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I was at Laoag airport on December 21st. For some reason, after getting my boarding pass, they weighed me and recorded my weight. They also weighed all of my hand-carry luggage and recorded that too.

It seemed like they were doing this for all passengers. Why?

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    It's to do with making sure the balance of the plane is correct (and that they have enough fuel for the journey). This is necessary with smaller planes that operate these routes. While I don't think this question is off-topic it may be a better fit for Aviation StackExchange where there are already questions addressing this – SpaceDog Jan 15 '16 at 10:06
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    Do you recall what type of aircraft you were flying on? (Currently, flights in and out of Laoag are on ATRs and mainline narrowbodies -- and even an ATR-sized plane isn't that sensitive to W&B) – UnrecognizedFallingObject Jan 16 '16 at 2:06
  • @UnrecognizedFallingObject: It wasn't a tiny plane. IIRC, I think it was 3 seats on each side of the aisle and perhaps 30-40 rows. – Kenny LJ Jan 16 '16 at 9:30
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The pilot needs to keep the aircraft balanced. This is really important. If you put all the heavy people at the front, it will push the nose down and the pilot will have to trim the controls against that, generating drag. If there is a sudden engine failure during take off, that extra drag could be extremely dangerous. The aircraft will also need more fuel to be loaded since the engine will have to run at a higher power to move the extra weight around. The aircraft will need to reach a higher speed on the runway before taking off. The aircraft will take longer to stop on the runway because it's heavier. The pilot needs to know all of this information precisely, in case there is a problem and he wishes to abort the take off.

On a large aircraft there are a large number of passengers and on average their weight can be estimated without weighing them individually. The standard adult weight is presently 87 kilograms. Some people will weigh more and some people less, but if you have 150 passengers, the average weight is good enough. So on a large aircraft it is not so important.

However it is not unusual to be moved around the cabin before take off to keep the weight distribution ideal. It was quite common on Concorde that a few people would be selected to move back a few rows, as that aircraft was enormously sensitive to balance.

Recently a Qantas aircraft got into difficulty during take-off because ninety children on board will accidentally assigned the standard adult weight instead of the standard child weight. This meant that when the pilots calculated the weight-and-balance of the aircraft before take-off, they got the answer wrong and therefore they used the wrong settings for the take-off. The pilot found the nose of the plane very heavy and he had considerable difficulty in performing the take-off without smacking the tail into the runway. It also meant that the calculated safety speed (the minimum speed in case there was a sudden engine failure) was also incorrect. Fortunately there were no further problems and the flight crew re-trimmed the aircraft during the climb out to relieve the problem. It was not a serious problem on a large aircraft. On a small aircraft it could have been very dangerous.

An aircraft is basically like a see-saw, balanced over the wings. Even a tiny change in the weight balance of the aircraft will cause it to tip forwards or backwards, pushing the nose up or down. If that isn't compensated for, the aircraft will begin to climb or dive. Therefore that change in balance needs to be accommodated by re-trimming the flight controls against the balance change.

Normally this will be done by the autopilot but if the autopilot is not available, it means the pilot will spend the entire flight constantly re-trimming the flight controls every time anyone goes to the bathroom.

  • luckily the very tiny planes I've been on don't even have bathrooms :-). One didn't have an aisle, so no worry about people moving around. – Kate Gregory Jan 15 '16 at 16:03
  • @KateGregory I inserted that part to show just how sensitive a plane is to the weight distribution, maybe I'll edit that out – Calchas Jan 15 '16 at 16:25
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    Don't edit it out, but maybe clarify that typically planes small enough to worry about weight and balance are used for very short flights and don't have some of the reasons why people would move about. Both of those reduce the "a passenger moved" likelihood. – Kate Gregory Jan 15 '16 at 16:29
  • I can't believe it's been almost 12 years since the US5481 crash, in which weight and balance was a major contributing factor. I was flying a lot of US Airways Express at the time, and remember it well. While I of course don't know what the cockpit crew was up to mid-flight, I know it was extremely common for passengers to be moved around the cabin for takeoff and landing when loads were light on the puddle jumpers. – choster Jan 15 '16 at 16:32
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    There was also a crash in DR Congo a few years back that was blamed on weight distribution problems due to passengers fleeing an escaped crocodile on board. – Michael Seifert Jan 15 '16 at 22:37

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