Aerial view of the crash site
|Date||October 31, 1994|
|Summary||Atmospheric icing leading to loss of control|
|Site||Near Roselawn, Indiana, U.S. |
|Aircraft type||ATR 72–212|
|Operator||Simmons Airlines for American Eagle|
|Flight origin||Indianapolis International Airport|
|Destination||O'Hare International Airport|
American Eagle Flight 4184 was a scheduled domestic passenger flight from Indianapolis, Indiana to Chicago, Illinois, United States. On October 31, 1994, the ATR 72 performing this route flew into severe icing conditions, lost control and crashed into a field. All 68 people aboard were killed in the high-speed impact.
The aircraft involved, registration N401AM, was built by the French-Italian aircraft manufacturer ATR and was powered by two Pratt & Whitney Canada PW127 turbo-prop engines. It made its first flight on March 7, 1994, and was delivered to American Eagle on March 24, 1994. It was operated by Simmons Airlines on behalf of American Eagle.:1 American Eagle was the banner carrier regional airline branding program of AMR Corporation's regional system, prior to the formation of the fully certificated carrier named American Eagle Airlines.
The captain of Flight 4184 was Orlando Aguilar, 29. He was an experienced pilot with almost 8,000 hours of flight time, including 1,548 hours in the ATR.:13 Colleagues described Aguilar's flying skills in positive terms and commented on the relaxed cockpit atmosphere that he promoted.:13 The first officer was Jeffrey Gagliano, 30. He was also considered to be a competent pilot by colleagues and he had accumulated more than 5,000 flight hours, of which 3,657 hours in the ATR.:14 The two flight attendants were 27-year-old Sandi Modaff, and 23-year-old Amanda Holberg, who was working her first day as a flight attendant with American Eagle.
Weather conditions in the area of Roselawn, Indiana, were recorded by National Weather Service. The summary showed a low pressure center in the area of west central Indiana, and "…cloud ceilings of less than 1,000 feet and/or visibilities of less than 3 miles, in rain,…" occurring in northern Indiana at 1600 local time. A cold front also extended from the low pressure center in a southwesterly direction. The surface temperature of the accident site was reported of 7 degrees Celsius.
The National Weather Service's analysis indicated a low pressure area whose center located in west central Indiana at 1800. The temperatures in the area where Flight 4184 was, were reported near 3 degrees Celsius with moisture evident. Temperatures were near minus 4 degrees Celsius with moisture evident in northern Indiana.
The weather conditions provided by Lowell Airport, which is located about 12 nautical miles northwest of the accident site, indicated broken clouds at 1,400 ft, overcast at 3,000 ft, gusty winds from southwest at 20 knots, with light drizzle falling. However, the report observation was made about 30 minutes after the accident.:17
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 LUCIT intersection at 10,000 ft (3,000 m). 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 8,000 ft (2,400 m). After this descent the pilots were ordered to enter another hold. During the descent, a sound indicating an overspeed warning due to the extended flaps was heard in the cockpit. After the pilot took action by retracting the flaps, a strange noise was heard on the cockpit voice recorder, followed by a sharp, uncommanded roll excursion that disengaged the autopilot. Flight recorder data showed that the aircraft subsequently went through at least one full roll, after which Aguilar and Gagliano regained control of the rapidly descending aircraft. However, another roll occurred shortly after as they engaged the autopilot again. This second occurrence was unrecoverable, and fewer than thirty seconds later, at 3:59 p.m., contact with Flight 4184 was lost as the plane crashed nose-down into a soybean field near Roselawn, Indiana, killing all 64 passengers and 4 crew on board.
The disintegration of the plane indicated extreme velocity, and data recovered from the flight data recorder showed that the plane had an indicated airspeed of 375 kn (694 km/h; 432 mph) at impact. There was no fire. The bodies of all on board were fragmented by the impact forces; therefore, the crash site was declared a biohazard.:73
Flight 4184 was the first loss and also the highest death toll of any aviation accident involving an ATR 72 aircraft. Sixteen years later, Aero Caribbean Flight 883 crashed into a high range of terrain, also due to icing conditions, resulting in the same number of fatalities.
As is customary in these reports, the National Transportation Safety Board (NTSB) issued a statement of "probable cause" near the end of its report. The probable cause statement in this report was considerably longer than is typical. The NTSB found that ATR (the manufacturer of that aircraft), the French Directorate General for Civil Aviation (the French counterpart of the American FAA), and the FAA itself had each contributed to that accident, because each had failed in its duty to ensure the highest possible level of safety to the traveling public.
The unabridged NTSB "probable cause" statement reads:
In March 1995, some families of the victims discovered remains of their loved ones on the accident site, giving rise to a suspicion that cleanup efforts were not thorough. In a statement, the Newton County coroner - referring to other comments made - said he was not surprised there were remains left, given how serious the accident was.
In April 1996 the FAA issued 18 Airworthiness Directives (ADs) affecting 29 turboprop aircraft which had the combination of unpowered flight controls, pneumatic deicing boots and NACA "five-digit sharp-stall" airfoils. 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.
In the years following this accident, AMR Corporation stopped using its American Eagle ATRs out of its northern hubs and moved them to its southern and Caribbean hubs at Dallas-Fort Worth International Airport, Miami, Florida, and San Juan, Puerto Rico, to reduce potential icing problems in the future. Other U.S. former ATR operators, particularly the SkyWest, Inc., subsidiary and Delta Connection operator Atlantic Southeast Airlines, operated ATR 72 aircraft in areas where icing conditions were not common.
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. Robert Boser believes the ADs still fail to deal with the findings of tests conducted by British regulators at MoD Boscombe Down, which demonstrated that ice could form as far back on the wing as 23% of the chord, and on the tail at 30% of the chord. Both percentages are well beyond the reach of the extended deicing boots installed in compliance with the FAA ADs. Those tests limited the size of the droplets to 40 micrometres, near the maximum limit of the 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 the accident revealed that airliners can encounter water droplets exceeding 200 micrometers in average diameter. 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.