Tuesday, February 25, 2014

When Blades Creep

What happened to the Caravan pictured below?  Turbine Blade Creep - the movement of a turbine blade from its normal alignment, causing it to strike the casing.  Caused by stress from high temperatures and high centrifugal forces.

When Blades Creep!  It sounds like the title of some horror movie, doesn't it?  Well, if you don't know what it is... it just might become the title of your very own horrific day.  Read on and study more.

On June 1st, 2008 Grand Caravan N102VE operated by Skydive Greensburg in Indiana experienced a total loss of engine power.  On its second load of the day, it was climbing through 7,000 feet MSL with 14 skydivers on board when there was a CT (compressor  turbine) failure caused by blade creep.  The pilot reported hearing a loud explosion followed by a metal grinding noise coming from the engine.  The aircraft began to vibrate and then smoke filled the cabin when the pilot began emergency shutdown procedures.

He leveled off at 5,000 feet so that the skydivers could exit, which they all did.  He attempted a forced landing at the airport, however he was too high and fast (a common problem during such situations) and landed in an adjacent cornfield upside down, after the left wing and propeller struck the ground first.  Luckily the pilot and all skydivers survived.

The engine manufacturer, Pratt & Whitney Canada had issued Service Information Letters (SILs) recommending borescope inspections of the CT blades to look for blade creep and fatigue cracks.  However, the owner of this aircraft said that he was unaware of the SILs and did not perform the inspections.

We as pilots can all learn from this accident.  Do not ever assume that the owner of the airplane that you're flying is in compliance with all of the required Airworthiness Directives AND recommended Service Information Letters.  I know a lot of you had never even heard of a SIL.  Stay sharp.... fly safe!