The Crash of American Airlines 587:
Accident or Terrorism?
It isn't any wonder so many fear this tragedy to be yet another act of
terrorism straight from the evil mind of Osama Bin Laden.
However, what we know so far doesn't seem to add up to the kind of crash
that would be produced by a deliberate act of sabotage.
All airliners are design-certified to be able to continue to climb, at maximum certified
gross weight and at the most critical time in the takeoff profile, in the event of
loss of power from one engine.
Then, why did that plane crash?
Witnesses were said to have seen smoke and flames trailing from one
engine, and finally observing that engine fall off, shortly before the crash. In addition, a loud
"explosion" sound was also reported by ground witnesses, prior to the crash.
That led to initial speculation that engine failure was the cause of
When thrust is lost from one engine, the pilot must quickly act by
pushing in the rudder and rolling in aileron, towards the side of the
remaining good engine. If a pilot fails to respond in that manner, the
plane would roll upside down and total control would quickly be
The rudder is attached to the trailing edge of the vertical
stabilizer. When a vertical stabilizer breaks free from a plane, the
rudder goes with it. At that point, the only way a pilot could
prevent the plane from rolling over on its back, is by retarding the
throttle on the remaining good engine. With the power from that
good engine no longer available to the pilot, he would have no choice but to
descend towards mother earth. If he tried to arrest that descent,
by pushing the throttle forward again, the plane would start to roll,
because the rudder was gone. Caught between a rock and a hard
place, a pilot could only try to extend his glide to a
certain crash, by advancing the thrust lever no more than his limited
aileron roll control would permit.
One thing is very certain: That if the
theory--- that an engine had a massive internal failure---had been
accurate, the plane was doomed to go
down once the pilot lost the stabilizer/rudder control. At that
point, the power of the remaining engine would have been not only useless, it
would have then
became a force of liability, determined to roll the plane upside down
and out of control, if that power wasn't promptly retarded.
However, now that we know neither engine had such a failure, we need to
examine other possible reasons for the in-flight breakup of AMR 587.
Pictures of the vertical stabilizer, as it was lifted from Jamaica
Bay, revealed a very clean break at the bottom edge, where it had been
bolted to the fuselage. It looked pristine, as if it was being
moved from a production line to be mated to a new production
fuselage. Without any visible damage to that stabilizer, one could
not reasonably conclude it had been ripped away by physical contact with
other parts flying off the plane. Neither would that pristine
condition allow for a terrorist bomb inside of the fuselage, as a
sensible explanation. The "black boxes" (CVR and FDR)
were found in the main crash site area, indicating the rest of the tail
section, below the departed vertical stabilizer/rudder, remained attached
to the fuselage. That would tend to indicate a bomb was not the cause of
the stabilizer/rudder separation from the fuselage.
The latest information:
a) There was no internal failure of either
b) Both engines separated from the plane prior to
c) The cockpit voice recorder (CVR) recorded a
"rattling" noise and the pilots commented about it being
"wake" turbulence. That means, they thought the noise
(and whatever vibration and shaking they might have been experiencing at
the same time) was caused by the wake left from the airplane that had
taken off ahead of them. Then, a second rattling sound was heard
by the pilots, one minute and 21 seconds after the start of the takeoff
roll. At 1+25, the First Officer called for "max
power." Control of the plane began to be lost at that
point. It rolled over and dove, nose-first, into the ground
d) The vertical stabilizer (and the rudder that was attached to
the trailing edge of that stabilizer) broke off the plane, probably
before the engines broke free.
What could have caused that stabilizer/rudder section to
separate? One possible explanation would be a severe
horizontal gust load. That means a horizontal wind hit the
side of that stabilizer with a force so strong that it exceeded the
strength and ability of that structure to withstand such a force.
That kind of force could be produced by a very rapid and severe
yawing motion (the tail suddenly moves sideways). Had the theory
of a sudden and catastrophic failure of one engine been accurate, then
one could also reasonably suspect that the forward thrust of that failed engine
might have not only
suddenly been eliminated, but there could also have been a reversed flow of
thrust, if the giant compressor, in the front section of that engine,
had stalled. Such a compressor stall would sound like an explosion, to
witnesses on the ground. However, the CVR did not
record any such explosive sound.
In theory, the airplane should be able to withstand a sudden yaw, yet
it is well known that severe and dangerous horizontal gust loads can be
imposed on vertical stabilizers under some flight conditions. That
is why they have computer monitoring of airspeed so as to reduce the
limit of rudder movement, on modern airliners: because
structural limits of the vertical stabilizer can be exceeded if the
rudder throw is too great when accompanied by a severe side loading.
It will take a very lengthy investigation to determine why that
vertical stabilizer failed.
The presence of corroded and/or
cracked structure bolts, reducing the total load limit strength, is one
possibility. Improper maintenance procedures and/or defective
design, another. Or, something might have gone wrong with the
rudder itself. Could a malfunction in the rudder computer control
system have caused the rudder to start moving rapidly from side to
side? I don't know if that is possible, but if that
actually happened, it could have imposed heavy side loads on the
vertical stabilizer to such an extent that design strength limits were
exceeded. If one of the attach bolts, which attached the rudder to
the trailing edge of the vertical stabilizer, broke, that might have
caused the rudder to start flopping rapidly as if in a dangerous flutter
mode. It is well known that flutter, if it develops on any tail
control surface, can lead to in-flight breakup in a matter of
If the catastrophic failure of the vertical stabilizer/rudder section
occurred first, it could have been the cause of the engines falling
off. If sudden yawing movements (sideways motion) was part of the
process of the failure of the stabilizer/rudder, then excessive loads
likely were imposed on the 3 shear pins that attach each engine to its
respective pylon. Those pins are designed to shear, in the event
of a massive engine breakup, allowing the engine to fall away from the
plane before it can destroy the wing.
It now seems the failure of the stabilizer/rudder is the key to
analyzing the causal factors in this accident. Could it have been
an act of sabotage? Nothing can be ruled out at this early stage
of the investigation, but I see that to be a very remote
possibility. Human failure in the design, operation, or maintenance of
the airplane is much more likely.
November 14, 2001
Robert J. Boser
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The Editor of this Web Page, now retired, was an
airline pilot for 33 years and holds 6 specific Captain's type-ratings
on Boeing Jet Airliners.