Deltabravo1123
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Airport Weighing Scales for Airliners

Fri Sep 01, 2017 12:44 am

Watching an Air Disaster episode, and they're talking about the pilots using standard weight estimates to calculate the weight of the aircraft. I guess, first off, are these industry standards or do the airlines create their own estimates? It then got me thinking about ways to weigh planes before takeoff to calculate the gross weight. What is the possibility that airports would ever have huge scales underneath a patch of the tarmac that could weigh the planes? The airlines would probably be charged an additional fee if something were to exist, but I can't imagine it would be too expensive. It'd be much more accurate and lessen the risk of accidents if estimates were ever wrong. I understand they used to have systems in landing gears that could weigh the planes, but these were unpopular due to added weight. Could this ever be an alternative?

Thoughts?
 
MalevTU134
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 12:56 am

This topic comes up every now and then... and the answer is no. First of all, if it was that simple, there would already be scales at airports. The main reason there isn't is really basic physics. Think about it yourself: What is really the digit a scale shows?... And what are those long things that stick out on the 2 sides of aircraft? And what do they do?
Last edited by MalevTU134 on Fri Sep 01, 2017 12:58 am, edited 2 times in total.
 
jetmatt777
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 12:57 am

Well using actual weight would be a nightmare -- you weigh the plane and know it weighs a certain amount but it would be a complete guess as to where that weight is distributed on board.

Assumed weights provide the best estimation, as if actual weights were used you would need to weigh each passenger and each bag separately and would be a logistical nightmare.
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JAGflyer
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 1:59 am

If I remember correctly, the aircraft is weighed periodically (every few years) using a scale that is put under landing gear. This weight of the usable fuel is subtracted. This makes up the basic empty weight (BEW) of the plane. Basic empty weight being the weight of the plane, engine fluids, and unusable fuel. The BEW plus the weight of things such as catering equipment and other items that regularly change between flights is considered the operational empty weight (OEW). In my company we have different OEWs based on the routing as different routes have different volumes of catering equipment and meals. It is said that aircraft generally increase in weight as they age due to dust accumulation behind panels and in unreachable areas.

You can see the weighing process here: https://www.youtube.com/watch?v=Nh1bESk8tvk
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Matt6461
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 4:27 am

jetmatt777 wrote:
where that weight is distributed on board.


Is there ever a case - or a contingency plan for a case - where pax/bags weight fluctuations move a plane into dangerous CoG territory? Or into dangerous TOW territory?

Think of the most extreme examples... I recall once in college my football team got split up into two separate regional flights on different RJ's. It so happened that the linemen were all traveling together, but AFAIK we weren't placed far fore or aft. Average weight pre-bags was near 300lbs/pax for our group; I could see that causing problems if we all happened to book as a block at the rear of the cabin. Would flight attendants alert the flight crew if they observed, say, a ~3,000lb load excess in the rear cabin versus fore cabin of a small RJ (assume 30 linemen at ~100lbs excess per man).

Other examples:
-Family reunion booked at back of cabin by enormous Wisconites (I know personally it is not rare for 20+ relatives all to average 300lbs in those parts)
-Sumo wrestlers all bound to a tournament, booked as a group
-At the other end of the spectrum, a young girl's swim team booked at the front of a plane.

...this is half-joking but the odds of these events happening seem on the order of engine failure on the runway after V1.
 
PanHAM
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 5:52 am

No one mentioned freight. ULDs are actually weighed before they are loaded. Modern scales take a second to Show the weight, even of heavy items. There is a rule that each and every box must be weighed before loading on a ship. That can be done while on the truck or by a build in scale on a reach stacker. In digital times there are no limits
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Redbellyguppy
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 7:50 am

The Airbus weighs itself on takeoff. Based on the speed at weight off wheels and the angke of rotation, it's just math. If there is a substantial variation from the plan using estimated weights it'll tell you. But there very rarely is.
 
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Starlionblue
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 8:14 am

Redbellyguppy wrote:
The Airbus weighs itself on takeoff. Based on the speed at weight off wheels and the angke of rotation, it's just math. If there is a substantial variation from the plan using estimated weights it'll tell you. But there very rarely is.


Where is your source for that?
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Flow2706
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 8:59 am

Starlionblue wrote:
Redbellyguppy wrote:
The Airbus weighs itself on takeoff. Based on the speed at weight off wheels and the angke of rotation, it's just math. If there is a substantial variation from the plan using estimated weights it'll tell you. But there very rarely is.


