compliance described in this document.

2.      Continued Safe Flight and Landing

For Category Enhanced aircraft, as detailed in MOC VTOL.2510, the aircraft must be able to perform a continued safe flight and landing after any single failure or combination of failures that are not classified as catastrophic.

All failures directly or indirectly affecting continued safe flight and landing should be considered and evaluated. The lift/thrust system loss is not the only type of failure of this system that could affect safe flight and landing: other types of failures may also be critical, for example a frozen RPM command to a lift/thrust unit or a flight control system actuator failure.

The continued safe flight and landing includes any transition phase between horizontal and vertical flight, if included in the applicable procedure, and the ground phase up to the complete stop of the aircraft and evacuation of the occupants.

It is acceptable to use emergency procedures during the continued safe flight and landing following a failure, for example emergency ratings of the lift/thrust units.

In order to assess the VTOL’s ability to perform a continued safe flight and landing, any changes in aircraft performance that affect the capability of the aircraft (e.g. range, expected height loss, remaining rate of climb) to continue the flight and perform a landing after a single failure or combination of failures not extremely improbable should be considered (see section 10 in this MOC, Certified Minimum Performance (CMP)). The characteristics of diversion vertiports that could be used after such failures can differ from the vertiport of intended landing. In this case, the necessary information on the required diversion vertiports should be established and decided prior to the flight to be able to plan the flight accordingly (e.g. distance required for a running landing, load carrying capability, dimensions). Additionally:

(a)      The remaining energy reserve following a failure condition should be no less than the sufficient reserve accepted for compliance with VTOL.2430(b)(4).

(b)     The performance and obstacle margins should be no less than the minimum accepted for compliance with VTOL.2115, VTOL.2120 and VTOL.2130.

(c)      The continued safe flight and landing should not require exceptional piloting skills, alertness, or strength. The Handling Qualities can be evaluated considering the Modified Handling Qualities Rating Method in MOC VTOL.2135.

(d)     The procedures for continued safe flight and landing should be designed so as to not injure occupants or people on the ground and should not introduce additional damages to the aircraft due to the landing.

3.      Controlled Emergency Landing

For Category Basic aircraft, as detailed in MOC VTOL.2510, the aircraft must be able to perform a controlled emergency landing after any single failure or combination of failures not classified as catastrophic. For Category Enhanced, controlled emergency landing procedures could also be published for catastrophic failure conditions.

A controlled emergency landing should be performed under control; in particular it should be possible to steer the aircraft towards a touchdown area with the remaining lift/thrust units. Therefore this objective cannot be met by the use of non-steerable parachutes.

While the objective is similar to a controlled glide or autorotation, some damage to the aircraft to absorb the impact forces can be accepted. Active systems could also be acceptable if they meet the safety requirements of VTOL.2510.

The procedures for a controlled emergency landing should be designed so as to not injure occupants if landing is achieved on a flat solid surface.

The controlled emergency landing includes the transition phase from horizontal to vertical flight, if applicable, and the ground phase up to the complete stop of the aircraft and evacuation of the occupants.

The operational context in which the aircraft is certified should be taken into account when defining the controlled emergency landing: The capability to steer the aircraft should be evaluated based on the gliding distance and the external visual cues necessary in case of a possible loss of instruments or information in the cockpit. In particular, if the aircraft is certified for IFR, the applicant should either demonstrate that the controlled emergency landing can be carried out in IMC, or specify the minimum height required to complete the manoeuvre once the visual references have been regained.

4.      Emergency Landing and Survivable Emergency Landing

As opposed to “Continued Safe Flight and Landing” and “Controlled Emergency Landing”, “Emergency Landing” and “Survivable Emergency Landing” do not correspond to design objectives but rather to design cases. They address the ultimate consequences at aircraft level of an uncontrolled landing which would be survivable by the occupants if appropriate design features are incorporated.

These design cases are consequently bound by the physical conditions within which a normal occupant would be reasonably expected to survive after contact of the aircraft with the ground (e.g. impact velocity, time exposure to a given acceleration level, etc.).

