art
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Parked Aircraft: How Often Do They Move?

Tue Mar 29, 2016 9:30 pm

A contact who works airside showed me a photo he took of an aircraft (777, I guess) that had moved several feet while being turned around. It seems it was not chocked. Is such an event an extremely rare occurrence or not? Dropping to the tarmac from a 777 would cause serious injury or could kill you, I imagine.
 
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TWA772LR
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RE: Parked Aircraft: How Often Do They Move?

Wed Mar 30, 2016 8:31 pm

I guess it depends. When I worked for LH and had to put on the upper jetbridge, I had to wait for clearance from the LH ops guys. They said to wait for clearance because the plane can move back as much as a foot, after the parking brake is set!

Quoting art (Thread starter):
It seems it was not chocked.

That seems incredibly unsafe. The most trust worthy tool to any job is one that doesn't move. I don't care how far technology has come, parking brakes can fail, but that 20 pound hunk of rubber sure isn't. It's a case of it only does one thing, and it does it well.

Also I've heard of planes being pushed around in tornadoes, not Cessnas, but 737-size planes.
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CanadianNorth
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RE: Parked Aircraft: How Often Do They Move?

Wed Mar 30, 2016 9:27 pm

If everything is done properly a parked aircraft shouldn't move more than an inch or two unless someone is pushing, pulling or driving it. I say an inch or two because chocks should be put in somewhat loosely as tires will sit up and then bulge out again as the aircraft is unloaded and loaded, but if your equipment is positioned anywhere close to properly then that gradual inch or two won't hurt anything and usually won't even be noticed as the aircraft will be moving up and down at least that much anyway as you add and remove weight.

Around here we usually chock our aircraft on a turn, and preferably via main gear (nose gear works on a nice day but can slide sideways if it's icy and/or windy). Also I've heard from various sources it's good to chock it and release the park brake as that will allow the brakes to cool better. I've never seen it myself but some of the old timers have also mentioned it's possible if you come in with hot brakes and leave the park brake on the brakes can actually stick on when you go leave again.

The standard arrival procedure here is the pilots will set the parking brake upon arrival at the parking spot, run their shutdown checklist, once the beacon is off the ramp kids will go insert the chocks, the marshaller will give the "cocks in" signal to the pilots, and they will then release the brakes and let the chocks do their thing.

When the aircraft is parked for anything longer than a turnaround it should most definitely be chocked, on every transport category aircraft I've worked on when everything is turned off the parking brake is working off of the accumulator(s), and the manuals will straight up tell you there is usually only enough in there to hold the aircraft for ~ 24 hours, if you started with them fully charged.

Also as a fun fact of the day side note, some aircraft you actually have to take the brake off during turns to do certain things, for example DC-10s with the centre main gear the parking brake must be off and the outer mains cocked while refueling due to the geometry of the gear causing the centre leg to roll a few inches as the oleo settles down.

[Edited 2016-03-30 14:42:41]
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strfyr51
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RE: Parked Aircraft: How Often Do They Move?

Thu Mar 31, 2016 4:31 am

isn't that what chocks are for?? you normally don't leave an airplane parked and un-chocked for an extended period, or without a Tug hooked to it.
 
Viscount724
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RE: Parked Aircraft: How Often Do They Move?

Thu Mar 31, 2016 5:15 am

Quoting TWA772LR (Reply 1):
Also I've heard of planes being pushed around in tornadoes, not Cessnas, but 737-size planes.

Parked NordStar 737-800 being spun around on a windy day at Norilsk (NLK) in Siberia.
http://www.youtube.com/watch?v=kGalRqZxuec

Quoting CanadianNorth (Reply 2):
Around here we usually chock our aircraft on a turn, and preferably via main gear (nose gear works on a nice day but can slide sideways if it's icy and/or windy).

Like this WestJet 737 at YHZ two years ago.
http://www.youtube.com/watch?v=nrl3ex7w6nA
 
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breiz
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RE: Parked Aircraft: How Often Do They Move?

Thu Mar 31, 2016 11:28 am

Quoting CanadianNorth (Reply 2):
If everything is done properly

Many thanks for an informative hands-on post.
 
roseflyer
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RE: Parked Aircraft: How Often Do They Move?

Thu Mar 31, 2016 12:20 pm

Quoting CanadianNorth (Reply 2):
When the aircraft is parked for anything longer than a turnaround it should most definitely be chocked, on every transport category aircraft I've worked on when everything is turned off the parking brake is working off of the accumulator(s), and the manuals will straight up tell you there is usually only enough in there to hold the aircraft for ~ 24 hours, if you started with them fully charged.

A properly maintained brake system will allow the accumulator to hold the parking brake for 24 hours. In the real world as airplanes age and things start to leak, the parking brake may only last for 8 hours or less. I've seen accumulators lose their pressure in a matter of hours.