Where is your source for that?

Not too sure about "your" Airbus, but on the A320 the FACs calculate/estimate the Vs1g from the current angle of
attack, speed/Mach, altitude, thrust, and CG when below 14500ft (which in turn in used to calculate Gross Weight) - above 14500ft the last Vs1g/GW before 14500 is memorized and adjusted for fuel consumption. (A320 FCOM DSC 22-40-30 Flight Envelope Function) So Redbellyguppy is not 100% correct, but close. This Gross Weight is used to calculate the speeds. On some A320s (depending on FMGC/Mod status) you are actually able to get this weight from the AIDS. Go to Alpha Callup and insert GWFK, which will return the FAC calculated gross weight in kg (should be GWFL for Gross weight in lbs). As I said, I am not sure how this works on 330/350, but I guess there is a similar system in place which uses different computers etc.
 
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Starlionblue
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 9:21 am

Flow2706 wrote:
Starlionblue wrote:
Redbellyguppy wrote:
The Airbus weighs itself on takeoff. Based on the speed at weight off wheels and the angke of rotation, it's just math. If there is a substantial variation from the plan using estimated weights it'll tell you. But there very rarely is.


Where is your source for that?

Not too sure about "your" Airbus, but on the A320 the FACs calculate/estimate the Vs1g from the current angle of
attack, speed/Mach, altitude, thrust, and CG when below 14500ft (which in turn in used to calculate Gross Weight) - above 14500ft the last Vs1g/GW before 14500 is memorized and adjusted for fuel consumption. (A320 FCOM DSC 22-40-30 Flight Envelope Function) So Redbellyguppy is not 100% correct, but close. This Gross Weight is used to calculate the speeds. On some A320s (depending on FMGC/Mod status) you are actually able to get this weight from the AIDS. Go to Alpha Callup and insert GWFK, which will return the FAC calculated gross weight in kg (should be GWFL for Gross weight in lbs). As I said, I am not sure how this works on 330/350, but I guess there is a similar system in place which uses different computers etc.


I get how GW and CG are calculated in flight. Pretty much the same as on the 330. I just don't see any references for "weighing itself " on take-off. If you don't plonk GW and CG numbers into the MCDU during the set-up you won't be having a good day.
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kalvado
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 12:06 pm

As far as I remember, there was some development for scales integrated in landing gear - but system never became fully operational.
Most likely old good cost-benefit doesn't add up for airlines, and problem is not serious enough to get regulators worried.
I suspect that things may be reconsidered when next gen narrowbody or RJs get old enough for fatigue to reduce design redundancy - with redundancy is smaller on well-simulated modern designs (not only in aviation). Once "it is rarely a problem" approach would line up with "it is still within tolerance" maintenance and some problem like hidden defect or strong wing shear completes the cheese stack, and if cost of the system is reduced enough...
 
jetmatt777
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 12:46 pm

PanHAM wrote:
No one mentioned freight. ULDs are actually weighed before they are loaded. Modern scales take a second to Show the weight, even of heavy items. There is a rule that each and every box must be weighed before loading on a ship. That can be done while on the truck or by a build in scale on a reach stacker. In digital times there are no limits


Right, all freight uses actual weight. But bags and passengers are all assumed weight. Even ULDs loaded with passenger bags are assumed weight based on the number of bags loaded into the can.
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KAUSpilot
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 2:20 pm

The B744/8F and probably some other Boeings have a nosewheel sensor that calculates aircraft weight and CG. It is only used as nice-to-know information, the externally calculated weight and balance produced by load planning/loadmasters is still the source of the performance numbers used for things like takeoff engine power and horizontal stabilizer trim settings. IIRC the airplane's calculated data is displayed on the main deck of the freighter to alert the loaders to potentially problematic center of gravity situations during loading. It is also displayed in the flight deck on the FMC as a gross error check during final performance number inputs.
 
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 4:01 pm

Matt6461 wrote:
jetmatt777 wrote:
where that weight is distributed on board.


Is there ever a case - or a contingency plan for a case - where pax/bags weight fluctuations move a plane into dangerous CoG territory? Or into dangerous TOW territory?

Other examples:
-Family reunion booked at back of cabin by enormous Wisconites (I know personally it is not rare for 20+ relatives all to average 300lbs in those parts)
-Sumo wrestlers all bound to a tournament, booked as a group
-At the other end of the spectrum, a young girl's swim team booked at the front of a plane.

