That's a huge amount of damage even at 24mph. It's crazy how that could happen though. Will be interesting to see the full report.

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masklinn 10 hours ago | parent | next [-]

The fire truck was flipped and moved to the side of the runway, this was not 24mph. 24mph is the final groundspeed recorded after the aircraft skidded off of the runway.

Per the ADSBx track the plane was at 101kts (115 mph / 185kph) just before crossing taxiway D, which would be where it hit the firetruck. It still had enough energy afterwards to reach taxiway E, 600ft away.

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bilekas 10 hours ago | parent | next [-]

Okay that makes far more sense the article didn’t really make that clear to me.

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cucumber3732842 9 hours ago | parent | prev [-]

The results seem on the high end but they check out at first glance.

A plane is basically a flimsy tube. A firetruck is a solid brick comparatively. The plane out weighs the fire truck by a lot and out speeds it by a lot. So yeah, destroying the whole front of the plane to punt the truck it sounds about right for a 25 on 5 or 35 on 10/15 type rear ending to me. Flipping doesn't really sound that unreasonable considering that the plane made contact with the top of the truck (just by virtue of comparative height) and contact may not have been straight on. Even if it left the pavement on it's wheels airport firefighters aren't exactly who I'd bet on (they're middle of the pack) to keep the truck on it's wheels if they got surprise kicked off the road especially if there's an embankment involved.

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masklinn 9 hours ago | parent [-]

A CRJ 9000 is 70000 lbs empty, 84500 lbs MTOW.

An Oshkosh 1500 4x4 is 62000 lbs GVWR (wiki says kerb weight but it’s incorrect).

The plane was landing and the truck was heading to an intervention, so they were likely close to empty and to GVWR respectively.

And again, 25mph is the final ground speed, after the plane punted the truck and kept on going for 600ft.

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moralestapia 2 hours ago | parent | next [-]

>25mph is the final ground speed

Wouldn't final ground speed be zero?

	▲	organsnyder 2 hours ago \| parent [-]
		Final ground speed reported.

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cucumber3732842 9 hours ago | parent | prev [-]

Pause the video at 13 sec. That firetruck is awfully intact for something that allegedly got hit at high speed. Basically just a bunch of top side sheetmetal damage (concentrated to the rear, obviously). In any case it didn't even get sent hard enough to screw up the cab exterior. And on the flip side, if you keep cranking the speed up you start getting to where the plane starts looking too suspiciously intact. There's just not much room to work backwards from the apparent results and get a high difference in speed or get very high initial speeds (100 onto 75 or whatever). If the plane was going fast the truck had to be going fast too or there'd be more carnage. But if they were both going fast you'd expect more damage from the after the fact barrel roll and the plane and truck to be a little farther apart in distance.

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PunchyHamster an hour ago | parent | next [-]

Fire truck is filled to brim with gear and doesn't care all that much about weight, plane is the opposite of that, lightness is money, so it makes sense fire truck looks better after crash than plane

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whycome 9 hours ago | parent | prev [-]

Where’s the video you’re referring to?

https://pbs.twimg.com/media/HEFF17eaYAA_sgq?format=jpg

I can’t tell what’s the truck and what’s the remains of the plane in this pic.

Another wider angle:

https://pbs.twimg.com/media/HEFDcS4bwAA8uu7?format=png&name=...

There’s no way this scene happens from a plane colliding with a truck at 24mph.

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cucumber3732842 8 hours ago | parent [-]

I'm talking about the headline video from TFA.

The back of a firetruck is not a working implement like a dump truck is nor is it sufficiently strong for mounting a crane or man bucket like utility bodies often are It's a bunch of sheetmetal boxes to hold stuff and cover stuff and there's a water tank back there somewhere. In the middle down low some pumps are buried. Basically don't think of it as being any more structural than a box truck body because it's not. All that stuff got shredded, obviously, since they're only really meant to bear their own weight and were subject to all the truck tossing forces here. Beyond that the truck is in pretty good shape. It's not uncommon for a good "off the highway and into the ditch" crash to rip tandems off, twist frames, etc. None of that has happened here. The plane is pretty rough, but that's expected. They are 100% tin cans. Ground equipment moving at idle speeds will absolutely shred them before the operator even feels resistance. A goose hit square on the leading edge of a small jet's wing will put a massive dent in (and apply red paint, lol).

24 sounds about right for a closing speed for plane onto truck. Whatever the baseline speed of the truck was cannot have been that high or the truck would be absolutely shredded from the barrel roll and as it stand the cab is barely pushed in.

	▲	whycome 8 hours ago \| parent [-]
		The article dropped the speed claim. The last recorded ground speed data of 24mph also shows a wildly different heading (going from 30deg ish to 170ish). So it probably happened after the collision and was part of its deceleration. As far as I know, the truck would have been crossing the runway so the effective speed perpendicular to the plane would be zero except for directional shear I guess.

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throw0101c 8 hours ago | parent | prev | next [-]

> That's a huge amount of damage even at 24mph.

The speed was much higher per sibling comment, but also remember that kinetic energy also involves mass (planes are heavy) and the square of the velocity.

* https://en.wikipedia.org/wiki/Kinetic_energy

The latter is why (e.g.) going 100 units/hour has twice the KE of going 70 units/hour in a car.

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hiddendoom45 11 hours ago | parent | prev | next [-]

It looks like that is based on the last recorded speed from flightradar24[1] which was 21kts(24mph). The previous data points were 11kts, and 58 kts(the last point before the track deviates off the runway). I do think it is likely that the collision occurred at a speed faster than 24mph.

edit: Looking into this a bit more it looks like the plane came to a stop around crossing E while the emergency vehicle was crossing at D(based on ATC recordings). Using the following map as reference[2], the 58kts point was around E, while the previous recorded point which was just before D was 114kts.

[1] https://www.flightradar24.com/data/flights/ac8646#3ede6c39

[2] https://www.flightaware.com/resources/airport/LGA/APD/AIRPOR...

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whycome 11 hours ago | parent | prev | next [-]

Very unlikely it was 24mph…The entire cockpit is gone.

(Though some of the major damage may have happened while deplaning the passengers)

	▲	Ekaros 11 hours ago \| parent [-]
		On other hand planes are really not designed to be crashed into things. Only for limited impacts. So we might not have right comparison for relatively thin and aimed to be light structure being impacted by bulkier object.

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globular-toast 9 hours ago | parent | prev [-]

Speed doesn't cause damage. Momentum causes damage. We understand speed, we do not understand momentum. It makes sense given our evolution.

People into boats need to understand this. Even a boat that travels no more than 4mph can crush you easily. This is why you never get on to moving boat from the front. Many people have made a mistake because speed is not high.

	▲	cucumber3732842 8 hours ago \| parent [-]
		Tugboats bump other boats all day. Hundred thousand pound pieces of machinery bury themselves into the dirt. All this as part of normal operation. It's not that simple. Speed, kinetic energy and acceleration are all interrelated and at the end of the day it's all forces (to some extent) and no amount of hand wringing commentary is going to replace genuine understanding of them.