Consultation expired with comments. The proposed Special Condition (SC) has been updated based on the comments received, and the corresponding Comment-Response Document (CRD) has been completed by the European Union Aviation Safety Agency (EASA).
Details
Identification of issue
EASA received applications for approval of changes to Type Certificates, consisting in the installation of a HMD system on a CS-29 rotorcraft.
In that context, EASA had previously consulted the proposed SC-HMD29-01. Due to the substantial amount of changes affecting basic assumptions and SC content, this document supersedes the previously proposed SC-HMD29-01, released on EASA website for public consultation between 23/03/2022 and 29/04/2022.
The HMD is carried as a monocular or binocular or bi-ocular system mounted on the pilot’s and co-pilot’s head, in the direct view of the eye, and interfaced to the aircraft systems allowing to display flight data and systems information tailored to the different flight phases.
The intended function of the system is to provide the crew with an additional source of primary flight information and system information, duplicating those already available in the basic cockpit instruments. Being located in front of the crew’s eye(s), the information remains within the line of sight, thus enhancing situational awareness for day and night VFR operations, unless the system is removed or turned off. However, the HMD information is not intended to substitute or to prevail over those provided by the basic aircraft cockpit instruments and displays (hereby referred as HDD).
NVIS and related combination of HMD with NVG are excluded from this SC at this stage.
The information provided to the crew includes flight and navigation instruments, powerplant parameters, navigation information and annunciators. Any other information or overlayed image (e.g. SVS, EFVS) is out of the scope of this SC.
Currently no EASA Certification Specifications with adequate or appropriate airworthiness criteria for HMD installations in CS-29 rotorcrafts are established, as this design is novel to civil applications (there is a good level of experience in military designs).
The FAA with FAR 29 at Amendment 29-57 has recently added FAR 29.773 (c) to specify requirements for “vision systems with transparent displays”.
In addition, SAE ARP5288 and SAE AS8055A contain recommended design practices and performance standards for HUD systems. Specific guidance for design, testing, development and intended functions of the HMD are also included in SAE ARP6377.
EASA considers the HMD as a vision system with a transparent display surface located in front of the pilot’s eye to be comparable to a HUD, as the information is presented head-up and does not always require transition of visual attention to the HDD. Despite the system is not considered as a PFD, the information provided is compelling to the pilot. As such, it shall be provided with reliability, characteristics, and dynamics suitable to the aircraft type in order to allow the crew to perform their tasks from their normal position without undue fatigue or strength in both normal and emergency conditions.
Consequently, the HMD installation, in addition to all applicable CS-29 requirements relevant for airworthiness compliance demonstration, shall meet the requirements included in this SC proposed below.
