Transportation Safety Board of Canada
www.bst-tsb.gc.ca
Aviation Recommendations - 2007
The following document is available for downloading or viewing:
For more information on accessing this file, please visit our help page.
Reassessment of the Response from Transport Canada to Aviation Safety Recommendation A07-08
Propulsion System Reliability
Background
On 21 January 2006, the Cessna 208B aircraft (registration C-GRXZ, serial number 208B0469) was en route at 9000 feet above sea level (asl), from Tofino, to Vancouver International Airport, British Columbia, when the engine failed.
The flight was over a designated mountainous region, on an instrument flight plan, in visual meteorological conditions above broken layers of cloud. Following the engine failure, the pilot began a right turn, declared an emergency to the Vancouver Area Control Centre and requested a range and bearing to the nearest airport. At this time, the aircraft's rate of turn increased, and the aircraft rolled out on a heading direct to the Port Alberni Regional Airport about 17 nautical miles (nm) to the northwest. The pilot had to enter cloud during the descent, and he requested navigational information to help keep the aircraft clear of the mountains.
Communication with the aircraft was lost as it descended through 7000 feet asl. Radar data show that, at about 6000 feet asl, the pilot entered a tight, left-hand, 360° turn, during which the rate of descent increased to about 2500 feet per minute. The aircraft came out of the turn at 4500 feet asl on a heading toward the Port Alberni Regional Airport. Aircraft in the area heard the pilot transmit a Mayday call indicating that he was attempting a forced landing on a logging road. The aircraft struck trees during a steep right-hand turn and crashed. Although fuel leaked into the cabin after the crash, there was no fire.
The accident occurred at about 1420 Pacific standard time, approximately 11 nm south-southeast of the Port Alberni Regional Airport. Five passengers survived with serious injuries; the pilot and the other two passengers were fatally injured.
The engine (PT6A-114A, serial number PCE19352) was removed from the wreckage and transported to an approved teardown facility. All of the compressor turbine (CT) blades were fractured, but one particular blade had fractured near the airfoil root platform, and the topography of the fracture surface showed signs of fatigue cracking. The compressor had seized because of bearing damage following the CT blade failure.
Single-engine instrument flight rules (SEIFR) authorization is based in part on the improved reliability of turbine engines as compared to piston engines. An essential element for SEIFR approval is that mean time between failure (MTBF) of the engine must remain high. Canadian Aviation Regulations (CARs) require the MTBF of the engine to be better than 0.01 per 1000 hours (that is, less than 1 failure per 100 000 hours of flight time).
The Board concluded its investigation and released report A06P0010 on 10 January 2008.
Board Recommendation A07-08 (10 January 2008)
While the engine type that was involved in this accident met the established reliability standard, it is important to note that, had the total number of In Flight Shut Down (IFSD) events (that is, loss of propulsion for all causes) been considered, the failure rate for the entire propulsion system would not have met the CARs standard in 7 of the last 10 years.
Any system failure that results in a loss of power and an emergency landing represents an elevated risk to the travelling public. Because the outcome of an engine failure in SEIFR operations can be catastrophic, the propulsion system reliability assessment should take into account all relevant variables and should not be limited to MTBF values alone.
Therefore, the Board recommended that:
The Department of Transport take into account all propulsion system failures when assessing the safety of single-engine commercial operations.
A07-08
Transport Canada's Response to A07-08 (04 April 2008)
In its response, Transport Canada (TC) stated that, to address this and other safety issues related to Canadian SEIFR operations, it will undertake a complete review of commercial SEIFR related CARs.
Board Assessment of the Response to A07-08 (21 July 2009)
TC has completed a review of SEIFR and has produced an interim report "Review of Single Engine Instrument Flight Rules (SEIFR) Operations Under Part 7 of the Canadian Aviation Regulations." The interim report, which was completed in April 2009, is intended to be reviewed by TC management in late June 2009.
TC is undertaking a review of its regulations as they pertain to commercial SEIFR; however, the review is not complete and in the meantime there is residual risk to the travelling public, should an engine fail in SEIFR operations.
The response is assessed as Satisfactory Intent.
Next TSB Action (21 July 2009)
The Board will follow up with TC to determine to what extent its review of SEIFR operations was able to assess the reliability of propulsion systems used in single-engine commercial operations.
Transport Canada Response to A07-08 (21 January 2011)
SEIFR Working Group recommendations were presented at a CARAC Technical Committee meeting and approved at the CARC. As a result, TC is in the process of drafting NPAs with anticipated presentation at the Spring 2012 CARAC Technical Committee.
Board Reassessment of the Response to A07-08 (09 March 2011)
TC is moving along the lengthy process to change regulations and it will not be until the draft changes are accepted that a final assessment can be made. In the meantime there is residual risk to the travelling public, should an engine fail in SEIFR operations.
The response is still assessed as Satisfactory Intent.
Next TSB Action (09 March 2011)
TSB staff will follow up with TC to determine to what extent the NPAs address the risk of SEIFR operations with regard to assessing the reliability of propulsion systems used in single-engine commercial operations.