...this is half-joking but the odds of these events happening seem on the order of engine failure on the runway after V1.


In 1984 while flying line assist for Boeing with MarkAir in Alaska ran into that once. MarkAir had a couple of 737-200QC's borrowed from Aloha. They'd fly from Anchorage west with cargo up front and passengers in the back then switch and fly Anchorage to Fairbanks, all passenger. One evening we were taking a college baseball team from Anchorage to Fairbanks. They were the only passengers onboard and they had all been assigned seats at the very back of the airplane with all their equipment -- fortunately we noticed that and told them to spread out. Takeoff probably would have been a little different had they stayed where they were assigned.
 
N0dak
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 4:07 pm

Matt6461 wrote:
jetmatt777 wrote:
where that weight is distributed on board.


Is there ever a case - or a contingency plan for a case - where pax/bags weight fluctuations move a plane into dangerous CoG territory? Or into dangerous TOW territory?

Think of the most extreme examples... I recall once in college my football team got split up into two separate regional flights on different RJ's. It so happened that the linemen were all traveling together, but AFAIK we weren't placed far fore or aft. Average weight pre-bags was near 300lbs/pax for our group; I could see that causing problems if we all happened to book as a block at the rear of the cabin. Would flight attendants alert the flight crew if they observed, say, a ~3,000lb load excess in the rear cabin versus fore cabin of a small RJ (assume 30 linemen at ~100lbs excess per man).

Other examples:
-Family reunion booked at back of cabin by enormous Wisconites (I know personally it is not rare for 20+ relatives all to average 300lbs in those parts)
-Sumo wrestlers all bound to a tournament, booked as a group
-At the other end of the spectrum, a young girl's swim team booked at the front of a plane.

...this is half-joking but the odds of these events happening seem on the order of engine failure on the runway after V1.


At my airline we do have specific policies from a flight crew perspective for passengers above the average passenger weight. In your examples, depending on how many sumo wrestlers are on board, we'd use their actual weights. For the girl's swim team, we'd use standard weights.
 
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aemoreira1981
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 5:19 pm

Matt6461 wrote:
jetmatt777 wrote:
where that weight is distributed on board.


Is there ever a case - or a contingency plan for a case - where pax/bags weight fluctuations move a plane into dangerous CoG territory? Or into dangerous TOW territory?

Think of the most extreme examples... I recall once in college my football team got split up into two separate regional flights on different RJ's. It so happened that the linemen were all traveling together, but AFAIK we weren't placed far fore or aft. Average weight pre-bags was near 300lbs/pax for our group; I could see that causing problems if we all happened to book as a block at the rear of the cabin. Would flight attendants alert the flight crew if they observed, say, a ~3,000lb load excess in the rear cabin versus fore cabin of a small RJ (assume 30 linemen at ~100lbs excess per man).

Other examples:
-Family reunion booked at back of cabin by enormous Wisconites (I know personally it is not rare for 20+ relatives all to average 300lbs in those parts)
-Sumo wrestlers all bound to a tournament, booked as a group
-At the other end of the spectrum, a young girl's swim team booked at the front of a plane.

...this is half-joking but the odds of these events happening seem on the order of engine failure on the runway after V1.


Another example (switches to Charles Barkley voice)...those big ol' San Antonio women with all the churros they can eat :D More seriously though, having passenger masses in mind is a good idea to avoid overloading, as guidelines presume a passenger with a mass of 77 kg. That said, if planes can weigh themselves, it should be standard on all aircraft. The cabin crew may still need to use their brains though.
 
RetiredWeasel
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 6:35 pm

On widbodies, an abundance of heavy passengers seldom causes the total weight to exceed the alloted margins. For every 300 pounder, you most likely have a 100 pounder to compensate. Cargo on passenger aircraft and especially on freighters is the main concern. Like posters have stated, it is weighed but there have been incidences where something slipped through the cracks. Crew members have to trust the numbers that load planning gives them because there is no other way for the Capt to know what a pallet weighs.

A fuel over-burn or difficulty in getting to flight planned altitude are clues that something is amiss. Doesn't happen much nowdays, but there are instances in the past where diverts were necessary due to an over-burn caused by unaccounted weight. My ex-airline would immediately do an audit of the paperwork and re-weigh the load if required if this happened.
 
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jetmech
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 7:13 pm

jetmatt777 wrote:
Well using actual weight would be a nightmare -- you weigh the plane and know it weighs a certain amount but it would be a complete guess as to where that weight is distributed on board.

