atomicstar
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Aircraft tilting back on ground due to weight imbalance

Thu May 30, 2019 8:52 pm

Here’s a video of a B737 tilting backwards while boarding due to weight imbalance (too many passengers walking to the back): https://youtu.be/JLWxD0gY__A

Here’s an image of a DC-10 freighter where likely most weight was at the back, causing the aircraft to tilt and sit on its tail:
Image

Thinking of this, how often does this happen?

I would assume this happens more often on freighters, when cargo loaders push heavy freight containers to the back with the front being empty. And I would also assume this may happen more often on airplanes with engine(s) at the back such as 727, DC-10, etc. But I doubt this happens frequently with passenger aircraft.

And if it does happen, how do they level the plane? If it is a freighter, would they get a forklift to push the front landing gear down and have cargo loaders remove the freight containers and rearrange them? For passenger planes, I would assume they will have passengers walk to the front and have people who are sitting at the front board first.

And lastly, what is the damage when the tail hits the ground? I’m pretty sure it will dent the metal, but will they fix the dent as soon as possible (whenever convenient), temporarily ground the aircraft for repair, or leave the dent there?
 
unimproved
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Re: Aircraft tilting back on ground due to weight imbalance

Thu May 30, 2019 9:27 pm

Freighters have a jack point at the tail to prevent this, and newer weight and balance systems will scream bloody murder before it's even close to tipping (or being jacked for a nose wheel change....). For passenger operations IIRC the 737-900 gets a tail stand as well due to its length.

When something like this happens it'll be grounded for a while, with pretty much the same inspection as a tail strike.
 
atomicstar
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Re: Aircraft tilting back on ground due to weight imbalance

Thu May 30, 2019 10:56 pm

unimproved wrote:
Freighters have a jack point at the tail to prevent this, and newer weight and balance systems will scream bloody murder before it's even close to tipping (or being jacked for a nose wheel change....). For passenger operations IIRC the 737-900 gets a tail stand as well due to its length.

When something like this happens it'll be grounded for a while, with pretty much the same inspection as a tail strike.


Thanks, I always wondered if a tail jack stand exists to prevent accidentally tipping.
 
E90SLAM
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Re: Aircraft tilting back on ground due to weight imbalance

Thu May 30, 2019 11:33 pm

Here's an example of a tail jack on a DL 737-900
Image

And here's one being used on 747-400M
Image
 
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fr8mech
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Re: Aircraft tilting back on ground due to weight imbalance

Thu May 30, 2019 11:50 pm

This does not happen often...in fact, it's rare, given the amount of aircraft and movements out there. I've been in the cargo business 30+ years, and not one of my operator's aircraft have tipped due to a loading issue.

We do not use tail stands on the MD11, or the B757/B767 aircraft. We do on the A300 & B747. We mitigate the risk of tipping through strictly adhering to process and procedure.

Righting the aircraft? The OEM provides an aircraft recovery manual that give guidelines for getting an aircraft back on its "feet". Airbags, cribbing, cranes, etc. would be utilized to stabilize the aircraft in order to put it in a position where the load can be shifted as necessary to right the aircraft.

The damage all depends on how hard it hit. Whether it gets fixed or not before further flight depends on the damage.
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VIflyer
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Re: Aircraft tilting back on ground due to weight imbalance

Fri May 31, 2019 5:49 pm

I don't know about freighters but back when my carrier operated turboprops both our Saab 340's and ATR's (both 42 and 72) our SOP was to keep everyone sitter until the tail stand was installed. While never heard of the Saab sitting on it's tail I've heard stories of the ATR 72 doing it in rare situations, the 72 was more prone due to the length of the fuselage. The procedure from our old manual was to reseat everyone then unload via last rows then moving forward.
The ATR one is just aft of the door and on the Saab one you can see the ramper either installing or removing it.
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Horstroad
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Re: Aircraft tilting back on ground due to weight imbalance

Sat Jun 01, 2019 1:14 pm

fr8mech wrote:
We do not use tail stands on the MD11

The MD11 doesn't have a jack fitting in the tail to support a tail stand. Some airlines use concrete blocks on the nose landing gear to keep it from tilting. Usually It's not necessary if you follow the correct order. At first the forward lower cargo compartment and the main deck positions forward of the main cargo door, then the main deck, then the center cargo compartment. Unloading in reverse.
Damage to the the skin is not so bad I suppose as it sinks rather slowly to the ground. I would be worried about the pressure bulkhead when freight moves downhill to the aft. And of course usually the center cargo door and surrounding structure is damaged by the highloader.
On passenger aircraft with "conventional" doors the entry door can be caught in the jetway and may need some repair.

We always use 7t ballast pallets when the aircraft is on the ground and not loaded. For flight the MD11 needs ballast fuel in the upper aux tank when empty to stay within CG limits.

