Introduction

The halon replacement effort is global in scale, spanning governments and their respective agencies. The FAA has been involved in the process through its International Halon Replacement Working Group (IHRWG); now known as the International Aircraft Systems Fire Protection Working Group (IASFPWG). The four facets of interest pertinent to replacing Halon within civil aviation are the lavatory trash receptacles, cargo holds, hand-held extinguishers, and the engine and auxiliary power unit (APU) compartments. This discussion focuses on engine and APU halon replacement efforts.

The IASFPWG has been pursuing halon replacement since October 1993. One component of the IASFPWG is interested in the engine/APU compartment. This subgroup initially focussed on a large-scale, multiphase program being run by the USAF. The partnership for the project consisted of representatives from the U.S. Army, Navy (USN), and Air Force (USAF), the FAA, and the aviation industry. This program, titled "Halon Replacement For Aviation" occurred in a three-phase process. The process was a broad brush stroke to evaluate many chemicals and eventually select one to act as the intermediate halon replacement agent until a better replacement, more like halon, could be found.

1. Phase one of the USAF program involved determining the most significant factors which would impact the quantity of an agent required to suppress a nacelle fire and the selection of three chemicals from a large list which would likely be replacements for Halon 1301. The three chemicals selected were CF3I, HFC-125, and HFC-227ea.
2. Phase two was implemented to select one of the three potential replacements for phase three. Work from phase two resulted in the selection of HFC-125 as the recommended replacement for Halon 1301 in the aircraft engine nacelle.
3. The third phase incorporated further work with HFC-125 which would eventually yield equations intended for designers to use in protecting aircraft engine nacelles.

Project Overview

As part of the International Aircraft Systems Fire Protection Working Group, the engine and auxiliary power unit (APU) subgroup exists to facilitate halon replacement in these exact compartments found aboard the aircraft. The subgroup is a representation of regulatory authorities and the aviation industry; participation spans oceans. The primary driver of the project is the community associated with transport category aircraft.

The IASFPWG engine subgroup has formulated a plan. This effort incorporates results from the USAF program but is more focussed on transport category aircraft. The commercial interests in the IASFPWG expressed a desire for information on all materials in the USAF phase two work. Additionally, the effort will require presentation of the final data for gaseous suppressants in the form of the familiar concentration-versus-time duration as seen during engine nacelle certification procedures.

The replacement process is described in a document titled "The Minimum Performance Standard for Engines and Auxiliary Power Unit Compartments" (MPSE). The plan describes the geometry of a nacelle simulator and a process that could be used to demonstrate the equivalence of a replacement agent to that of Halon 1301. The backbone of the plan is the maintenance of the current level of safety; Halon 1301 at 6% volumetric concentration throughout the protected zone for a duration of one-half second.

The project consists of three components.

1. Applicable documentation. This information describes potential replacements for Halon 1301 as specified by the IASFPWG and a process to demonstrate the ability of a replacement for Halon 1301 in these applications. Descriptions and documentation are provided.
   • "Options for Aircraft Engine Fire Protection," September, 2000
   • "User Preferred Fire Extinguishing Agents for Engine and Auxiliary Power Unit (APU) Compartments," Report No. DOT/FAA/AR-96/80.
   • "The Minimum Performance Standard for Engine and Auxiliary Power Units."
2. Test Facility. This facility is a result of "The Minimum Performance Standard for Engine and Auxiliary Power Units" document. The facility incorporates a test fixture and data gathering abilities. A description with illustrations is provided.
   • Test Article and data gathering equipment.
3. Additional Commentary. Items of interest, but not directly applicable to the project.
   • "Aircraft Engine/APU Fire Extinguishing System Design Model (HFC-125)," AFRL-VA-WP-TR-TR-1999-3068, May 1997.
   • Brief history of Halon 1301 and development of gas analysis in the engine nacelle fire extinguishment application.
   • "General Guidelines for Measuring Fire-Extinguishing Agent Concentrations in Powerplant Compartments," Advisory Circular 20-100, September, 1977.
   • Simulating Halon 1301 distribution with HFC-125.
   • Correction of Halonyzer discrepancies during gas analysis. This discussion addresses discrepancies noted during recent testing.