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After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’

seattletimes.com

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Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’

#71

Post by zaroth »

jcutrell wrote: post #55
zaroth wrote: post #25

Earlier quoted context omitted.

Calculating the appropriate amount of liftoff thrust based on the weight of the plane is universal for flight ops. This feature of capitalism caused the money to be invested to achieve this efficiency, and also the systems and processes in place to ensure it was implemented properly; with sanity checks, authoritative oversight to halt ops when something was determined to be off, manual backup systems in place and wel…

I’m not sure that thrust calculation is actually incredibly common. I’d be curious what the handbook on these aircraft say, but common practice for many aircraft is full thrust on takeoff - rarely is there a negative safety penalty for too much thrust. Just an earlier rotate. Comment OP isn’t wrong entirely - this is the result of an economic decision. Not without it’s good effects - both can be true, but this is not…

“Common practice for many aircraft is full thrust on takeoff” - not for the class of aircraft we are discussing. What hobbyists do on their Turbo Props is irrelevant to the operation of a 737.

There are many considerations to setting takeoff thrust like climb speed limits, tire speed limits, elevation, temperature, engine-out safety margins, and many more I’m sure I don’t know about with my limited flight knowledge.

This is before we get into discussing weight load, which is primarily a factor of fuel load, which is also not just filled to 100% for every flight, but carefully calculated based on distance, weight, wind speed, etc. to not carry unnecessary fuel, which is also a huge efficiency boost.

In short there are safety reasons to use the appropriate (non-maximum) thrust on these types of planes just as much as there are efficiency reasons.

Capitalistic market forces are a big reason we have such an amazing airline industry with planes that are technological marvels of comfort, speed, and efficiency. Capitalism drove 120 years of relentless R&D into commercial flight systems, from the very first flight in 1903.

Not paying for necessary safety inspections is not “capitalistic” in any way. It seems like an ideological battle to use the term that way.

Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’

#72

Post by salawat »

Merad wrote: post #53

I was under the impression that SOP for most aircraft was to take off at full power, and if you happen to be lightly loaded you just get into the air faster. Was I wrong, or is this a recent change? If so, it seems like a concerning way for airlines to cut costs. Having excess power available at take off means there's a greater margin for error to handle emergencies (engine failure, bird strike, etc.).

Everyone else's (consumer's/engineer's/pilot's) "safety margin" is an executive's "cost to be optimized".

Make no mistake. The Exec/finance class will cut into any margin that you aren't willing to make them directly legally culpable for.

Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’

#73

Post by sithadmin »

737-900s are notoriously tail-heavy. Some airlines require that they use tail stands when parked, and some airlines (like United) have taken measures to redistribute weight forward of the rear landing gear (by moving one of the economy lavatories so that it sits directly behind first class/in front of most economy seating).

Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’

#74

Post by gdmt »

Merad wrote: post #53

I was under the impression that SOP for most aircraft was to take off at full power, and if you happen to be lightly loaded you just get into the air faster. Was I wrong, or is this a recent change? If so, it seems like a concerning way for airlines to cut costs. Having excess power available at take off means there's a greater margin for error to handle emergencies (engine failure, bird strike, etc.).

My understanding is that using less than full power prolongs the life span of engine components and makes fatigue-related engine failures less likely.

Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’

#75

Post by sokoloff »

Merad wrote: post #53

I was under the impression that SOP for most aircraft was to take off at full power, and if you happen to be lightly loaded you just get into the air faster. Was I wrong, or is this a recent change? If so, it seems like a concerning way for airlines to cut costs. Having excess power available at take off means there's a greater margin for error to handle emergencies (engine failure, bird strike, etc.).

Jets have been using reduced power takeoffs for many decades, with good operational results. There’s an AC about it from 35 years ago: https://www.faa.gov/documentLibrary/media/Advisory_Circular/...

Note that these are manufacturer-sanctioned procedures, not applicable to small piston aircraft, which should be using full power/RPM if the AFM/POH calls for that.

Note also that the full rated power (and sometimes more) is available in the case of an abnormal or emergency.

Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’

#76

Post by [deleted] »

basch wrote: post #4
Aloha wrote: post #2

This seems like mostly how it ought to work - * There were two unusual events in very short order * Someone quickly noticed and gave the order to go to ground stop * The problem was figured out quickly and a work-around was developed * Flights Resumed after successfully deploying the work around to the 'production process' * A patch was quickly developed and deployed once the underlying bug was uncovered. I think eve…

The purpose of telling pilots thrust was to save money and fuel. It’s a “least viable” optimization. >“The goal is to lower the power used on takeoff,” he said. “That reduces engine wear and saves money” on fuel and maintenance. >Flights to Hawaii are typically full, with lots of baggage and a full load of fuel for the trip across the ocean. The planes are heavy. > That morning, a software bug in an update to the Dyn…

[deleted]

Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’

#77

Post by howinteresting »

cratermoon wrote: post #15
sudhirj wrote: post #10

> 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. That seems horribly wrong to me. I can understand software being slow under load, but being wrong under load sounds like a horrible internal architecture problem.

Concurrency is hard. Thread unsafe operations that end up getting executed in multi-threaded contexts are a huge source of heisenbugs

Should have used Rust.

Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’

#78

Post by brookst »

1101010010 wrote: post #52
brookst wrote: post #39

Earlier quoted context omitted.

You think it would be more ideal to wear out engines sooner and burn more fossil fuels? If efficiency is the curse capitalism brings us, I’m feeling a little better about it.

If efficiency is the goal, packing people into a standing-only flight would also save fuel and reduce wear, I suppose you don't see any problem with that either? https://www.theguardian.com/business/2012/feb/28/ryanair-sta...

Are you saying that unless I’m willing to travel in uncomfortable conditions, you see no reason to reduce environmental impact of flights?

You’re trolling, right? That seems like a really implausible world view.

Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’

#79

Post by jki275 »

hn_throwaway_99 wrote: post #26
sudhirj wrote: post #10

> 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. That seems horribly wrong to me. I can understand software being slow under load, but being wrong under load sounds like a horrible internal architecture problem.

> but being wrong under load sounds like a horrible internal architecture problem. Tons of software can be "wrong under load" - things like race conditions and memory leaks are common problems, and they don't necessarily point to a huge architectural defect. E.g. Cloudflare had a bug years ago that caused highly sensitive data to leak, but only for a teeny (relatively) portion of their site. Similar issue happened to…

That's still an architecture defect.

Software's accuracy being affected by load is completely unacceptable.

Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’

#80

Post by speed_spread »

cratermoon wrote: post #15
sudhirj wrote: post #10

> 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. That seems horribly wrong to me. I can understand software being slow under load, but being wrong under load sounds like a horrible internal architecture problem.

Concurrency is hard. Thread unsafe operations that end up getting executed in multi-threaded contexts are a huge source of heisenbugs

I refuse to believe that summing up weights for each of 300 planes is so hard that it can't be made correct by a team of moderately competent developers operating under sane management. There might be some complexity, but it's 2023 and we have enough knowledge and tools to solve that kind of stuff routinely and reliably. Somebody fucked up big time and should be fired never to work in software again.
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