Hello,
I take the example of an A350. Is it possible to perform the weighing outdoors if no hangar space available ? If so, what are the conditions to be met ?
Thanks,

All you need is a level floor, so if you have that outdoors you should be fine. Plus all the equipment needed to prepare it for weighing, GPU for power b/c no APU fuel, etc.

No wind or precipitation falling would also be necessary

No. Outdoors is not possible for weighing. Wind blowing over the wings and elevators will create lift, skewing the results. Likewise, rain and condensation would also offset the results.
Aircraft weighing is done under very specific conditions, and regulations in all places I am aware of, clearly state it must be in a closed hangar.

Anybody that operates an A350 can afford a hangar

If you open a hanger door while an airplane is up on the scales, if there is ANY wind, you can see scale weights change as the wind changes because of the door being opened and closed. Planes are weighed after being painted when new and after that, only after major mods, interior reconfiguration or major repairs if they effected the aircraft's zero fuel weight and/or CG.

Back in the 70's, I had heard of a 707 being weighed outdoors by Iberia IIRC. When you weight an aircraft, you have to switch the load cells and weigh it once more per the procedure. For the second weigh, they had to wait something like 3 weeks for the weather conditions to be identical to the same conditions as the first weigh so they could do the required 2nd weigh.

So no, weighing outdoors all though possible in theory, isn't really practical and in the case of a newer first tier aircraft still being operated in it's as delivered config, it would not even be required to be weighed.

stratclub wrote:

If you open a hanger door while an airplane is up on the scales, if there is ANY wind, you can see scale weights change as the wind changes because of the door being opened and closed. Planes are weighed after being painted when new and after that, only after major mods, interior reconfiguration or major repairs if they effected the aircraft's zero fuel weight and/or CG.

Back in the 70's, I had heard of a 707 being weighed outdoors by Iberia IIRC. When you weight an aircraft, you have to switch the load cells and weigh it once more per the procedure. For the second weigh, they had to wait something like 3 weeks for the weather conditions to be identical to the same conditions as the first weigh so they could do the required 2nd weigh.

So no, weighing outdoors all though possible in theory, isn't really practical and in the case of a newer first tier aircraft still being operated in it's as delivered config, it would not even be required to be weighed.

I'm not sure about that last bit. IIRC, regular weighing of a portion of the fleet is required even without changes to config. Happy to be proven wrong on that. I'm not in the aircraft weighing part of the operation.

The outdoor weighing thing? Just something I heard years ago. IDK if it's true or not. Sure sounds like a hilarious "Doing it Wrong" story, though ))

I think I have heard of the fleet averaging thing. Makes sense though. If you have a block of airplanes that are virtually identical and the same config, any 2 aircraft in that block would most likely have the same zero fuel weight and CG. I think it would be part of a sampling plan where planes would be selected randomly to be weighed and if a planes weight differ from plane to plane the sampling plan would be tightened up to where more of the fleet are weighed and possibly to the point where every plane become RII (Required Inspection Item) for the weighing requirement.

My experience is as an AMT so I was the guy on the floor setting up planes to be weighed.................

We recently had our large biz jet weighed after paint and interior mods were made. It was explained to me that all hangar doors must be closed and even hangar ceiling fans are turned off during weighing. Definitely NOT outside.

question is about error margin. I don't know how much lift would be created by the wind on a relatively calm day, but I would bet on 1-2% of plane weight at most. This can be unacceptable from the regulatory standpoint, but can be a solid check against certain mistakes (remember an accident where crew typed in aircraft weight as something like 140 instead of 240 tons?)

Regular weighing is part of maintenance. Takes about 3 shifts altogether, with most of the work in preparation and restoration.

IIRC it's mostly used to check CoG.

Actually CG and Zero fuel weight. I don't think I have ever weighed an aircraft were it took 3 shifts and I have weighed hundreds of aircraft in my career. the largest time span would be defueling and draining the sumps which does happen during 1 shift, and the the actual weighing can be performed in about 4 hours if the equipment is available and ready to use. Defueling and draining sumps usually happens prior to the aircraft being put in the hanger.

kalvado wrote:

question is about error margin. I don't know how much lift would be created by the wind on a relatively calm day, but I would bet on 1-2% of plane weight at most. This can be unacceptable from the regulatory standpoint, but can be a solid check against certain mistakes (remember an accident where crew typed in aircraft weight as something like 140 instead of 240 tons?)

