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Self Loading Freight
24th Feb 2008, 13:14
Following on from the thread in R&N, where an a/c had a tailstrike following a ten tonne loadsheet error - why aren't there sensors connected with the landing gear that provide an actual weight after loading? Also, assuming that the CoG is somewhere within the geometry of the wheels (surely a safe assumption!), that could be detected and any out-of-safety discrepancy reported.

There are plenty of factors that armchair designers miss, cost/benefit tradeoffs and the usual unforeseen consequences of adding yet more complexity to the already fearsomely complex mix that is a modern aircraft, but none suggest themselves in this case. There are already squat switches - just need to get the resolution up a bit from the "one aircraft" range.

R

mutt
24th Feb 2008, 13:34
How do you account for the "lift" created by the wind whilst on the ground?

Mutt

Daysleeper
24th Feb 2008, 13:54
How do you account for the "lift" created by the wind whilst on the ground?

Simple algorithm fed by the air data computer...:}


Besides didn't the Vickers Merchantman weigh itself oh what 30 years ago.

TowerDog
24th Feb 2008, 14:15
Weight sensors on the landing gear was an option on the B-747-200.

The data was fed into a small "computer" and weight as well as CG could be read in the cockpit. Kuwait Airways had that option on some, if not all of their -200s.

IO540
24th Feb 2008, 16:12
It's not hard, or expensive.

In the early 1980s I designed a system, for a major UK articulated lorry fleet operator (some 200 lorries IIRC) who wanted to load them to the limit without getting busted on random weighbridge checks, on total weight or axle weight.

It involved fitting strain gauges to the leaf springs but they could go in other places, near the suspension mounting points.

Production implementation weas handed over to somebody and I don't know how far they got, but I remember that many patents had existed on these systems even back then.

On a large jet, the simplest way would be to measure the compressive strain of the steel of each landing gear centre leg. Very easy with a strain gauge, and accurate to maybe 1%.

Obviously it would only work at standstill.

Meikleour
24th Feb 2008, 16:23
This was actually done on the Merchantman(Vanguard Freighter) as long ago as 1972 The system was called STAN (sum total and nosewheel) and weighed the aircraft and computed the c of g. Also available on B747-200F in the eighties. Both systems were notoriously unreliable and their use discontinued.

JW411
24th Feb 2008, 17:34
The Air Bridge Merchantmen always used to stop on a level piece of taxiway and weigh themselves on their way out to the runway.

I seem to remember that the Lockheed C-5 also has an inbuilt system.

CR2
24th Feb 2008, 17:40
747-400F also has a weight & balance computer. Tolerance is about 2%; given that mtow is almost 400T, you could be 8T out. Discrepancies of 4-5T are investigated prior dispatch. One other detail is that for the system to work properly, the aircraft has to be on a flat bit of tarmac; slopes affect the readings.

At the end of the day, proper care and attention must be given when issuing a loadsheet. There really is little else to say.

ppppilot
24th Feb 2008, 18:05
I always have thought there should be sensors at the TO point of the rwy with a digital readout of your actual TO weight in view to the pilot. As mutt said the wind could be a factor. But could it be a solution for sure. I prefer an alternative to the weight measured by the operator and an alarm sign to some pirates.
Tailwinds

randomair
24th Feb 2008, 18:07
I believe that if you actually weighed every a/c and got the actual weight (not some estimated value-using standard pax and baggage figures) 9 out of every 10 a/c wouldn't have the performance for some of the more limiting airports.

Especially if you've got Americans on board.:ok:

randomair

Mad (Flt) Scientist
24th Feb 2008, 18:19
the problem with any kind of weight and balance takeoff warning system (other than the economic issue cynically (but perhaps accurately) referenced above) is that the accuracy of the available systems would be such that either:

1. The system has a false warning rate so high as to render it more of a liability than an asset; or
2. The system would have warning thresholds set so unconservatively as to render the system all-but useless except in the case of errors so gross that massive system failures would be required to get there in the first place.

