# NTSB FTW96IA045: Saab-Scania 340B, N344SB, Corsicana, TX, November 17, 1995 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: November 17, 1995, 08:45 local (14:45 UTC) - Place: Corsicana, TX - Location: 32.0824° N, 96.4667° W: Placed by OpenAirDocs: center of Corsicana, TX, within about 6 miles (OpenAirDocs) - Nearby events: https://openairdocs.org/map.md?lat=32.0824&lon=-96.4667&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 33 uninjured - Status: Completed, report June 25, 1996 - Report: Approved by Office Director - NTSB case key (mKey): 19667 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW96IA045 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/19667/pdf - Page: https://openairdocs.org/ntsb/FTW96IA045 ## Probable cause Total loss of power in the left engine from ice ingestion; and failure of the left-engine auto-relight system caused by an open fuse in the Digital Electronic Control Unit (DECU), which prevented an automatic relight of the left engine. Factors relating to the incident were: inadequate design of the engine air inlet anti-ice system, which allowed ice/slush accumulation; inadequate action by the FAA to ensure compliance with certification requirements regarding inlet ice accumulation; and an inadequate procedure in the flight manual concerning use of the engine synchrophaser during single-engine operation. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(total) - nonmechanical, descent - normal - 1 engine - weather condition - icing conditions - anti-ice/deice system,nacelle anti-ice - inadequate (contributing factor) - acft/equip,inadequate design, manufacturer (contributing factor) - inadequate certification/approval,aircraft, faa(organization) (contributing factor) - engine assembly - ice ingestion (cause) - Airframe/component/system failure/malfunction, descent - normal - electrical system,fuse - open (cause) - ignition system,auto re-light system - inoperative (cause) - Loss of engine power(partial) - nonmechanical, descent - normal - 1 engine - propeller system/accessories,synchro mechanism - engaged - aircraft manuals,procedure information - inadequate (contributing factor) - procedure inadequate, manufacturer (contributing factor) - precautionary landing - performed, flightcrew ## Analysis During descent, after exiting light icing conditions, the left engine lost power, & power fluctuations of the right engine were noted. The flightcrew declared an emergency, diverted to the nearest airport, & made an uneventful landing. There were indications of engine ice ingestion, but no engine damage. During ground runups, the right engine performed normally. The left engine ran normally, except its auto-ignition & overspeed protection were inoperative due to an open fuse in the Digital Electronic Control Unit (DECU). The open fuse would have prevented an automatic relight after a flameout. The Saab 340 fleet has a history of power losses associated with in-flight icing, dating back to 1985. The manufacturer (Saab) had determined that ice/slush could accumulate on the rear wall of the inlet protective device (bird catcher) & shed from the 'splitter lip' into the engine airflow path. As a preventive measure, Saab had developed an auto-ignition system to provide automatic relighting of the engine. Also, Saab was testing an improved heating system to prevent ice/slush from accumulating on the splitter lip. Title 14 CFR Part 25 requires that airplanes be designed so that engine inlet ice that would adversely affect engine operation cannot accumulate. During flight tests with the left engine inoperative & the propeller synchrophaser engaged, multiple power fluctuations of the right engine occurred. Instructions to turn the synchrophaser 'off' were not included in the engine failure checklist. ## Factual narrative HISTORY OF FLIGHT On November 17, 1995, approximately 0845 central standard time, a Saab 340B, N344SB, experienced a total power loss on the left engine and power fluctuations on the right engine during descent. An emergency landing was made in Corsicana, Texas. There were no injuries to the 3 crew members and 30 passengers and the airplane was not damaged. The airplane was being operated by Simmons Airlines as American Eagle Flight 3570 under Title 14 CFR Part 121. The flight departed Corpus Christi, Texas, at 0720 and the intended destination was Dallas/Fort Worth Airport, Texas. Instrument meteorological conditions prevailed en route and an IFR flight plan was filed. At the time of the power loss, the airplane had descended into visual meteorological conditions. According to the flight crew, they had flown in light precipitation at 17,000 feet MSL for approximately 45 minutes and had accumulated "trace ice on the wing leading edges." During descent, the airplane exited the cloud layer and "one or two minutes" later the left engine "abruptly" lost power. The right engine began to "surge and a popping noise was heard." The flight attendant informed the crew that "flames" were coming out the right engine exhaust. According to the Fort Worth Air Route Traffic Control Center, at 0844:46, the pilot declared an emergency, and at 0847:42, made a request to divert to the nearest airport. The attached cockpit voice recorder (CVR) transcript begins at 0843:16 as the airplane was descending through an altitude of "fifteen eight for one three thousand." At 0844:00, the captain stated that an engine "just failed," and at 0844:23, the flight crew initiated the engine shutdown procedure. Immediately following the captain's statement (at 0845:55) that the propeller "has feathered," the first officer remarked (at 0845:56) that the remaining engine was "starting to surge." During a transmission to air traffic control, at 0848:57, the captain reported "numerous power surges" of the right engine were occurring. At 0851:01, approximately 5 minutes prior to touchdown, the captain started to read the single engine landing checklist. At 0855:22, the captain read the final items in the checklist including "prop sync's off." An uneventful landing was made, about 0856, in Corsicana. After the airplane was parked, the flight crew had a conversation during which the first officer remarked that he thought the left engine "ingested a bunch of ice" and both crew members stated "there was no auto ignition." AIRCRAFT INFORMATION The Saab 340B is equipped with a limited authority propeller synchrophaser system. The system uses the left propeller as the master, while the right propeller is the slave. When the synchrophaser is engaged, the