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Wednesday, 14 November, 2001, 17:12 GMT
Puzzling clues about jet's final moments
Tail fin of Airbus
What caused the tail fin to break off?
By BBC News Online's Peter Gould

The crash of Flight 587 continues to raise more questions than answers.

The latest clues, provided by the two "black boxes" recovered from the wreckage of the Airbus, have shed some light on the plane's final moments.

At this early stage, the National Transportation Safety Board is understandably reluctant to provide a definitive verdict on the competing theories put forward to explain the disaster.


There are several comments suggesting loss of control of the aircraft at 127 seconds after the take-off roll

George Black
NTSB investigator

But so far at least, investigators have found nothing that points to terrorism, and early speculation about a problem with one of the plane's two engines is now being discounted.

George Black, of the NTSB, told a news conference: "Initial inspection shows no evidence of any sort of internal failure of the engines. They appear to be in one piece."

Startling

The US Federal Aviation Administration recently raised safety concerns over the CF6 engine used to power the American Airlines plane and many other aircraft around the world. But the manufacturers, General Electric, say it is "phenomenally reliable".

Wreckage of engine
No sign of any internal damage to the engines
Also apparently ruled out is the possibility that the airliner flew into a flock of birds as it was climbing out of JFK airport.

Even a single bird ingested into a jet engine can cause enormous damage, and there was speculation that this might have caused Flight 587 to lose power at a critical moment.

But crash investigators have yet to explain one startling discovery. The aircraft's vertical stabiliser, or tail fin, was found in the waters of Jamaica Bay, half a mile from the main crash site.

Remarkably, the fin appeared virtually intact, raising questions about how it became detached from the fuselage of the plane. Investigators will be looking very closely at the bolts that held it in place on the tail of the A300.

What is clear is that without the vertical stabiliser, the pilots would have found it impossible to control the aircraft, making the crash inevitable.

Catastrophic

But was the loss of the tail fin the primary cause of the crash? Or was it part of a sequence of events that resulted in the aircraft falling out of the sky?

Final moments of Flight 587
107 seconds after take-off begins: Rattling noise heard by pilots
114 seconds: Captain reports "wake encounter"
121 seconds: Second airframe rattling sound
127 seconds: Control of the plane is lost
144 seconds: Recording ends as plane crashes

Whatever happened to Flight 587 was sudden and catastrophic. The wreckage of the aircraft was scattered over a wide area. Apart from the fin, one or both engines were ripped off the wings before the impact.

The cockpit voice recorder shows that an apparently routine take-off turned into disaster in little more than two minutes.

On the tape a loud rattling sound is heard, apparently coming from the airframe. After the noise begins a second time, the co-pilot asks for full power. But within seconds, the crew lose control and the jet dives into the ground.

One comment from the flight deck raises another possible factor. Between the rattling noises, the captain reports a "wake encounter".

Disturbing

This is a term used by pilots to refer to air turbulence caused by another aircraft. In this case, the disturbance in the airflow appears to have been caused by a Boeing 747 taking off from JFK shortly before Flight 587.

Wreckage of Flight 587
All the wreckage will be closely examined for clues
The potential threat to all airliners means that air traffic controllers always try to keep a minimum distance between planes taking off and landing, particularly when the preceding aircraft is a "heavy" like a jumbo jet.

Could turbulence have caused the crew of the American Airlines plane to lose control, stressing the airframe beyond its limits?

Now that crash investigators have recovered the flight data recorder, they should have a picture of all the aircraft's systems, and the actions taken by the crew as they fought in vain to save the plane.

It is a perplexing case, but one that demands an explanation as quickly as possible.

Although it will be a relief if terrorism is firmly ruled out, the loss of Flight 587 still raises disturbing questions.

 WATCH/LISTEN
 ON THIS STORY
The BBC's Nick Higham
"Increasingly the investigation is focusing on the plane's tail section"
Marion Blakely, Chairwoman, NTSB
"We are launching a major investigation"
Aviation industry analyst Robert Hewson
"Inside the engines they'll be looking for signs of damage"

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