American Eagle Flight 4184

Infobox Airliner accident
name=American Eagle Flight 4184
Date=October 31 1994
Type=Loss of control
Site=near Roselawn, Indiana
Fatalities=68
Injuries=0
Aircraft Type=ATR 72-212
Operator=American Eagle Airlines
Tail Number=N401AM
Passengers=64
Crew=4
Survivors=0

American Eagle Flight 4184 was a regional airline flight that crashed after flying into known icing conditions on October 31, 1994. Control was lost and all aboard were killed.

History

The aircraft, N401AM, was an ATR 72-212 operated by Simmons Airlines on behalf of American Eagle (a subsidiary of the AMR Corporation). The flight was en route from Indianapolis International Airport, Indiana to O'Hare International Airport, Chicago, Illinois. Bad weather in Chicago caused delays, prompting air traffic control to hold Flight 4184 over the nearby [http://www.airnav.com/airspace/fix/LUCIT LUCIT intersection] at convert|10000|ft|m|abbr=on

While holding, the plane encountered freezing rain — a dangerous icing condition where supercooled droplets rapidly cause intense ice buildup. Soon after, they were cleared to descend to convert|8000|ft|m|abbr=on During this descent the aircraft experienced an uncommanded roll excursion, which disengaged the autopilot. Flight recorder data showed that it subsequently went through at least one full roll, and the crew was unable to regain control of the rapidly descending aircraft. Less than two minutes later, contact was lost as the plane impacted a soybean field near Roselawn, Indiana, killing all 64 passengers and 4 crew on board. The disintegration of the plane indicated an extreme velocity, and data recovered from the flight data recorder verified that the plane was traveling convert|375|kn|km/h indicated airspeed at impact [http://aviation-safety.net/database/record.php?id=19941031-1 ASN Aircraft accident description Aérospatiale/Aeritalia ATR-72-212 N401AM - Roselawn, IN ] ] .

Cause

The National Transportation Safety Board (NTSB) stated that the probable cause of this crash was the flight into known icing conditions, with the aircraft being operated outside its "icing certification envelope". While the ATR's deicing boots were able to remove ice along the leading edge, it rapidly re-formed "behind" the boots as "runback ice", where it could not be removed. This separated the airflow from the wing's surface and made the aileron control inadequate or non-existent. The ATR family of aircraft has had a history of known and reported control problems in icing conditions. For that reason, the NTSB also mentioned as contributing factors the "inadequate response" on part of the manufacturer and the French DGAC and United States' Federal Aviation Administration aviation authorities to these reports.

Aftermath

In the years following this accident, AMR Corporation stopped using its American Eagle ATRs out of their northern hubs and moved them to their southern and Caribbean hubs in Dallas, Texas; Miami, Florida and San Juan, Puerto Rico to alleviate potential icing problems in the future. Other U.S. ATR operators, particularly the SkyWest, Inc. subsidiary and Delta Connection operator Atlantic Southeast Airlines, continue to operate ATR-72 aircraft in areas where icing conditions are not common.

In April, 1996 the American FAA issued 18 Airworthiness Directives (ADs), in an apparent attempt to prevent further icing accidents in ATR aircraft. They included significant revisions of pilot operating procedures in icing conditions (higher minimum speeds, non-use of the autopilot, different upset recovery procedures) as well as physical changes to the coverage area of the de-icing boots on the airfoils.

While the ATR-42 and ATR-72 aircraft are now compliant with all icing condition requirements imposed by those 18 ADs, the de-icing boots still only reach back to 12.5% of the chord. Prior to the accident, they had extended only to 5% and 7%, respectively. They still fail to deal with the findings of the Boscombe-Down tests, conducted by the British, which demonstrated ice could form as far back on the wing as 23% of the chord, and on the tail at 30% of chord. Both percentages remain well beyond the limits of the extended deicing boots, installed in compliance with those FAA ADs.

Those tests limited the size of the droplets to 40 micrometres, near the maximum limit of the archaic FAA design certification rules for Transport Category aircraft (Part 25, Appendix C), still in effect at that time of the Roselawn crash. Extensive airborne testing, following that accident, revealed it is possible for airliners to encounter water droplets exceeding 200 micrometres in average diameter. [http://www.airlinesafety.com/letters/atr.htm]

It is likely that the lack of further ATR icing accidents is attributable to the changes in pilot operating procedures, as well as the moving of those aircraft to operating areas where severe icing is not a problem, rather than to the modest extension of the de-icer boots to 12.5% of the chord. [Unheeded Warning: The inside Story of American Eagle Flight 4184]

Dramatization

This crash was featured on the Discovery Channel program "The New Detectives" and in the theatrical production, "Charlie Victor Romeo".

Following the crash near Roselawn, longstanding problems with the ATR aircraft operating in some icing conditions were revealed by a Stephen Fredrick (a whistleblower later fired by the airline) in the book "Unheeded Warning - The Inside Story of American Eagle Flight 4184". The book was published in July, 1996 by McGraw-Hill. American Eagle has since phased out service using ATR aircraft in cold-weather areas, replacing the aircraft with regional jets. However, ATR-72 aircraft are still used for Caribbean operations from Miami and San Juan, Puerto Rico, where ice is not an issue.

References

External links

* [http://aviation-safety.net/database/record.php?id=19941031-1 Aviation Safety Network summary]
*PDF| [http://www.ntsb.gov/Publictn/1996/aar9601.pdf NTSB AAR-96/01 – detailed Aircraft Accident Report] |3.58 MiB , 340 pages)
*PDF| [http://www.ntsb.gov/Publictn/1996/aar9602.pdf NTSB AAR-96/02 – comments of Bureau Enquète-Accidents] |4.42 MiB , 341 pages)
* [http://www.planecrashinfo.com/1994/1994-71.htm PlaneCrashInfo.Com entry on Flight 4184]
* [http://www.tv.com/the-new-detectives/witness-to-terror/episode/530549/summary.html?tag=ep_list;title;9 Tv.Com - New Detectives: Witness to Terror (Details Flight 4184 investigation)]