FTW01IA051

The flight was in cruise, in icing conditions, when both engines experienced momentary power fluctuations (PF) as a result of ice ingestion. Evaluation of the flight data recorder information revealed that the left engine experienced four Type II (compressor stall) PF events, and the right engine experienced one Type I (partial/full quenching of the engine's combustor flame) PF event and one Type II event. The flight descended, the power fluctuations ceased, and the flight proceeded to land at its intended destination. The Saab 340 fleet has undergone extensive research, with regards to power fluctuations, since it was certified in the U.S. in 1985. In 1985, it was determined that ice accumulates on the engine inlet splitter lip, breaks off, and enters the engine resulting in a flame-out. An auto-ignition system was developed to provide a means to re-light the engine. Aircraft certification rules require that no accumulation of engine inlet ice occur that will adversely affect engine operation. In 2000, the FAA's position was that even though no re-design of the engine inlet was found that would preclude ice accumulation on the splitter lip, the risk associated with a PF event was acceptable. Furthermore, the FAA determined that the risk of a dual engine power loss due to the existence of an icing condition and failure of both engines' auto-ignition systems was acceptably low. Lastly, the FAA stated that inappropriate crew response risks associated with PFs combined with an in-flight shut down were quantitatively indeterminate, but deemed qualitatively acceptable by FAA certification pilots and human factors specialists.

History of flight

On January 10, 2001, at 1025 central standard time, a Saab 340B, N394AE, operated by American Eagle Airlines, Inc., as Eagle Flight 301, experienced dual engine power fluctuations (PF) while in cruise flight at flight level (FL) 200 (20,000 feet). The airplane was registered to First Security Bank of Salt Lake City, Utah, and did not sustain damage. The captain, who held an airline transport pilot certificate, the first officer (FO) who held a commercial pilot certificate, the flight attendant, and the 24 passengers were not injured. The flight was in instrument meteorological conditions (IMC) at the time of the incident, and an instrument flight rules (IFR) flight plan was filed for the 14 Code of Federal Regulations Part 121 scheduled passenger flight. The flight originated from the Dallas-Fort Worth International Airport (DFW), Texas, at 0912 and was destined for Laredo, Texas (LRD).

According to NTSB-conducted interviews with the flight crew, documents provided by American Eagle that were completed by the captain, and the digital flight data recorder information, the flight departed from DFW without incident. The captain was the flying pilot for the DFW-LRD leg. The engine anti-ice switches for both engines were turned to the ON position at 3,550 feet during the initial climb-out and, subsequently, the flight entered IMC conditions while climbing through 6,000 feet. The flight continued climbing to its cruising altitude of FL 200 and the engine anti-ice switches remained in the ON position for the duration of the flight.

The flight had been airborne approximately 30 minutes, and was 30 miles north of the San Antonio Very High Frequency Omnidirectional Range (VOR) navigational facility (024 degree radial), when both pilots heard "one loud pop," a change in the sound of an engine, and observed that the white ignition light for the left engine had illuminated. Following the loud pop, the captain observed the left (#1) engine's torque gauge needle drop from 65% to 60%, and then return to 65%. One passenger, who was seated in 12A, observed smoke discharge from the left engine. At the time of the event, the outside air temperature (OAT) was -18 degrees Celsius (0 degrees Fahrenheit) and the airplane was configured as per the following:

Airspeed: 190-205 knots

Torque: 65%

Propellers: 1,230 rpm

Continuous Ignition Switches (#1 & #2 Engine): NORMAL

Engine Anti-Ice Switches (#1 & #2 Engine): ON

Propeller Anti-Ice Switches (#1 & #2 Engine): OFF

Following this first event, the FO referenced the American Eagle Aircraft Operating Manual (volume one) and began to read the SYSTEM section, page 30, titled "Powerplant Phenomena."

