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“Watch Your Units!” Part 3 – Space Mountain and the Gimli Glider

Posted November 19, 2018 12:00 AM by RSBenner

“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:

https://forums.wdwmagic.com/threads/cause-of-the-space-mountain-incident-determined.33269/


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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Guru
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#1

Re: “Watch Your Units!” Part 3 – Space Mountain and the Gimli Glider

11/19/2018 1:37 PM

I'm surprised the Air Canada plane was allowed to take off with a faulty fuel gauge. Hope the pilots got a huge bonus for bringing that plane in safely!

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#2
In reply to #1

Re: “Watch Your Units!” Part 3 – Space Mountain and the Gimli Glider

11/19/2018 1:50 PM

It was actually a miscommunication. The pilot believed that the plane had been flown in that condition previously and, therefore, was OK for him to fly. In fact, it had not been flown in this condition and should not have been flown at all.

Although the plane was landed without loss of life, the captain was demoted for six months, the first officer was suspended for two weeks and three maintenance workers were also suspended. This all due to the failure of communication.

The pilots were, however, given an Outstanding Airmanship award in 1985.

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Guru
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#3
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Re: “Watch Your Units!” Part 3 – Space Mountain and the Gimli Glider

11/19/2018 3:05 PM

Ironic -- punishment and praise. I'm glad the captain and first officer were recognized. I can't imagine gliding a huge plane down from 35,000 feet! Sheesh!

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#4
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Re: “Watch Your Units!” Part 3 – Space Mountain and the Gimli Glider

11/19/2018 3:53 PM

I remember the controversy at the time.

Some people thought the pilots should have been fired for ever taking off with the plane in that condition in the first place and, others thought they were heroes for landing it safely. Both had a valid point.

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#8
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Re: “Watch Your Units!” Part 3 – Space Mountain and the Gimli Glider

12/10/2018 2:11 AM

I've looked through the accident report (long ago). The overall situation was far more complex than usually stated. I'm happy that the pilot was badly mis-informed of some highly relevant facts and while he COULD have kept asking questions, the information that he was given was credible.

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Guru

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#6
In reply to #1

Re: “Watch Your Units!” Part 3 – Space Mountain and the Gimli Glider

11/20/2018 11:53 AM

I remember the incident well.

If I have my facts correct: At that time the aircraft was allowed to fly with a faulty fuel indicator IF THERE WAS A MANUAL CHECK.

The pilot and crew screwed that up, pilot error - hence the discipline from the airline and Transport Canada.

That said, they did a spectacular recovery - the airfield was closed and the pilot knew of it because he had local knowledge - if I have my facts correct.

(Closed airfields are generally not normally on the current maps)

The later recognition of their landing skill I believe was outside of the legal system.

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#5

Re: “Watch Your Units!” Part 3 – Space Mountain and the Gimli Glider

11/20/2018 7:41 AM

You would have thought that they could tell the difference in the weight of the airline and how easily it left the ground. This should have been their first hint of an error.

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Guru

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#7
In reply to #5

Re: “Watch Your Units!” Part 3 – Space Mountain and the Gimli Glider

11/20/2018 5:22 PM

This is not the only successful glided landing of a loaded passenger aircraft.

An Airbus ran out of fuel mid-atlantic because of a fuel leak which was itself the result of faulty maintenance. The pilots glided to a successful landing in the Azores.

https://en.wikipedia.org/wiki/Air_Transat_Flight_236

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