It's analagous to the "takeoff acceleration" warning systems people keep proposing; the idea is nice, but there's no real "sweet spot" where you could have a warning system that worked when it was supposed, and didn't go off when not required.

There are already conservativisms in takeoff performance and in weight and cg envelopes which account for normally expected variability, and procedures should be designed to account for these two. If those procedures have broken down to the extent of allowing a seriously unsafe loading to develop, the "takeoff weight warning system" might just end up being one more thing the accident report records as being ignored/bypassed or simply inop....

ppppilot
24th Feb 2008, 20:59
I agree that technically it is difficult to develop. But the actual margin it is not safe at all. I have noticed on some airports, always the same ones, that I always burn a minimum of 1% more than predicted for the flight. One or two tonns is too much when you plan to land with 8 tonns. I suspect that they do not stop excessive hand baggage and they do accept more than authorized luggage weight. Heavy luggage is usual at vacational destinies. The actual standard ICAO weight is insufficient for the big trolleys nowadays. Small errors on each of 300 pax becomes a big error.

411A
25th Feb 2008, 01:00
The system was called STAN (sum total and nosewheel) and weighed the aircraft and computed the c of g. Also available on B747-200F...

Also on the B707, worked OK in my experience, although expensive to maintain.

john_tullamarine
25th Feb 2008, 03:35
The concept is simple (usually leg loads) and, from personal experience with a system on a small fleet of 727 freighters, usually there was a reasonably constant error delta but the variations from the expected error position correlated consistently with the load sheet data... ie the system was a very useful taxy check on the paperwork.

On those occasions folk taxied back for a check, the load was wrong with respect to the paperwork.

IFIX
25th Feb 2008, 03:41
My first reply here,

The MD-11 is fitted with just such a system, comprised of strain gauges on each axle which feed data to two weight and balance computers.
The calculated a/c weight is compared with the loadsheet prior to dispatch.
The system is also used as an alerting system in the event of possible a/c tip-over during loading.
The alert is triggered by the load on the nosewheels decreasing below a set value.
Once triggered it also cuts power to the cargo loading systems.
Works fine, as long as the housing for the strain gauges is kept perfectly sealed from any fluid leakage and carbon dust from the brakes.

ppppilot
25th Feb 2008, 20:04
After reading all these posts I believe that the only reason for not having such a system on the basic model of every plane must be the airlines opposition because of maintenance costs, cause of delays, etc. Considering the actual level of sophistication and security JAA and pilots should force manufacturers to mount it for free. I would rather to have that, than a sun protector behind the windshield.

Hawker-rider
25th Feb 2008, 20:06
Hi,

I've indeed flown MD-11's that have this system as some 747 (200's and 400's) as a customer option. I know of some cargo airlines that have them installed in their fleet.

So it's already there, and seems to be working allright.

CR2
25th Feb 2008, 20:09
I was involved with Airbus for the A380F; we asked them for a 1% tolerance and were told that was nigh-on impossible & the costs would be horrendous.

As an aside, if I remember correctly, BOG has a weighbridge which ATC directs you to at random.

wigglyamp
25th Feb 2008, 20:15
The system on the Merchantman worked by measuring the hydraulic pressure in each undercarriage strut using a transducer mounted at the top of the leg. The main inaccuracy came if the strut wasn't charged correctly or was leaking. The system was tested by the crew and gave a fixed weight and C of G value determined from set resistors in each transducer - this ensured the continuity of all the system wiring. It was still in use at AirBridge in the late 80's.

old,not bold
25th Feb 2008, 20:32
I recall studies being done (80s? 90s?) on installing weighing machines on taxiways and/or aprons, but not the outcome.

This would be a much more cost effective way than having each aircraft weigh itself..it's not only the cost of installing the sensors etc in the aircraft. but the extra weight they crate, maintenance costs etc.

