10 ms·

> Peyton added that even though the update to the DynamicSource software had been tested over an extended period, the bug was missed because it only presented w

> Peyton added that even though the update to the DynamicSource software had been tested over an extended period, the bug was missed because it only presented when many aircraft at the same time were using the system. There are only two hard problems in computer science: - cache invalidation - naming things - off-by-one errors - concurrency/race conditions - concurrency/race conditions

cratermoon 4y ago
Here's a bit of detail. The software was supposed to calculate the speed based on the weight of the aircraft and determine if the available runways were adequate. The nature of the bug was that if it couldn't find a usable runway, it would lower the weight until it did fit the runway it could find. That's right, the software would say, "oh, the aircraft can't take off on the runway with this weight, let me just lower the weight so it can". Apparently the runway data was missing or wrong, but instead of saying, "no, you can't take off from there" the software said "here's a solution allowing you to take off, but at this lower weight". I'm not sure how/if that was caused by a concurrency bug, but that's what I know.
- cptcobalt 4y ago
  what! that's incredible — do you have a link to the source (of this information), by chance?
  - cratermoon 4y ago
    It's something I learned from someone who works there. I can vouch for its reliability. Make what you will of that.
- dghlsakjg 4y ago
  That makes sense. If you are flying out of Denver (high altitude) on a summer day, you need a TON of runway to get off the ground. There are some aircraft that simply can't take off fully loaded from high altitude with the runways that exist. The solution is to not take off fully loaded (lower the weight) So you either don't fully fuel up, or you remove cargo/passengers. It's very common, and by design. The software exists so that you know not to fully load the cargo bays if the conditions don't allow it (cargo makes airlines a lot of money).
  - cratermoon 4y ago
    Yes, those runways are called "hot and high". Another one is Albuquerque. Without knowing more I can't say why the software would return a result using a different weight from what was input without clearly alerting the humans of that change, or else return an error with no attempt to give performance parameters at all.
- he0001 4y ago
  If that’s the case, it sounds more like a forgotten feature.

cratermoon 4y ago

Here's a bit of detail. The software was supposed to calculate the speed based on the weight of the aircraft and determine if the available runways were adequate. The nature of the bug was that if it couldn't find a usable runway, it would lower the weight until it did fit the runway it could find. That's right, the software would say, "oh, the aircraft can't take off on the runway with this weight, let me just lower the weight so it can". Apparently the runway data was missing or wrong, but instead of saying, "no, you can't take off from there" the software said "here's a solution allowing you to take off, but at this lower weight". I'm not sure how/if that was caused by a concurrency bug, but that's what I know.

cptcobalt 4y ago
what! that's incredible — do you have a link to the source (of this information), by chance?
- cratermoon 4y ago
  It's something I learned from someone who works there. I can vouch for its reliability. Make what you will of that.
dghlsakjg 4y ago
That makes sense. If you are flying out of Denver (high altitude) on a summer day, you need a TON of runway to get off the ground. There are some aircraft that simply can't take off fully loaded from high altitude with the runways that exist. The solution is to not take off fully loaded (lower the weight) So you either don't fully fuel up, or you remove cargo/passengers. It's very common, and by design. The software exists so that you know not to fully load the cargo bays if the conditions don't allow it (cargo makes airlines a lot of money).
- cratermoon 4y ago
  Yes, those runways are called "hot and high". Another one is Albuquerque. Without knowing more I can't say why the software would return a result using a different weight from what was input without clearly alerting the humans of that change, or else return an error with no attempt to give performance parameters at all.
he0001 4y ago
If that’s the case, it sounds more like a forgotten feature.