 N823NK, the aircraft involved in the incident, in July 2003 | |
| Incident | |
|---|---|
| Date | June 4, 2002 |
| Summary | In-flight loss of thrust on both engines in icing conditions |
| Site | In-air; 23 mi (37 km) west of Wichita, Kansas |
| Aircraft | |
| Aircraft type | McDonnell Douglas MD-82 |
| Operator | Spirit Airlines |
| IATA flight No. | NK970 |
| ICAO flight No. | NKS970 |
| Registration | N823NK |
| Flight origin | Denver International Airport, Colorado |
| Destination | Fort Lauderdale–Hollywood International Airport, Florida |
| Occupants | 111 |
| Passengers | 105 |
| Crew | 6 |
| Injuries | 0 |
Spirit Airlines Flight 970 was a scheduled domestic passenger flight from Denver to Fort Lauderdale that suffered an in-flight loss of thrust from both engines on June 4, 2002. The McDonnell Douglas MD-82 aircraft was flying at 33,000 ft (10,000 m) with 105 passengers and 6 crew members when it flew into icing conditions, causing the engine inlet probes to be blocked. This generated a false engine pressure ratio (EPR) reading, which caused the autothrottle to reduce thrust on both engines. The crew were able to initiate a decent and restore power to both engines before diverting the flight to Wichita Mid-Continent Airport.
Passengers and crew edit
At total of 111 passengers and crew members were on board the flight. The captain had been a Spirit Airlines pilot since February 1998 and a captain since February 2000. He had a total of 7,200 flight hours, 1,720 of which were in the MD-82. The first officer had a total of 8,900 flight hours, though only 376 of which were in the MD-82.
Aircraft edit
The aircraft in the incident was a 20-year-old McDonnell Douglas MD-82, with registration N823NK and serial number 48020. The aircraft was powered by two Pratt and Whitney JT8D-219 turbofan engines. It was first delivered to Austrian Airlines in February 1982. In April 1997, it was acquired by South African Sun Air and in January 2000, by Argentine Dinar Líneas Aéreas. It was finally acquired by Spirit Airlines in August 2001.
Incident edit
The aircraft took off from Denver International Airport bound for Fort Lauderdale at 11:40 a.m. At 12:38 p.m. Central Daylight Time while cruising at 33,000 feet with the engine anti-ice disabled, a loss of power of thrust on both engines. The stall warning started to sound as the airspeed started to decrease rapidly. The captain took manual control of the flight and disconnected the autopilot to start an emergency decent. At 17,000 feet, the right engine was successfully restarted and a short time after that, the left engine restarted on its own. The flight was soon diverted to Wichita Mid-Continent Airport.
Investigation edit
The National Transportation Safety Board (NTSB) launched an investigation into the cause of the incident. They conducted a telephone interview with the two flight crew members. The captain stated that the flight was uneventful until both he and the first officer noticed the EPR and the low-pressure compressor speed were abnormally low on both engines. Along with this, he noticed that the airspeed was decreasing rapidly. He then took manual control of the aircraft and started an immediate descent. At 17,000 feet, as the MD-82 broke out of the clouds, he and the first officer managed to restart the right engine with the left engine starting a short time later. The first officer told the NTSB in another telephone interview a similar story. He also said that at one point, the captain pushed the engine throttles forward without a response. They both said that the engine anti-ice was off at the time of the incident.
On June 5, the day after the incident, the NTSB conducted an examination of the aircraft and its engines. Only minor damage on the right engine compressor blades could be related to the incident. The digital flight data recorder (DFDR) data recovered showed that in the preceding nine minutes before the engine thrust was reduced to idle, EPR indications were unusually high. This led the autothrottle to reduce engine thrust and as a result, a decrease in airspeed. The airspeed got as low as 187 kn (346 km/h) in the seconds after the reduction of thrust.
The probable cause of the incident was concluded to be, "The flight crew's failure to verify the engine instrument indications and powerplant controls while on autopilot with the autothrottles engaged, and their failure to recognize the drop in airspeed which led to an aerodynamic stall associated with the reduction in engine power. Factors were the presence of ice crystals at altitude, and the icing of the engine inlet probes resulting in a false engine pressure ratio indication."
Aftermath edit
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In the aftermath of the crash of Air Algérie Flight 5017, the French Bureau of Enquiry and Analysis for Civil Aviation Safety (BEA) noticed similarities between that crash and three other incidents: West Caribbean Airways Flight 708 (2005), Air France Flight 447 (2009), and Spirit Airlines Flight 970 (2002). In the BEA's "safety recommendations" section in the Flight 5017 final report, the BEA noted recommendations that the NTSB made in relation to Spirit Airlines Flight 970. These recommendations were making sure crews were made aware of the effects of high-altitude icing conditions on aircraft performance, the use of engine anti-icing systems, and the possibility of developing an ice detector on the engine inlet probes.
N823NK, the aircraft involved in the incident, went through a variety of South African owners between 2005 and 2007. In February 2008, the aircraft was stored at Roswell International Air Center.
References edit
ASN description NTSB report Aircraft description Air Algérie Flight 5017 report