Depending on the severity of this ground contact and its consequences, the following definitions are established:

—         Emergency Landing: Impact (crash) where the occupants are given every reasonable chance of escaping serious injury. The occupants should be able to evacuate the vehicle without assistance. The impact conditions are detailed in VTOL.2270 and associated MOC.

—         Survivable Emergency Landing: Impact (crash) which is potentially survivable, even with serious injuries to the occupants. The occupants should be protected from post-impact hazards as described in VTOL.2325(a)(4), VTOL.2430(a)(6) and associated MOC.

Accordingly, these design cases should be considered irrespective of their probability of occurrence at least in the definition of: features for the structural protection of occupants (VTOL.2270), means of egress and emergency exits (VTOL.2315), features to minimise the initiation a fire (VTOL.2325) and features to ensure energy retention and minimisation of hazards by the lift/thrust system (VTOL.2430).

Due to their low probability of occurrence, emergency procedures for these design cases are not mandatory and would not need to be demonstrated for compliance with VTOL.2620. Nevertheless, the Agency recommends the definition of such procedures when this would contribute to the survivability of occupants (VTOL.2620).

5.      Person-carrying

An aircraft is considered person-carrying if it carries crew, passengers or both.

6.      Lift/thrust unit

A lift/thrust unit is considered to be any engine that directly contributes to providing lift or thrust and includes its controller, the connected effector (e.g. rotor, propeller, fan) and any related actuators (e.g. pitch change, tilting, vectoring).

7.      Lift/thrust system

The lift/thrust system is composed of the lift/thrust units and their related energy storage, distribution and management systems as well as any other related ancillary systems (e.g. lubrication, cooling or transmission).

8.      Flight control system

The flight control system is composed of the pilot controls, computers, wiring, actuators, sensors, and all those elements necessary to control the attitude, speed and flight path (trajectory) of the aircraft. The lift/thrust units can be functionally considered to be actuators of the flight control system and therefore part of the flight control function.

In reference to the lift/thrust unit definition provided in Section 6 of this MOC, any engine directly contributing to providing lift or thrust, its controller, and fans shall comply with applicable engine certification provisions (e.g. SC-EHPS) while the other elements (rotors, propellers, and related actuators) shall comply with SC VTOL.

9.      Exceptional piloting skills

The term “exceptional piloting skills” is usually recalled when addressing the Handling Qualities requirements. The Handling Qualities should be such that the aircraft can be operated “without exceptional piloting skills”, which means that the flight crew is expected to have an “average” competency and currency to carry out the task. To ensure that the competency and currency, that will be subjectively evaluated by the applicant, correspond to the expected “average”, the evaluation should be carried out by more than one flight crew with final verification of the compliance finding by the Agency. The Operational Suitability Data (OSD) certification will establish the minimum syllabus of pilot type rating training to ensure that pilots are properly trained to the required level of proficiency.

10.     Certified Minimum Performance (CMP)

The Certified Minimum Performance (CMP) is the set of performance data obtained by considering the effect of single failures and combinations of failures that are not extremely improbable on the nominal performance parameters. The CMP should also take into account the effects of the fires that are considered in VTOL.2330.

Depending on the aircraft architecture, the CMP for different performance parameters may be the result of different failures. For example, for a given aircraft, the range may be the most degraded as a result of a battery failure while the best rate of climb may be the most degraded by an electric engine failure. The failure of the battery and of the electric engine would then become, for the respective flight phase and performance parameter, the critical failure for performance (CFP, see section 11 in this MOC).

The CMP is part of the type data and is associated with limitations on the continued safe flight and landing for Category Enhanced and on the controlled emergency landing for Category Basic, to be established in accordance with VTOL.2510 and VTOL.2620.

11.     Critical Failure for Performance (CFP)

A critical failure for performance (CFP) is a failure or combination of failures that results in the maximum degradation for a given flight phase and performance parameter. The set of critical failures for performance is used to establish the Certified Minimum Performance and as part of the safety assessment process of VTOL.2510.