Quoting art (Thread starter):
A contact who works airside showed me a photo he took of an aircraft (777, I guess) that had moved several feet while being turned around. It seems it was not chocked. Is such an event an extremely rare occurrence or not? Dropping to the tarmac from a 777 would cause serious injury or could kill you, I imagine.

No one should ever depend on the parking brake holding an airplane still for long periods of time when the airplane is powered down. The parking brake works great when there is hydraulic power on the airplane, but a slow leak in the system will cause it to lose pressure fast and you don't want to risk an airplane moving on its own. That is why chocks are used at every gate and anywhere that a plane is parked when powered down.

There is one exception and that is the 787. It has electric brake actuation, so there is no brake accumulator to bleed down. All it needs is electrical power.
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KC135Hydraulics
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RE: Parked Aircraft: How Often Do They Move?

Thu Mar 31, 2016 6:09 pm

I don't know if this contributes to the question asked, but in my experience you should never trust the aircraft's parking brake any longer than is necessary to install chocks. Never underestimate the power of a chock. I was on a launch once and part of our procedure was to pull the chocks on the main gear and relocate one set to the nosewheels for quicker removal prior to taxi. My partner had removed the chocks from the right gear, and I not knowing that, pulled the left main chocks and the aircraft immediately began to roll away backwards. In a panic I got behind the aircraft and slammed a chock behind the aft tires and managed to get the plane to stop rolling. My career caution light was blinking wildly for a few seconds there.
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Horstroad
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RE: Parked Aircraft: How Often Do They Move?

Thu Mar 31, 2016 6:50 pm

Quoting KC135Hydraulics (Reply 7):
In a panic I got behind the aircraft and slammed a chock behind the aft tires and managed to get the plane to stop rolling.

You were incredibly lucky. Once they gained just a little bit of momentum aircraft easily roll over a chock like it isn't there.
 
CanadianNorth
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RE: Parked Aircraft: How Often Do They Move?

Fri Apr 01, 2016 6:06 am

Quoting roseflyer (Reply 6):
A properly maintained brake system will allow the accumulator to hold the parking brake for 24 hours. In the real world as airplanes age and things start to leak, the parking brake may only last for 8 hours or less. I've seen accumulators lose their pressure in a matter of hours.

This as well. I say 24 hours as typically that's what they were meant to do and often will do if everything is performing as advertised. In the real world I've also seen some "tired" airplanes only hold their brake pressure for maybe three or four hours on a good day.
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RE: Parked Aircraft: How Often Do They Move?

Fri Apr 01, 2016 8:42 am

Quoting TWA772LR (Reply 1):

Also I've heard of planes being pushed around in tornadoes, not Cessnas, but 737-size planes.

I've seen a King Air 200 floating a foot off the ground. It was blowing 90MPH and the tiedowns were the only thing holding it in place.

The state had to park their Road Grader and loader for removing snow from the runway in front of block the wind.
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lapper
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RE: Parked Aircraft: How Often Do They Move?

Fri Apr 01, 2016 11:47 am

Quoting CanadianNorth (Reply 2):
the marshaller will give the "cocks in" signal to the pilots

I'd like to see what that signal looks like!  
 
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larshjort
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RE: Parked Aircraft: How Often Do They Move?

Fri Apr 01, 2016 2:22 pm

Quoting lapper (Reply 11):

I'd like to see what that signal looks like!


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KC135Hydraulics
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RE: Parked Aircraft: How Often Do They Move?

Fri Apr 01, 2016 2:23 pm

Quoting lapper (Reply 11):
I'd like to see what that signal looks like!

Oh yeah, I'm familiar with that hand signal. You make a circle/hole with one hand, and you insert a single finger into it. It's like the hand signal for external power, but just one finger.  
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CaptainKramer
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RE: Parked Aircraft: How Often Do They Move?

Sun Apr 03, 2016 12:39 am

I remember seeing footage on Youtube, from a few winters ago when a Canadian airlines B738 parked at the gate during a turn around, started to slide sideways away from the Airbridge in high winds courtesy of a slippery apron.

The chocks were in place to prevent rearward roll, not side ways slide, in this instance would deploying spoilers at the gate prevent this dangerous movement?

I just found it on Youtube, type : must watch! Westjet slides away from airbridge in strong winds.

[Edited 2016-04-02 17:45:29]

[Edited 2016-04-02 17:46:13]
 
Viscount724
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RE: Parked Aircraft: How Often Do They Move?

Sun Apr 03, 2016 2:16 am

Quoting CaptainKramer (Reply 14):
I just found it on Youtube, type : must watch! Westjet slides away from airbridge in strong winds.

You're a little late. I posted that video in Reply 4 a few days ago.
 
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RE: Parked Aircraft: How Often Do They Move?

