Accidents and incidents

Confusion over units during the process of metrication can sometimes lead to accidents. One of the most notable examples was during metrication in Canada. In 1983, an Air Canada Boeing 767, nicknamed the "Gimli Glider" following the incident, ran out of fuel in midflight. The incident was caused, in a large part, by the confusion over the conversion between litres, kilograms, and pounds, resulting in the aircraft receiving 22,300 pounds of fuel instead of the required 22,300 kg.^[85]
While not strictly an example of national metrication, the use of two different systems was a contributing factor in the loss of the Mars Climate Orbiter in 1998. The National Aeronautics and Space Administration (NASA) specified metric units in the contract. NASA and other organizations worked in metric units, but one subcontractor, Lockheed Martin, provided thruster performance data to the team in pound force-seconds instead of newton-seconds. The spacecraft was intended to orbit Mars at about 150 kilometres (93 mi) in altitude, but the incorrect data meant that it descended to about 57 kilometres (35 mi). As a result, it burned up in the Martian atmosphere.^[86]
On 25 September 2009, the British Department for Transport published a draft version of legislation to amend its road signs legislation^[87] for comment. Among the proposed changes was an amendment to existing legislation to make dual-unit height and width warning and restriction signs mandatory. This was justified in Paragraph 53 of the Impact Analysis^[88] by the text "... Based on records from Network Rail's incident logs since April 2008, approximately 10 to 12 percent of bridge strikes involved foreign lorries. This is disproportionately high in terms of the number of foreign lorries on the road network." This proposal was shelved with the change of government in 2010, though many bridges are now signed both ways. The latest signage guidance consultation has proposed this once again.