Author Topic: Question about big passenger planes (Boing/Airbus) (Read 381 times)

Naudet · « **on:** August 02, 2002, 02:19:40 AM »

OK i know it's a little offtopic, but still fits to the "aircraft" section.

A friend of mine made a guided tour through an airport. And the guide told that the gear of modern passenger planes (Boings & Airbuses) are not able to withstand a landing of a fully loaded passenger plane.
The guide further explained that this is the reason why - in case of an emergency - the plane has to dump most of it fuel in the air.

I am a little bit supicious now.
I always thought the fuel dumping was due to the fire risk if a fully loaded jet has to make a "non-standard" landing.
I can not believe that the gear of modern jets is not lay out for the full take-off weight.
So can someone here answer this question:
Is the gear of modern passengers jets strong enough to withstand the landing forces of a fully loaded condition?

Seeker · « **Reply #1 on:** August 02, 2002, 02:48:16 AM »

It's absolutly normal that max take off wieght is more than max landing weight; and it's always been that way....

Take off doesn't stress the gear nearly as much as landing (even if it's a good 'un

) ; and it's a given you'll be burning fuel (and therefore lightening the structure) as soon as the engines roll.

Reschke · « **Reply #2 on:** August 02, 2002, 07:36:55 AM »

Well I remember hearing something about the weight of a fully fueled and loaded 747 being somewhere near 1,000,000 pounds. That is a hell of a load coming down on the gear on landing if it has to happen.

whgates3 · « **Reply #3 on:** August 02, 2002, 07:54:48 AM »

i was on a PDX to Dulles flight a few months ago that had to land about 20 min after takeoff (at PDX) - if the fuel was dumped it was over a heavily populated area - & the refueling time was under 15 min...

HFMudd · « **Reply #4 on:** August 02, 2002, 09:18:49 AM »

Boeing 747-400:

Max Fuel Capacity: 57,285 US Gallons
Max Takeoff Weight: 875,000 lb

FTJR · « **Reply #5 on:** August 02, 2002, 09:40:20 AM »

Large Commercial jet aircraft do have takeoff weights far in excess of their landing weights.

For example the B767-300 ( i flew it for 6 years) has a takeoff weight of 186 000 Kg's but a landing weight of 145 000 kgs. In a lot of cases we could only dump around 36000 kgs of fuel from the centre tank so if we had a problem for over-weight landings. BUT this required an inspection after landing. The aeroplane WILL NOT BREAK.

As to dumping if you climb to over 6000 feet above the ground the fuel will disapate enough so as not to affect the people below. Obviously we would avoid built up areas and try to climb higher, but that would depend on the emergency.

Hope this answers your questions.

Naudet · « **Reply #6 on:** August 02, 2002, 10:07:27 AM »

But would the gear even withstand the stress in a worst case scenario?
Such as you take-off, something goes wrong and you must touch down, Minutes or so after take-off, without the chance of dumping fuel.

Actually the question is if an overweight landing with nearly full fuel load will not break the gear? (i.e. your 767-300 has to land at say 182 000 kg)

Shiva · « **Reply #7 on:** August 02, 2002, 10:52:11 AM »

The Navy's F-14 has the same 'problem'; if you shoot off a carrier with a full warload of Phoenix missiles (six), the aircraft isn't rated for a carrier landing with that load, so you've got to dump two $1,000,000 missiles into the water before they'll let you back on the CV.

Obviously, they don't hang six Phoenixes on the birds for normal operations.

FTJR · « **Reply #8 on:** August 03, 2002, 10:09:36 AM »

Returning for an immediate overweight landing is an extreme emergency situation.

Therefore the priority is it to get it on the ground and evacuate the people as quickly as possible.

A normal landing force (that is- the rate of descent on touchdown) even at 186000 kgs would not cause the aeroplane to break in two or more pieces if thats what your question is.

It may not fly again but unless the pilot in his haste bangs it on the ground it *should* remain intact ( unless a fire has weakened the metal.. thats outside my knowledge)

mora · « **Reply #9 on:** August 03, 2002, 01:57:12 PM »

Quote

Originally posted by Naudet
But would the gear even withstand the stress in a worst case scenario?

As FTJR said it probably would but the plane would need some maintenance after that kind of landing. Some planes cant even dump fuel, DC-9 series comes to mind.

doug69 · « **Reply #10 on:** August 03, 2002, 03:16:35 PM »

Was in Atlanta and our 767 had two faulty lavs. They switched us to an alternate aircraft. However, it was fueled for a flight to the west coast instead of our hop to Orlando. We had to sit on ramp for ~1 hour while the plane was defueled (only 1 truck set up for that service) so we would be under max landing wieght on arrival.

Interesting fact...the fuel that was removed is considered contaminated and can not be loaded onto another a/c until it goes through a treatment facility.

funkedup · « **Reply #11 on:** August 03, 2002, 11:08:21 PM »

Naudet it comes down to metal fatigue. You might be able to land the jet once with the full load, but will it land safe the second time, or the 10th time or 20th time? The more times the plane lands with overload, the shorter the life of the airframe will be. So to maintain the full life of the expensive airframe they will dump all of the relatively inexpensive fuel. And jet fuel won't burn too easily in the air. Compared to gasoline it's pretty safe.

BTW ultimate load (load which will fail some part of the airframe) is usually 1.5 times the design limit load (maximum permitted load).

Naudet · « **Reply #12 on:** August 04, 2002, 02:38:55 AM »

Thx a lot all.

Those answers helped.