Sun Apr 03, 2016 5:46 pm

Quoting horstroad (Reply 8):
Quoting KC135Hydraulics (Reply 7):
In a panic I got behind the aircraft and slammed a chock behind the aft tires and managed to get the plane to stop rolling.

You were incredibly lucky. Once they gained just a little bit of momentum aircraft easily roll over a chock like it isn't there.

You are incredibly lucky. In my former company a junior mechanic slipped and was run over by a 757 main gear while trying such a stunt. He barely survived and still has a lot o problems, never being able to play soccer being just one of them. In fact he is an invalid now, in his mid 20s. Two weels went right across his hips and tights.

Jan
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CanadianNorth
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RE: Parked Aircraft: How Often Do They Move?

Mon Apr 04, 2016 2:06 am

Quoting CaptainKramer (Reply 14):
The chocks were in place to prevent rearward roll, not side ways slide, in this instance would deploying spoilers at the gate prevent this dangerous movement?

I could be wrong, but my understanding was the wind was pushing the tail/empenage sideways with enough force to pivot the aircraft around on the main gear while the nose gear slid sideways on the ice, basically creating a giant weathervane. This occurred because the chocks were only on the nose gear which would have still been free to slide sideways between them, and the mains were free to roll (in Westjet's case the port main would roll forward while the starboard main rolled aft) and allow the aircraft to pivot around its centre. If both mains are chocked this could still happen with enough ice and wind however it would take a much stronger wind to have the same effect as it would either have to slide the chocks and wheels along and/or roll the wheels up and over the chocks.

Spoilers might help slightly by putting some more weight on the wheels if the wind was travelling in the right direction, but I don't think they would make that much difference in most cases. Also that's assuming someone is in the cockpit at the time, notices what's happening, and thinks to deploy them, all of which are big ifs. Also I would guess that if the wind was coming from slightly aft having the spoilers out might just give it more surface area to push on and make things worse?
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CaptainKramer
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RE: Parked Aircraft: How Often Do They Move?

Mon Apr 04, 2016 9:20 am

Thanks for the reply CanadianNorth. May give the Chock Companies a new challenge to manufacture a Winter Chock, for such events featured in the Youtube clip.

Sorry Viscount724, completely missed your post..
 
diverted
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RE: Parked Aircraft: How Often Do They Move?

Mon Apr 04, 2016 12:42 pm

This is a few years old but even a 747 can get tossed around a bit in wind.
http://www.youtube.com/watch?v=cHhZwvdRR5c

I've seen the results of a few dash-8's get tossed around on a windy day, they ended up getting blown right into a terminal, causing significant damage.
 
CanadianNorth
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RE: Parked Aircraft: How Often Do They Move?

Mon Apr 04, 2016 7:19 pm

Quoting CaptainKramer (Reply 18):
May give the Chock Companies a new challenge to manufacture a Winter Chock

We have lots here, one of the local guys makes them for us. They're just home made steel chock with a couple of studs welded onto the front end of the bottom side so if the aircraft rolls the chock will bite into the ice/snow instead of sliding over it. They work great, just have to be careful in the summer as on warm days those same studs can leave a bite mark on your asphalt too!
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GavinSharp
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RE: Parked Aircraft: How Often Do They Move?

Tue Apr 05, 2016 12:25 am

Quoting diverted (Reply 19):
This is a few years old but even a 747 can get tossed around a bit in wind.
http://www.youtube.com/watch?v=cHhZw...dRR5c

Though that one was stripped in a boneyard, without engines - not a fair comparison!  
 
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RE: Parked Aircraft: How Often Do They Move?

Tue Apr 05, 2016 2:07 am

Quoting CanadianNorth (Reply 20):
Quoting CaptainKramer (Reply 18):
May give the Chock Companies a new challenge to manufacture a Winter Chock

We have lots here, one of the local guys makes them for us. They're just home made steel chock with a couple of studs welded onto the front end of the bottom side so if the aircraft rolls the chock will bite into the ice/snow instead of sliding over it. They work great, just have to be careful in the summer as on warm days those same studs can leave a bite mark on your asphalt too!

I don't think I have ever seen one of those work on hard frozen ice. The "teeth" just can't bit into the ice.

Plus as you mention there is the potential for tarmac damage.
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MerlinIIIB
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RE: Parked Aircraft: How Often Do They Move?

Sat Apr 09, 2016 6:37 am

Quoting roseflyer (Reply 6):
A properly maintained brake system will allow the accumulator to hold the parking brake for 24 hours. In the real world as airplanes age and things start to leak, the parking brake may only last for 8 hours or less.

Some years ago, a B737 at Stavanger Airport in Norway moved 200 metres after being parked by pilots after a ferry flight. No ground crew assisted at arrival, no chocks. The accumulator lasted approx 8 hours and the empty aircraft collided with an air bridge. The event was observed by the tower guys. Must have been quite a sight.

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