CH146 Griffon Exceedances - Epilogue

Report / April 30, 2009 / Project number: CH146-D-Cat

TYPE: CH146 Griffon
LOCATION: Kandahar Airfield, Afghanistan
DATE: 2008 - 2009 Period

This investigation examined exceedances of aircraft Inlet Turbine Temperature (ITT), Speed Never Exceed (VNE), Main Rotor Revolutions Per Minute (Nr) droop, and Angle of Bank, discovered over a period of several months mostly through the monitoring of aircraft Health Usage Monitoring System (HUMS) data. Several issues in these investigations were also present in CH146434’s accident, 6 July, 2009 as follows:

• ITT: From December 2008 to November 2009, HUMS recorded 1,120 ITT exceedances between 810ºC and 940ºC for more than five seconds.
• VNE: On CH147 Chinook escort missions, VNE was often exceeded to remain in a position to provide close protection. Crews believed the exceedances were justified by their mission to protect the Chinooks. In one extreme case, a crew flew at 135 knots for an extended period of time despite environmental conditions having reduced VNE to 95 knots.
• Nr Droop: Although it was determined to be a frequent occurrence, only one crew reported a droop below the normal operating range. In this case the Nr droop recorded was 92.4% (crew estimation was 90%) while taking-off from a forward operating base in a dust ball.
• Angle of Bank: Flight data analysis determined that 14.7% of all deployed CH146 turns were in excess of aircraft’s maximum angle of bank limit of 50 degrees. Several were above 60 degrees and, in some cases, up to 88 degrees.

Cause Factors included crews intentionally exceeding limitations and operating the aircraft beyond its capabilities. A lack of confidence in the accuracy of performance charts combined with errors in these charts led crews towards incomplete pre-flight performance calculations. Also, the differences between the aircraft flight manual and the maintenance manuals regarding limits were poorly understood. Crews were not reporting exceedances to the chain of command or Flight Safety, which led to the large number of occurrences to go unnoticed prior to preventative action being taken.

CH146 crews displayed strong mission motivation, believing that the exceedances were justified due to nature of the missions. Unfortunately, some crews were unaware of the consequences on aircraft components when routinely exceeding limits.

Finally, the chain of command provided inadequate guidance to tactical level crews to carry out the assigned roles and missions. Certain missions were authorized without due consideration for the operating environment, the threat and the aircraft limitations allowing crews to drift away from normal and expected cultural, procedural and operational norms.

Safety actions proposed include re-emphasis of respecting operating limits and amendments to training and manuals to improve performance calculations. Recommendations include clarification of helicopter pitch and roll limits, enhancing information contained within aircrew manuals as well as improved education on the Power Assurance Check and on the consequences on aircraft components when routinely exceeding limits. Improvements to aircraft gauges and modifying the Attitude Indicator to include a mark at the 50 degree limit were also recommended.

In addition, recommendations include amendments to the Commanding Officer’s and the Flying Supervisor’s courses to deal with deviations from limits, orders and regulations; to understand operational and technical authority levels; and to identify the challenges between training, domestic and deployed operations. Lastly, DFS recommends the implementation of a military flight operations quality assurance program for all CF aircraft.