Assuming that a weighing system measured the weight of the entire aircraft with fuel, passengers and cargo, surely you could work out the C of G location from the total aircraft weight and the individual weight on each landing gear?

Regards, JetMech
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CrimsonNL
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Re: Airport Weighing Scales for Airliners

Fri Sep 01, 2017 11:53 pm

Matt6461 wrote:
Other examples:
-At the other end of the spectrum, a young girl's swim team booked at the front of a plane.



This happened a few years ago on a Qantas flight where a group of children was sitting in the back of a 737, thankfully an extremely rare occurence;

http://time.com/3266087/qantas-takeoff- ... nt-advice/

jetmatt777 wrote:
But bags and passengers are all assumed weight. Even ULDs loaded with passenger bags are assumed weight based on the number of bags loaded into the can.


In Europe pretty much all airlines use actual weights for bags as a total. And then an average weight per piece when it comes to the weight distribution. I can only think of EI who uses a standard bag weight these days without taking the actual checked weight into account. But as I understand it a lot of airlines in the USA do this as well.

My two (euro) cents,

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mat66
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Re: Airport Weighing Scales for Airliners

Sat Sep 02, 2017 12:08 am

jetmatt777 wrote:
PanHAM wrote:
No one mentioned freight. ULDs are actually weighed before they are loaded. Modern scales take a second to Show the weight, even of heavy items. There is a rule that each and every box must be weighed before loading on a ship. That can be done while on the truck or by a build in scale on a reach stacker. In digital times there are no limits


Right, all freight uses actual weight. But bags and passengers are all assumed weight. Even ULDs loaded with passenger bags are assumed weight based on the number of bags loaded into the can.


So they weigh my bag at check in to see if it is inside the limit but don't actually use this information to get a sum of all checked passenger bags? Strange. It would be so easy to do so.
 
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Starlionblue
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Re: Airport Weighing Scales for Airliners

Sat Sep 02, 2017 12:25 am

mat66 wrote:
jetmatt777 wrote:
PanHAM wrote:
No one mentioned freight. ULDs are actually weighed before they are loaded. Modern scales take a second to Show the weight, even of heavy items. There is a rule that each and every box must be weighed before loading on a ship. That can be done while on the truck or by a build in scale on a reach stacker. In digital times there are no limits


Right, all freight uses actual weight. But bags and passengers are all assumed weight. Even ULDs loaded with passenger bags are assumed weight based on the number of bags loaded into the can.


So they weigh my bag at check in to see if it is inside the limit but don't actually use this information to get a sum of all checked passenger bags? Strange. It would be so easy to do so.


Easy with current technology, yes. 20 years ago it would have been much more work.

Ease notwithstanding, it would be an extra cost, both in initial investment and in system maintenance. Probably not worth doing.
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Dalmd88
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Re: Airport Weighing Scales for Airliners

Sat Sep 02, 2017 12:55 am

So back to the OP's idea, weigh each airplane after it loads.

Each plane would have to be towed or taxied on to the three large scales like they have at truck stops. As a mechanic I've weighed a bunch of aircraft so we will ignore all the getting the plane to the right level mark for this experiment. Just getting three scales in an arraignment that most airplanes fit might be an issue. The next issue is getting all the conga line over the scales in a timely manner. Next is the timing. Flight planning and load planning are pretty much done before the plane is loaded. So what happens when the actual weight from the scales shows a problem?
 
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zeke
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Re: Airport Weighing Scales for Airliners

Sat Sep 02, 2017 5:05 am

jetmatt777 wrote:
Right, all freight uses actual weight. But bags and passengers are all assumed weight. Even ULDs loaded with passenger bags are assumed weight based on the number of bags loaded into the can.


We use actual weights for bags, I know a number of other airlines do as well. Assumed weights for passengers and crew.
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HAWKXP
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Re: Airport Weighing Scales for Airliners

Sat Sep 02, 2017 5:29 am

While having a beer with a 737-900 driver a while back; she/he said that a dispatch paperwork mistake sent them off 20K over. They were lucky to get 200fpm climb. This was a 91 not 121 (yes they do exist) non USA flight. A real brown underware moment. They would have loved to have been scaled before takeoff.
Last edited by HAWKXP on Sat Sep 02, 2017 5:31 am, edited 1 time in total.
 
kalvado
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Re: Airport Weighing Scales for Airliners

Sat Sep 02, 2017 5:31 am

Dalmd88 wrote:
So back to the OP's idea, weigh each airplane after it loads.

