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ASN Wikibase Occurrence # 147131
Last updated: 2 October 2019
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Date:02-JAN-2006
Time:14:39
Type:Silhouette image of generic SF34 model; specific model in this crash may look slightly different
Saab 340B
Owner/operator:American Eagle Airlines, Inc.
Registration: N390AE
C/n / msn: 340B-390
Fatalities:Fatalities: 0 / Occupants: 28
Aircraft damage: None
Category:Accident
Location:over Santa Maria, CA -   United States of America
Phase: En route
Nature:Domestic Scheduled Passenger
Departure airport:San Luis Obispo, CA (SBP)
Destination airport:Los Angeles, CA (LAX)
Investigating agency: NTSB
Narrative:
After departure and during the cruise climb phase, the flight encountered airframe ice and departed from controlled flight.

The flight crew encountered light rime icing on the inbound leg while descending from 9,000 to 5,000 feet. Before the incident takeoff, they reviewed the dispatch package weather and noted two AIRMET (airmen's meteorological information) reports for icing in clouds. The captain decided to perform the departure and turn control of the airplane over to the first officer after completing the climb checklist at the acceleration altitude. In accordance with the operator's minimum equipment list (MEL), the airplane was dispatched with the continuous mode of the boot deice system inoperable, which would require the crew to manually operate the deice boots. Company procedures require activation of the deice system at the first sign of ice accretion, and operation of the deice boots continually thereafter while in icing conditions. The departure was into level 2 weather conditions (defined as 10 degree Celsius or colder with visible moisture).

The airline's Airplane Operating manual (AOM) for the airplane calls for computation of a minimum speed (Vcln 15) in icing conditions, which for this flight was 141 KIAS. The limitations section stipulates that Indicated Air Speed (IAS) is the only authorized flight director/autopilot mode while climbing when ice accretion is occurring or with residual ice on the airframe. In IAS mode, the flight control computer gives pitch commands to maintain the selected indicated airspeed as opposed to the Vertical Speed (VS) mode where the autopilot sacrifices airspeed to maintain climb rate. Even though the crew had encountered icing on the inbound leg and the dispatch weather reports predicted an icing encounter during the climb on the outbound leg, the captain engaged the autopilot in the medium (M) climb mode and shortly after taking the controls at 2,500 feet, the first officer changed the autopilot to VS mode.

As the airplane climbed through 11,700 feet, the captain noted light rime ice accumulating on the windshield wiper blades and about a 1/2-inch-wide area of ice on the left wing. During this time, the crew failed to detect a decaying indicated airspeed due to the ice that was accumulating. As he began to activate the manual deice boot system, he felt a heavy vibration in the airframe and the windscreen immediately turned white with ice. The airplane's nose and left wing dropped and the autopilot disconnected. As he was grabbing the yoke, the clacker sounded (indicating an imminent stall), the stick shaker activated, and the ground proximity warning system emitted a "bank angle" aural warning. Digital Flight Data Recorder (DFDR) data showed that the indicated airspeed went from 144 to 130 KIAS over the 26 seconds before the upset, and that the rate of airspeed decay accelerated in the final 10 seconds before the autopilot disconnected. The airplane departed controlled flight at an indicated airspeed of 130 knots, and before the stall warning activated. The data establishes that the airplane went through a series of roll and pitch excursions, reaching maximum values of 86 degrees left wing down, 140 degrees right wing down, 23 degrees nose up, and 40 degrees nose down before the flight crew recovered control. The data also revealed that about 26 seconds before the stall while the airplane was at a speed of 144 KIAS, the airplane began to experience a likely ice-induced slight rolling anomaly that was counter to the direction of the aileron input. Aileron input from the autopilot arrested this slight rolling motion.

The DFDR data also disclosed that 14 seconds after the initial stall, both ailerons simultaneously traveled to the full up position for approximately 14 seconds. The Safety Board believes that the initial stall that occurred prior to stall warning, the upset, and the aileron upward deflections were caused by ice accreted on the wing in supercooled liquid droplets (SLD) conditions. Furthermore, the period of simultaneous upward deflection
Probable Cause: An in-flight loss of control due to ice accreted in supercooled liquid droplets (SLD) conditions, and the flight crew's failure to maintain the specified minimum airspeed in icing conditions. Contributing to the accident was the flight crew's decision to climb the airplane in known and forecast icing conditions using an autopilot mode contrary to that specified in the operator's Airplane Operations Manual for climbs during periods of ice accretion or when ice was present on the airframe.

Sources:

NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20060109X00033&key=1


Images:

Photo of N390AE courtesy AirHistory.net


Los Angeles - International (KLAX / LAX)
4 May 2005; (c) Mick Bajcar


Revision history:

Date/timeContributorUpdates
26-Jul-2012 07:21 harro Added
27-Nov-2015 14:54 harro Updated [Source, Narrative, Photo, ]
21-Dec-2016 19:28 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
05-Dec-2017 10:03 ASN Update Bot Updated [Operator, Other fatalities, Departure airport, Destination airport, Source, Narrative]

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