The difficulty was allowing for the different dimensions of different aircraft, as well as wind etc (previous posts) but they should not have been insuperable, I would have thought.

Dan Winterland
26th Feb 2008, 00:28
The WABC (Weight And Balance Computer) system is ano option on most Airbus and Being aircraft. SOme of the 744s I used to fly had it. But we always ignored the WABC figures and went for the loadsheet figures. Flying out of JFK with a couple of hunderd 'average' Americans on board, with their "3kg" of hand baggage often showed the latter's futility. I have seen a TOW indicated on the WABC some 20 tonnes (yes, 20 tonnes!) greater than the loadsheet. And I have also seen the WABC say we were several tonnes over MTOW once.

The Airbus FBW aircraft measure the weight when airborme through the Flight Augmentation Computers (FACs) from data provided by the angle of attack. Our A321s are always a couple of tonnes out, always heavier. And from the way the aircraft performs, I suspect the FACs are correct. The FACs provide the protection speeds wheras the FMC provides the approach speed from the loadsheet weights input at the planning stage. Adding a few knots to Vapp is the norm.



PS. The last time I was notional weight, I was age 16. Time to change the notional weights methinks!

Beg Tibs
26th Feb 2008, 06:05
I can get an up to date weight by accessing the appropriate page on the ACARS. type in GW, FQL,FQR,FFL,FFR and you get a current Gross weight, Fuel quantities in left and right tanks and left and right engine fuel flow :)

Self Loading Freight
26th Feb 2008, 11:13
Thanks.

So it's not economical, not reliable and not that useful.

Apart from that, it's a great idea!

I'm a bit surprised that it's so unattractive and difficult to make worthwhile. You're constantly moving known mass into and out of the a/c during refuelling and engine operation, giving a great opportunity for auto-calibration. Likewise, slopes are easy to detect and factor into the sums.

But I guess that the number of expensive accidents and fuel inefficiencies caused by weight discrepancies are too low to justify the expense of yet another system...

(This may change. I was talking to a chip maker about embedded supercomputers, where you effectively have a real-time physical model of your vehicle running on a few teraflops of cheap silicon inside the vehicle itself. As things change over time, the model spots non-optimal operations, models 'what-if' experiments on the fly and recommends optimising operational changes. The chip guy was of the opinion that this could compensate far better for things like control surface failures than pilots ever could. Well, maybe. But any system using such ideas would have to be very well instrumented, I'm sure to the extent that the weight and distribution would be accurately known at all times).

R

mutt
26th Feb 2008, 11:55
I can get an up to date weight by accessing the appropriate page on the ACARS. type in GW, FQL,FQR,FFL,FFR and you get a current Gross weight This works using the concept of garbage in, garbage out!

SLF, maybe airlines dont want to know the exact weight?

Mutt

ppppilot
26th Feb 2008, 18:18
I believe that when the FAC of the bus uses the angle of attack, it can only determine where is the cg regarding on the trim used to maintain that AoA at a given PA. You must take into account that during the flight the cg changes also with the cabin crew moving with the catering. For the weight, it is also involved the thrust, the speed, and the perf fac. Is it not?
I have heard that the only moment to check the cg is at the lift off. When you introduce the cg at the pre flight, you calculate a trim for the TO run. Someone told me that this cg must correspond with the one that the ap uses during the 2 segment. I don’t know if that is true.
I have been searching for a perf table within the OM to check the cg in flight. The only reference I have seen is under abnormal procedures, not reliable speed indications. Sorry if I missed the translation.
I would like to know if using the correct weight to the flight means some benefit to the airline. I suspect it doesn’t. A Spanish mayor airline, several years ago used to count the pax within the plane to check total with the loadsheet given by the gate desk. As more than 70% figures didn’t match (because bad count of the gate desk or crew) delaying the flight, the airline nowadays accepts the loadsheet as counted only at the gate. Does BA and other mayor airlines count pax OB?
Good flights

tristar 500
26th Feb 2008, 20:54
STAN system
wigglyamp says,
The system on the Merchantman worked by measuring the hydraulic pressure in each undercarriage strut using a transducer mounted at the top of the leg. The main inaccuracy came if the strut wasn't charged correctly or was leaking. The system was tested by the crew and gave a fixed weight and C of G value determined from set resistors in each transducer - this ensured the continuity of all the system wiring. It was still in use at AirBridge in the late 80's.