A few years ago they forgot to put the tail stand under a 747F for loading. They intended to and placed it near the jack fitting, but forgot in the end. When the Aircraft tilted, the tail stand punched a hole through the horizontal stabilizer (or elevator, can't quite remember)
 
BravoOne
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Re: Aircraft tilting back on ground due to weight imbalance

Sat Jun 01, 2019 4:34 pm

Horstroad wrote:
fr8mech wrote:
We do not use tail stands on the MD11

The MD11 doesn't have a jack fitting in the tail to support a tail stand. Some airlines use concrete blocks on the nose landing gear to keep it from tilting. Usually It's not necessary if you follow the correct order. At first the forward lower cargo compartment and the main deck positions forward of the main cargo door, then the main deck, then the center cargo compartment. Unloading in reverse.
Damage to the the skin is not so bad I suppose as it sinks rather slowly to the ground. I would be worried about the pressure bulkhead when freight moves downhill to the aft. And of course usually the center cargo door and surrounding structure is damaged by the highloader.
On passenger aircraft with "conventional" doors the entry door can be caught in the jetway and may need some repair.

We always use 7t ballast pallets when the aircraft is on the ground and not loaded. For flight the MD11 needs ballast fuel in the upper aux tank when empty to stay within CG limits.

A few years ago they forgot to put the tail stand under a 747F for loading. They intended to and placed it near the jack fitting, but forgot in the end. When the Aircraft tilted, the tail stand punched a hole through the horizontal stabilizer (or elevator, can't quite remember)



Can you describe the "upper aux tank" as I have never heard it described as such?
 
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fr8mech
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Re: Aircraft tilting back on ground due to weight imbalance

Sat Jun 01, 2019 4:50 pm

BravoOne wrote:
Can you describe the "upper aux tank" as I have never heard it described as such?


It’s the large fuel tank that sits just above the Lower Aux Tank. :smile:

Seriously, it, with the Lower Aux, makes up what Boeing would call the Center Tank. It’s the tank that fuel is transferred to/from, in conjunction with the tail tank for CG management.
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RetiredWeasel
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Re: Aircraft tilting back on ground due to weight imbalance

Sat Jun 01, 2019 5:19 pm

As I recall several airport cargo bays had nosewheel tethers to prevent tipping due to mistakes in loading sequence on freighters. My many walkarounds on 747 freighters with NW, I observed these or the tail stands installed. Often there was neither, but the loaders were still loading pallets through the main deck cargo door. I guess it just 'depended'.
https://cargo.koreanair.com/sites/defau ... ring_b.gif
 
BravoOne
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Re: Aircraft tilting back on ground due to weight imbalance

Sat Jun 01, 2019 6:33 pm

fr8mech wrote:
BravoOne wrote:
Can you describe the "upper aux tank" as I have never heard it described as such?


It’s the large fuel tank that sits just above the Lower Aux Tank. :smile:

Seriously, it, with the Lower Aux, makes up what Boeing would call the Center Tank. It’s the tank that fuel is transferred to/from, in conjunction with the tail tank for CG management.


Never heard it described as such? Is this a MD term or some tribal terminology? The MD11 aux tank I have seen were forward of the Center tank and had dedicated boost pump. Each held about 13,500# as I recall.
 
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fr8mech
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Re: Aircraft tilting back on ground due to weight imbalance

Sat Jun 01, 2019 6:54 pm

BravoOne wrote:

Never heard it described as such? Is this a MD term or some tribal terminology? The MD11 aux tank I have seen were forward of the Center tank and had dedicated boost pump. Each held about 13,500# as I recall.


All our books refer to #1, #2, #3, upper aux, lower aux & tail tank. As I recall, the #2 tank is split between the left and right wings and connected by plumbing. I could be mistaken in that, but that configuration sticks in my mind.
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You are not entitled to a public safe space.
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Horstroad
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Re: Aircraft tilting back on ground due to weight imbalance

Sat Jun 01, 2019 7:54 pm

fr8mech wrote:
All our books refer to #1, #2, #3, upper aux, lower aux & tail tank. As I recall, the #2 tank is split between the left and right wings and connected by plumbing. I could be mistaken in that, but that configuration sticks in my mind.

Exactly.


BravoOne wrote:
Never heard it described as such? Is this a MD term or some tribal terminology? The MD11 aux tank I have seen were forward of the Center tank and had dedicated boost pump. Each held about 13,500# as I recall.


I think You are talking about optional fuel tanks in the forward cargo compartment for extended range... the forward aux tanks:

Image

I prepared the standard config schematic for easier reading for another topic:

Image
 
BravoOne
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Re: Aircraft tilting back on ground due to weight imbalance

Sat Jun 01, 2019 8:07 pm

Thanks for the clarification, much appreciated and yes, the aux tanks I referred to are the ones that replace the cargo bins.
 