Someone probably got some numbers very wrong when they recorded them perhaps. With weighing, accuracy is very important because it determines the data the flight crew uses to determine V-Speeds, RTO decision distances from the end of the runway, thrust settings, and weight and balance. Yes, hanger doors closed and hanger fans off is a prerequisite for weighing by any aircraft operator.

Something I learned from validation testing is that the only thing worse than no data is wrong or unreliable data.

stratclub wrote:

kalvado wrote:

question is about error margin. I don't know how much lift would be created by the wind on a relatively calm day, but I would bet on 1-2% of plane weight at most. This can be unacceptable from the regulatory standpoint, but can be a solid check against certain mistakes (remember an accident where crew typed in aircraft weight as something like 140 instead of 240 tons?)

Someone probably got some numbers very wrong when they recorded them perhaps. With weighing, accuracy is very important because it determines the data the flight crew uses to determine V-Speeds, RTO decision distances from the end of the runway, thrust settings, and weight and balance. Yes, hanger doors closed and hanger fans off is a prerequisite for weighing by any aircraft operator.

Something I learned from validation testing is that the only thing worse than no data is wrong or unreliable data.

1% of weight offset should mean about 1 knot offset in speeds. Uncertainty of passenger weight would be on the same page.
Yes, after fans are turned off and data carefully recorded - everything actually runs on guesstimates and safety margins.

stratclub wrote:

Actually CG and Zero fuel weight. I don't think I have ever weighed an aircraft were it took 3 shifts and I have weighed hundreds of aircraft in my career. the largest time span would be defueling and draining the sumps which does happen during 1 shift, and the the actual weighing can be performed in about 4 hours if the equipment is available and ready to use. Defueling and draining sumps usually happens prior to the aircraft being put in the hanger.

ZFW doesn't really change too much to be relevant. Unless it becomes less than the previous weighings, that gets a lot of people very nervous.

It's usually one shift to defuel, tow, drain, service all oil levels, and remove anything extra in the cabin, another to set up weighing equipment and do the weighing, and the night shift to return it back to service. These numbers are for a 773, a 737 could be done much faster of course.

kalvado wrote:

question is about error margin. I don't know how much lift would be created by the wind on a relatively calm day, but I would bet on 1-2% of plane weight at most. This can be unacceptable from the regulatory standpoint, but can be a solid check against certain mistakes (remember an accident where crew typed in aircraft weight as something like 140 instead of 240 tons?)

Yep, see here: https://en.wikipedia.org/wiki/Emirates_Flight_407

unimproved wrote:

stratclub wrote:

Actually CG and Zero fuel weight. I don't think I have ever weighed an aircraft were it took 3 shifts and I have weighed hundreds of aircraft in my career. the largest time span would be defueling and draining the sumps which does happen during 1 shift, and the the actual weighing can be performed in about 4 hours if the equipment is available and ready to use. Defueling and draining sumps usually happens prior to the aircraft being put in the hanger.

ZFW doesn't really change too much to be relevant. Unless it becomes less than the previous weighings, that gets a lot of people very nervous.

It's usually one shift to defuel, tow, drain, service all oil levels, and remove anything extra in the cabin, another to set up weighing equipment and do the weighing, and the night shift to return it back to service. These numbers are for a 773, a 737 could be done much faster of course.

Sure give or take. When we were doing NAMS (Nautical Air Mile Survey), validation flights on the 787 we would weigh the aircraft twice (fuel left from last flight and fuel in the aircraft after refueling) and do all of the turn around requirements for the next days flight in a 12 hour shift with time to spare. NAMS is kinda like figuring out the aircraft MPG and requires several days of test flights. Basically, the crew would take off, punch a hole in the sky until they were down to minimums and land back home.

