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1989—international accident investigation organizations, congressional committees, and other government authorities—began to promote research into methods of hardening aircraft and ULDs against explosives. In the United States, the FAA began funding research on hardened containers, including blast characterization analyses and the development of blast-tolerant design concepts. The basic goal was to develop operationally feasible HULDs that could withstand the blast and fragmentation forces of an explosion.

Initial operational concepts were based on the idea that an aircraft could be protected by using blast-resistant HULDs in place of all standard ULDs. However, for this idea to be feasible, HULDs would require similar cost, weight, and operational capabilities as standard ULDs.

Design Guidelines and Procurement

Following Pan Am 103, the British Air Accident Investigations Branch recommended that "airworthiness authorities and aircraft manufacturers undertake a systematic study with a view to identify measures that might mitigate the effects of explosive devices" (British Air Accident Investigation Branch, 1990). Major initiatives on hardened containers were begun in the early 1990s, when the FAA launched a series of concept studies, including analyses, testing, and development, with approximately 15 different contractors and support organizations (similar efforts were undertaken in Europe). Studies included government-funded research and development by the U.S. Navy, U.S. Air Force, U.S. Army, Boeing, Northrop, Jaycor, Galaxy Scientific Corporation, the Great Lakes Composites Consortium (GLCC), and others. In addition, many companies initiated internally funded independent efforts on the assumption that hardened containers represented an emerging market area. Research and development continued through the mid-1990s and produced data on blast characteristics, material properties, the feasibility and effectiveness of HULD concepts, and modeling and simulation requirements.

After about five years, however, because of slow progress on an effective, feasible design concept—and because of a less than enthusiastic response from the airlines—no major breakthroughs had been made. Although many concepts were investigated, none was identified as a "silver bullet" that would immediately replace current ULDs. Research did not lead to a hardened container that looked, behaved, and cost the same as a standard ULD, and airlines were not willing to support concepts that would add weight, cost, or operational constraints to their infrastructures.

Although the FAA has considered many approaches to deploying HULDs, in the past few years the focus has been on HULDs as an integral component of the entire security system that would be deployed at the level of one or two per aircraft in conjunction with passenger screening and CAPS (this approach is consistent with the TAAS approach recommended in this report). Only a small percentage of passenger bags carried in the HULD would be based on predetermined selection criteria. The FAA hoped this approach would be acceptable to the airline industry because it would reduce the requirements for the deployment of HULDs.

In 1996, the FAA announced the first of two procurement solicitations for hardened containers that could contain an explosion from a defined explosive threat size and could be deployed into normal airline operations. Six proposals were submitted by various suppliers. However, after determining that none of the proposed concepts would meet the design blast criteria, the FAA decided not to award any contracts (Hacker, 1998a). After redefining the requirements, the FAA released a second solicitation in January 1997 (FAA, 1997d). The requirements for the second solicitation are given in Box 5-1. The FAA received eight proposals in response to the second solicitation, and two proposals, by Jaycor and Galaxy, were selected for development and testing. Both were required to demonstrate compliance with the standards listed in Box 5-2.


Under the terms of the FAA HULD contracts, Jaycor and Galaxy were contracted to provide prototype HULDs that could withstand the blast effects from a bomb of a certain size and configuration (the blast-resistance criteria for HULDs are classified [ISO 6517]). Each company was required to demonstrate the survivability of its HULD design either through a blast test or a simulation analysis. Both companies decided to meet this requirement through blast tests.

Prior to 1997, the FAA and industry had conducted numerous blast tests on earlier designs and had developed test standards (ISO 6517) for the two candidate HULD designs. The HULD test program, which was initiated in late 1997 in Tucson, Arizona, was performed in a salvaged, unpressurized, lower cargo-hold section from a Boeing 747 aircraft that included the basic aircraft structure (e.g., airframe, stringers, skin panels, shear clips, wall liners, cargo floor beams, and passenger floor beams), as shown in Figure 5-1. Although most of the major aircraft systems had been removed, much of the wiring, cables, and air ducts were intact. Each HULD was placed separately into the cargo-hold area at a standard container lock-down location. No other containers were included in the tests. Test objectives included verification (1) that the HULD could withstand the explosive blast with no rupture or fragmentation; (2) that no fragments penetrated the HULD or the aircraft structure; (3) that the HULD had not moved or jumped causing structural damage to the aircraft (i.e., airframe, cargo floor, or passenger floor); and (4) that no fire had erupted after the blast.

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