A Maintenance Manager with an IA (Inspection Authorization) rating reports about a Eurocopter BK-117 engine flame out after a fuel quantity indicator calibration check. Aircraft Maintenance Manual cited as not being not adequate in addressing potential engine flameouts due to air in fuel lines.
Synopsis
A Maintenance Manager with an IA (Inspection Authorization) rating reports about a Eurocopter BK-117 engine flame out after a fuel quantity indicator calibration check. Aircraft Maintenance Manual cited as not being not adequate in addressing potential engine flameouts due to air in fuel lines.
Narrative
The aircraft was at downtown heliport. The aircraft had undergone fuel quantity indicator calibration two days previously. When the pilot attempted to start the engines; neither one of them would start. Maintenance was on hand and determined that the fuel system had not been purged of air after the previous work had been completed. The fuel lines of both engines were purged and then both engines started normally. The aircraft was positioned for take-off and after reaching approximately 5-10 knots; the number one engine failed without any advanced warning. Fuel system was not completely bled; engine flamed out. The pilot was able to gain airspeed and recover to a local airport which was a five minute flight from take-off to landing.I went to the airport and the number one engine was again purged with a significant amount of air still in the line. The number one engine was again started but there was significant fluctuations in the TOT (Turbine Outlet Temperature) during start. After running the engine for approximately ten minutes and hovering for several minutes the aircraft was repositioned back to ZZZ. During subsequent starts; the TOT continued to fluctuate abnormally. Troubleshooting was continued the next morning. The fuel filter bowl was removed; inspected; reinstalled; and re-bled. Subsequent engine starts were non-events. [Suggest that] mechanics should take the time to bleed the fuel system completely after fuel quantity indicator system calibration. There is no Maintenance Manual requirement for this step.
NASA callback
Reporter stated the maintenance procedure to calibrate the fuel quantity system requires de-fueling the Eurocopter BK-117 fuel tank in the aircraft's belly; under the cabin floors. When de-fueling the main fuel cell; fuel also drains from the fuel lines going up to both Honeywell/Textron engine main fuel controls. There is no check valve installed at the fuel pump outlet; which would have prevented fuel from completely draining down from the upper fuel lines. Other helicopter make models do have a check valve installed at the pump outlets. Reporter stated the BK-117 has a main fuel cell with two electric supply pumps and a smaller; approximately ten gallon; feeder tank with two internal primer pumps that sit inside the main fuel cell. The supply pumps keep the feeder tank full for engine start requirements.Reporter stated Honeywell/Textron owns the Engine Maintenance Manual (EMM); which includes bleeding air from the gear driven engine fuel pump; fuel control and fuel filter; but Eurocopter is responsible for the Aircraft Maintenance Manual; including the fuel lines up to the engines. Other experienced mechanics told him that air in the fuel lines is a serious problem that is not explained very well in the Maintenance Manual (MM). The MM is just not sufficient enough in notifying mechanics about air remaining in the fuel lines after refueling. Reporter stated he submitted his report; hoping to at least get a 'CAUTION' or 'WARNING' note added to that section of the MM; informing mechanics to be aware of possible engine fuel starvation due to air remaining in the fuel lines. He has not received any response yet about his MM revision suggestion.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.