One of our NAMS flights. ZA5 IIRC

VSMUT wrote:

Aircraft weighing is done under very specific conditions, and regulations in all places I am aware of, clearly state it must be in a closed hangar.

Since I was bored, I spent a little bit of time looking for a regulation (FAA) that says an aircraft must be weighed in a hangar. I searched "weighing" in 14CFR, and could not find that requirement. I also searched "weigh" which brought up 491 hits in 14CFR. I browsed the results, didn't find anything there, but could have missed it.

14CFR25.29 tells us what is included in empty weight, but does have this statement:

(b) The condition of the airplane at the time of determining empty weight must be one that is well defined and can be easily repeated.

Of course, putting an aircraft into a hangar would make the process "easily repeated".

14CFR125.91 tells us the aircraft has to be weighed every 36 months.

14CFR135.185 tells us that Part 135 aircraft are treated a little differently when it comes to the 36 month constraint.

So, I looked in our maintenance manuals for directions. All aircraft types pointed to our Weight and Balance Manual.

I found this paragraph for each aircraft type:

Weighing Facilities and Equipment

The aircraft should be weighed inside a closed facility that will:
• Exclude all wind and drafts.
• Permit shutdown of air conditioning during the weighing operation.
• Maintain a relatively constant temperature.
• Provide a level weighing surface and sufficient overhead clearance.

Note the word "should" as opposed to "shall" or "must".

The take-away from this little exercise, about weighing:

Yes, it is good practice to weigh an aircraft inside a hangar where the environment can be controlled. But, there is no regulatory requirement that an aircraft must be in the hangar when being weighed...at least not here where I work.

If someone can find a regulation (FAA) concerning this, please post.

If the AMM specifies indoors, it’s essentially a regulation.

GF

GalaxyFlyer wrote:

If the AMM specifies indoors, it’s essentially a regulation.

GF

Agreed, but our AMM does not specify that. It refers us to the Weight and Balance Manual, which uses the word "should".

Horses for courses mostly. Sometimes you have to just interject common sense into the conversation. I've weighed 100's of aircraft and the tribal knowledge on the hanger floor is to weigh the aircraft inside a hanger with the doors closed and the hanger ventilation system off, no exceptions. I could care less about the exact regulation. Those requirements have to be met or the aircraft just doesn't get weighed period.

I hate it when people like bean counters with no real idea of the process try to modify processes that have been proven to be tried and true hoping to save money. If you don't have a hanger to weigh an aircraft, the answer is quit simple. Get one. You can always get an FAA ferry permit if you can prove you can make a one time ferry flight safely to a location that has the services you need.

Tribal knowledge or not, my point is there is no regulation. Now, the operator you work(ed) for may have it in their GMM (or equivalent), and that makes it the equivalent of a regulation. But, there is no federal regulation that I could find.

Tribal knowledge has gotten plenty of people in trouble.

Given a choice, I would absolutely weigh an aircraft in a closed hangar, or if at all possible get the aircraft to a suitable hangar, but push comes to shove, if you can meet the requirements of the FAR's and your book, you can do it outside.

fr8mech wrote:

VSMUT wrote:

Aircraft weighing is done under very specific conditions, and regulations in all places I am aware of, clearly state it must be in a closed hangar.

Since I was bored, I spent a little bit of time looking for a regulation (FAA) that says an aircraft must be weighed in a hangar. I searched "weighing" in 14CFR, and could not find that requirement. I also searched "weigh" which brought up 491 hits in 14CFR. I browsed the results, didn't find anything there, but could have missed it.

It is specifically mentioned under EASA regulations. There are even a few questions about this specific subject in the ATPL question bank.

stratclub wrote:

Those requirements have to be met or the aircraft just doesn't get properly weighed period.

