# Does an airplane weigh less after the passengers have eaten their meals? **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [July 4, 2006, 1:12pm UTC](https://boards.straightdope.com/t/does-an-airplane-weigh-less-after-the-passengers-have-eaten-their-meals/363153 "2006-07-04T13:12:38Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![dmLemming](https://avatars.discourse-cdn.com/v4/letter/d/a88e4f/32.png) [@dmLemming](https://boards.straightdope.com/u/dmLemming)\ **Post date:** [July 4, 2006, 1:12pm UTC](https://boards.straightdope.com/t/does-an-airplane-weigh-less-after-the-passengers-have-eaten-their-meals/363153/1 "2006-07-04T13:12:38Z")
[Airplane weight](http://www.straightdope.com/classics/a3_144.html) Cecil? Did the plane shut its engines off during the meal? If so - Then of course you’re correct - Otherwise, by the time the Meal is over, the plane would of lost a significant amount of weight - Namely, the amount of jet fuel that the plane uses as the passengers finish their meal. (just picking nits) ---
**Author:** ![Oakminster](https://avatars.discourse-cdn.com/v4/letter/o/77aa72/32.png) [@Oakminster](https://boards.straightdope.com/u/Oakminster)\ **Post date:** [July 4, 2006, 1:21pm UTC](https://boards.straightdope.com/t/does-an-airplane-weigh-less-after-the-passengers-have-eaten-their-meals/363153/2 "2006-07-04T13:21:26Z")
Cecil already picked that nit, in the column you linked: \*We’ll also ignore–I hate to have to throw all these qualifications in here, but I’m surrounded by nitpickers–weight loss due to jet fuel consumption during the meal. \* ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [July 4, 2006, 5:10pm UTC](https://boards.straightdope.com/t/does-an-airplane-weigh-less-after-the-passengers-have-eaten-their-meals/363153/3 "2006-07-04T17:10:53Z")
[QUOTE=Oakminster] Cecil already picked that nit, in the column you linked: \*We’ll also ignore–I hate to have to throw all these qualifications in here, but I’m surrounded by nitpickers–weight loss due to jet fuel consumption during the meal. \* [/QUOTE] While we’re at it, let’s also ignore mass-energy lost by thermal radiation to the (colder) surrounding air. ---
**Author:** ![SiXSwordS](https://avatars.discourse-cdn.com/v4/letter/s/49beb7/32.png) [@SiXSwordS](https://boards.straightdope.com/u/SiXSwordS)\ **Post date:** [July 4, 2006, 7:01pm UTC](https://boards.straightdope.com/t/does-an-airplane-weigh-less-after-the-passengers-have-eaten-their-meals/363153/4 "2006-07-04T19:01:26Z")
This seems as good a place as any to ask when the toilet tanks are purged. People eat their meals, run to the toilet… (I guess they could just use the airsick bag, but who wouldn’t prefer to barf in private?) When the system gets full, it has to be purged, right? I doubt there’s any doubt that dumping a bunch of [blue ice](http://www.santacruzsentinel.com/archive/2003/June/15/local/stories/03local.htm) would lighten a plane. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [July 4, 2006, 9:42pm UTC](https://boards.straightdope.com/t/does-an-airplane-weigh-less-after-the-passengers-have-eaten-their-meals/363153/5 "2006-07-04T21:42:49Z")
[QUOTE=SiXSwordS] This seems as good a place as any to ask when the toilet tanks are purged. People eat their meals, run to the toilet… (I guess they could just use the airsick bag, but who wouldn’t prefer to barf in private?) When the system gets full, it has to be purged, right? [/QUOTE] Right. But [according to the FAA](http://www.agl.faa.gov/AGLNews/HowDoesItWork/pdf/BlueIce.pdf), only when the plane is on the ground: > [@](#): > > It’s physically impossible for a pilot to dump a tank while in flight. That exterior lever means only the ground crew can operate the valve that opens the tank while the plane is on the ground. ---
**Author:** ![SiXSwordS](https://avatars.discourse-cdn.com/v4/letter/s/49beb7/32.png) [@SiXSwordS](https://boards.straightdope.com/u/SiXSwordS)\ **Post date:** [July 5, 2006, 8:26pm UTC](https://boards.straightdope.com/t/does-an-airplane-weigh-less-after-the-passengers-have-eaten-their-meals/363153/6 "2006-07-05T20:26:03Z")
[QUOTE=Fear Itself] Right. But [according to the FAA](http://www.agl.faa.gov/AGLNews/HowDoesItWork/pdf/BlueIce.pdf), only when the plane is on the ground: [/QUOTE] Granted, this is from 2003, but if you visit the link in my previous post, you’ll see that part of the issue is that some planes are fitted with different equipment. > [@](#): > > Airline forced to pay for dropping blue ice on boat ---
**Author:** ![SiXSwordS](https://avatars.discourse-cdn.com/v4/letter/s/49beb7/32.png) [@SiXSwordS](https://boards.straightdope.com/u/SiXSwordS)\ **Post date:** [July 5, 2006, 8:34pm UTC](https://boards.straightdope.com/t/does-an-airplane-weigh-less-after-the-passengers-have-eaten-their-meals/363153/7 "2006-07-05T20:34:14Z")
BTW, I really tried to post earlier, but couldn’t get on the boards. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [July 6, 2006, 3:07am UTC](https://boards.straightdope.com/t/does-an-airplane-weigh-less-after-the-passengers-have-eaten-their-meals/363153/8 "2006-07-06T03:07:51Z")
[QUOTE=SiXSwordS] Granted, this is from 2003, but if you visit the link in my previous post, you’ll see that part of the issue is that some planes are fitted with different equipment. [/QUOTE] But that different equipment merely reduces leaks in newer planes, leaks that allowed ice to form outside the plane. Nowhere did it say that older planes were able to intentionally dump the holding tanks in flight.