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 “Watch your units!” Unit conversion errors can be found most anywhere, even in Japan and Canada. For Part 3 of this series, we will look at Tokyo Disneyland and Air Canada.
Tokyo Disneyland's Space Mountain Derailment
On December 5, 2003, one of the rocket vehicles of the Space Mountain attraction at Tokyo Disneyland derailed just before the end of the ride, forcing it to come to a sudden stop. Luckily, no one was injured due to the derailment. However, investigation proved the problem was caused by unit conversions.
The Space Mountain attraction at Tokyo Disneyland opened with the park on April 15, 1983. Based off the original, which opened in Florida in 1975, the coaster was built and maintained using US customary units (USC). In 1995, design specifications for the axles and bearings were updated to reflect the International System of Units (SI). However, the original drawings were never purged. So, when axles were ordered in August of 2002, the incorrect (USC) drawings were used, resulting in incorrectly sized axles. This resulted in a gap between the axle and its bearing to be over 1 mm, while the design specified a gap of 0.2 mm. Excessive vibration and stress occurring during operation due to this large gap and caused the rear wheel axle to break and the vehicle to derail.
The attraction was closed for two months during which all axles were inspected and (I assume) old drawings were purged.
References:
The Gimli Glider
On July 23, 1983, Air Canada flight 143 departed Montreal for a transcontinental flight to Edmonton. However, the flight never made it there due to faulty fuel gauges and an incorrect unit conversion.
About one hour after departure, while cruising at 41,000 feet, both engines stopped operating. In addition to flight power, these engines also supply electrical power to the instrumentation and supply power to the hydraulic system. With the engines off, only a few battery-powered emergency flight instruments were operational and very limited hydraulic power was available. Despite these difficulties, the crew glided the aircraft and successfully landed it at a closed air force base, Station Gimli in Manitoba, with only minor injuries to the 69 people on-board.
Investigation into the “Gimli Glider,” as it became known, determined that a major factor in this near disaster centered around a unit conversion issue. In 1983, Canada was in the process of converting to SI units, and their new fleet of Boeing 767 jets would be the first to completely use this system. Because of the inoperative fuel gauge on Flight 143 the fuel level had to be checked manually. Calculations were then performed in order to determine how much fuel needed to be added to the plane before take-off. During this calculation, the ground crew, less familiar with the SI system, used a USC conversion factor in error. This resulted in the addition of 4,917 liters of fuel rather than the required 20,088 liters. Therefore, the reason for the engine failure was determined to be lack of proper fuel supply due to a faulty unit conversion.
What can I say except, “Watch your units!”
Reference:
https://en.wikipedia.org/wiki/Gimli_Glider
https://airlinegeeks.com/2018/07/23/remembering-the-gimli-glider-incident-on-its-35th-anniversary/
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Re: “Watch Your Units!” Part 3 – Space Mountain and the Gimli Glider