Fixed that for you.
The bigger question is what "properly" means in this case. Any measurement one can do has an inherited uncertainty, and that uncertainty is growing with air movement over airfoils. Would that uncertainty have operational or safety consequences?
Biggest one I see is change of maximum range as small changes in amount of fuel for the fully loaded plane can produce significant range implications. 1% of empty weight probably translates into a few %% of fuel load - hence range - which may be a big deal.
I don't see that 1% of weight critically affecting anything else. Moreover, seems that airlines and FAA are comfortable with that level of uncertainty when pax weight is first estimated, and then gate-checked bags are brought into cabin so they don't count against weight limits.
Bottom line: error in weight is acceptable when it helps dispatch reliability... Pre-flight weight may make things difficult, so it is bad.

fr8mech wrote:

VSMUT wrote:

Aircraft weighing is done under very specific conditions, and regulations in all places I am aware of, clearly state it must be in a closed hangar.

Since I was bored, I spent a little bit of time looking for a regulation (FAA) that says an aircraft must be weighed in a hangar. I searched "weighing" in 14CFR, and could not find that requirement. I also searched "weigh" which brought up 491 hits in 14CFR. I browsed the results, didn't find anything there, but could have missed it.

14CFR25.29 tells us what is included in empty weight, but does have this statement:

(b) The condition of the airplane at the time of determining empty weight must be one that is well defined and can be easily repeated.

Of course, putting an aircraft into a hangar would make the process "easily repeated".

14CFR125.91 tells us the aircraft has to be weighed every 36 months.

14CFR135.185 tells us that Part 135 aircraft are treated a little differently when it comes to the 36 month constraint.

So, I looked in our maintenance manuals for directions. All aircraft types pointed to our Weight and Balance Manual.

I found this paragraph for each aircraft type:

Weighing Facilities and Equipment

The aircraft should be weighed inside a closed facility that will:
• Exclude all wind and drafts.
• Permit shutdown of air conditioning during the weighing operation.
• Maintain a relatively constant temperature.
• Provide a level weighing surface and sufficient overhead clearance.

Note the word "should" as opposed to "shall" or "must".

The take-away from this little exercise, about weighing:

Yes, it is good practice to weigh an aircraft inside a hangar where the environment can be controlled. But, there is no regulatory requirement that an aircraft must be in the hangar when being weighed...at least not here where I work.

If someone can find a regulation (FAA) concerning this, please post.

The acceptable procedures are in Section 2 10-5 of AC No: 43.13-1B “ ACCEPTABLE METHODS, TECHNIQUES, AND PRACTICES AIRCRAFT INSPECTION AND REPAIR”

“ Weigh the aircraft inside a closed building to prevent error in scale reading due to wind.”

“Title 14 of the Code of Federal Regulations part 43, section 43.13(a) states that each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer’s maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, or practices acceptable to the Administrator, except as noted in section 43.16.”

Bottom line, use the manufacturers AMM, if it’s not listed in there use AC No: 43.13-1B.

I always have to chuckle at these pedantic discussions where someone's only argument for doing something is essentially "it's not illegal." Wearing nothing but a Speedo to the grocery store isn't illegal either but people are probably going to question your judgement if you do.

It seems like arguing against weighing an aircraft in a hangar falls in that same category.

Can someone post a pic of a hangar with the weighing equipment? Thanks

Gr8Circle wrote:

Can someone post a pic of a hangar with the weighing equipment? Thanks

Two main types of scales I have seen, a pad type which aircraft are rolled into. The other type is a load cell that sits between a jack or stand and the aircraft.

dennypayne wrote:

I always have to chuckle at these pedantic discussions where someone's only argument for doing something is essentially "it's not illegal." Wearing nothing but a Speedo to the grocery store isn't illegal either but people are probably going to question your judgement if you do.

It seems like arguing against weighing an aircraft in a hangar falls in that same category.

Of course it’s pedantic, but that’s the nature of an industry that is highly regulated. Ever sit in front of an FAA inspector during an investigation or an FAA lawyer in a deposition? Talk about pedantic.

We are, in essence, debating the word “should” in our Weight and Balance manual. That’s it.

When dealing in maintaining aircraft, my alarm bells go off when someone uses terms like “always”, “every”, “all”, etc. That’s when I start asking questions.