speed of the right propeller is adjusted to match the speed of the left propeller. The synchrophaser's authority to adjust propeller speed is limited to changes of +/- 30 rpm with corresponding torque variations of +/- 3 percent. A review of the operator's Quick Reference Handbook for the Saab 340B revealed that instructions to turn the synchrophaser "off" were not included in the engine failure checklist. Instructions to turn the synchrophaser "off" were included in the single engine landing checklist as one of the final items before landing. FLIGHT RECORDERS The digital flight data recorder (DFDR) and the cockpit voice recorder (CVR) were removed from the airplane and sent to the National Transportation Safety Board for readout. A CVR Group Chairman's Report and a DFDR Factual are attached to this report. According to the DFDR data, both cockpit engine anti-ice switches were placed in the "on" position approximately 8 minutes after takeoff, at 9,952 feet MSL, with an outside air temperature (OAT) of 5 degrees Celsius. About 57 minutes later, at 15,232 feet MSL, with an OAT of -7 degrees Celsius, the left engine lost power. Approximately 3 minutes later, the right engine experienced a power interruption, during which all parameters associated with the engine fluctuated for about 2 seconds. At the time of the right engine power interruption, the airplane was at 11,200 feet MSL and the OAT was 2 degrees Celsius. In addition to the right engine power interruption, the DFDR recorded approximately 30 fluctuations confined to right engine torque and propeller rpm parameters. These fluctuations began when the left propeller stopped rotating and continued for about 6 minutes. The fluctuations consisted of propeller speed decreases of approximately 30 rpm accompanied by torque increases of approximately 3 percent. During these fluctuations, the core engine parameters (compressor speed, compressor discharge pressure, and turbine temperature) remained stable. TESTS AND RESEARCH Borescope examination of both engines by the operator's maintenance personnel revealed no physical evidence of foreign object damage. Engine ground runs were conducted. The right engine performed within specifications. The left engine auto-ignition and overspeed protection systems were found to be inoperative. These systems are controlled via the Digital Electronic Control Unit (DECU.) After replacement of the left DECU, the left engine performed within specifications. According to the operator, the left DECU had accumulated 4,543 hours total time and 5,151 cycles at the time of the incident. The most recent functional check of the auto-ignition system had been accomplished 69 hours prior to the incident, during the airplane's last "A" check, on November 6, 1995. "A" checks are conducted at intervals of 400 hours. Examination and testing of the DECU at the engine manufacturer's facility revealed that a fuse in the unit was open. The function of this 1 amp fuse is to protect the power supply unit which provides power to the auto-ignition circuit. Without supply voltage for the auto-ignition logic, the DECU was not able to command the auto-ignition relay to energize. Further examination of the fuse disclosed evidence that the fuse element became discontinuous "due to Joule heating" and "the current level that caused final melting was relatively low." For additional details of the DECU examination see the attached Systems Group Chairman's Factual Report. A flight test was conducted by the airframe manufacturer on January 17, 1996, in order to determine "the results of single engine operation with the synchrophaser engaged." Testing was conducted in a Saab 340B production aircraft. With the synchrophaser engaged, the left engine was shut down in flight and the propeller feathered. Intermittent drops of approximately 20 rpm in right propeller speed together with corresponding peaks in right engine torque occurred. The manufacturer's flight test report stated that "a change in the frequency of the internal noise induced by a sudden drop in the propeller speed will be apparent to the crew and could be mis-interpreted as pops." ADDITIONAL INFORMATION On June 27, 1984, the Saab 340A was issued a type certificate by the FAA. In December 1985, following five occurrences of engine flameouts in icing conditions, the FAA issued Telegraphic Airworthiness Directive (AD) T85-25-52 prohibiting revenue operation of the Saab 340A in icing conditions. Research by the manufacturer determined that the flameouts were caused by the ingestion of ice/slush into the engine compressor. On August 18, 1986, the AD was amended to permit operations in icing conditions provided continuous ignition was selected, and further amended on June 17, 1988, to allow the use of a newly developed auto-ignition system as an equivalent alternative to continuous ignition. On August 15, 1989, the Saab 340B, a derivative of the Saab 340A, was added to the existing type certificate. The major difference between the two models is the substitution of the General Electric (GE) CT7-9B engine for the CT7-5A used on the 340A. An auto- ## Aircraft - Registration: N344SB (not matched to a registry record) - Reported make and model: Saab-Scania AB (Saab) 340B - Category: Airplane - Serial number: 340B-344 - Airframe hours: 4543 - Engines: GE CT7-9B 1870 horsepower turbo prop - Damage: No damage - Flight: Part 121 - Operator: Simmons Airlines, doing business as American Eagle - Registered owner: Amr Leasing Corp. - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, November 6, 1995, 69 hours before - Departed: CRP, CORPUS CHRISTI, TX - Destination: CRS, DALLAS/FT WORTH, TX - Flight plan: IFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 46; airline transport, flight instructor; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--w/ waivers/lim; seat: left; flight hours: 15,071 total, 5,237 in this make and model, 12,627 as pilot in command, 245 in the last 90 days, 132 in the last 30 days, 6 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 180° at 7 knots - Visibility: 50 statute miles - Lowest ceiling: 15,000 ft overcast - Temperature: 50 °F ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Incident 19951117041939I](https://openairdocs.org/incident/19951117041939I), Nov 17, 1995: Saab 340B, Corsicana, TX. Narrative: the PIC reported that the flight had been in light precipitation at FL170 for approximately 45 minutes. He stated that there was approximately 1/16… From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.