## Murphy's Law(s)

About the time I was a brand new graduate engineer (1960), Murphy's Laws were new and fun. They were real and funny - which seems to make for good humor.

an example -

If anything can go wrong, it will,
especially in a demo before a big customer.
In these days of pre-canned videos, the dependence upon live demos is reduced, and so is the tension and excitement. In any case, Murphy's Laws are now largely relegated to discussions by old duffers. We view web sites such as Murphy's laws site - All the laws of Murphy in one place and remember the multiple proofs of their reality.

However, occasionally Murphy comes from nowhere - and causes trouble again.
The following apparently true list of sequential failures has been "lifted" from
HUMBLE PI: When Math Goes Wrong in the Real World by Matt Parker.

### Bad Math, and the Greatest Plane Non-Crash Ever

How calculation errors and misunderstandings led to a very lucky landing.

Aircraft fuel is calculated in terms of its weight, not its volume. Temperature changes can cause things to expand and contract; the actual volume fuel takes up depends on its temperature, so it’s an unreliable measurement of quantity. Weight stays the same. So when Air Canada flight 143 was taking off from Montreal on July 23, 1983, to fly to Edmonton, it had been calculated to need at least 22,300 kilograms of fuel (plus an extra 300 kilograms for taxiing, and so on).

There was still some fuel left from the flight in to Montreal, and this was measured to check how much fuel needed to be added for the next flight. Except that both the ground maintenance personnel and the flight crew performed their calculations using pounds instead of kilograms. The amount of fuel required was in kilograms, but they filled the aircraft using pounds, and 1 pound equals only 0.45 kilograms. This resulted in the aircraft taking off with approximately half as much fuel as it required to make it to Edmonton. The Boeing 767 was now going to run out of fuel mid-flight.

In an unbelievably lucky twist of fate, the aircraft, flying with a dangerously low amount of fuel, had to make a stop in Ottawa, where the fuel levels were to be double-checked before the plane took off again. The plane landed safely, with its crew members and passengers unaware how close they had come to running out of fuel in the air. It’s a near miss that reminds us that using the wrong units can put people’s lives in danger.

But then, in an unbelievably unlucky twist of fate, the crew doing the fuel check in Ottawa made exactly the same kilogram/pound unit error, and the aircraft was allowed to take off again without nearly enough fuel.

The fuel then ran out mid-flight.

There should be several alarm bells going off as you read this story. It’s so unbelievable as to strain credulity. Surely a plane will have fuel gauges to indicate how much fuel is left. Cars have such a gauge, and if one runs out of fuel, it merely rolls to a stop and causes a mild inconvenience: You have to walk to the nearest gas station. If a plane runs out of fuel, it also rolls to a stop—but only after dropping thousands of meters (or many more thousands of feet) out of the sky. The pilots should have been able to glance at the fuel gauge and see that they were running low.

This was not some light aircraft with a dodgy fuel gauge either. It was a brand-new Boeing 767 recently acquired by Air Canada. A brand-new Boeing 767 ... with a dodgy fuel-gauge system. The Boeing 767 was one of the first aircraft to be furnished with all manner of avionics (aviation electronics), so much of the cockpit was electronic displays. And, like most electronics, that is all great until something goes wrong.

Because of the lack of roadside assistance when you’re thousands of feet up, in aviation, redundancy is the name of the game. Airplanes need to bring their own spares. So the electronic fuel gauge was linked to sensors in the fuel tanks by two separate channels. If the two numbers coming from each tank agreed, then the fuel gauge could confidently show the current fuel level. The signals from the sensors in the tanks (one in each of the airplane’s wings) went into a fuel-level processor, which then controlled the gauges. Except this processor was on the blink.

One flight before its disastrous trip, the Boeing 767 was sitting in Edmonton and a certified aircraft technician named Yaremko was examining the faulty fuel gauges. He found that, if he disabled one of the fuel-sensor channels going into the processor, the gauges started working again. He deactivated the circuit breaker for that channel, labeled it with a piece of tape marked “inoperative,” and logged the problem. The aircraft could still be compliant with the Minimum Equipment List (required for the plane to be flown safely), as long as a manual fuel check was carried out. So now the fuel double-check consisted of the gauge system with one sensor channel and someone physically measuring the amount of fuel in the tank before takeoff.