Maybe it stems from my time in QC, my time in QA, my time in Tech Support, or my tenure on the ERC for our MXASAP. I look for answers, and I look for the “why”.

zeke wrote:

The acceptable procedures are in Section 2 10-5 of AC No: 43.13-1B “ ACCEPTABLE METHODS, TECHNIQUES, AND PRACTICES AIRCRAFT INSPECTION AND REPAIR”

“ Weigh the aircraft inside a closed building to prevent error in scale reading due to wind.”

“Title 14 of the Code of Federal Regulations part 43, section 43.13(a) states that each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer’s maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, or practices acceptable to the Administrator, except as noted in section 43.16.”

Thank you for that. I’ll review the AC when I get to work tonight. While AC43.13 does provide acceptable methods, I’m reluctant to use it as acceptable data when maintaining aircraft maintained under an acceptable Part 121 maintenance program.

zeke wrote:

Bottom line, use the manufacturers AMM, if it’s not listed in there use AC No: 43.13-1B.

Which brings us back to our manuals and the use of the word “should”.

Gr8Circle wrote:

Can someone post a pic of a hangar with the weighing equipment? Thanks

If you Google “aircraft weighing” or something like that, you’ll find plenty of images of aircraft being weighed.

fr8mech wrote:

Which brings us back to our manuals and the use of the word “should”.

That’s what you get with Part 121 under 43.13, “ (c) Special provisions for holders of air carrier operating certificates and operating certificates issued under the provisions of Part 121 or 135 and Part 129 operators holding operations specifications. Unless otherwise notified by the administrator, the methods, techniques, and practices contained in the maintenance manual or the maintenance part of the manual of the holder of an air carrier operating certificate or an operating certificate under Part 121 or 135 and Part 129 operators holding operations specifications (that is required by its operating specifications to provide a continuous airworthiness maintenance and inspection program) constitute acceptable means of compliance with this section.”

It would be a very courageous person to not follow the AMM because they interpreted “should” when it comes to maintenance tasks to mean optional.

How do you think such a courageous interpretation would be viewed by the courts or in the newspapers, or here on a.net ?

zeke wrote:

It would be a very courageous person to not follow the AMM because they interpreted “should” when it comes to maintenance tasks to mean optional.

Our various AMM’s all refer us to our Weight and Balance manual, which is FAA accepted data, and the word “should” is used instead of “must”.

zeke wrote:

How do you think such a courageous interpretation would be viewed by the courts or in the newspapers, or here on a.net ?

First, I couldn’t care less of how the intrepid folks here on A-Net view any of my actions. But, to your point, I most certainly would not want to try and defend my actions if I was somehow in the position of approving the weighing of an aircraft outside a controlled hangar environment. I’m just saying there is an argument to be made that an organization can weigh an aircraft outside, so long as they can meet the requirements of the FAR’s, the manufacturer and their internal documents.

Take a look at this:

https://www.faa.gov/about/initiatives/p ... mandatory/

kalvado wrote:

question is about error margin. I don't know how much lift would be created by the wind on a relatively calm day, but I would bet on 1-2% of plane weight at most. This can be unacceptable from the regulatory standpoint, but can be a solid check against certain mistakes (remember an accident where crew typed in aircraft weight as something like 140 instead of 240 tons?)

Checking the empty weight within 1-2% won't help with performance data entry mistakes. We just know the ZFW weight on the day.

After the incident (not an accident) which you mention, Emirates 407 at MEL, Airbus added additional gross error check logic to the flight management system.


The regulations aren't there for their own sake. 1-2% error margin in empty weight would put fuel burn calculations outside the error margins. 2% higher empty weight on a widebody could be 3-4 tons. The extra burn from carrying 3-4 tons more weight on a 12-hour flight can be 1 more ton.

Weighing a plane should be done indoor, but let's have fun and look at what errors we can expect if weighing is done outdoor. Obviously the error will depend on plane type and wind force and direction.

I will assume a plane 200,000 lb heavy, which will fly straight and level at 200 KIAS, and parked with the nose into a 2 kt wind. The scales will show it to be lighter than its actual weight. Not that much because lift generally increase with the square of airspeed. Here is how much: 200,000 lb / (200 / 2)^2 = 20 lb. Yes, the scale will show 20 lb too little.