The system is still fitted to G-APEP at Brooklands & still works, unsure how accurate it is though!!

Tristar 500

747dieseldude
26th Feb 2008, 21:07
read this article:

http://www.nlr-atsi.com/downloads/NLR-TP-2007-153.pdf

john_tullamarine
26th Feb 2008, 23:06
Likewise, slopes are easy to detect and factor into the sums

not necessarily... one of the problems with a lot of transducers relates to sideloads on the cell. This is a big problem with routine maintenance aircraft weighings .. and can account for (an unpredictable) several hundred kilos per cell ...

ppppilot
27th Feb 2008, 00:52
Good paper that. I remember when working for a cargo airline, Metro II, Metro III and Merlin IV. Dozens of times when I arrived to the plane the nose wheel was almost in the air and when I asked to the ramp agent, he always was sure the airplane was perfectly loaded. Reading the article, I can see that the heavy opposition comes from cargo operators. Another curiosity is that FAA requires a 1% of accuracy to the system. Therefore. FAA is assuming that only a 1% of error could be found on 100% of flights or that only a 1% of the flights do not comply with the loadsheet?… Boy, we don’t live in the same world. Probably all of us have seen those small tractors to pushback the bus, remote control commanded that only lifts the right or left main gear. It could be a good weighting device by only applying measure units to the strength needed to lift the wheel. Sequentially the 3 wheels, of course. If such a cheap thing or the nitrogen pressure of the wheels, could be used to random control of the airplanes and FAA only finds a 5% of error then I fly for free the rest of my life. Is it not the same difficult to weight the fuel on board? That weight could be used to check the onboard weight system. Ok I know I am going too far. Only trying to give some thoughts just in case someone of the FAA or the CAA read my post.:ok:

ppppilot
27th Feb 2008, 18:05
John Tullamarine. I ask you as a moderator. Pprune has a very good reputation all over the world and there are thousands of persons involved in the aviation that comes here daily. Could we initiate a thread to get the attention of authorities, Boeing and Airbus to include the on board weight system in all the basic models? The title could be something like “To the attention of CAA, FAA, AAA, Boeing and Airbus. OB wgt & bal sys”. And the first post could be something like. “All the people posting in this message would like the onboard weight and balance system to be mandatory to all airplanes of MTOW 25000 kg or more. If you agree with this send an empty post to this thread”. Would be also very interesting if people from outside pprune could send a mail just to count on.

mutt
27th Feb 2008, 20:27
ppppilot

Have you considered that maybe airlines dont want to know the exact weight?

With a 400,000 kg airliner, a 1% tolerance equals 4,000 kgs, so what do you think an airline is going to do, offload fuel, cargo or passengers and cause total chaos, or behave like an ostrich?

Mutt

DC2 slf
27th Feb 2008, 20:49
I have been told that wind effects on the wings make measurement through the landing gear (by pressure, strain gauges or other means) unsatisfactory

787FOCAL
27th Feb 2008, 21:24
Hard landings and the system is no longer very accurate.

slip and turn
27th Feb 2008, 21:46
You mean it's a sensitive measure of hard landings too ? And if it shows 'out of calibration' next time someone wants to use it, that's a good clue of how hard it landed last night ? :E

Then surely it is a 'must have' :ok:

john_tullamarine
27th Feb 2008, 22:13
Could we initiate a thread to get the attention of authorities

Not much point, I suggest. You are looking at a design standard sort of thing and that is processed at a much higher level than PPRuNe. More importantly, while on-board systems have their uses, at the end of the day, certification is not an exact science and involves weight tolerances. It would be quite unreasonable to look to "precise" (whatever that might mean) weight data for line operations when the flight test regimes are, at best, no better than routine line ops weight data ...

that's a good clue of how hard it landed last night ?

well proposed, that man ..

