# US Airways Jet sinks into blacktop at DCA



## PRR 60

Fill in the blank...

_It was so hot that _______!_

How about this: _a plane sank into the blacktop at Washington Reagan and was stuck._

It was US Airways (Air Wisconsin) Flight 3935 using a Canadair Regional Jet (CRJ-200).

From the Washington Post, July 8:



> Things were proceeding normally Friday evening as a US Airways flight was leaving the gate at Reagan National Airport to begin its flight to Charleston, S.C. But the temperature reached 100 degrees in Washington on Friday and that apparently softened the airport paving enough to immobilize the airplane. The small vehicle that usually tows planes away from the gate tugged and pulled, but the plane was stuck.


The full story is HERE.


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## railiner

That's some story. Not said is the possibility of doing some damage to the landing gear by the excessive force needed to eventually yank it out of that mess.

Looks like the airport authority will have to rethink the composition of the tarmac, to prevent that from reoccurring...


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## Devil's Advocate

railiner said:


> That's some story. Not said is the possibility of doing some damage to the landing gear by the excessive force needed to eventually yank it out of that mess. Looks like the airport authority will have to rethink the composition of the tarmac, to prevent that from reoccurring...


Something obviously went wrong, although the article is not very clear on what exactly happened. As I understand it runways, taxiways, and parking areas for commercial jets are typically made of specially formulated cement that is specifically designed to handle their enormous weight, even during heat waves. However, this formulation is too expensive to just use everywhere. As a result there is often a layer of softer asphalt based pavement nearby for use by conventional vehicles and as part of the runway and taxiway buffer areas. These areas are not intended to support the weight of a commercial aircraft and if a pilot accidentally crosses into such an area the plane can quickly sink into it and become stuck. Merely sinking into the pavement is unlikely to seriously damage the landing gear. However if there are other items in the area, such as signs or lamps, they may get crushed and caught up in the gear causing more serious problems.


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## xyzzy

Photo and text at the Washington Post website indicate that the aircraft was being pushed back from the gate for departure and the aircraft was astride the yellow painted guideway just like it's supposed to be. This isn't a case of putting the aircraft somewhere it wasn't supposed to go.


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## Anderson

This is an extreme version of deformations I see a lot in parking lots (or in fact that I once saw with an overloaded cart I was moving food on...you'd get a dent in the pavement while loading it and then have to get it out of the dent before hauling stuff inside). Also, I think that heat _has_ closed or capacity-limited other airports before.


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## PRR 60

Texas Sunset said:


> ...As I understand it runways, taxiways, and parking areas for commercial jets are typically made of specially formulated cement that is specifically designed to handle their enormous weight, even during heat waves. However, this formulation is too expensive to just use everywhere.
> 
> ...


The only difference between a pavement designed for motor vehicles and one designed for commercial aircraft is thickness and, for conventional concrete, reinforcing steel size and spacing. The materials used are the same for both. It appears that at least the ramp area at DCA used a flexible pavement design - what is commonly called "blacktop." A full-thickness flexible pavement uses multiple layers of bituminous paving with the thickness designed to spread the aircraft wheel load to an area that the soil below the pavement (subgrade) can support. It is also possible that the blacktop is simply an overlay on top of an old concrete pavement, put in as a cheap and dirty way to renew an old ramp area. Either way, the mechanism that led to this incident is the same.

It may be that the CRJ, with it's smaller tires and fewer wheels, imposes a higher concentrated load on the surface of the pavement than a larger, mainline jet that has bigger tires and more of them. The surface of a blacktop pavement can get really hot on a hot day in direct sunshine. As is the nature of flexible pavements, the material softened. Even though it is not supposed to happen, it sure looks like this aircraft sat at the gate long enough to grossly deform the surface course of the ramp pavement and get stuck. In the end, it sounds like it was no big deal once US rolled over a larger, mainline tug (except for the pax who were three hours late getting to Charleston). I'm guessing DCA did a little pavement repair this weekend.


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## The Davy Crockett

Having just spent the last two weeks working outside on the National Mall, it does not surprise me in the least that there was a bit of melting going on just across the river. :wacko:


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## Devil's Advocate

xyzzy said:


> Photo and text at the Washington Post website indicate that the aircraft was being pushed back from the gate for departure and the aircraft was astride the yellow painted guideway just like it's supposed to be. This isn't a case of putting the aircraft somewhere it wasn't supposed to go.


When I first read it the article was a lot vaguer about what had happened. Or maybe I’m just going blind. Both possibilities seem equally plausible at this point. ;-)



Anderson said:


> Also, I think that heat _has_ closed or capacity-limited other airports before.


To my understanding that’s generally a completely different issue involving lift and load in the air. Planes don’t normally sink into the pavement on runways, taxiways, and aprons.



PRR 60 said:


> The only difference between a pavement designed for motor vehicles and one designed for commercial aircraft is thickness and, for conventional concrete, reinforcing steel size and spacing.


After a second look the mix formula does not appear to differ substantially, except for newer overrun areas, so in that regard I was wrong and you are absolutely correct.


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## George Harris

When asphalt pavement deforms under load, it does so slowly, so the plane had to have been stopped there. The time did not necessarily need to be long, maybe even only a minute or two. As PRR60 said, it is unit load, not total load. When the spike heels first came out, the dints in pavement at crosswalks were very obvious. The statment made was the the pressure exceeded that of an elephant. How so? Because the load of the 120 pound woman was spread over less than one square inch. The load of the four ton elephant was spread over a couple of square feet.

For planes like regional jets on short flights temperature is unlikely to be an issue relative to the flight itself for two reasons: First, they are unlikely to need full or near full fuel tanks, so they are no where near maximum allowable take off weight. Second: Even though a higher temperature, and with it lower air density, means a longer takeoff run is neede, for a major airport the longer takeoff run is still not likely to approach that allowed for the runway.


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## saxman

If I had to guess, I bet this aircraft weighed about 48,000 to 50,000 lbs at push back. Most of that is on the main gear. And George is right about the temperature. While heat does play a roll in takeoff distance, it doesnt change it by all that much. It is very rare to be limited by the runway length, even on a hot day. I'd say most times when a CRJ is overweight, is because of landing weight limitations at the destination.


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## railiner

In my experience, sometimes aircraft in the summertime, especially if taking off from high elevation airports like Denver, are weight-restricted. And if usual summer time afternoon thunderstorms are forecast, they have to carry some extra fuel for alternate landing airports. In some cases, due to the combination of hot and high takeoff condition, compounded with the need to carry the extra fuel, the aircraft will have to takeoff with less than a full payload of passengers and/or cargo.

As a 'standby' passenger, it has left me stranded many times.....


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