If we increase the wind from 2 to 20 kt, then we will have instead: 200,000 lb / (200 / 20)^2 = 2,000 lb.

These are just rough numbers to indicate the rough magnitude or the errors. Actually the errors will be slightly smaller due to the Reynolds Number effect. Some planes (A330/340 minus 330F) stand with a nose down attitude. 737NG and 737MAX have different length nose gear. Etc. etc. So there are plenty of variables to deal with.

At the end of the day, a hangar floor will normally be flat and level. Outdoor tarmac on the other hand will be slightly sloped to deal with rain. The latter obviously influences lateral balance and CoG measurements, which are probably more important than exact mass.

Amazing. I have seen some loony tunes stuff done in the quest for expediency. The best thing you can do with any process is to do it in a way that has the least potential of errors, go home that night and have a clear conscience that what you did will never come back to bite you.

Legal or not, why anyone would put a large plane up on jacks to weigh outdoors is beyond me. A lot of risks.

GalaxyFlyer wrote:

Legal or not, why anyone would put a large plane up on jacks to weigh outdoors is beyond me. A lot of risks.

The preferred method for weighing the aircraft, in our book, is to use pad scales. You tow the aircraft over the scales.

But, we jack outside all the time. That's not a big deal, and is explicitly allowed for in the AMM. We have spots on our ramp that have been surveyed and declared "level".

stratclub wrote:

Amazing. I have seen some loony tunes stuff done in the quest for expediency. The best thing you can do with any process is to do it in a way that has the least potential of errors, go home that night and have a clear conscience that what you did will never come back to bite you.

Again, I'm not saying that I'd do it, or even allow it to be done, if I'm given that authority. All I'm saying is, it appears that as the rules are currently written, it is allowed. Which, is the OP's question.

stratclub wrote:

Back in the 70's, I had heard of a 707 being weighed outdoors by Iberia IIRC.

Iberia didn't operate any 707s. Unless it was third party Mx. Iberia did over see the Spanish Air Force's fleet of four B707s(T-17).

You can jack up an airplane outside, but weighing it? Fool's errand.

On another note, when balancing flight controls, we usually do it in the an enclosed room, with the AC off. It makes a difference.

fr8mech wrote:

Our various AMM’s all refer us to our Weight and Balance manual, which is FAA accepted data, and the word “should” is used instead of “must”.

Our company weight and balance manual has nothing in it regarding weighing an aircraft, it has the empty weights and index units discovered during weighing. That manual is about the operational loading of passengers, fuel, and cargo.

Boeing and Airbus also have weight and balance manuals which form part of the TCDS. Contents of an approved AMM cannot change the certification basis (TCDS).

For example your AMM may indicate the procedure to change the pin programming on an engine to increase or decrease thrust, you cannot use that procedure under the AMM unless that S/N is specifically authorised.

fr8mech wrote:

First, I couldn’t care less of how the intrepid folks here on A-Net view any of my actions. But, to your point, I most certainly would not want to try and defend my actions if I was somehow in the position of approving the weighing of an aircraft outside a controlled hangar environment.

And this is the crux of your issue, you are not approved to do the procedure. Those people approved to do the procedure have to follow the restrictions on their approval as well as other approved data.

Where I work mechanics are not approved to weigh aircraft, it is done by DERs. DER procedures are not in the AMM.

If I were to weigh an aircraft I first look to the manufacturers weight and balance manual, the TCDS etc first to determine the datum and levelling means, not the AMM. I don’t like using pads on large aircraft, you need to rely on the IR data then for the attitude. I prefer to jack the aircraft to the correct attitude and directly measure the load cells.

fr8mech wrote:

I’m just saying there is an argument to be made that an organization can weigh an aircraft outside, so long as they can meet the requirements of the FAR’s, the manufacturer and their internal documents.

I don’t see any such argument at all.

zeke wrote:

Our company weight and balance manual has nothing in it regarding weighing an aircraft,

Ours does. Kinda surprised me, but there you have it.

zeke wrote:

And this is the crux of your issue, you are not approved to do the procedure.

