Re: 747 forced ocean landings -- survival odds

From:         drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Organization: Boeing Commercial Airplane Group
Date:         03 Jan 95 01:40:41 
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In article <airliners.1994.1793@ohare.chicago.com>,
Pete Mellor  <pm@csr.city.ac.uk> wrote:
>> There's a blazing discussion underway in rec.aviation.misc about
>> forced ocean landings of 747s.  At issue are the odds of the plane
>> staying in one piece, how long it would stay afloat and whether it
>> would begin to leak through hull weep holes or other openings,
>> whether or not passengers would be better off remaining in the cabin
>> or proceeding to life rafts, etc, etc.

A quick answer:  The airplane fuselage is likely to remain in one piece.
The engines will likely be shed.  The landing *will* be violent.  The
aircraft will sink after some amount of time, even in calm waters
(something over 10 hours I think, but I don't have a reference handy).  The
passengers are very definitely better off in the raft.

Hi Peter!

>A few thoughts:- 
>
>The hull is designed to withstand positive pressure *inside*. Once under 
>water (assuming it would sink *before* the water filled the cabin), every 
>device for keeping pressure *in* would work "the wrong way round". (The 
>plug doors would be forced open by the external pressure, for example.) 
>If passengers donned life-jackets, they could presumably bob up to the 
>surface, *provided they could get out of the doors against a rush of 
>incoming water*. (Not a cheerful survival prospect, IMHO.) 

Actually, the doors aren't likely to leak (take a look at the latching
mechanism next time you get the opportunity.  The drain masts on the
ventral side of the aircraft may well leak, but they are quite small and
the airplane is a very light vehicle compared to the volume it displaces,
giving it good endurance in that sort of condition.
>
>The main question is, how long would it float? I have not flown on a 747 
>recently, but I did fly on a 737-400 last week. The safety card shows the 
>aircraft floating on the water after ditching, with the passengers sitting 
>calmly on the wings in their life-jackets after making an exit through the 
>over-wing doors. I was sufficiently surprised the first time I saw this to 
>ask one of the cabin staff if the 737-400 really was designed to float, but 
>I didn't get a particularly authoritative answer. 

Yep, it will float.  For quite a while, too, assuming no extreme damage to
the skin panels.
>
>> Would someone with knowledge of this issue please make a posting
>> to rec.aviation.misc and share some insight?
>
>Please feel free to repost this, if you think it is useful. I would be 
>interested in any opinions on the 737's qualities as a flying boat! 

Actually, all of Boeing's airplanes are designed with ditching in mind.  On
the New Large Airplane, it caused us to put several extra life rafts up
forward (most, if not all, jets tend to float nose up).  Our aft doors on
the main deck would let water in if opened.

There are two schools of thought on designing for ditching.  One says that
we need to take every possible precaution to protect our final customers,
the passengers (this is a very conservative group, by and large).  The
other group says, "Hey, there is only *one* recorded instance of a jetliner
deliberately ditching (a DC-9 in the Virgin Islands, if memory serves) so
why burden the design with these sorts of Neaderthalian requirements?"  For
one thing, it eliminates high-wing configurations from study because of
their notoriously bad ditching characteristics.

Terry

-- 
Terry
drinkard@bcstec.ca.boeing.com
"Anyone who thinks they can hold the company responsible for what I say has
more lawyers than sense."