In-Flight Icing Encounter and Loss of Control, Simmons Airlines, dba American Eagle Flight 4184

340 Pages·1997·3.58 MB·English

F
PB96-91040I
NTSB/AAR-96/01
DCA95MA001
NATIONAL
TRANSPORTATION
SAFETY
BOARD
WASHINGTON, D.C. 20594
AIRCRAFT ACCIDENT REPORT
IN-FLIGHT ICING ENCOUNTER AND LOSS OF CONTROL
SIMMONS AIRLINES, d.b.a. AMERICAN EAGLE FLIGHT 4184
AVIONS de TRANSPORT REGIONAL (ATR)
MODEL 72-212, N401AM
ROSELAWN, INDIANA
OCTOBER 31,1994
VOLUME 1: SAFETY BOARD REPORT
6486C
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NTSB/AAR-96/01 PB96-910401
NATIONAL TRANSPORTATION
SAFETY BOARD
WASHINGTON, D.C. 20594
AIRCRAFT ACCIDENT REPORT
IN-FLIGHT ICING ENCOUNTER AND LOSS OF CONTROL
SIMMONS AIRLINES, d.b.a. AMERICAN EAGLE FLIGHT 4184
AVIONS de TRANSPORT REGIONAL (ATR)
MODEL 72-212, N401AM
ROSELAWN, INDIANA
OCTOBER 31, 1994
Adopted: July 9, 1996
Notation 6486C
Abstract: Volume I of this report explains the crash of American Eagle flight 4184, an
ATR 72 airplane during a rapid descent after an uncommanded roll excursion. The
safety issues discussed in the report focused on communicating hazardous weather
information to flightcrews, Federal regulations on aircraft icing and icing certification
requirements, the monitoring of aircraft airworthiness, and flightcrew training for unusual
events/attitudes. Safety recommendations concerning these issues were addressed to
the Federal Aviation Administration, the National Oceanic and Atmospheric
Administration, and AMR Eagle. Volume II contains the comments of the Bureau
Enquetes-Accidents on the Safety Board's draft of the accident report.

September 13, 2002
The National Transportation Safety Board adopted revisions
to the findings and probable cause for this accident, as
summarized below.

For more information, see the full
Response to Petition for Reconsideration.

Findings 21, 23, 24, 25, 26, 35, and 36 (and the corresponding text on pages 177, 178, 179, 179-
80,181, 193, and 194, respectively) are revised as follows:
21. Prior to Before the Roselawn accident, ATR recognized the reason for the
aileron behavior in the previous incidents and determined demonstrated that ice
accumulation behind the deice boots, at an [angle of attack] sufficient to cause
an airflow separation, would cause the ailerons to become unstable. Therefore,
it would have been prudent for ATR to examine the combinations of icing
conditions and airplane configurations that could produce the performance,
stability, and control characteristics (including aileron hinge moment shifts)
exhibited in the prior incidents, and the possible repercussions of such aileron
hinge moment shifts had sufficient basis to modify the airplane and/or provide
operators and pilots with adequate, detailed information regarding this
phenomenon.
23. ATR(cid:146)s proposed post-Mosinee AFM/FCOM changes, even if which were not
adopted by the DGAC and the FAA, would not have provided flightcrews with
sufficient information to identify or recover from the type of event that occurred
at Roselawn, and the actions taken by ATR following the Mosinee incident were
insufficient.
24. The 1992 ATR All Weather Operations brochure was misleading and minimized
did not adequately communicate the known catastrophic potential of ATR
operations in freezing rain.

25. Information provided by ATR failed to disseminate adequate warnings and
guidance to operators after the late 1980s and early 1990s about ice-related
incidents did not give adequate warnings and guidance to operators about the
adverse characteristics of, and techniques to recover from, ice-induced aileron
hinge moment reversal events; and ATR failed to develop additional airplane
modifications, which led directly to this accident.
26. Prior to the Roselawn accident, the DGAC failed to require ATR to examine the
combinations of icing conditions and airplane configurations that could produce
the performance, stability, and control characteristics (including aileron hinge
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moment shifts) exhibited in the prior incidents, and the possible repercussions of
such aileron hinge moment shifts; take additional corrective actions, such as
performing additional icing tests, issuing to issue more specific warnings
regarding the aileron hinge moment reversal phenomenon,; developing
additional airplane modifications, and providing to provide specific guidance on
the recovery from a hinge moment reversal., which led directly to this accident.
35. Because the DGAC did not require ATR, and ATR did not to provide to the
operators of its airplanes, information that specifically alerted flightcrews to the
fact that encounters with freezing rain could result in sudden autopilot
disconnects, aileron hinge moment reversals, and rapid roll excursions, or
guidance on how to cope with these events, the crew of flight 4184 had no
reason to expect that the icing conditions they were encountering would cause
the sudden onset of an aileron hinge moment reversal, autopilot disconnect, and
loss of aileron control.
36. Neither the flight attendant(cid:146)s presence in the cockpit nor the flightcrew(cid:146)s
conversations with her contributed to the accident. However, aA sterile cockpit
environment would probably have reduced flightcrew distractions and could
have promoted a more appropriate level of flightcrew awareness for the
conditions in which the airplane was being operated.