Max Q
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Re: Aircraft tilting back on ground due to weight imbalance

Thu Jun 06, 2019 4:11 pm

RetiredWeasel wrote:
As I recall several airport cargo bays had nosewheel tethers to prevent tipping due to mistakes in loading sequence on freighters. My many walkarounds on 747 freighters with NW, I observed these or the tail stands installed. Often there was neither, but the loaders were still loading pallets through the main deck cargo door. I guess it just 'depended'.
https://cargo.koreanair.com/sites/defau ... ring_b.gif




Seems like a good idea but if it starts to tip
and is restrained by this method are the
nose gear and it’s attachment points stressed for what must be a considerable
‘pull force’ ?
The best contribution to safety is a competent Pilot.
 
RetiredWeasel
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Re: Aircraft tilting back on ground due to weight imbalance

Fri Jun 07, 2019 4:02 am

Max Q wrote:
RetiredWeasel wrote:
As I recall several airport cargo bays had nosewheel tethers to prevent tipping due to mistakes in loading sequence on freighters. My many walkarounds on 747 freighters with NW, I observed these or the tail stands installed. Often there was neither, but the loaders were still loading pallets through the main deck cargo door. I guess it just 'depended'.
https://cargo.koreanair.com/sites/defau ... ring_b.gif




Seems like a good idea but if it starts to tip
and is restrained by this method are the
nose gear and it’s attachment points stressed for what must be a considerable
‘pull force’ ?


Good question and I have no idea. But you'd think who ever designed them would have figured out the stress requirements. But again, I never saw one that was actually being stretched and the nosewheel off the ground.
 
B777LRF
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Re: Aircraft tilting back on ground due to weight imbalance

Fri Jun 07, 2019 8:39 am

Max Q wrote:
Seems like a good idea but if it starts to tip
and is restrained by this method are the
nose gear and it’s attachment points stressed for what must be a considerable
‘pull force’ ?


Our bean counters ran the numbers quite a few years ago, and came to the conclusion that potential damage cost to the NLG was higher than a tail-strike. Neither Boeing, nor Airbus, was particularly fond of the idea of a nose-tether either, repeatedly reminding us that the NLG is built to withstand compression, not stretching, forces.

In the end we decided to go with neither of the options. Strict adherence to procedures is the way to go, and we never sat one on its tail. If memory serves me right another major cargo carrier, Lufthansa Cargo, is the only airline never to have sat an MD-11F on it's arse. They also have some of the strictest procedures and controls in place.
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Max Q
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Re: Aircraft tilting back on ground due to weight imbalance

Fri Jun 07, 2019 3:47 pm

B777LRF wrote:
Max Q wrote:
Seems like a good idea but if it starts to tip
and is restrained by this method are the
nose gear and it’s attachment points stressed for what must be a considerable
‘pull force’ ?


Our bean counters ran the numbers quite a few years ago, and came to the conclusion that potential damage cost to the NLG was higher than a tail-strike. Neither Boeing, nor Airbus, was particularly fond of the idea of a nose-tether either, repeatedly reminding us that the NLG is built to withstand compression, not stretching, forces.

In the end we decided to go with neither of the options. Strict adherence to procedures is the way to go, and we never sat one on its tail. If memory serves me right another major cargo carrier, Lufthansa Cargo, is the only airline never to have sat an MD-11F on it's arse. They also have some of the strictest procedures and controls in place.



Thanks for the interesting information, you emphasize a good point, the nosewheel and its attachment points are not stressed
for such an unexpected pull force


Probably not a problem for a mild imbalance but a significant one could do a lot of damage
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slcguy
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Re: Aircraft tilting back on ground due to weight imbalance

Sun Jun 09, 2019 6:19 am

The B-727-200 (passenger or freighter) could easily tip back during loading/unloading if the tail stairs are not lowered first. Seen a couple over the years when ground crews got complacent and didn't lower the stairs. If aircraft is to be parked for awhile with stairs up, they may add some additional fuel if needed to keep the CG far enough forward or place a jack stand under the tail skid to prevent tipping. Strangest one was a parked 727 balancing on the main gear only. Something didn't look right, upon closer look it was sitting on main gear only with nose gear about 9" off the ground. Good thing there were light winds at the time, one good gust could have tipped it back on it's tail.
 
WPvsMW
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Re: Aircraft tilting back on ground due to weight imbalance

Sun Jun 09, 2019 6:35 pm

At HNL, WN uses a tail jackstand on every B738 parked at a "gate" (pax ramp). Are jackstands mandatory (SOP) when a WN frame is at a gate?
 
