layman's aviation questions

ongarboy

Hi all, sorry if these are really obvious questions to the more informed aviation experts among you but I was reading an article the other day about a passenger who took ill on a transatlantic flight and the plane had to return to Ireland for emergency medical attention fr the passenger. The article said the plane had to dump 1000s of gallons of fuel into the ocean but didn't explain why.

2 questions: Why did it have to dump the fuel and secondly if the plane was over land would it still be able to dump fuel? (ie would 1000s of gallons of fuel falling over a populated area not pose a hazard?)

Sterling Archer

1. They have to dump fuel, otherwise they would be overweight to land
2. No generally there sent out over the sea to dump fuel

lord lucan

It has to dump fuel in oder to get the weight of the aircraft down basically. If it didn't it'd risk being far too heavy to land safely.

Fuel dumps are preferable over water but have been known over land. Usually if it's over land it'll be at a very high altitude so most of the fuel thins out as it falls.

CaptainSkidmark

if its at 30,000 feet it would be after vaporising by the time it got to ground so sometimes it does it above ground like if your half way across russia

lord lucan

CaptainSkidmark wrote: »

if its at 30,000 feet it would be after vaporising by the time it got to ground so sometimes it does it above ground like if your half way across russia

There was a lot of it iirc on 9/11 when the FAA grounded all aircraft over continental USA. Many would've been well inland and nowhere near the coasts so would've had to dump at high altitude over land.

CaptainSkidmark

iirc?

helimachoptor

CaptainSkidmark wrote: »

iirc?

if i recall correctly

xflyer

As the others said. Essentially an aircraft can take off safely with more weight than it can safely land with. Overweight landings do happen but are to be avoided because of the risks. Also for example, a runway may be too short for the aircraft to either safely or legally land at the weight. So fuel must be dumped.

A320

and of course risking damage to the landing gears

ongarboy

thanks everyone for your responses - interesting to know!

Quaderno

...and while many people think that it must be a huge waste to dump tons of perfectly good fuel, it is actually not.
The ability to shed weight for an unplanned landing allows for much lighter planes, which in turn save a lot of fuel every time they take to the sky. If they couldn't dump fuel in those relatively rare cases they would need much heavier undercarriages and an overall sturdier and therefore much heavier structure.
Short-haul aircraft (like the very common Boeing 737 and Airbus A320 series) don't carry as much fuel and so the weight difference between the empty and the fully fuelled plane is not as big. So they don't need (and are not able) to dump fuel but rather have to burn it before landing or simply land overweight.

Quaderno

lord lucan wrote: »

Fuel dumps are preferable over water but have been known over land. Usually if it's over land it'll be at a very high altitude so most of the fuel thins out as it falls.

And then there is a third way to get rid of the fuel:
http://www.youtube.com/watch?v=a2L7WP8MAzo&feature=fvwrel

Steyr

Quaderno wrote: »

And then there WAS a third way to get rid of the fuel:
http://www.youtube.com/watch?v=a2L7WP8MAzo&feature=fvwrel

Fixed for you.

Fratton Fred

I thought this thread was going to answer the real burning question of commercial aviation, namely, why do airlines serve warm beer and cold red wine, why don't they swap them around?

Oh well, I guess these were kind of burning questions as well.:)

castie

Flew on Virgan Atlantic London - Sydney Aircraft: 346
and also Singapore Airlines London - Sydney Aircraft A380

For Virgin they turned off the AVOD system for takeoff.
For Singapirore Airlines they left it on.

Any particular reason for the difference?
Is it a system/aircraft difference or just procedural?

Tenger

castie wrote: »

For Virgin they turned off the AVOD system for takeoff.
For Singapirore Airlines they left it on.

Any particular reason for the difference?
Is it a system/aircraft difference or just procedural?

I would guess it is an airline procedure. They want you to be able to hear any commands at this time rather than distracted by watching the screen with earphones in.....

EDIT: Well asking you not to keep earphones in is an acknowledgement that you must be able to hear any spoken commands.
By 'commands' I mean the crew shouting at you to evacuate the aircraft. Evac commands are not normally given over the PA, it may not be working in an incident.
In relation to the 'no earphones' rule perhaps VS decide not to take the chance and thus have it off to ensure no-one ignores that request(which is actually an order)

castie

Tenger wrote: »

I would guess it is an airline procedure. They want you to be able to hear any commands at this time rather than distracted by watching the screen with earphones in.....

They ask you not to have the earphones in
Also announcements coem through that system too.