Self Loading Freight
28th Feb 2008, 18:21
not necessarily... one of the problems with a lot of transducers relates to sideloads on the cell. This is a big problem with routine maintenance aircraft weighings .. and can account for (an unpredictable) several hundred kilos per cell ...

That sounds like a design flaw - or an inappropriate choice of transducer. A while ago, I did some work with accelerometers and strain gauges (albeit dealing in fractions of a newton rather than a 747's worth of tin and blood), and we worked in three axes without any particular difficulty. I'm sure that if you don't design for this, it won't work well - and a bit surprised that it's a big problem in an area where I'd expect the technology to be mature and well-understood.

Is there some reason why this is so problematical?

R

john_tullamarine
28th Feb 2008, 20:05
That sounds like a design flaw - or an inappropriate choice of transducer

Just the way things are .. (caveat - there may be better units available these days). Consider that design is for axial loading, as is calibration. I would need to refer the present state of play question to a colleague who designs and manufactures such animals ..

To give you an example, many years ago I was tasked with sorting out the dreadful weighing history on a fleet of GIIs. Turned out that, due to the jackpad geometry, any rotation of the hull to level accentuated lateral loading of the jacks (and load cells). Consecutive weigh cell variations could easily be in the order of several hundred kilos (might have been pounds - can't recall after nearly 30 years). When we tried locking the oleos and levelling prior to jacking ... the problems all promptly disappeared and the weigh variations were negligible. This is why some of us insist on level and locked for jackpad weighings ..

SouthpawSLF
29th Feb 2008, 01:31
As a result of the investigation, the TSB issued a rec (A-06-07) to worldwide regulators for development and requirement of an on-board 'performance monitoring' system which would alert crews of a weight or cg problem...

