In May of 2000, now more than 22 years ago, air accident investigators in the United Kingdom searched the bottom of a lake near London Stansted Airport for panels of depleted uranium from a crashed Korean Air Boeing 747. At the time that the BBC reported this, investigators had recovered 17 out of 20 of the panels, which were part of the aircraft’s structure and function.
The final Air Accidents Investigation Branch (AAIB) report eventually noted that “all of the weights bar one were identified and disposed of during recovery.” So what exactly was the function of these weights? And why was depleted uranium selected over other materials in the first place? Let’s take a look back and find out.
Older 747s use depleted uranium as counterweights
As unlikely as it seems, depleted uranium was actually used for a counterbalance in hundreds of Boeing 747 aircraft that were built before 1981. The AAIB notes that, before the practice became controversial, it was typical of these early jumbo jets to have mass balance weights made of depleted uranium. The areas that these weights were used in were the outboard elevators and upper rudder.
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The AAIB also notes that the early 747 was built with 20 weights (panels) installed. Six were present on each outer elevator, while eight weights were installed on the upper rudder. But why exactly was uranium used in the first place?
Uranium’s density made it an ideal choice
Depleted uranium was selected as a counterweight for early Boeing 747 aircraft due to its high density. As such, it had much more mass relative to its volume. In other words, compared to other metals and materials, it didn’t take up much space but weighed enough for its role as a mass balance weight, making it a prime choice.
A counterweight is used in the aerodynamic control of aircraft, to maintain its center of gravity. Having a high density in this respect is important. However, the connotations of uranium might have you wondering whether its use was safe.
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Were these weights safe to use?
For many people, simply hearing the term ‘depleted uranium’ usually conjures up Hollywood images of hazmat suits in the mind, or far-fetched stories of supervillain terrorists. In this particular case, however, the depleted uranium weights used in the Boeing 747 did not carry anywhere near the same level of threat. Instead, these weights were clad with thin layers of nickel and cadmium.
In addition to this, the weights were then painted with a primer and then a topcoat. These could be a hazard if sufficiently damaged by fire or corrosion. The result of this damage would be exposure to uranium oxide. For this to pose a real danger, ‘intimate contact’ would need to be made, which, as an example, could mean “transferring it to the mouth from contaminated hands.” The AAIB adds:
“A fire in the tail section of the airplane of sufficiently high temperature and duration to generate significant amounts of airborne uranium is unlikely if not impossible.”
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However, separate studies completed by both Boeing and the United States Army have proven that no danger exists from the uranium weights in the event of a crash. Data collected by the WISE Uranium Project notes that since 1981, Boeing has provided customers with tungsten replacement counterweights, and tungsten counterweights have since been installed in new Boeing 747 aircraft.
El Al flight 1862
The topic of uranium counterweights in older Boeing 747s also came to the fore following the crash of El Al flight 1862. This 1992 accident involved a cargo-carrying 747, which, as pictured above, crashed into a Dutch apartment block.
There was 282 kg (622 lb) of uranium onboard, which was unknown during rescue operations. When this later became known, studies were undertaken to consider whether its presence might have been linked to the health issues that surviving residents of the affected building had suffered. However, this was eventually deemed to have been unlikely, with the chance of uranium poisoning being minimal.
Did you know about this interesting bit of aircraft history? Have you ever flown on a pre-1981 Boeing 747? Let us know your thoughts and experiences in the comments!
Sources: AAIB, BBC, Ratical, WISE Uranium Project