Each plane would have to be towed or taxied on to the three large scales like they have at truck stops. As a mechanic I've weighed a bunch of aircraft so we will ignore all the getting the plane to the right level mark for this experiment. Just getting three scales in an arraignment that most airplanes fit might be an issue. The next issue is getting all the conga line over the scales in a timely manner. Next is the timing. Flight planning and load planning are pretty much done before the plane is loaded. So what happens when the actual weight from the scales shows a problem?

so you prefer the plane to actually fly with that problem?
 
JAGflyer
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Re: Airport Weighing Scales for Airliners

Sat Sep 02, 2017 5:47 pm

jetmatt777 wrote:
PanHAM wrote:
No one mentioned freight. ULDs are actually weighed before they are loaded. Modern scales take a second to Show the weight, even of heavy items. There is a rule that each and every box must be weighed before loading on a ship. That can be done while on the truck or by a build in scale on a reach stacker. In digital times there are no limits


Right, all freight uses actual weight. But bags and passengers are all assumed weight. Even ULDs loaded with passenger bags are assumed weight based on the number of bags loaded into the can.


In my experience, pax weights are assumed based on an average. We have two separate weights for our operation based on the season (heavier in the winter to account for more clothing, jackets, etc). Using the number of males/females/children/infants we figure out the passenger weight (each of the 4 categories has it's own weight). Baggage weight is established based on the check-in weights of the bags (which are in the system when the flight closes). The load sheet states the breakdown and any additonal weight (such as cargo) can be added after. For planning purposes (as a dispatcher) we have an average weight that includes baggage which is multiplied by the estimated pax load then added to the weight of any booked cargo to get the payload weight.
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FlyHossD
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Re: Airport Weighing Scales for Airliners

Sat Sep 02, 2017 8:06 pm

If I recall correctly, BOG has a scale built into one of the taxiways (much like a truck stop or Port of Entry) and occasionally would ask a flight to taxi to that spot to be weighed (it's been several years since I last flew there, though).
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VSMUT
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Re: Airport Weighing Scales for Airliners

Sat Sep 02, 2017 9:14 pm

Matt6461 wrote:
jetmatt777 wrote:
where that weight is distributed on board.


Is there ever a case - or a contingency plan for a case - where pax/bags weight fluctuations move a plane into dangerous CoG territory?


I can think of two incidents. There was the 747 crash in Bagram where a bunch of armoured trucks/MRAPs tore themselves loose, and then the infamous crocodile on a plane incident somewhere in Africa:

http://avherald.com/h?article=46183bb4

http://www.telegraph.co.uk/news/worldne ... hears.html
 
kalvado
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Re: Airport Weighing Scales for Airliners

Sun Sep 03, 2017 12:37 am

VSMUT wrote:
Matt6461 wrote:
jetmatt777 wrote:
where that weight is distributed on board.


Is there ever a case - or a contingency plan for a case - where pax/bags weight fluctuations move a plane into dangerous CoG territory?


I can think of two incidents. There was the 747 crash in Bagram where a bunch of armoured trucks/MRAPs tore themselves loose, and then the infamous crocodile on a plane incident somewhere in Africa:

http://avherald.com/h?article=46183bb4

http://www.telegraph.co.uk/news/worldne ... hears.html

While not an in-flight shift, excess weight of pax resulting in exceeding MTOW and CoG out of limits was one of two contributing factors for the crash in 2003:
https://en.wikipedia.org/wiki/Air_Midwest_Flight_5481
 
Okie
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Re: Airport Weighing Scales for Airliners

Sun Sep 03, 2017 1:23 am

Just this last week.

COG was off (tail heavy)
As soon as take off power was applied the Airbus 320 dragged her tail on the runway.
Decreased power and the nose sat back down and then took an exit off the runway.

I would say lucky they did not get airborne.


http://avherald.com/h?article=4ad68f32&opt=0


Okie
 
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Matt6461
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Re: Airport Weighing Scales for Airliners

Sun Sep 03, 2017 3:26 am

Wow. Thanks everyone for the responses. This seems like a far from unheard of problem. Maybe only a matter of time before sumos or Wisconites cause a disaster. I might be eyeing the weight distribution on my next flight, especially if it's on a small plane.