http://www.tsb.gc.ca/en/reports/air/2004/A04H0004/a04H0004.pdf

ppppilot
29th Feb 2008, 13:06
OK Gents. What are you afraid of?
JT. A thread like I am proposing it would be vary in relevance from as much as a small grain of sand to nothing, depending on the interest shown by our colleges. Not too pretentious. Only trying to be a sign of our interest on to not forget a safe and useful device like OBWABS.
Actual OB weighting systems can be expensive or inaccuracy mainly because no one gives a penny to investigate. The fuel metering device, at its beginnings was a cork and a lever with a variable resistor.
Don’t all of you agree that weight procedures are archaic? How can anybody accept to load a 747 with the weight given by the person that pays for that weight? When I flew cargo I remember to discover at the arrival very dangerous goods camouflaged into a printer package. If the sender do that what is he expected to do with the weight?
How can anybody accept at the actual stage of technology, lets say?... Ok women weights in summer 81 kg and 83 in winter and men 91 kg and 93… And transsexuals? Same at Congo than at Minnesota? Very complicated, best 84 kg for all. Sign it like that and lets celebrate with scotch all night long.
Is there any regulation on checking the weighing equipment at the check-in desks or the pallets scale since the day they were installed there?
But all of us accept go to the limits with performance, using software programs to use the last millimetre of the rwy for TO.
Mutt. If you are talking about behave like an ostrich by the time their pilots are dealing with an overloaded airplane, in my opinion those airlines shouldn’t to exist. Same opinion than CAA, FAA, AAA, and all the A’s over this world and the others. But if you are talking about serious airlines I believe that of course they do like to know the exact weight on the plane, because that weight means money. Money out or money in. I am sure that I am carrying thousands of kg for free. Nobody pays for them, because nobody knows that they are there. That’s money out. The extra fuel for that extra weight is money out. Serious airlines don’t play with its future. I have seen to my company very few times going to the limits and for example when I had to TO into a “tropical storm becoming a hurricane”, they gave me a million of analysis for TO with max pax possible. I took the more conservative and from there a couple of tons down, just in case. Specially because I am not comfortable with the weighting systems at those funny destinies. That is money for the company. I know, and far away also my money. None of my bosses told me a word, because they would acted the same. They do want nobody playing with their future.
In my experience the bigger the airplane the most usually limited at ldg. The smaller at TO. Probably that depends on the plane and the range of flights. Mine is 275t MTOW, 178t MZFW, 190t MLW. That makes 97t of fuel from where I have TOW limitation and that means over 15 to 16 flight hrs. My flights are maximum 11 hrs. In that situation only will be a security margin to performance calculation. That would be the primary use I would like to use it. Always using the bigger numbers from the loadsheet and WABC. My company use to give me 10 tons margin at 190t Ldg. I adjust it to 3t. That is a more than 1,5%.
I understand you are saying that some airlines doesn’t want to have such a system in their airplanes because of maintenance cost and inaccuracy? I better would say that companies would like the OBWBS but at a state of no significant maintenance cost and a level of accuracy of 0,1%. What they do not want to pay for is the cost of investigation to obtain such a system. Those are economical facts. Therefore airlines are defending money. As a pilot I am talking on behalf not only money but my life also. That’s safety and what I am trained for. So Mutt my opinion is, we both pilots and companies must have the same relevance on designing the airplanes and their systems. I think both positions are important and direct related. There it goes a couple of examples that I personally know.
At my very beginnings I flew in an aerial photography company. The most beautiful job I have ever done. I became Director of Operations and then I was all the time fighting with the boss (owner).- Fly lower, photos are better…No I don’t.- That other company has bought the engines half of the price than you did… That other company stopped that plane one month later burning more oil than fuel. Etc. I was 8,5 years and we broke all benefit records without a single incident. Then I decided to leave that beautiful job to live the beautiful live the airline pilots do. They took a pilot well experienced 5 years flying the same job and same planes. Unfortunately less than a year later he crashed one of the planes into a roof half an hour from TO full of gas. The fire was so heavy that not a piece of the pilot and photographer bodies could be found, except teeth. 3 years later that company didn’t exist anymore. Boss or pilot guilty? Both in my opinion.
The second example, all of you have been talking about it here.
IB overrun at Quito. Crazy airport. 92000 ft elev. Surrounded by 15000 ft mountains. Bad weather, worst ATC. 2600m LDA downhill slope, nobody knows the real elev since last time they took off the rubber of the rwy. ILS displaced from PAPI. 182 gs at touch down with high pitch attitude. A340 Flap limited at 20000’, select 1 at 15000, 2 at 13000 and then turn 200º to final app. Better maintain selected speed at least 10 knt faster at the beginning of the turn… Crazy.
Everybody knows what you read or you hear, but you also must know that initially IB was flying the A340-300. When the plane began to be full and the company was loosing pax they decided to fly the A340-600. On the papers it is perfectly possible. But Spanish pilots are not better nor worst than the rest and our maximum aspiration is as yours, get to retire with no incidents. 250 tons at ldg with those conditions is going to the limit. So IB pilots recommended many times to the company not flying the 600 there. Daily frequency, thousands ldgs with no problem, but everyone can have a bad day and better not be at the limit then. The rest all of you knows. Today the 300 is back flying to Quito.
By the way, about good clue of how hard it landed last night. Do you know there is an Airbus maintenance program that any airline may subscript? The bus ACMS reports via ACARS to the company exceeded parameters, included G at LDG. If you are in the program that ACARS is also sent to Airbus. At airbus they investigate the causes, the solution and if the company has the spare parts in the stock. It is supposed that only if you contract that. But I know a guy, flying for a company out of that program, who landed an A330 somewhere at South America the same sweet manners than a rugby player giving the welcome to the opposite having the ball. The crew didn’t say a word of that and when the plane arrived back to its base, Airbus phoned to the company to stop that plane.:}
Hey, this seems closer to be one of those disregarded accident analysis than a post. It is too long to read it again for mistakes. I hope all of you will send corrections for me.
Tailwinds

