Loss of Tailfin the Focus of Crash Probe

Air Safety Week, Nov 19, 2001

Role of wake turbulence in disaster debated

Separation of the tail, and why it broke off, followed by separation of both engines, is likely to be the main focus of the investigation now under way into the November 12 crash of an American Airlines [AMR] twinjet. All 260 aboard and at least five on the ground were killed.

The crash of the 13-year old Airbus A300 Model B4-605R is not the first in which tail and engines have broken off in flight. But it is a rare occurrence. The catastrophic sequence of events left the flight crew with no options as the plane plunged to its doom just 3 minutes after a 9:14 a.m. takeoff from New York's John F. Kennedy International Airport (JFK) on a flight to Santo Domingo, Dominican Republic.

Portions of the airplane wreckage fell into four distinct places - the tail into the waters of Jamaica Bay, the engines into two locations about a block apart, and the main impact area about a quarter mile away from the engines.

It is not the first time a transport-category aircraft has lost its tail and/or engines. ASW Contributing Editor Rudy Kapustin recalled a 1966 accident involving a British Overseas Airways Corporation (BOAC) B707. The captain had requested a modification to the flight plan to allow his passengers a rare close-up view of Japan's Mt. Fuji.

Descending closer to this prominent landmark, the airplane flew into turbulence. The loads imposed by the turbulence, along with pre-existing metallurgical weakness from fatigue, were enough to cause the empennage section to separate, followed by the outer panel of the starboard wing and departure of all four engines. All 124 aboard were killed. A helicopter sent to search for the wreckage encountered severe turbulence.

In 1959 a B707 operating on a customer acceptance and training flight shed its number 1, 2 and 4 engines during the performance and subsequent "Dutch roll" maneuvers where one of the rolls exceeded maximum bank angle restrictions. Four of the eight crewmembers were killed during the emergency landing.

In 1964 a U.S. Air Force B-52 encountered moderate turbulence and lost a major chunk of its vertical stabilizer and, in this fortunate case, was able to make an emergency landing.

The one-two punch of suicide hijackings September 11 and the crash last week seems likely to further fuel potential passengers' anxieties about the safety of air travel. The Flight 587 disaster may come at precisely the wrong time for the industry. Prior to the crash, one would have dismissed the likelihood of a jetliner taking off out of JFK, flying normally on climb-out and just falling to pieces in a few seconds. The flying public may not find much comfort in the thought that wake turbulence could cause catastrophic failure at low speed, low altitude, and in non-maneuvering flight. Peoples' perceptions are shaped by images - in this case of a broken tail being hoisted dripping out of the water.

Coming just two months and a day after the September 11 hijackings, the possibility of a terrorist attack clearly was in the air. Officials were quick to discount a bomb or hijacking scenario, declaring that an accident investigation is now under way into the crash of American Flight 587. However, agents from the Federal Bureau of Investigation (FBI) are conducting a probe into the possibility of sabotage, and the wreckage is being combed for traces of explosives. As the saying goes, "theories thrive where data is lacking," and numerous scenarios have been raised about the cause of the crash.

The known details

However, this much can be said with confidence. The tail separated from the airplane first. The engines, their mounts subjected to high side loads, ripped off, and the rest of the airplane plunged into the Belle Harbor residential area seaward of JFK.

The accident airplane had been following a Japan Air Lines (JAL) B747 by some 90 seconds, according to the latest reports. The prescribed time is reported to be two minutes. Pending detailed analysis of the radar tracking tapes, the actual distance between the two airplanes will not be known. The vertical and horizontal separation between them is of paramount importance in the analysis of the possible strength and effect of the trailing vortexes from the B747. Wind velocity and direction is also of great importance in making this assessment.

The sequence of events revealed the speed with which the anticipated routine flight turned to catastrophe:

Time: 9:14 a.m
Elapsed Time: .  0
Event: Flight 587 takes off, approximately 1 min. 45 seconds after the JAL B747

began its takeoff roll. Throughout the flight of AA 587, the horizontal
distance
between the two planes was estimated at 4.0-4.3 miles. The JAL jet was about
800
feet higher, generally speaking.

Time: 9:15:47
Elapsed Time: 1 min. 47 secs.
Event: Sound of "shaking" or rattling from fuselage picked up on cockpit voice
recorder (CVR). (ASW: first wake encounter)

Time  : 9:15:54
Elapsed Time  : 1 min. 54 secs.
Event: 7 seconds after shaking sound, CVR picks up Capt. Edward States comments

about wake turbulence from the jet ahead.

Time: 9:15:56
Elapsed Time: 1 min. 56 secs.
Event: Flight data recorder (FDR) begins to show aircraft movement "consistent
with wake encounter." The plane responds normally at first. Then come three
side
acceleration excursions.

Time: 9:16:01
Elapsed Time: 2 min. 1 sec.
Event: A few seconds later, rattling noise heard again, quickly followed by
voice of First Officer Sten Molin, who was flying the takeoff, calling for more

power.

Time: 9:16:06
Elapsed Time: 2 min. 6 secs.
Event: Rudder position data becomes unreliable. More side acceleration
excursions. First a 0.3 G excursion in one direction, than a 0.4 G excursion in

the same direction, then a 0.3 G excursion in the opposite direction (ASW:
tailfin oscillation or flutter?). Over the next couple of seconds the airplane
undergoes dramatic course changes. Bank angle increases through 25? with the
left wing down. Pitch drops to 30? nose down. (ASW: tail detached, as suggested

by cessation of drumming noise and suddenly ineffectual rudder pedals).

Time: 9:16:08
Elapsed Time: 2 min. 7 secs.
Event: Several comments from crew suggesting loss of control

Time: 9:16:25
Elapsed Time: 2 min. 24 secs
Event: 17 seconds later CVR ends (possibly from loss of electrical power when
the engines separated).

Time: 9:17
Elapsed Time: 3 min
Event: ATC loses radio and radar contact. Witnesses report jet on fire
(streaming flaming fuel from severed fuel lines) in spiraling dive.