CrimsonNL wrote:
This happened a few years ago on a Qantas flight where a group of children was sitting in the back of a 737, thankfully an extremely rare occurence;


This example is particularly frightening compared to my (rare but not unimaginable) hypotheticals. A group of football linemen, sumo wrestlers, or obese Americans would easily exceed the standard adult by more than the standard adult-child delta.

I guess these events aren't definitively catastrophic in the way that engine failure after V1 would be without the V2 climb requirement - the pilots can remediate if they're good enough - but sooner or later you'd have to guess a freak event - and failure to remediate - will cause a big disaster.
 
snasteve
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Re: Airport Weighing Scales for Airliners

Sun Sep 03, 2017 6:27 am

kalvado wrote:
VSMUT wrote:
Matt6461 wrote:

Is there ever a case - or a contingency plan for a case - where pax/bags weight fluctuations move a plane into dangerous CoG territory?


I can think of two incidents. There was the 747 crash in Bagram where a bunch of armoured trucks/MRAPs tore themselves loose, and then the infamous crocodile on a plane incident somewhere in Africa:

http://avherald.com/h?article=46183bb4

http://www.telegraph.co.uk/news/worldne ... hears.html

While not an in-flight shift, excess weight of pax resulting in exceeding MTOW and CoG out of limits was one of two contributing factors for the crash in 2003:
https://en.wikipedia.org/wiki/Air_Midwest_Flight_5481


The Bagram crash, the 747 could still have recovered if the MRAP hadn't impacted the horizontal stabilizer as it did. :(
 
jarheadk5
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Re: Airport Weighing Scales for Airliners

Sun Sep 03, 2017 8:43 pm

snasteve wrote:
The Bagram crash, the 747 could still have recovered if the MRAP hadn't impacted the horizontal stabilizer as it did. :(

Highly, highly doubt that.
Not right after takeoff, barely above V2, with a 20k+ lb. MRAP on the loose in the aft end of the cargo compartment. That's assuming the other 4 MRAPs remained secured, which seems highly suspect given the method used to "secure" them.
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trijetsonly
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Re: Airport Weighing Scales for Airliners

Tue Sep 05, 2017 8:25 am

Deltabravo1123 wrote:
Watching an Air Disaster episode, and they're talking about the pilots using standard weight estimates to calculate the weight of the aircraft. I guess, first off, are these industry standards or do the airlines create their own estimates? It then got me thinking about ways to weigh planes before takeoff to calculate the gross weight. What is the possibility that airports would ever have huge scales underneath a patch of the tarmac that could weigh the planes? The airlines would probably be charged an additional fee if something were to exist, but I can't imagine it would be too expensive. It'd be much more accurate and lessen the risk of accidents if estimates were ever wrong. I understand they used to have systems in landing gears that could weigh the planes, but these were unpopular due to added weight. Could this ever be an alternative?

Thoughts?


In the real world, you can neither weigh an aircraft on the apron nor on the taxiway due to the wind.
Remember that aircraft consist of very large aerodynamical surfaces. I've seen aircraft on weighing scales in a hangar with the hangar doors open. The weight was jumping in a range of +-20.000kg for a 747.
That's why European registred aircraft are required by law to be weighed in a hangar with closed hangar doors and aircondition turned off.
Weighing the aircraft at the gate would just confuse everyone.
Of course on a day with no wind it would work. But that's just nothing you can rely on.

The onboard weight and balance system is available for several aircraft, 747 for example. It consists of sensors in the landing gear axles that measure the bending of the axle and calculate the weight by that.
But being in the axle the system is subject to a pretty harsh environment with landing hits and so on. The reliability is not that good and most airlines did not order the system due the poor reliability and the chance that a malfunctioning system may cause a delay because it shows something different than the calculated loadsheet.
Happy Landings
 
Amiga500
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Re: Airport Weighing Scales for Airliners

Tue Sep 05, 2017 10:44 am

Deltabravo1123 wrote:
Thoughts?


Its a bit archaic that each of the landing gear legs are not capable of reporting back the load its under.

Every one of them consist of oleo struts. Measuring the pressure* of the N2 within the strut, and knowing the contact area of the face would quickly tell you the load on the strut.

Essentially a slightly more complex version of P = F / A.


*to add redundancy, measuring temperature and the oleo displacement allows you to back calculate pressure via the perfect gas law.
 
Amiga500
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Re: Airport Weighing Scales for Airliners

Tue Sep 05, 2017 10:50 am

trijetsonly wrote:
In the real world, you can neither weigh an aircraft on the apron nor on the taxiway due to the wind.


