Assessing Equivalent Level of Safety Argument
Overview
In this scenario you are a member of the MAA evaluating the certification evidence provided by the Attack Helicopter (AH) DT to contribute to the TCR.
This Type Certification Review will require you to analyse and assess an ELoS argument. This will give you some valuable insight into the MAA’s role as the independent regulator during this stage of the MACP.
A scenario for a non-compliance with the AH Mk2 is detailed below. The DT have provided an MCRI with an ELoS proposed.
In your role as MAA, you were consulted by the DT when they generated the ELOS and have seen the evidence that is detailed below. You are to assess the ELoS the TAA submitted in the form of an MCRI and decide whether the ELoS argument merits agreement and an MSF.
You are to brief the other syndicates using the ppt slide template provided and explain to them whether you (as the MAA) would accept the ELOS and provide an ESF or reject the ELoS argument, giving reasons why. You have a maximum of 10 minutes for your brief.
AH Mk2 ELOS
The Attack Helicopter (AH) Mk 1 is a twin-turboshaft attack helicopter with a tailwheel-type landing gear arrangement and a tandem cockpit for a crew of two. It features a nose-mounted sensor suite for target acquisition / night vision systems and is armed with a chain gun carried between the main landing gear, under the aircraft’s forward fuselage, and four weapons points mounted on stub-wing pylons for carrying armament and stores, typically a mixture of missiles and rockets.
In preparation for a potential operation where the AH Mk 1 would be embarked aboard a Royal Navy ship, a number of type design changes were made to the AH Mk 1, including; folding main rotor head, marinized main landing gear and an emergency floatation system (EFS). This latter capability was deemed essential for operations over water as the helicopter’s poor buoyancy, high centre of gravity and outward opening canopy meant that the helicopter was not compliant with certification requirements for ditching (specifically CS29.801 and its associated UK Military Delta UK29.801a) and that the resultant Risk to Life from this non-compliance was assessed by the Aviation Duty Holder as not tolerable.
After 2 decades of successful AH Mk 1 in-Service operation, the Attack Helicopter (AH) Mk 2 was selected as its replacement under the Successor AH Programme. The AH Mk 2 is a remanufacture of the previous AH Mk 1 design with several capability enhancements, including: new avionics and displays, uprated engines and ability to fire addition weapon systems.
However, as part of the AH Mk 2 programme, the decision was made not to bring into core a number of capabilities that had been introduced to the AH Mk 1 as UORs, including the ability to embark onboard ship and therefore the associated EFS. Deleting these requirements enabled additional capabilities (enhanced Defensive Aids Suite (DAS) and over-wing air-to-air missiles) to be incorporated in the fuselage areas previously used for EFS.
However, running alongside, but unrelated to, the AH Mk 2 procurement project was the MOD’s Helicopter Basing Study (HBS) which sought to reduce the number of helicopter operating bases. A key driver for this reduction in operating bases was the collocation of all Defence helicopter training, across all helicopter types, to the Defence Flight Training School at RAF Valley on Anglesey island.
As a result, toward the end of the AH Mk 2 procurement project, it was realised that the AH Training Flight had already relocated to RAF Valley and was using its EFS-equipped AH Mk 1 helicopters to transit to the numerous military training areas in Wales. However, the AH Mk 2 was not EFS-equipped and there was insufficient funding, time or opportunity to enable the new AH Mk 2 helicopters to be delivered with an EFS capability.
Consequently, whilst preparing the Type Certification Exposition during Phase 4, the TAA was directed by the programme Sponsor to ensure that a ditching capability was included within the AH Mk 2 Type Certification Basis. However, with no EFS, the TAA knew that compliance with Def Stan 00-970 ditching and escape requirements would not be possible, specifically:
| CS 29.801 Ditching (b) Each practicable design measure, compatible with the general characteristics of the rotorcraft, must be taken to minimise the probability that when ditching, the behaviour of the rotorcraft would cause immediate injury to the occupants or would make it impossible for them to escape. (d) The probable behaviour of the rotorcraft during ditching water entry must be shown to exhibit no unsafe characteristics. (e) The rotorcraft must be shown to resist capsize in the sea conditions selected by the applicant. CS 29.803 Emergency Evacuation (c) If certification with ditching provisions is requested by the applicant: (1) ditching emergency exits must be provided such that following a ditching, in all sea conditions for which ditching capability is requested by the applicant, passengers are able to evacuate the rotorcraft and step directly into any of the required life rafts; |
Therefore, noting that there was no opportunity to design out the non-compliance, the TAA decided to approach the Aviation Duty Holder in an attempt to establish operating controls, factors and mitigations that would enable an Equivalent Level of Safety to be claimed.
The MCRI
The MCRI that has been proposed by the TAA, click on the link to access it.
To access the slides, click on the link.