This is where everything gets unbelievably unfortunate: The disaster makes it through several checks that could have identified and solved the problem.

The plane was flown from Edmonton to Montreal by a Captain Weir, who had misunderstood a conversation with Yaremko and thought the fuel-gauge problem was an ongoing issue and not something that had just happened. So when he handed the aircraft to Captain Pearson in Montreal, he explained that the fuel-gauge system had a problem, but that enough fuel should be in the tank to make it to Edmonton. Captain Pearson took this to mean that the cockpit fuel gauges were completely inoperative.

While this pilot-to-pilot conversation was happening in Montreal, a technician named Ouellet was checking the aircraft. He did not understand the note Yaremko had logged about the fuel-gauge system, so he tested it himself, which required reactivating the circuit breaker. This caused all the gauges to go blank, and Ouellet went off to order a new processor, forgetting to re-deactivate the circuit breaker. Captain Pearson then got into the cockpit to find all the fuel gauges blank and a label on one channel circuit breaker saying “inoperative,” which is exactly what he expected from his misunderstood conversation with Captain Weir. Because of this unfortunate series of events, a pilot was now prepared to fly an aircraft with no working fuel gauge.

Of course this would have been fine, if the fuel calculations had been performed correctly. But it was the early 1980s, and Canada was still transitioning from imperial units to metric units. In fact, the new fleet of Boeing 767s were the first aircraft for Air Canada that used metric units; all other Air Canada airplanes still measured their fuel in pounds. To add to the complication, the conversion from volume to weight used the enigmatically titled factor “specific gravity.” Had it been called “pounds per liter” or “kilograms per liter,” the problem might have been avoided. But it wasn’t. So after measuring the depth of the fuel in the tank in centimeters and successfully converting that to liters, everyone then used a specific gravity of 1.77 to do the conversion: This is the number of pounds per liter for the fuel at that temperature. The correct specific gravity of kilograms per liter would have been around 0.8. And a conversion mistake was made both before takeoff in Montreal and again during the stopover in Ottawa.

So, sure enough, in mid-flight after leaving Ottawa, the plane ran out of fuel and both engines failed within minutes of each other. This resulted in an error noise Bong! that no one in the cockpit had ever heard before. I get nervous when my laptop makes a noise I’ve never heard before; I can’t imagine what it’s like when you’re flying a plane.

The major problem with both engines failing is that indeed the plane no longer has any power to fly. A smaller but still important issue is that all the new fancy electronic displays in the cockpit needed power to work, and when the engines died, all the avionics went dead too. The pilots were left only with the analog displays: a magnetic compass, a horizon indicator, one airspeed indicator, and an altimeter. Oh yeah, and the flaps and slats, which would normally control the rate and speed of descent, also used the same power, so they were dead as well.

In the one stroke of good luck, Captain Pearson was also an experienced glider pilot. This suddenly became super useful. He was able to glide the Boeing 767 over 40 miles to a disused military base airfield in the town of Gimli. It was only a 7,200-foot runway, but Captain Pearson was able to hit the ground within 800 feet of the start of it.

In a second stroke of good luck, the front landing gear failed, causing the front of the aircraft to scrape along the ground, providing some much-needed braking friction, and the plane came to a halt before the end of the runway—much to the relief of the people staying in tents and campers at the far end, which was now used as a drag-racing strip.

Here’s the thing about turning off all the engines on a 767: They fly much more silently. Some people had the fright of their life when a jet airliner suddenly appeared on the disused runway, seemingly out of nowhere.

It became known as the Gimli Glider and achieved a reasonable level of fame.

It was eventually retired in 2008 and sent to an airplane scrap yard in California. An enterprising company bought some sections of its fuselage and now sells luggage tags made from the metal skin of the Gimli Glider. I guess the idea is that the aircraft was lucky to survive a dangerous situation, so having a part of the plane should bring good luck. But then again, the vast majority of airplanes don’t crash at all, so strictly speaking, this plane was bad luck.

I bought a piece of the fuselage and attached it to my laptop, which does not seem to have crashed more or less than usual.