Exercise 4: Preparing the Equivalent Level of
Safety (ELoS) Argument
Following successful delivery of the IFF Mode 5 and ADS-B Major Type Design Change for the KC-18 Mk 8 Tanker you have now transferred your attention to the C-18 Mk 5. You are supervising the certification of a design change to introduce a new role fit for the C-18 Mk 5 (). You are in Phase 4 of the MACP for this fourth exercise and are preparing the Type Certification Exposition for submission to the MAA. However, a non-compliance has been identified and you are preparing an Equivalent Level of Safety argument for presentation to the MAA via an MCRI.
Below is a brief on the design change and specific non-compliance you are addressing.
C-18 Mk 5 Mixed Passenger and Luggage Container Configuration
The C-18 Mk 5 is a stretched / extended range version of the C-18 Mk 4 Pax / Freight Transport. It has a freight door on the port side of the fuselage to the rear of the mainplane. The C-18 Mk 5 also has a quick fit floor system that permits re-role of the Air System from a full passenger role to a freighter role using pallets. An Urgent Capability Requirement (UCR) has been raised to mitigate a Tactical Air Transport capability gap, enabling rapid deployment of Troops along with the required kit. To meet the UCR this Major design change introduces a Troop and Kit (TaK) Fit cabin layout.
The C-18 Mk 5 TaK Fit incorporates a configuration where the forward section of the cabin comprises 54 passenger seats mounted onto seat pallets and the aft section of the cabin is configured with 6 pallet-mounted luggage containers. A restraint net is provided across the top of each of the 6 luggage containers to secure the contents. dangerous air cargo will not be carried in these containers; they are designed
specifically for the transport of personal carry-on luggage (rucksacks and s
oft bags).
The luggage containers are Commercial off the Shelf (COTS) and have been sourced from an aircraft interior design company in order to meet UCR timeframes. Redesign and manufacture of the containers within the UCR timeframe has not been possible. Figures 2 and 3 illustrate this role fit on the C-18 Mk 5.
Figure 1 C-18 Mk 5 Increased Baggage Stowage Capacity
Figure 2 C-18 Mk 5 Cabin Layout
The Issue with the revised role fit.
In assessing the design change, a non-compliance with the agreed TCB has been identified for the mixed passenger and luggage container configuration by the TAA.
Def Stan 00-970 Part 5, Clauses CS 25.815, UK25.815a – Aisle Width.
The introduction of the mixed passenger and luggage container configuration will result in the aisle width being 110mm less than the minimum certification requirement (510mm) above the 640mm height threshold, in the aft section of the cabin due to the width of the baggage containers.
The TAA decided that CS25.803 and UK25.803a – Emergency Evacuation (see below for details) could be affected by this change due to the reduction in aisle width and the possible impact on time to egress the aircraft in an emergency. As a result of this decision an emergency evacuation demonstration was performed.
Def Stan 00-970 Part 5 Sect 2.4 Sub Part D, Clauses CS25.803 – Emergency Evacuation.
CS25.803 requires that for aeroplanes with a seating capacity of more than 44 passengers that the aircraft can be evacuated within 90 seconds.
Def Stan 00-970 Part 5 Sect 2.4 Sub Part D, Clauses UK25.803a – Emergency Evacuation.
UK25.803a requires that “Evacuation testing appropriate to role should include military-specific requirements, such as personnel wearing/carrying body armour, weapons and kit”.
Equipment Contribution to Residual Risk to Life (ECtRtL)
A potential ECtRtL has been identified as a result of the non-compliance. The potential ECtRtL could be created if increased time is required to evacuate the Air System due to the non-regulatory compliant aisle width.
Why an Equivalent Level of Safety (ELoS)?
When compliance with an airworthiness requirement cannot be adequately demonstrated, it may be possible to show that the airworthiness outcome of the requirement is still met by assessing the non-compliance at a system level. This is known as demonstrating an Equivalent Level of Safety (ELoS). An ELoS assessment generated by the TAA will be assessed by the MAA and if they are content, the MAA will issue an Equivalent Safety Finding (ESF).
This process permits the TAA to articulate both the problem and proposed solution, discuss it formally with the MAA and come to an agreement.
Writing an ELoS Argument
The ELoS shall be written as an MCRI, the format for which is illustrated below. Guidance for the formatting of which is available in AET Tool 8U (Regulatory Compliance Military Certification Review Item Guidance and Template). You are only required to fill in the following sections:
2.1 Statement of Issue
2.2 Affected Requirements
3.1 TAA Position
The remaining sections have been greyed out or completed for you. In addition, a Claims, Argument, Evidence structured table has been included in Section 3.1 to assist you I the structuring of your case.
Use the following MCRI template to record your argument, link here.
Your task is to use your knowledge from your training and the guidance available from the AET Tools to fill out fields 2.1, 2.2 and 3.1. In addition to the details contained within this brief, a selection of facts, statements and references regarding the topic are available in Table 1. These facts will form a basis, allowing you to form a Claim, Argument, Evidence approach.