Comment by Arch-TK | Hacker News Reader

Comment by Arch-TK | Hacker News Reader

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An intersection takeoff is a takeoff where you do not use the full length of the runway. When you are a large aeroplane with a full load, reaching the necessary takeoff speeds required to rotate (pull up and begin lifting from the ground) can take longer than normal, at which point the climb speed will also be reduced if not properly compensated for (e.g. you miscalculate something and set the wrong elevator trim/takeoff thrust/something else).

When you are taking off, you have a short portion of the runway which you can use to abort the takeoff depending on failures, but that portion can become even shorter depending on the length of the runway.

Usually the first part of takeoff you would abort for almost any reason, and the second part you would only abort in a serious emergency, once you reach a certain point you simply cannot afford to abort because you will not stop in time to crash into whatever is at the end of the runway at which point you must take-off even if you are going to immediately request an emergency landing afterwards.

So if you are heavily loaded, with a lot of people on board, and you do an intersection takeoff, you are taking a risk that if you made a mistake or something goes wrong you will not have the ability to safely recover. That's why it's a terrible practice in this case. All it does is save a little bit of time which would be spent taxiing to the actual start of the runway.

Why is it a thing? Everything else in aviation seems to have good amounts of checks, balances and buffers. It feels the same to me as skimping a couple percent on fuel or doing less frequent maintenance. Both also reduce turnaround time.

Usually some form of mis-management which in this case may have put pressure on the pilot to accept a shorter take-off option due to some minutes of time saved. Sometimes pilots also might get their priorities wrong. There's a concept of "get-there-itis" which is also a common cause of crashes but it's currently unclear if it was a factor in this case.

I imagine in a while we will all be able to read the investigation reports, since the aircraft crashed shortly after take-off the black box recorder should contain all the information we need to figure out most of what happened including possibly the reasoning for the decision to make an intersection takeoff.

A recent, famous case of "get-there-itis" would be the 2020 Calabasas helicopter crash (that killed Kobe Bryant and several friends/family members).

Good question. False sense of routine, experience? Definitely a pet peeve.

Was flying as a passenger on a really small airline (8 seater plane, Green Air) out of San Jose in Costa Rica. We got cleared for takeoff ahead of a United 737, at most 500 feet into the humongous runway for that plane. Yet the pilots still put in the 2 minute effort to taxi back to the beginning of the runway, even though they could have easily taken off from where we entered it. Don’t know if it was their protocol or the pilots decision, but I will trust this airline for a very long time.

If something large had just taken off ahead of you, it was probably not safe to go anyway. Wake turbulence can kill you. If you need to wait 2 minutes, why not back taxi? It'll feel like doing something vs nothing and you get the extra extra runway.

We took off ahead of them.

Pilot here: even in my small Cessna I will backtrack do you know why? Because it gives me that money more options to work with in case something goes wrong with my take off.

The most useless things in the world are runway behind you, altitude above you, and fuel in the fuel truck.

Less time on runway means more throughput for a given buffer time between planes or larger buffer for a given throughput.

Now, obviously there's a discussion to be had about where the line is and what should and shouldn't be standard operating procedure but there's basically no safety improvement to have even a fully loaded 757 or Learjet or whatever drag it's butt to the very end of a 15000ft runway.

A pilot may be trying to scoot out of there ASAP because he knows based on the radio and who's where that's gonna make everyone else's jobs a little easier. An airport is run by professionals all of whom are trying to make things run smooth. It's at the complete opposite end of the spectrum from a school or Starbucks parking lot.

Depends on the circumstances. Probably not the case with a jet like a 787, but sometimes ATC will allow small planes to 'cut the line' with an intersection takeoff.

This runway was over 2 miles long. If you are in a smaller commuter prop plane or small jet, you don't need half that space for the takeoff. You call up ATC and they give you the option of taking off at an intersection now, or being #15 in line behind the heavies, its totally fine to do that if you are within the operating margins of the aircraft. The pilots have already done the math to know exactly how long of a runway they need for the worst case scenario (rejected takeoff just below V1), so if they know that they need 5k feet worst case scenario, and are offered an intersection takeoff with 7k feet of an 11k foot runway, there is already pretty big margin built in.

The thing to remember is that the aviation community and manufacturers have decided that once a jet is past a certain speed, you are committed to taking off and climbing out no matter what is going on. There is no circumstance where airliners will go beyond that speed and then try to reject the takeoff, and land back on that same runway.

As far as fuel, you might be distressed to know that you rarely fly with full tanks. They typically fly with the amount of fuel their route uses for the load they have + a margin for diversion. This is both a cost savings measure, as well as an operational concern (for example at Denver during a hot summer day, a lot of planes can't be loaded to maximum weight and still be able to do a rejected takeoff)

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