They Built An Airport That Nobody Wanted

[Kip Powick]

_FQIS...and

_{much human error}

[Seeker]

_FQIS...and

_{much human error}

Yes, but how did the FQIS fail? There is a particular failure mode that subverted some of the engineered redundancy in the system. Don't bother reading the wikipedia article since it's not described there.

[Kip Powick]

A pre-flight inspection by a maintenance engineer showed that the plane’s Fuel Quantity Indicator System (FQIS) was malfunctioning. The FQIS had a built-in redundancy in which the plane’s remaining fuel was measured by two separate sensors and the results were compared to ensure accuracy. The pilot and co-pilot were shown only one amount however, assuming the two measurements agreed. The engineer in Edmonton noticed that the FQIS quit working entirely unless he pulled the fuse for one of the measuring sensors. He informed the pilot of this and the flight was made with the FQIS working with only one measurement sensor.

Once in Montreal, another Air Canada engineer looked at the FQIS and reconnected the second measuring sensor, which caused the system to stop working again entirely. The engineer was then called away to check another system and left the FQIS in non-working order. The new flight’s captain, Robert Pearson, and First Officer Maurice Quintal were told about the FQIS problem by the pilot who had flown the plane from Edmonton to Montreal earlier in the day. However, they were under the mistaken belief that the FQIS was not working at all on the earlier flight, so were not alarmed when the gauge was blank as they entered the cockpit. Instead of grounding the flight, the crew decided to measure the fuel via dripstick and track fuel consumption via the Flight Management Computer.

[Seeker]

A pre-flight inspection by a maintenance engineer showed that the plane’s Fuel Quantity Indicator System (FQIS) was malfunctioning. The FQIS had a built-in redundancy in which the plane’s remaining fuel was measured by two separate sensors and the results were compared to ensure accuracy. The pilot and co-pilot were shown only one amount however, assuming the two measurements agreed. The engineer in Edmonton noticed that the FQIS quit working entirely unless he pulled the fuse for one of the measuring sensors. He informed the pilot of this and the flight was made with the FQIS working with only one measurement sensor.

Once in Montreal, another Air Canada engineer looked at the FQIS and reconnected the second measuring sensor, which caused the system to stop working again entirely. The engineer was then called away to check another system and left the FQIS in non-working order. The new flight’s captain, Robert Pearson, and First Officer Maurice Quintal were told about the FQIS problem by the pilot who had flown the plane from Edmonton to Montreal earlier in the day. However, they were under the mistaken belief that the FQIS was not working at all on the earlier flight, so were not alarmed when the gauge was blank as they entered the cockpit. Instead of grounding the flight, the crew decided to measure the fuel via dripstick and track fuel consumption via the Flight Management Computer.

Yes, exactly what it says on Wikipedia but you're missing the point.

Earlier in the thread chockalicious said that he liked to read the history and background of YMX and that he liked coming to the AEF because of threads like this. Props2you made a sarcastic comment (in a friendly way) suggesting that the history of YMX should be familiar, comparing it to the Gimli glider incident implying that, essentially, all the details were common knowledge. I proposed a few questions about the specifics of the Gimli Glider to show that even though something might be generally known, YMX and GG for example, there are still facts known to certain people that are not available on wikipedia or google. The actual failure mode of the FQIS is not given in the wikipedia article. In the same way details of the history of YMX might not be available on wikipedia.

What I'm trying to say is that I also like to coming to AEF to read threads that give information that is not available elsewhere or to read analysis from expert insiders.

[Guest]

The root cause if I recall correctly, was a 'cold soldier' in a component (don't recall what it was- some type of processor?), that occurred during the manufacturing process of the component.

Is that what you are looking for?

[Seeker]

Ding Ding Ding, we have a winner - BTW it's cold solder, not cold soldier. A cold solder connection on channel 2 of the Fuel Quantity Processor - an interesting failure because it's allowed some voltage to pass, some but much less than the normal 5 volts. A broken solder joint would have disabled channel 2 and channel 1 would have simply continued normal operation but a cold solder joint which allowed partial current flow was not accounted for in the design and caused the Processor to completely drop offline. This is the reason why pulling the breaker for channel 2 restored normal function in channel 1 and this is a significant factor in the timeline of the incident.

[Guest]

Funny thing is I even quickly did a web search of that word, because I was unsure of the spelling- and even Google misled me (or maybe I allowed Google to mislead me!).