Ah, but here, being approved is just a matter of being assigned to our heavy maintenance department, and being given that responsibility,

So, as we know, or should know, different operators can have different rules, its' just a matter of getting the rules approved by the regulator.

fr8mech wrote:

Ah, but here, being approved is just a matter of being assigned to our heavy maintenance department, and being given that responsibility,

So, as we know, or should know, different operators can have different rules, its' just a matter of getting the rules approved by the regulator.

Still thinking we are talking cross purposes here, never seen a mechanic do the weighing, do the maths, and issue the trim sheet.

This is normally done by DERs as the weighing is only part of the process, there are lots of limits to be considered with the above and below floor loading (like running and position floor loading limits), and the different options when issuing a trim sheet (for example some of our aircraft have 1060 or 2120 kg portable water options) and multiple weight limits. The envelope varies for takeoff and landing, and the weight variant.

extender wrote:

stratclub wrote:

Back in the 70's, I had heard of a 707 being weighed outdoors by Iberia IIRC.

Iberia didn't operate any 707s. Unless it was third party Mx. Iberia did over see the Spanish Air Force's fleet of four B707s(T-17).

You can jack up an airplane outside, but weighing it? Fool's errand.

Agreed. The rumor didn't come with a specific airlines just that it might have been a Spanish airlines. Pretty wacky story though.

Might be different for a military transport (having however a civil EASA TC) but FWIW: from the A400M AMM chapter Mass and Balance – General maintenance procedure

In the Required conditions the need for a level area is mentioned, nothing about hangar.

Then, the first step of the procedure, Preparation for Aircraft Weighing starts with this:
NOTE: To get accurate results, we recommend that you weigh the aircraft on a level area in a hangar with:
- The hangar doors and windows closed
- The hangar heating, air conditioning and ventilation system stopped.
Airflows and wind prevent accurate results.

And it’s the unique occurrence of the word “hangar” in the whole chapter.

To me it seems that if operator is happy having less accuracy it's fine to weigh outside hangar.

zeke wrote:

Still thinking we are talking cross purposes here, never seen a mechanic do the weighing, do the maths, and issue the trim sheet.

I guess we are. I'm not really talking about the process, so much as what is allowed.

Based on my reading of the FAR's, the AMM, and the W&B Manual, and our GMM, we can weigh outside.

And, while I can't envision a scenario where we would have to weigh outside, I'm pretty darned sure that permission to do that would come from, at the minimum, the AMC Manager, but more likely from the DOM.

I will note, for the sake of accuracy, I read through the summary of all our aircraft in the W&B manual, and our legacy Douglas aircraft MUST be weighed in a hangar. But, that's the only one that says "must".

prebennorholm wrote:

Weighing a plane should be done indoor, but let's have fun and look at what errors we can expect if weighing is done outdoor. Obviously the error will depend on plane type and wind force and direction.

I will assume a plane 200,000 lb heavy, which will fly straight and level at 200 KIAS, and parked with the nose into a 2 kt wind. The scales will show it to be lighter than its actual weight. Not that much because lift generally increase with the square of airspeed. Here is how much: 200,000 lb / (200 / 2)^2 = 20 lb. Yes, the scale will show 20 lb too little.

If we increase the wind from 2 to 20 kt, then we will have instead: 200,000 lb / (200 / 20)^2 = 2,000 lb.

These are just rough numbers to indicate the rough magnitude or the errors. Actually the errors will be slightly smaller due to the Reynolds Number effect. Some planes (A330/340 minus 330F) stand with a nose down attitude. 737NG and 737MAX have different length nose gear. Etc. etc. So there are plenty of variables to deal with.

At the end of the day, a hangar floor will normally be flat and level. Outdoor tarmac on the other hand will be slightly sloped to deal with rain. The latter obviously influences lateral balance and CoG measurements, which are probably more important than exact mass.

Another factor to keep in mind regarding CoG: the elevators. Wind blowing over them will affect the CoG quite a bit, depending on position and trim.

Starlionblue wrote:

kalvado wrote:

question is about error margin. I don't know how much lift would be created by the wind on a relatively calm day, but I would bet on 1-2% of plane weight at most. This can be unacceptable from the regulatory standpoint, but can be a solid check against certain mistakes (remember an accident where crew typed in aircraft weight as something like 140 instead of 240 tons?)

