Newsgroups: sci.aeronautics.airliners
From: rdd@cactus.org (Robert Dorsett)
Subject: Yet more on the El Al crash
Date: 14 Dec 92 14:11:42 PST

Today, I ran across a copy of a real, live, 747-200 Airplane Flight Manual.
The AFM is the manufacturer's legal statement of airplane capabilities; it
is custom-outfitted for each customer configuration, must be kept up to date,
and is kept in the actual airplane: it's the bottom line for normal
operations, , "outranking" even normal pilot Operations Manuals, which
present processed data, based on the AFM, in a more user-friendly format.

It contained some information which might be of interest to the net,
particularly given the impression some people seemed to have of the
ramifications of a two-engine failure.  I'm also referring to the AvLeak
of October 12 for particulars on the flight.

The manual describes a 747-200, with CF6-50E engines, which produce a
static thrust of ~52,000 lbs.  The El Al airplane was powered with JT9D-7J's,
which produce ~50,000 lbs of thrust).  So it's not entirely applicable to
the El Al crash, and I emphasize that the following is simply a "what-if,"
using the crash profile.  We'll use a basic operating weight empty of 170,000
kgs, and the actual cargo load of 114,000 kg and the fuel load of 70,000 kgs.
That gives us a gross weight of 354,000 kgs.

The crash airplane achieved a maximum altitude of 5000' at 285 knots.  It later
achieved a maximum airspeed of 313 knots at 4900'.  About six minutes after
the initial failure, the captain reported problems with flaps.  By the time
the plane had descended to 2900', 25 seconds later, the crew issued a mayday
call, indicating they were losing control; impact was 45 seconds after that.
The slowest airspeed the airplane attained was 260 knots or so.

The AFM gives some information that wasn't available during the original
discussion.

Such as:

    - 2-engine operation is *certainly* an in-envelope contingency.
    - It is possible to maintain altitude at up to 360,000 kgs.

Some numbers.  Draw your own conclusions: again, we're talking a different
airplane, with different thrust capabilities.

1.  Placarded flap speed limits.  We can assume that if the crash airplane
was following these limits, it was at flaps-up by the time the failure
occurred.

    1    275 knots
    5    250 knots
    10   238 knots
    20   231 knots
    25   205 knots

2.  Gear-up stall speeds at 355,000 kgs:

    Flaps    Speed
    1        203 knots
    5        153 knots
    10       150 knots
    20       144 knots

    25       124 knots (landing flaps: assumes weight is down to 295,000 kgs).

3.  At 355,000 kgs, *with two engines out*, our -200 would have been able
to maintain level flight.  It should also have been able to establish a climb
gradient of 0.4% (175 ft./min) at 280 knots, the prescribed en route climb
speed for this condition.




---
Robert Dorsett
rdd@cactus.org
...cs.utexas.edu!cactus.org!rdd

Newsgroups: sci.aeronautics.airliners
From: gregory@bcstec.ca.boeing.com (Greg Wright)
Subject: Re: Boeing fuse pin revisited
Date: 08 Jul 93 01:28:00 PDT

In article <airliners.1993.490@ohare.Chicago.COM> rdd@cactus.org (Robert
Dorsett) writes:

>It does contain an interesting note, though, that Airbus apparently doesn't
>believe in "break-away" engines (the fuse pins installed on Boeing airplanes
>are there to permit the engine to shear away following substantial engine
>vibration, on the theory that it's better to drop an engine than risk damage
>to the airframe or wing).  "If an Airbus crash-lands, the plane can even skid
>on its engines without their falling off."

The main reason for the "Break-Away" engines was to keep the engines from
rupturing the fuel cells in the wing in the event of a crash landing.

>An issue of Aviation Week & Space Technology reported earlier this year that
>Boeing had found the problem was that Boeing had underestimated shear forces
>in one part of the assembly by 1000% or so.

It wasn't really underestimated, more like we found 'hidden' forces. In a
new FE analysis of the part on a new generation of computers it was found
that there existed very small areas of very high forces.  In the past it
was to computationally intensive to find these.

--
 ________Greg Wright________    OS2 2.1!!!!     High Lift Development
| gregory@bcstec.boeing.com |   Falcon 3.0      747/767 Aerodynamics
|    gregory@halcyon.com    |
|__uunet!bcstec!gregory_____|      NOT A BOEING SPOKESPERSON.