Destroy to protect - tests show how to prevent another Lockerbie

Early summer haze hangs over a little-known airfield in the English midlands. In the midday stillness a small gathering waits, gazes and fixes lenses intently on a white Boeing 747 about 400m (1,300ft) away across the grass. Suddenly, the aircraft shudders and, just as the soundwave from the destructive explosion reaches the crowd, the massive fuselage bursts open, ejecting debris, then crumples and sags. Silence falls as the dust descends around the broken hull.

The surreal aura is enhanced when a scientist declares the experiment a success. It is the climax of a research programme to enable aircraft to survive terrorist bombs, and this scene of devastation is, he says, what his research team had been expecting. Meanwhile, there is a car parked near the airfield gathering, and stickers in its windows pronounce: "Lockerbie. Let the truth be known."

If technology tested on that May day had been applied to the Pan American Boeing 747 blown up by a terrorist bomb over Lockerbie, Scotland, in December 1988 killing the 259 people on board, the aircraft might well have landed safely, according to initial assessments of this explosive experiment. The 17 May test, carried out at Bruntingthorpe airfield, involved the detonation of four explosive charges simultaneously inside a fully pressurised 747-100. Three of the charges caused negligible damage, according to the testing agencies. Almost all the havoc was wrought by the one charge which was in a standard baggage container, like the Lockerbie bomb.

The scientists' initial reaction is that even an airborne 747 would probably have survived the "bombs" placed in all but the unprotected container, but full analysis of the test is not expected to be complete until mid June. The UK Defence Evaluation and Research Agency (DERA), contracted to conduct the experimental work for the Civil Aviation Authority, says that the test went perfectly.

The four separate explosive charges were used to test the effectiveness of four different levels of blast-protection. The need to detonate them simultaneously was driven by cost considerations. Another hull, which the DERA describes only as "a wide-bodied European aircraft", was blown up at Shoeburyness, UK, in September 1995 as part of the same four-year research programme, and resources were only sufficient to buy one 747. To have set off charges separately would, after the first explosion, have meant that the 747 hull could not have been pressurised for the others. From the earlier tests, the DERA's chief materials scientist Prof Chris Peel and his team have created computer models of various tapes of explosions and their effects.

On 17 May, the 747 was pressurised to 0.62 bar (91b/in2) to simulate the differential pressure expected at more than 35,000ft. The "bombs" were placed in four containers. Container No 1 was "hardened", produced by the US Federal Aviation Administration as a part of its contribution to this international programme. The FAA declines to give details of the materials used, just as DERA will not give details of the explosive materials or quantities used, for security reasons. No 2 was a standard container next to a cargo-hold wall which was covered by a flexible Kevlar-fibre protective lining; the third was a standard container with a 200mm-thick lining; No 4 was a standard luggage container.

The 747's cargo holds were loaded also with other containers packed with rags to simulate the reality of a normal aircraft with luggage and cargo on board. Peel says that the future holds several options as to how to use the newly gained knowledge. These include modifying the design of new-build aircraft hulls, using blast-attenuating containers and having protective lining for cargo holds. All these would add to the aircraft weight, the DERA says, commenting that the hold-lining would add about 3t to a 747 using present materials.

This experiment is a test for theories developed over four years of research, and it allows adjustments to be made to a software model which will prove invaluable for further work. Finally, there is a feeling that the loop has been closed: the aircraft type which suffered the disaster giving rise to this research has been put to the test, but this time with some help.

David Learmount

Source:
Flight International, 28th May - 3rd June 1997