True you'll never get an exact measurement - but there are means to mitigate against:

1. RMS of the load over a reasonable timescale.
2. Factor in wind gusts as measured by the pitot static tubes around the airframe.
3. Use the FBW to adjust control surfaces during gusts - allowing the system to quantify the strength of the gust - coupling that to the measurements in (2).

Combining all the above, you will arrive at a number likely good enough to tell you if you are in danger of being beyond the trim conditions. Its not a substitute for a proper loadmaster, but its a useful independent check.
 
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exFWAOONW
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Re: Airport Weighing Scales for Airliners

Wed Sep 06, 2017 2:51 pm

Again, it will come down to costs. A weigh-in-motion scale could be built into a taxiway easily enough. But who would pay for it? The chances of an overload are so small, it wouldn't be justified. Most commercial jets have a lot of excess capacity baked into the MTOW to prevent this sort of thing. I can think of only one time I had to tell the captain to burn x lbs of fuel before take-off to be safely within limits. It was on the edge of the CG envelope (still good) and I didn't want to take any chances. It may have had a longer than usual take-off roll.
Is just me, or is flying not as much fun anymore?
 
MadMatt
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Re: Airport Weighing Scales for Airliners

Fri Sep 08, 2017 2:11 pm

Commercial aircraft are required to be weighed every 4 years. All fuel(completely dump drained dry!), galley carts, in flight magazines etc are taken off, leaving only sick bags and safety cards. The aircraft is then pulled on to scales(not unlike bathroom scales) tow bar disconnected and flight deck windows and door closed. Brake man taken off and door closed. This gives you the total empty weight, and the C/G can be worked out.
On the first weigh(of a 4 year old airbus A320) the weight would have increased by over 500kg's due to moisture in the insulation mainly. This then levels off for the life of the aircraft.
I personally weighed an A320 yesterday and it had gained 12kg since it's last weigh(it is now 8 years old)
As stated in past comments sensors in the gear are not practical due to the beating they would get, and you need a calm environment with zero wind to be accurate.
The aircraft(A320 family) does not work out its weight at all on takeoff, that is worked out by the flight crew and enter red into the MCDU before takeoff. Due to the only variable, the passenger weights, in flight, especially on rotation,the THS, or stabiliser moves to reduce drag(so the elevator isn't permanently deflected)
This can be seen by the black and white wheel moving in the middle console of the flight deck on YouTube videos.
I hope this sheds some light for you.
If we could weigh each passenger and then space them in the cabin for perfect balance that would save absolutely millions on fuel costs but the 2 problems with this is the problem of allocating seats after everyone has checked in and been weighed, and bloody stupid human rights! You are not allowed to insist to know the weight of someone!
 
jarheadk5
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Re: Airport Weighing Scales for Airliners

Fri Sep 08, 2017 10:37 pm

Amiga500 wrote:
Its a bit archaic that each of the landing gear legs are not capable of reporting back the load its under.

Every one of them consist of oleo struts. Measuring the pressure* of the N2 within the strut, and knowing the contact area of the face would quickly tell you the load on the strut.

Essentially a slightly more complex version of P = F / A.


*to add redundancy, measuring temperature and the oleo displacement allows you to back calculate pressure via the perfect gas law.

Ever been aboard an aircraft while it's being fueled? The "jerkiness" of the aircraft periodically settling on the struts is why that method wouldn't be accurate; it takes a lot of force to overcome the friction of the various seals in the landing gear struts.
-Boom stowed, leaving position.
 
Dardania
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Re: Airport Weighing Scales for Airliners

Mon Sep 11, 2017 7:44 am

MadMatt wrote:
Commercial aircraft are required to be weighed every 4 years. All fuel(completely dump drained dry!), galley carts, in flight magazines etc are taken off, leaving only sick bags and safety cards. The aircraft is then pulled on to scales(not unlike bathroom scales) tow bar disconnected and flight deck windows and door closed. Brake man taken off and door closed. This gives you the total empty weight, and the C/G can be worked out.
On the first weigh(of a 4 year old airbus A320) the weight would have increased by over 500kg's due to moisture in the insulation mainly. This then levels off for the life of the aircraft.
I personally weighed an A320 yesterday and it had gained 12kg since it's last weigh(it is now 8 years old)
As stated in past comments sensors in the gear are not practical due to the beating they would get, and you need a calm environment with zero wind to be accurate.
The aircraft(A320 family) does not work out its weight at all on takeoff, that is worked out by the flight crew and enter red into the MCDU before takeoff. Due to the only variable, the passenger weights, in flight, especially on rotation,the THS, or stabiliser moves to reduce drag(so the elevator isn't permanently deflected)
This can be seen by the black and white wheel moving in the middle console of the flight deck on YouTube videos.
I hope this sheds some light for you.
If we could weigh each passenger and then space them in the cabin for perfect balance that would save absolutely millions on fuel costs but the 2 problems with this is the problem of allocating seats after everyone has checked in and been weighed, and bloody stupid human rights! You are not allowed to insist to know the weight of someone!