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aeromoe
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Re: Aircraft tilting back on ground due to weight imbalance

Mon Jun 10, 2019 9:06 pm

Back in early 90s at Mojave, CA a friend and I watched a Pan Am 727-200 get brought back onto the nose gear after high winds the night before caused the aircraft to rotate back onto its tail. It was quite the show...and I got it all on video and lots of photo documentation. I believe Mike Potter (of Mojave CV-880 fame) was involved with this procedure.
AA AC AS BA BD BF BN BR BY B6 CO CP(2) DG DL EA EI EN FL FT F9 HA HP ICX JI JQ J7 KE KS LH MC NW OC OO OZ(1) OZ(2) PA PI PT QF QQ RM RO RV(1) RV(2) RW SK SM SQ S4 TI TS TW UA UK US UZ VS VX WA WN WS W7 XV YV YX(2) ZZ 9K
 
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tb727
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Re: Aircraft tilting back on ground due to weight imbalance

Tue Jun 11, 2019 8:18 pm

I had a 320 going back on it's tail in LGA once. The gate we parked at was sloped slightly uphill and I was doing the walk-around and noticed it was strange that the APU exhaust was much lower than I had noticed before. Like I could almost jump up and touch where the intake is. Looked up at the nose gear and it was nearly fully extended, it had looked kinda tall when I started my walk-around. I ran up the jet bridge and stopped pax from deplaning until the people in the back started coming forward. The front of the plane just deplaned much quicker than the last few rows of the plane.

The 727 was prone as many have said above. We always set the trim nose full down on overnights and put 30,000 pounds of fuel on board for a ramp load to help it from tipping or spinning in the wind. When loading freight the first pallet would always go forward of the cargo door into position 1. When offloading, position 1 would be the last to come off. We left the aft airstairs down and had a heavy duty tail stand we always left on when on the ground(and a couple times in flight, thankfully not to me)
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WPvsMW
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Re: Aircraft tilting back on ground due to weight imbalance

Wed Jun 12, 2019 6:41 pm

tb727 wrote:
We left the aft airstairs down and had a heavy duty tail stand we always left on when on the ground(and a couple times in flight, thankfully not to me)


How did the a/c push back from the gate with tailstand attached? Seems like pushback would produce a "retractable" (retracted?) tailstand and manage empennage damage.
 
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tb727
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Re: Aircraft tilting back on ground due to weight imbalance

Wed Jun 12, 2019 7:13 pm

WPvsMW wrote:
tb727 wrote:
We left the aft airstairs down and had a heavy duty tail stand we always left on when on the ground(and a couple times in flight, thankfully not to me)


How did the a/c push back from the gate with tailstand attached? Seems like pushback would produce a "retractable" (retracted?) tailstand and manage empennage damage.


It was on a freight ramp with no rampers or any support like that. It was the FE's duty to make sure it was removed. Most were stowed on the airstairs so you could look through the window on the after bulkhead door if you couldn't remember. Some were stowed in the front belly in a cabinet. I don't think anything retractable was designed because it wasn't necessary in the pax days because of the aft airstairs. One of the tail stands exited the aircraft in SoCal and was never found to my knowledge. The other was bent but stayed on the aircraft.
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SheikhDjibouti
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Re: Aircraft tilting back on ground due to weight imbalance

Thu Jun 13, 2019 12:48 am

atomicstar wrote:
And I would also assume this may happen more often on airplanes with engine(s) at the back such as 727, DC-10, etc. But I doubt this happens frequently with passenger aircraft.

So far in this thread, every example of a tail stand appears to be an external device fitted by ground crew.

Then there is the Ilyushin Il-62, which carries it's own rather elegant solution, and doesn't need any help from ground crew.
SP-LAG at BOS shows a good close up of fully extended tail stand, complete with it's own set of wheels that presumably allow some sort of limited mobility

SP-LAE at LHR, and SP-LAC at JFK both appear to show the tail stand in the process of being extended whilst the a/c taxies to it's parking position on arrival.


BTW - after looking at a LOT of photos on the database, it is pure coincidence that Polish a/c feature in all three photos above. :lol:

Finally, this Aeroflot example at ZRH shows the tail stand fully retracted, but with the wheels still protruding. After a short while thinking about this, it seems a stroke of genius because if the aircraft over-rotates on take-off, these wheels will absorb the initial impact and possibly save some damage to the aircraft skin. :bigthumbsup:

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planecane
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Re: Aircraft tilting back on ground due to weight imbalance

Thu Jun 13, 2019 2:55 am

WPvsMW wrote:
At HNL, WN uses a tail jackstand on every B738 parked at a "gate" (pax ramp). Are jackstands mandatory (SOP) when a WN frame is at a gate?

I don't know if it is SOP but a few weeks ago at MDW I saw them on all Southwest 738s.

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