Yet more on the El Al crash

From:         rdd@cactus.org (Robert Dorsett)
Date:         14 Dec 92 14:11:42 PST
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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