Very interesting - so the performance figures being cited for the A320neo from the first few months in service may be a bit premature?
 
VSMUT
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Re: Airport Weighing Scales for Airliners

Mon Sep 11, 2017 10:39 am

Amiga500 wrote:
trijetsonly wrote:
In the real world, you can neither weigh an aircraft on the apron nor on the taxiway due to the wind.


True you'll never get an exact measurement - but there are means to mitigate against:

1. RMS of the load over a reasonable timescale.
2. Factor in wind gusts as measured by the pitot static tubes around the airframe.
3. Use the FBW to adjust control surfaces during gusts - allowing the system to quantify the strength of the gust - coupling that to the measurements in (2).

Combining all the above, you will arrive at a number likely good enough to tell you if you are in danger of being beyond the trim conditions. Its not a substitute for a proper loadmaster, but its a useful independent check.


But what about rain, snow, deicing fluid, frost or ice then? I was once on a 767 flight in Africa where the entire wing was covered with grasshoppers during a fuel stop, those would need to be compensated for as well.
 
Amiga500
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Re: Airport Weighing Scales for Airliners

Mon Sep 11, 2017 11:41 am

jarheadk5 wrote:
it takes a lot of force to overcome the friction of the various seals in the landing gear struts.


Given the software would likely not be able to refine calculations without at least some taxiing from the gate to introduce a semi-controlled variable to aerodynamic loading, vibrations of the taxiway will remove out the (fairly small) oleo friction effects.
 
Amiga500
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Re: Airport Weighing Scales for Airliners

Mon Sep 11, 2017 11:44 am

VSMUT wrote:
But what about rain, snow, deicing fluid, frost or ice then? I was once on a 767 flight in Africa where the entire wing was covered with grasshoppers during a fuel stop, those would need to be compensated for as well.


Snow and ice would be a problem, but they should be removed anyway pre take-off.

The rest are noise when weighing the weight distribution of a 70 tonne aircraft - you need to consider that any rain/de-icer/frost will be fairly evenly distributed fore-aft of the aircraft gravity centre so won't move it by any measurable amount.
 
VSMUT
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Re: Airport Weighing Scales for Airliners

Mon Sep 11, 2017 8:10 pm

Amiga500 wrote:
The rest are noise when weighing the weight distribution of a 70 tonne aircraft


Why go to the lengths of weighing the aircraft then? The primary advantage of weighing over the current method would be to get an exact weight. The current method already considers such variables as "noise", and is much simpler to do.

Amiga500 wrote:
Snow and ice would be a problem, but they should be removed anyway pre take-off.


But in many airports you don't remove it until shortly before the runway, at which point it is a bit late to turn back to the gate if the CG is out of limits.
 
Amiga500
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Re: Airport Weighing Scales for Airliners

Tue Sep 12, 2017 8:11 am

VSMUT wrote:
Why go to the lengths of weighing the aircraft then? The primary advantage of weighing over the current method would be to get an exact weight. The current method already considers such variables as "noise", and is much simpler to do.

But in many airports you don't remove it until shortly before the runway, at which point it is a bit late to turn back to the gate if the CG is out of limits.


The point of weighing is a backup to the hand calcs.

We already design in all sorts of redundancies for systems and structure, so why not the weight and balance calcs?

If the c.g. is out of range, its never too late to turn back as long as your wheels are still on the ground!
 
MadMatt
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Re: Airport Weighing Scales for Airliners

Fri Sep 29, 2017 9:38 am

Very interesting - so the performance figures being cited for the A320neo from the first few months in service may be a bit premature?[/quote]

Not really, it is well known where and how much weight is added in the first four years, and how this affects cg and the performance. The manufacturers may tell dry empty weight calcs, just as mpg figures for a car are only achievable in a room with no wind resistance, but if you are buying a £40M jet you will know its real life performance(one would hope anyhow!)

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