| Date | 24 May 1993 |
| Registration | G-LONG |
| | Registration Details from G-INFO |
| |  |
| Aircraft Type | B206L |
| Manufacturer | Bell Helicopter Textron |
| Fatal | No |
| Narrative | DURING TRANSITION FROM LAND FLARE TO HOVER TAXY, BANG HEARD & ENGINE FAILED. HEAVY LANDING. TAIL BOOM DAMAGED. NO INJS. |
| Details | ACCIDENT OCCURRED AS A RESULT OF AN UNCONTAINED FAILURE OF THE FIRST STAGE TURBINE WHEEL. METALLURGICAL EXAMINATION OF THE FIRST STAGE TURBINE FRAGMENTS INDICATED THAT THE MAJOR PORTION OF THE FRACTURE HAD OCCURRED AS A FAST BRITTLE MODE, WHICH HAD EMANATED FROM A RADIAL CRACK WHICH EXHIBITED HEAVILY OXIDISED FATIGUE LIKE FEATURES. EVIDENCE OF A CONSIDERABLE NUMBER OF SMALL RADIAL CRACKS WAS FOUND IN THE RIM OF THE TURBINE WHEEL DISC, WHICH HAD BEEN GENERATED BY A THERMAL FATIGUE MECHANISM. EXAMINATION OF THE ONLY REMAINING FULL LENGTH TURBINE BLADE REVEALED EVIDENCE THAT TURBINE HAD BEEN SUBJECTED TO AN OVER TEMPERATURE CONDITION WITHIN THE RECENT PAST. ENGINE MFR ISSUED COMMERCIAL SERVICE LETTERS ADVISING ON OPTIMISING THE STARTING TECHNIQUE FOR ALLISON C28 & C30 ENGINES IN JULY 1980, THIS INFO BEING LATER INCORPORATED INTO ALLISON OPERATION AND MAINT MANUALS. AS A RESULT OF THIS ACCIDENT BELL HELICOPTER ARE TO ISSUE AN ALERT SERVICE BULLETIN REQUIRING THAT BELL 206L A/C ARE FITTED WITH A TURBINE TEMPERATURE GAUGE INCORPORATING A "TELL TALE" LIGHT TO ASSIST OPR'S IN AVOIDING INADVERTENT TURBINE OVERHEAT DAMAGE DURING START UP. SEE AAIB BULLETIN 12/93, REF EW/C93/5/2. CAA CLOSURE: APPROPRIATE PUBLICITY GIVEN. HAZARD CONSIDERED ADEQUATELY CONTROLLED BY EXISTING REQUIREMENTS/PROCEDURES. |
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