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After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’
171–180 of 189 posts
Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’
#172Dumb question. A heavier aircraft should be slower to accelerate. Given that these planes were at least 13% heavier than was thought and the force applied during takeoff is known, shouldn’t there have been some kind of alarm? “We think you should be going 120 mph but you’re actually going 100 mph”.
And based on the inferred mass, can’t you directly calculate what the takeoff velocity should be?
Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’
#173Earlier quoted context omitted.
That means rotating at a higher speed than calculated Vr, this is also bad as you put more wear in the tires and use more fuel (rolling on the tires vs flying in the air) to take off. The Vr is an optimal speed, below is dangerous, above is wasteful.
I think the more important factor is that it eats runway and takes longer to reach safe speeds. If there is a problem at rotation you want as much runway available as possible. If you delay rotation not only are you further down the runway before "really rotating", but you're traveling faster. A 10-knot increase in speed means 20% more energy to disipate. And you're even further above the brake's certified performace…
V_r is almost always above V_1, which is the decision speed. If you're going to abort a takeoff, that decision needs to be made before V_1, otherwise you're likely to overrun the end of the runway.
So, once you get to the stage where you're ready to rotate, or even late in rotating, you're committed to getting the plane off the ground.
Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’
#174It's a bit of a shame the way journalism works this story will do the rounds with the headlines associating "Alaska Airlines" with "tailstrikes" ("takeoff incidents", whatever term gets used), while actually it looks like Alaska Airlines were the heroes of this story.
Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’
#175Earlier quoted context omitted.
I think the more important factor is that it eats runway and takes longer to reach safe speeds. If there is a problem at rotation you want as much runway available as possible. If you delay rotation not only are you further down the runway before "really rotating", but you're traveling faster. A 10-knot increase in speed means 20% more energy to disipate. And you're even further above the brake's certified performace…
V_r is almost always above V_1, which is the decision speed. If you're going to abort a takeoff, that decision needs to be made before V_1, otherwise you're likely to overrun the end of the runway. So, once you get to the stage where you're ready to rotate, or even late in rotating, you're committed to getting the plane off the ground.
On a big airliner yes. V1 depends on the runway length so a smaller aircraft will easily reach Vr before V1. Because most runways are made for the biggest planes.
Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’
#176737-900s 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).
Do 737s in the US still even have first class?. I'm surprised. I've never seen any in Europe in the last 15 years on short haul which is of course what a 737 is used for.
Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’
#177It’s software. It’s made of bugs.
So is oil but it works fine :P
Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’
#178Lots of blame to pass on the software, but the real culprit is spelled out clearly in the middle of the article: > the computer then calculates just the right amount of engine thrust so the pilots don’t use more than necessary. “The goal is to lower the power used on takeoff,” he said. “That reduces engine wear and saves money” on fuel and maintenance. This is not an accident, but rather a feature of capitalism, this…
Less fuel is better for the environment. That should be counterbalanced with safety, which they did - even with a bug and a heavy plane the plane still took off safely. This means they are also leaving a safety margin of fuel, even though that costs extra money.
A tail strike is not a safe takeoff! That nothing happened doesn't mean there was no danger.
Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’
#179Earlier quoted context omitted.
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…
Based on my experiences reading aviation accident and safety reports, air transport pilots have a _lot_ of divorces.
This could also mean divorces played a role in accidents of course.
But it could also just be statistically true. Being in a position of power, surrounded by beautiful coworkers, lots of overnight hotel stays..
Without further investigation a conclusion can't be drawn though.
Re: After Alaska Airlines planes bump runway, a scramble to ‘pull the plug’
#180This 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 bug is in the weight of the payload of the plane. I don't believe pilots have any way to measure the actual weight of the payload of the plane, they rely on that sort of estimates to determine how much fuel they need, take-off speed, etc. It's not really a loss of authority. Bad weight estimates have resulted in crashes in the past.
I wonder if it would be possible to put a weighing pad at airports for a double-check. Like on the access ramp to the runway, meaning you'd only need a handful per airport and planes pass them naturally.