Checking the empty weight within 1-2% won't help with performance data entry mistakes. We just know the ZFW weight on the day.

After the incident (not an accident) which you mention, Emirates 407 at MEL, Airbus added additional gross error check logic to the flight management system.


The regulations aren't there for their own sake. 1-2% error margin in empty weight would put fuel burn calculations outside the error margins. 2% higher empty weight on a widebody could be 3-4 tons. The extra burn from carrying 3-4 tons more weight on a 12-hour flight can be 1 more ton.

Very good explanation why high accuracy is actually required.
Now why passengers are not weighted and baggage is sometimes manipulated - that is a diferent story...

VSMUT wrote:

prebennorholm wrote:

Weighing a plane should be done indoor, but let's have fun and look at what errors we can expect if weighing is done outdoor. Obviously the error will depend on plane type and wind force and direction.

I will assume a plane 200,000 lb heavy, which will fly straight and level at 200 KIAS, and parked with the nose into a 2 kt wind. The scales will show it to be lighter than its actual weight. Not that much because lift generally increase with the square of airspeed. Here is how much: 200,000 lb / (200 / 2)^2 = 20 lb. Yes, the scale will show 20 lb too little.

If we increase the wind from 2 to 20 kt, then we will have instead: 200,000 lb / (200 / 20)^2 = 2,000 lb.

These are just rough numbers to indicate the rough magnitude or the errors. Actually the errors will be slightly smaller due to the Reynolds Number effect. Some planes (A330/340 minus 330F) stand with a nose down attitude. 737NG and 737MAX have different length nose gear. Etc. etc. So there are plenty of variables to deal with.

At the end of the day, a hangar floor will normally be flat and level. Outdoor tarmac on the other hand will be slightly sloped to deal with rain. The latter obviously influences lateral balance and CoG measurements, which are probably more important than exact mass.

Another factor to keep in mind regarding CoG: the elevators. Wind blowing over them will affect the CoG quite a bit, depending on position and trim.

Probably not that much, especially if elevators are trimmed to horizontal position - air flow near ground would be mostly level..
And in absolute values, lift generated by stabilizer is much lower than that of the wing, and those values are eslimated.

Just pulled up a work card for weighing procedures on a 777-200. The first steps involve de fueling the airplane, completely draining the sumps, draining the potable water and servicing the waste tanks. These steps can and should be performed outdoors. The next step calls for " position the aircraft on a reasonably level area in the hangar. Close the hangar doors."

euroflyer wrote:

Hello,
I take the example of an A350. Is it possible to perform the weighing outdoors if no hangar space available ? If so, what are the conditions to be met ?
Thanks,

A level base, nearly zero wind. and are you weighing on pressure Pads or Jacks? the rest is airplane cleaning defueling and prep for weighing like empty galley carts and such.

A brochure on one model of scales, it is certified to be 0.1% accurate across the full range. A check around load cells in the 50 ton capacity indicate available accuracies of 0.02 to 0.1% for crane scales, a similar application. Tower cranes incorporate a 250 lb test block along with the test weight of around 12K lb. At a certain radius the crane was checked daily with its load block, lifted and held for a few minutes, then lift again with the 250 lb block must trip the overload cutout. That was 2%. On a 77W, at 975,000 lb MTOW a 0.1% error is basically 1,000 lb. Combined the scale system probably needs to be accurate to 0.25% to be effective on an airplane.

Wind and drafts would probably not affect the weight to any extent, but it could really screw up the COG calculations - down draft onto the tail could approach 1/2 PSF from a regular hanger HVAC system. That could change the nose wheel weight by 400 or 500 lbs for a 777.

Does say 787 aircraft employ load cells in their gear. As the gear compression is hydraulic it would be easy to have accurate pressure readings so the actual weight and CG could be checked, in outdoor it could be a few % off, but it would backcheck the calculated weight and CG.

https://www.intercompcompany.com/docume ... C30-60.pdf

Under axle style
http://airbusscales.com/index.html