Approximately 2 minutes had elapsed since the first event, when both pilots heard "continuous popping noises from both engines" and observed that the white ignition lights for the left and right engines were illuminated. The captain initiated a descent to 8,000 feet. At 1026:14, the flight contacted the Houston Air Route Traffic Control Center (HOU ARTCC) and requested a descent to 8,000 feet. HOU ARTCC approved the request, and subsequently, at 1029:44, the flight crew reported to HOU ARTCC that ice had ingested into the engines, and that the engines were experiencing "rollbacks." HOU ARTCC asked the flight crew to report on the type of icing that they were experiencing, and the flight crew replied "light rime" ice conditions. At 1031:17, the flight crew added that "they haven't had any problem in the past but we uh we were having both engines at the same time trying to flame out and relighting." The FO reported that engine operation returned to normal "just after [they] had initiated the descent." The airplane descended (descent rate of 1,000 feet per minute) to 8,000 feet in 11.5 minutes. The flight remained at 8,000 feet for 16 minutes before beginning its final descent into Laredo, and subsequently, landed without further incident at 1114.

The flight attendant reported that she contacted the flight crew after she heard the first loud bang, and the FO stated that "it was a rollback." The flight attendant asked the FO why a rollback happens, and the FO replied, "water gets in the engine and causes that." The flight attendant reported that following the second set of "rapid fire popping noises," the captain made an announcement to the passengers during which he stated that, "we had engine rollbacks and they automatically restarted just fine. We have descended to a lower altitude, so we shouldn't have that problem again."

In the American Eagle Flight Department Debrief and an American Eagle Saab 340 Power Interruption Report, the captain reported that at the time of the events, "minor rime ice accumulation [was observed] on the wing boots" and "on the windshield wipers."

Personnel information

The captain held an airline transport pilot certificate and was type rated in the Saab 340. He had accumulated a total of 13,300 flight hours, of which 9,200 were in the Saab 340. On November 13, 2000, he was issued an Federal Aviation Administration (FAA) first class medical certificate with no waivers or limitations.

The first officer held a commercial pilot certificate and was instrument rated. He had accumulated a total of 2,630 flight hours, of which 1,099 were in the Saab 340. On October 24, 2000, he was issued an FAA first class medical certificate with no waivers or limitations.

Aircraft information

The Saab 340B was equipped with two General Electric (GE) CT7-9B turboprop engines. The airplane was operated under a transport category airworthiness certificate and maintained in accordance with American Eagles' Approved Inspection Program.

On January 10, 2001, following the power fluctuations, American Eagle maintenance personnel inspected the left (#1) and right (#2) engine inlets in accordance with the GE maintenance manual 72-00, and no defects were noted.

Flight recorders

The airplane was equipped with a digital flight data recorder (DFDR). Following the in-flight events, the data was downloaded by American Eagle and sent to GE for analysis.

The data confirmed that the initial event occurred on the left engine. At the time of the event, the outside air temperature (OAT) was -18°C and the following values/trends were recorded over a 4 second time period:

Inlet Turbine Temperature (ITT): 15 Degree Rise

Torque (Tq): 5% Decrease

Gas Generator Speed (Ng): Less than 5% Decrease

The auto-ignition system was automatically activated during the event.

The data revealed that 3 minutes after the initial event on the left engine, the right engine experienced its first event. At the time of the event, the OAT was -17°C, and the following values/trends were recorded over a 3 second time period:

ITT: 25 Degree Decrease

Tq: 16% Decrease

Ng: 6% Decrease

The auto-ignition system was automatically activated during the event.

The data revealed that just before power was restored after the right engine's first event, a second, and final, event occurred on the right engine. The following values/trends were recorded over a 2 second time period:

ITT: 5-10 Degree Rise

Tq: 8% Decrease

Ng: Decrease

The auto-ignition system was automatically activated during the event.

The data revealed that as the right engine experienced its final event, the left engine experienced a second event. The following values/trends were recorded over a 2 second time period:

ITT: 12 Degree Rise

Tq: 1.5 % Decrease

Ng: 1.5 % Decrease

The auto-ignition system was automatically activated during the event.

The data revealed that 5 seconds after the left engine's second event, it experienced a third event. The following values/trends were recorded over a 2 second time period:

ITT: 17 Degree Rise

Tq: 10% Decrease

Ng: 3% Decrease

The auto-ignition system was automatically activated during the event.

The data revealed that 3 seconds aft