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Overview

To provide for emergency egress, modern military aircraft utilize canopy fracturing systems or hatch severance systems to create an egress window through flight vehicle structure. These systems utilize a linear explosive cutting or fracturing charge to create an egress window for aircrew. Linear explosive charges are normally mounted to the aircraft canopy or structure, and provide sufficient impetus to sever or fracture the target material. Explosive transfer lines, initiation manifolds and retention provisions are typically considered part of the egress system as well.

Application

This basic technology is applicable to many kinds of manned aircraft and spacecraft. Using linear explosive charges, a wide variety of structural metallic and non-metallic materials can be effectively severed to allow escape of crew members directly through a canopy or other aircraft structure.

Design Considerations

The application of a linear explosive based cutting or fracturing system is driven by one critical requirement – the need to very rapidly escape from a damaged or inoperable aircraft. Alternate technologies, such as canopy jettison and mechanical release systems require a significantly longer time window, decreasing crew survival rates. In applications for smaller aircraft (such as fighter and trainer aircraft), a canopy fracturing or severance system is used to provide for crew egress. For less robust cast acrylic canopies used in these applications, metal clad linear explosive MDF (Mild Detonating Fuse) is used to fragilize a canopy prior to crew ejection. For more robust canopies made of stretched acrylic or polycarbonate, a Liner Shaped Charge (LSC) is typically utilized to sever the canopy into two or more large sections.

In larger aircraft (such as bombers and cargo vehicles), emergency egress requires the cutting of vehicle skin or structural panels. Similar to canopy severance systems, these systems utilize a linear explosive charge (typically LSC) to sever metallic or non-metallic structure.

In all cases, careful egress system design requires consideration of a number of different factors. Explosive backblast and overpressure must be minimized to ensure crew safety during system function. Age life and maintainability requirements require consideration of mounting and change-out procedures. Reliability and system robustness demand careful and precise control over explosive initiation interfaces and linear charge positioning. The behavior of the canopy or hatch fragments after severance must be carefully evaluated, due to the complex pressure gradients that may exist on the exterior of the disabled air vehicle.