AOPA Pilot Magazine - March 2015 - 81

traffic to O'Hare was backed
up, so Flight 4184 was told to
hold at LUCIT Intersection,
southeast of O'Hare. The ATR
entered the holding pattern at
10,000 feet, then was cleared to
8,000 feet. In the hold, the captain remarked how "this thing
gets a high deck angle in these
turns." The first officer asked,
"do you want flaps 15?"
"I'll be ready for that stall
procedure here pretty soon,"
the captain said. So the flaps
were set to a 15-degree deflection, the
nose came to a more level attitude, and
the crew advanced power. "That's much
nicer, flaps 15," the first officer said. Seven
seconds later, one of the pilots said, "I'm
showing some ice now." Some six minutes
later, someone said, "we still got ice." It was
the crew's last mention of icing conditions.
During the descent to 8,000 feet in
the hold, the ATR's airspeed went to 186
KIAS-fast enough to trigger the flap-overspeed warning. The captain then retracted
the flaps to the 0-degree position. Passing
through 9,130 feet, the airplane's angle of
attack increased through five degrees, then
the ailerons deflected to the right wing
down (RWD) position. A half-second after
that, the ailerons suddenly deflected more,
to 13.43 degrees RWD-and the autopilot
simultaneously disconnected, automatically. A roll 77 degrees to the right ensued,
followed by a roll back to 59 degrees RWD,
then there was a brief return to wings level.
The pitch attitude went 15 degrees nose
down, the captain exerted strong aft-stick
pressure, and then the airplane rolled rapidly back to the right, at a rate of 50 degrees
per second. With both pilots hauling back
on their yokes, the ATR went through 120
degrees of roll, and finally stopped at 144
degrees RWD.
After this, the airplane rolled left, then
right again as airspeed built to 260 KIAS.
Going through 6,000 feet, the airplane
was in a 60-degree nose-down attitude,
and experiencing between two and 2.5
Gs. Ultimately, the pitch attitude reached

THE NASA GLENN RESEARCH CENTER'S

icing wind tunnel uses an array of
spray bars to create the varying
conditions defined in icing certification
regulations. Nozzles at the spray bar
trailing edges can be made to eject
droplets that create icing clouds of
differing properties.

a maximum of 73 degrees nose down as
the airplane reached 300, then 375 KIAS
and 3.6 Gs. The ATR hit the ground in
a partially inverted attitude, killing all
68 persons aboard. Based on flight data
recorder information, the NTSB said that
this fatal upset happened just 24 minutes
after the first icing-induced drag increases
occurred.

AOPA LIFESTYLES

NTSB RECOMMENDATIONS

A slew of recommendations came from
the NTSB accident report. Yes, the airplane had ice protection and was certified
for flight into known icing (FIKI); and yes,
the crew had the ice protection gear in
operation. But it turns out that the icing
conditions that felled Flight 4184 were
poorly defined, let alone understood.
To be blunt, we didn't know much at all
about the kind of icing phenomenon that
contributed to the crash. And because we
didn't know about it, the FAA hadn't developed the certification rules to ensure that
airplanes could be protected against it.
The ATR-72-like other FIKI-approved
types-might have been certified for flight
www.aopa.org/pilot AOPA PILOT | 81

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AOPA Pilot Magazine - March 2015

Table of Contents for the Digital Edition of AOPA Pilot Magazine - March 2015
