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BreninTW
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How Accurate Are Check-in Scales?

Wed Sep 09, 2015 6:09 am

I've always expected check-in scales to be super-accurate, but a recent business trip has got me questioning that.

At the beginning of the trip, I checked in a bag that the check-in counter said weighed 15 or 16 kg (TPE), which is in line with what I got on my bathroom scale. In that bag, I had a Chromebook and some candy that weighed about 2 kg.

During the course of the trip, the Chromebook and candy were taken out and left in various locations, but I added two duvets, some extra clothing and a few other odds and ends.

A handheld scale told me, just before I left for the airport, that the bag weighed 20 kg. However, the boarding pass tells me that the bag I checked in weighed 16 kg (LHR T5).

I find it hard to believe that the stuff I added to my bag was only 3 kg or so ... so, how accurate are those scales?

If the scales are under-weighing to the tune of 4 kg or so per bag, wouldn't this be a concern for CoG? Or is it simply so minor in the greater scheme of things that it's acceptable?
 
rwessel
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RE: How Accurate Are Check-in Scales?

Wed Sep 09, 2015 6:51 am

Scales do malfunction, but I assume they'd be inspected by the local department of weights and measures on a regular basis. Particularly since the airline can charge you based on what the bag weighs. This is no different than the scale at your local deli counter.

In practice, I'd guess airport scales are lower priority than things like deli scales and gas pumps, but I have seen inspection stickers on scales at ORD.

Scales can also read poorly if loads are placed improperly (hanging off the edge, for example), and if you're traveling in a group, who knows which bag's weight got recorded for you.
 
mmo
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RE: How Accurate Are Check-in Scales?

Wed Sep 09, 2015 8:43 am

Quoting BreninTW (Thread starter):
If the scales are under-weighing to the tune of 4 kg or so per bag, wouldn't this be a concern for CoG? Or is it simply so minor in the greater scheme of things that it's acceptable?

In the "bigger scheme" of things, the under/over reading of scales is pretty minor. The CG will not be affected to any great degree to really influence the CG. When we are talking about a 748 or 380 the change might result in a .1 change in the MAC which you can't even read from the cockpit when setting the trim. As long as the trim is in the green band range, there will be no problems.
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tommy1808
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RE: How Accurate Are Check-in Scales?

Wed Sep 09, 2015 8:50 am

Quoting BreninTW (Thread starter):
I find it hard to believe that the stuff I added to my bag was only 3 kg or so ... so, how accurate are those scales?

depends on local legal requirements I would think. Here they are frequently calibrated, I did assume the same is true elsewhere.

Best regards
Thomas
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CXfirst
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RE: How Accurate Are Check-in Scales?

Wed Sep 09, 2015 2:49 pm

In the grand scheme of things, it won't really impact CoG on large airliners.

For instance, when I load a flight at my airline, the bag weights that are used are standard weights (15kg) per piece, and we might load 20 bags in a certain compartment, but that compartment could realistically hold 20 light bags or 20 heavy bags. It won't be 100% accurate.

Now, this might seem odd at first, but keep in mind, that right above the bags in a full cabin of passengers, who all are loaded onto the aircraft using standard weights depending on if they are male, female, a child or an infant. Now, the discrepancy up there is likely to cause more problems than slightly off bag weights.

-CXfirst
 
Woodreau
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RE: How Accurate Are Check-in Scales?

Wed Sep 09, 2015 6:34 pm

The wonders of airplane math.

For example:
That bag you packed that weighs 15 or 16kgs or 20kgs even.

What does it weigh?

The answer is it depends on where you put the bag on the airplane.

If you check it at the ticket counter and it goes into the cargo hold, it "weighs" 30lbs.
If you decide to take it through security and carry it onto the plane with you. You put into the overhead bin, your bag weighs "nothing."
When you get to the gate, the aircraft is a regional jet, and they won't let you take it onto the regional jet because it's too large to fit in the overhead bin. They valet check your bag and put it in the cargo hold, it "weighs" 20lbs.

So how much does your bag weigh? It doesn't matter if it really weights 15kgs or 20kgs, as long as it doesn't weigh more than 50lbs, all bags "weigh" 30lbs. Once it weighs more than 50lbs/22.6kgs, the bag "weighs" 60lbs.

The scale at the ticket counter is used to determine whether the bag will count as a 30lb weight or a 60lb weight. The actual weight of the bag doesn't count.

Every person on the airplane weighs 190lbs/195lbs. Doesn't matter if you're thin tiny gymnast that barely weighs 90lbs wet, or a 300lb football player. Everyone weighs 190 or 195lbs. with the 5lbs difference for extra clothing a person might be wearing during the winter months.

T
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vikkyvik
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RE: How Accurate Are Check-in Scales?

Thu Sep 10, 2015 1:55 am

Quoting Woodreau (Reply 5):
Every person on the airplane weighs 190lbs/195lbs. Doesn't matter if you're thin tiny gymnast that barely weighs 90lbs wet, or a 300lb football player. Everyone weighs 190 or 195lbs. with the 5lbs difference for extra clothing a person might be wearing during the winter months.

That 190/195 lbs is intended to include carry-on baggage too, correct?
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JAAlbert
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RE: How Accurate Are Check-in Scales?

Fri Sep 11, 2015 11:53 pm

How the heck did you fit two duvets into a single suitcase?

I've had the same experience with scales at airports - my suspicion is that they get an awful lot of abuse and not a lot of testing. Maybe its time the NYT turns its focus from Wholefoods to the airport scale!
 
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BreninTW
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RE: How Accurate Are Check-in Scales?

Mon Sep 14, 2015 12:45 am

Quoting JAAlbert (Reply 7):
How the heck did you fit two duvets into a single suitcase?

LOL -- quite easily actually: It was a large, hard-shell suitcase (much bigger than was necessary for what I actually carried over), so I folded the duvets and put them in the lid of the case, then sat on it to close.

They were light/medium weight down duvets, so very compressable.
 
Leezyjet
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RE: How Accurate Are Check-in Scales?

Mon Sep 14, 2015 1:50 am

In the UK they are calibrated every 1-2 years IIRC, but they do develop errors. I've worked on desks that indicated as much as 5kgs with nothing on them, so you had to take that into account for each bag, so you didn't unfairly charge people excess.

Here's a cheeky little tip, if your bag is heavy/overweight, stand next to the scales when you're checking in, and wedge your foot under the scale and lift the front of your foot up to take some of the weight of the scales, it might just put you back under. Try and keep as still as possible so the numbers on the scale don't keep changing though.
 
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