ballpoint
29th Feb 2008, 13:26
My company operates 747-400 combi aircraft which are fitted with a W&B system.
Our pilots must make a logbook entry when the indicated ZFW differs more than 10 tonnes from the loadsheet ZFW.
Many times our aircraft took off 10 tonnes heavier than what we were paid for.
Because that´s the trick: 10 tonnes of cargo having a free ride.
Company detectives paid a visit to that specific station (JNB) and voilá, no loadsheet discrepancies anymore.
The W&B system pays for itself I think. Not to mention the safety advantage of a well monitored center of gravity.


Regards,

Ballpoint.

Zorst
29th Feb 2008, 19:54
Why don't aircraft weigh themselves? (http://www.pprune.org/forums/showthread.php?t=315101)

The unpalatable truth:

1. Because most aircraft now weigh considerably more on the taxiway than they do on paper, and this suits the operator's bottom line.

2. Because nowadays there are very, very, few performance related accidents involving big aircraft or events where the fact that a big aircraft was slightly overweight was critical, and so...

3. Regulators and investigatory authorities never weigh big aircraft after accidents (though they often comment that small aircraft were overweight, which they often are).

ft
2nd Mar 2008, 09:52
But we always ignored the WABC figures and went for the loadsheet figures. Flying out of JFK with a couple of hunderd 'average' Americans on board, with their "3kg" of hand baggage often showed the latter's futility. I have seen a TOW indicated on the WABC some 20 tonnes (yes, 20 tonnes!) greater than the loadsheet. And I have also seen the WABC say we were several tonnes over MTOW once.

That's one of the main reasons for the system not becoming widespread. If it can't be made exact enough to be the sole means of W&B you always have do the manual W&B anyway. In that situation, you save nothing but may end up cancelling a few flights due to finding out that while the load sheet said you were OK you were in fact above MTOW.

Airlines want to be able to load the aircraft right up to the limit. If the system cannot be made without safety margins larger than the manual load sheets, they will be able to load less. I e, until the system can be proven to have the same tolerances as manual calculations, it will not become widely used.


PS. The last time I was notional weight, I was age 16. Time to change the notional weights methinks!


Another reason. If all the other airlines are using dated standard weights, airline XYZ will not use actual weights (on-board W&B) if it means they can fly less pax around than the competition.

Check out the Society of Allied Weight Engineeers' (http://www.sawe.org) Recommended Practise for On Board Weight and Balance Systems (http://www.sawe.org/technical/rp/rp1).

I have been told that wind effects on the wings make measurement through the landing gear (by pressure, strain gauges or other means) unsatisfactory

True. Imagine what a stiff wind coming down over the roof of the adjacent terminal onto the aircraft will do to the indicated C.G.

In summary: Unless it can be built more accurate and with better repeatability than is currently technically feasible, it will not be commercially viable. Hence it is not likely to happen unless regulations change to require it.

As a result of the investigation, the TSB issued a rec (A-06-07) to worldwide regulators for development and requirement of an on-board 'performance monitoring' system which would alert crews of a weight or cg problem...

They're essentially looking at acceleration monitoring during the take-off run. It would alert the crew to overweight or underpower conditions, but not to out of CG range. Not a bad idea IMHO. A simple speed check halfway down the TORA would suffice.

In the world of smaller aircraft operating out of short fields, I've heard it argued that every runway should have midpoint markings to facilitate such a check. Makes sense to me.

Cheers,
/Fred

AVApilot
3rd Mar 2008, 03:22
You are right, there is a scale in BOG, ATC sends you randomly and it's a pain.