Slashdot Mirror
Comair Done In by 16-Bit Counter
Gogo Dodo writes "According to the Cincinnati Post, the Comair system crash was caused by an overflowed 16-bit counter. Perhaps Comair should have paid for the software upgrade to MaestroCrew." You heard it here first...
It's interesting because it provides a lesson in software design - arbitary limits will trip you up eventually. It's not as if nobody knew to avoid them before, though.
I'm scared of numbers that can't be written as a fraction. It's an irrational fear.
This assumes that they had the resources. Given the current competitive environment in terms of consumer price and fuel costs, it would not be surprising if IT got the short end of things.
A Pirate and a Puritan look the same on a balance sheet.
Now my question would be, since they're owned by Delta, why wouldn't Comair flights be handled within Delta's own reservation/flight tracking system?
p.s. I've traveled through CVG, on Delta, during the holidays. Not anymore... One weather-delayed flight and the whole system falls apart.
I'd have a personalized plate on my car, but "toxic bachelor" won't fit into 7 letters.
That's not true.
Even if a system is outsourced it doesn't provide a company with 100% stable system. Frequently businesses define the type of system they want hardware/software and the amount they're willing to pay for it.
I work in a company that provides outsourced solutions. Monthly we provide info to businesses about their system. Also, we frequently make recommendations to augment the systems to improve performance. Businesses often choose to ignore our reports and recommendations.
Nothing's more frustrating then a meeting with a business having them tell us we mucked it up and in return we drop off the last 6 months of recommendations on upgrades to provide them additional hardware for their growing requirements and question why they choose to ignore it.
Now I'm not saying the provider didn't muck up. But, what I am saying is your statement that it's all the provider's fault may not be the case as the airlines probably choose to stay on that system as it 'met' their needs as they saw them.
So it turned out to be problematic to use a signed 16-bit integer.
...
But the real problem is a lack of error checking. It sounds like the code had something like:
int num_crew_changes;
crew_change_list[++num_crew_changes] = blah;
And the counter wrapped and the system crashed.
The code should have said:
if (num_crew_changes == MAXINT)
{
ERROR(E1234, "too many crew changes");
}
The system is still degraded after 32767 crew changes. It might be so degraded as to be unusable. But at least the company would know the extent of the degradation and could pull out the appropriate "Plan B". It's much safer and better to work around a known problem of known scope than to work around a system crash when you don't know the exact problem.
Rubbish. Don't judge yesteryear's programs by today's standards. Back then 4MB RAM cost more than $200. That's how important memory conservation was. In 1989 using an int was a perfectly acceptable choice. If you were programming back then you'd know how loathe programmers were to use longs when they didn't have to. (Granted an unsigned int would've worked better here, but that 64K limit could've also been reached.)
The software spec probably says something to the effect of "Don't attempt to schedule more than 32,767 crew changes." If you're running software that's more than a decade old you need to know what the limits of your software are.
Have fun: Join D.N.A. (National Dyslexics Association)
I work in the industry, so I might be able to provide an alternate viewpoint. Esentially what happened to the airline industry is that the market changed from a luxury market (high profit margins, low competition) to a commodity market (low profit margins, intense competition). Unfortunately, the airlines had all made long term deals with the trade unions that presumed stagnate market conditions - so when the market changed, they could not change with it.
The smaller carriers all have one thing in common - no unions. They do not pay their pilots as much, and their pilots do not get paid if they don't fly. The number one expense for an airline is fuel, but the number two expense are the pilots, stewardesses, mechanics, and baggage handlers. There was no way for older airlines to meet the new market conditions (fly more for less profit per flight) without paying people less. The problem is that no one wants to be paid less, so instead they get rid of the least powerful people (who also happen to be the least paid). This is also specified in the union contract... all laying off actions must be FILO.
Essentially, the major carriers are hamstrung by the unions, and they will not survive long term. Unions work by artificially limiting labor supply - but that doesn't work if there is not enough work.
The unions say how evil it is that they are getting pay cuts, but where exactly do they expect the money to come from? The government really should not prop up certain providers when others are eager to take there place. Competition works for the most part. Air travel is becoming a commodity market, like cars. Market transitions cause upheavals, and change the market leaders - especially if the current leaders cannot change their bussiness structure.
I have to say that I totally disagree about management being incompetant - the current management (at least the upper level ones I deal with) are extremely good. They may even get the airline to survive and change to the current market conditions. But what has really destroyed the airlines is the changing markets, and the unions preventing the old airlines to change with the times. The only thing management could have done would be to have rejected the union contracts earlier. But I doubt if that was possible.
Unions seem to believe that society owes them a living. The problem is that society (except in the form of government) is not a person, and so recognizes no debts. Fighting that is totally ineffective because there is no one to fight.
while (sig==sig) sig=!sig;