The probable cause is amended as follows:
The National Transportation Safety Board determines that the probable causes cause of
this accident were was the loss of control, attributed to a sudden and unexpected aileron
hinge moment reversal, that occurred after a ridge of ice accreted beyond the deice boots
because: 1) ATR failed to completely disclose to operators, and incorporate in the ATR
72 airplane flight manual, flightcrew operating manual and flightcrew training programs,
adequate information concerning previously known effects of freezing precipitation on
the stability and control characteristics, autopilot and related operational procedures
when the ATR 72 was operated in such conditions; while the airplane was in a holding
pattern during which it intermittently encountered supercooled cloud and drizzle/rain
drops, the size and water content of which exceeded those described in the icing
certification envelope. The airplane was susceptible to this loss of control, and the crew
was unable to recover.

Contributing to the accident were 1) 2) the French Directorate General for Civil
Aviation(cid:146)s (DGAC(cid:146)s) inadequate oversight of the ATR 42 and 72, and its failure to take
the necessary corrective action to ensure continued airworthiness in icing conditions;
2)3)the DGAC(cid:146)s failure to provide the FAA with timely airworthiness information
developed from previous ATR incidents and accidents in icing conditions, as specified
under the Bilateral Airworthiness Agreement and Annex 8 of the International Civil
Aviation Organization. Contributing to the accident were: 1) 3) the Federal Aviation
Administration(cid:146)s (FAA(cid:146)s) failure to ensure that aircraft icing certification requirements,
a-2
operational requirements for flight into icing conditions, and FAA published aircraft
icing information adequately accounted for the hazards that can result from flight in
freezing rain and other conditions not specified in 14 Code of Federal Regulations (CFR)
Part 25, Appendics C, and 2) 4) the FAA(cid:146)s inadequate oversight of the ATR 42 and 72 to
ensure continued airworthiness in icing conditions; and 5) ATR(cid:146)s inadequate response to
the continued occurrence of ATR 42 icing/roll upsets which, in conjunction with
information learned about aileron control difficulties during the certification and
development of the ATR 42 and 72, should have prompted additional research, and the
creation of updated airplane flight manuals, flightcrew operating manuals and training
programs related to operation of the ATR 42 and 72 in such icing conditions.

The following paragraph is removed from page 75:
Hydraulically powered flight controls can overcome high control forces resulting from
normal in-flight control surface hinge moments. If properly designed, they can also
prevent control surface anomalies from being transmitted back through the control
system and into the cockpit. According to ATR engineers, hydraulically powered
ailerons were discussed during the preliminary design of the ATR 42. It was determined
that adequate lateral control characteristics could be obtained without the additional
weight and complexity of a hydraulic system. Hydraulic aileron control was again
discussed informally among ATR engineers after an incident involving a Simmons
Airlines ATR 42 in Mosinee, Wisconsin, in December 1988. ATR management has
since stated that hydraulically powered ailerons have never been (cid:147)officially(cid:148) considered
for either the ATR 42 or 72.

