Mechanic reports he was instructed by his Shop Supervisor to reset the Total Outlet Temperature (TOT) Overtemp light that had illuminated during an engine start on a Bell 206 L-4 helicopter with an Allison/Rolls Royce engine. He failed to ask the pilot if the engine had actually overtemped; which would require a Hot Start Inspection.
Synopsis
Mechanic reports he was instructed by his Shop Supervisor to reset the Total Outlet Temperature (TOT) Overtemp light that had illuminated during an engine start on a Bell 206 L-4 helicopter with an Allison/Rolls Royce engine. He failed to ask the pilot if the engine had actually overtemped; which would require a Hot Start Inspection.
Narrative
I was working when the Shop Supervisor directed me to make a Start/Enrichment adjustment on a Bell 206-L4 helicopter. I was told that it wanted to start hot. After reviewing the appropriate Maintenance Manual (MM); I adjusted the Start /Enrichment per the applicable MM. While at the aircraft; I assisted the pilot who had the starting problem in resetting the Turbine Outlet Temperature (TOT) Overtemp light. After the Fuel Control Unit (FCU) adjustment was complete; I signed-off the Engineering report properly.Approximately one hour later; the pilot made another attempt to start but aborted due to low battery voltage. The battery was replaced with a Serviceable like item and subsequent start was uneventful. One day later; I was notified by the Chief Pilot that the government agency [we contract our helicopters with] submitted a Safety Report regarding the Bell 206-L4 I had worked on the day before that had overtemped.I immediately called the pilot and he verified that the TOT exceeded 927C for no more than a second. The Chief Inspector and I confirmed that an overtemp condition had occurred on that start. A Hot Start Inspection was performed on the aircraft Indicating System and the Turbine section per applicable MMs; with no defects noted. The aircraft was ground run and flown. Aircraft was returned to service. The lack of communication between the pilot; Shop Supervisor and myself could have possibly caused the loss of aircraft and/or life.
NASA callback
Reporter stated a special key (tool) is required to reset (extinguish) the Turbine Outlet Temp (TOT) Overtemp light once the light has illuminated. He never thought to ask the pilot if the engine had in fact; overtemped; during his engine start-up. Since he was instructed by his Shop Supervisor to go over and reset the Overtemp light and adjust the Fuel Control Unit (FCU); he didn't realize there was an issue with an actual overtemp situation requiring a Hot Start Inspection; thinking there was a lower temperature turbine gauge installed.Reporter stated there are two different Turbine Temperature gauges; with different settings for illuminating the Turbine Overtemp light; that are interchangeable on the Bell 206-L1; L3 and L4 helicopters per Bell. The Bell-L1 and L3 helicopter engines are Lycoming and the Overtemp light comes on at a lower 768C (degrees Centigrade) compared to the Allison/Rolls Royce engines that are standard on the B206-L4s; which run hotter with a 927C Overtemp light. Reporter stated there is nothing in the Bell Maintenance Manual or Rolls Royce Maintenance Manual (MM) informing Mechanics about the interchangeability of the TOT gauges. Mechanics and pilots have to look in the Airframe Manual and Flight Manual under 'Starting' and in the 'Turbine Outlet Temperature' section to determine what engine is installed and then use that information with a temperature table in the Flight Manual to know what the Overtemp setting should be. If a Bell 206-L1 or -L3 helicopter has an L4-type Turbine Temperature gauge installed; than pilots and mechanics must be aware the Turbine Temperature settings are different.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.