The mood in the cockpit snapped suddenly from jovial relaxation to deadly seriousness last Halloween as American Eagle's Flight 4184 lurched out of control and began its lethal spiral to the ground, recordings showed Monday.
Pilot Orlando Aguiar and co-pilot Jeffrey Gagliano, who minutes earlier had been chatting with flight attendants and kidding about a visit to the restroom, barked out a terse, disciplined exchange during the final, horrifying seconds before the plane crashed.
"Mellow it out . . . mellow it out . . . nice and easy," Aguiar shouted as he and Gagliano fought the controls of the twin-engine turboprop.
"OK . . . OK . . . OK," Gagliano replied.
The last words from the cockpit were an oath from Gagliano. They were followed by what the National Transportation Safety Board described as a "loud crunching sound" as the commuter plane slammed into a soybean field about 110 miles northwest of here, killing all 68 on board.
The transcript of the cockpit voice recorder was released here on Monday as the NTSB began the first day of hearings on the accident. The cause of the crash has yet to be determined officially, but NTSB investigators said they believe accumulating ice had distorted the shape of the European-built ATR-72's wings and control surfaces, creating a mounting instability that hurled the twin-engine turboprop from the sky.
Experts say the way the pilots had configured their plane--deploying the flaps to make the aircraft easier to fly slowly in a holding pattern while waiting to land at Chicago's O'Hare Airport--exacerbated the problem. Flaps are flat metal slabs on the trailing edges of the wings that can be extended back to increase the wings' lift at low speeds.
The performance of the ATR-72 and its smaller precursor, the ATR-42, in icing conditions has been the subject of controversy for several years.
The crash of Flight 4184 prompted the Federal Aviation Administration to issue a Dec. 9 order that grounded all ATRs whenever icing was suspected or forecast.
Dozens of flights were canceled, and major commuter carriers like American Eagle--a subsidiary of the AMR Corp., which also operates American Airlines--had to transfer their ATR fleet south to warmer climates.
In January, after ATRs performed well during most of a series of icing tests at Edwards Air Force Base, the FAA rescinded the grounding order, but it said airlines must train pilots in new safety procedures intended to reduce the risks of flying in icing conditions. Among these procedures are new restrictions on the use of flaps in a holding pattern.
Last Halloween, as Flight 4184 circled at about 200 m.p.h. in a holding pattern over Roselawn, the pilot deployed the ATR-72's flaps.
Aguiar and Gagliano noted that ice was building up on the aircraft, but neither seemed worried. Investigators believe that as Flight 4184 continued circling, the unusual "nose down" attitude caused by the flap deployment was hastening the accumulation of ice atop the wings, permitting a ridge of it to build up behind the inflatable de-icing boots activated by the cockpit crew. The NTSB says that because the plane was on autopilot, the crew did not sense the problem through the controls.
Air traffic controllers told Flight 4184 to begin its descent, and as it descended, the plane began to speed up, setting off a cockpit alarm warning that flap damage could occur at the increased speed.
Responding to the alarm, the pilots started retracting the flaps, setting off a tragic series of events.
Investigators say that as the flaps continued to retract, the nose of the plane rose and air began tumbling back over the ridge of ice on the right wing, creating a vacuum that sucked up the right aileron--one of the hinged plates beside the flaps that move up and down to make the aircraft bank and turn. Ailerons are linked, and the rise of the right aileron depressed the aileron on the left wing, throwing the plane into a hard right bank that developed quickly into what pilots call a "death spiral."