The following sentence is removed from page 117:
Also, with respect to Flight 4184, the chief test pilot for ATR testified that the type of roll
anomaly the flight crew experienced would not have been recoverable by the average line
pilot.

a-3

CONTENTS
EXECUTIVE SUMMARY................................................................ vii
1. FACTUAL INFORMATION
1.1 History of Flight................................................................................... 1
1.2 Injuries to Persons................................................................................ 12
1.3 Damage to Airplane............................................................................. 12
1.4 Other Damage...................................................................................... 12
1.5 Personnel Information.......................................................................... 12
1.5.1 The Captain.......................................................................................... 12
1.5.2 The First Officer................................................................................... 13
1.5.3 The Flight Attendants .......................................................................... 14
1.5.4 Air Traffic Control Personnel.............................................................. 14
1.5.4.1 DANVILLE Sector Controller............................................................. 14
1.5.4.2 BOONE Sector Controller................................................................... 15
1.5.4.3 BOONE Sector Developmental Controller......................................... 15
1.6 Airplane Information ........................................................................... 15
1.6.1 Flight 4184 Dispatch Weight and Balance Information...................... 17
1.6.2 ATR 72 Wing Design History............................................................. 17
1.6.3 ATR 72 Lateral Flight Control System Description ........................... 18
1.6.3.1 ATR 72 Directional Flight Control System......................................... 21
1.6.4 ATR 72 Stall Protection System.......................................................... 23
1.6.5 Autoflight System Description............................................................ 24
1.6.6 ATR 72 Ice and Rain Protection Systems........................................... 25
1.6.7 ATR 42/72 Type Certification History................................................ 30
1.6.7.1 General................................................................................................. 30
1.6.7.2 ATR 72 Icing Certification Program................................................... 30
1.6.7.3 Postaccident Certification Review....................................................... 35
1.7 Meteorological Information................................................................. 44
1.7.1 General................................................................................................. 44
1.7.2 Flight 4184 Dispatch Weather Information......................................... 45
1.7.3 Weather Synopsis................................................................................. 48
1.7.4 Pilot Reports (PIREPs) and Other Weather Information.................... 53
1.7.4.1 Witness Descriptions of Weather Conditions ..................................... 54
1.7.5 Hazardous In-flight Weather Advisory Service (HIWAS)................. 57
1.7.6 Information About Freezing Rain/Freezing Drizzle and General Icing
Conditions.......................................................................................... 57
1.7.7 Classification of Icing Conditions....................................................... 60
iii
1.7.8 Forecasting of In-flight Icing Conditions............................................ 61
1.8 Aids to Navigation............................................................................... 63
1.9 Communications.................................................................................. 63
1.10 Aerodrome Information....................................................................... 63
1.11 Flight Recorders................................................................................... 63
1.11.1 Cockpit Voice Recorder....................................................................... 63
1.11.2 Digital Flight Data Recorder................................................................ 64
1.12 Wreckage and Impact Information...................................................... 64
1.12.1 General Wreckage Description............................................................ 64
1.12.2 The Wings............................................................................................ 67
1.12.3 Empennage........................................................................................... 71
1.12.4 Engines and Propellers......................................................................... 72
1.13 Medical and Pathological Information................................................ 73
1.14 Fire ....................................................................................................... 73
1.15 Survival Aspects .................................................................................. 73
1.16 Tests and Research............................................................................... 74
1.16.1 ATR 42/72 Lateral Control System Development History................. 74
1.16.2 Previous ATR 42/72 Incidents/Accidents........................................... 75
1.16.3 Communication of Airworthiness Information Between FAA,
DGAC and ATR................................................................................. 88
1.16.4 Investigation of Lateral Control System Behavior.............................. 91
1.16.5 Postaccident NASA Icing Research .................................................... 92
1.16.6 ATR 72 Icing Tanker Tests.................................................................. 94
1.16.7 Historical Aspects of Icing Research and Aircraft Icing Certification
Requirements ..................................................................................... 97
1.17 Organizational and Management Information..................................... 100
1.17.1 Simmons Airlines................................................................................. 100
1.17.2 AMR Eagle Organization .................................................................... 101
1.17.3 FAA Oversight of Simmons Airlines/AMR Eagle.............................. 103
1.17.4 FAA Partnership in Safety Program.................................................... 103
1.17.5 Simmons Airlines/AMR Eagle Pilot Training .................................... 104
1.17.5.1 General Training Information.............................................................. 104
1.17.5.2 AMR Eagle Flight Training................................................................. 106
1.17.6 Flight and Airplane Operating Manual................................................ 107
1.17.7 Unusual Attitude and Advanced Maneuvers Training........................ 117
1.18 Additional Information........................................................................ 118
1.18.1 Air Traffic Control............................................................................... 118
1.18.1.1 Chicago Area Airspace........................................................................ 118
1.18.1.2 Air Traffic Control System Command Center .................................... 118
iv