N911MK

HISTORY OF FLIGHTOn January 26, 2017, about 2145 central standard time, a Eurocopter Deutschland GMBH MBB-BK 117 C-2 helicopter, N911MK, sustained minor damage when it experienced an inflight engine fire and made an emergency landing at Joe Foss Field Airport (FSD), Sioux Falls, South Dakota. The airline transport pilot and two crewmembers were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 135 air ambulance flight.

In his post-incident statement, the pilot reported that while conducting a night helicopter air ambulance flight en route, the No. 2 engine twist grip caution light illuminated. He checked that the throttle was in flight mode, and then checked the first limit indicator (FLI) and tachometer, which were both indicating normally. The twist grip light disappeared then reappeared and flickered a few more times. He stated that the engine instrumentation was indicating in the proper range. Seconds later the caution advisory display (CAD) illuminated with ENG PA DIS (engine parameter discrepancy) cautions on both engines; both of the FLI needles were married, and all parameters were in the proper ranges. Shortly after the ENG PA DIS lights illuminated, he heard a "winding down sound," and then, " a hissing sound” and detected “the smell of exhaust in the cabin." He responded by turning off the cabin heat, lowering the collective, and turning toward FSD. During the turn, the No. 2 engine FIRE light illuminated. The airspeed was above 100 knots when he noticed an orange glow from the back right side of the helicopter. He continued to slow below 100 knots to meet the requirements for one engine inoperative (OEI) flight procedures. Once below 100 knots, he broke and raised the red plastic switch guard and pressed the emergency off switch (EMER OFF SW). Subsequently the FLI needles split, and the ACTIVE and BOT 1 lights illuminated, so he pressed the BOT 1 push button. The BOT 2 light illuminated and since the FIRE light was still illuminated, he pressed the BOT 2 push button. About two seconds after pressing the BOT 2 push button, the FIRE light extinguished. He then completed all of the emergency checklist items for an engine fire. During the fire emergency, the No. 1 engine FLI never exceeded 10.5 and the mast moment indication did not increase into the yellow region. He noted that the helicopter had descended about 300 ft. Since the FIRE light was extinguished, he continued the flight in order to make an emergency landing at FSD. The pilot kept the helicopter at 500 ft while en route. About 13 nm southwest of FSD, the pilot radioed the tower controller and declared an emergency and was cleared to land on runway 3. He executed a low approach with a running landing and stopped on the runway in less than 100 ft.

AIRCRAFT INFORMATIONMaintenance Information

On December 27, 2016, a 400-hour periodic check was performed by the operator at 6,146 hours engine time since new (TSN), and 2,551 hours engine time since overhaul (TSO) on the engine's module 3. During the check they inspected the oil filter and the rear bearing's magnetic plug. There was no record of the inspection results.

On December 14, 2016, a spectrometric oil analysis program (SOAP) was performed by the operator at 6,114 hours engine TSN, and 2,519 hours engine TSO on the engine's module 3. There was no record of the analysis results.

On October 22, 2016, an 800-hour and a 1,200-hour periodic check were performed by the operator at 5,988 hours engine TSN, and 2,393 hours engine TSO on the engine's module 3. During the 800-hour check they drained the oil system and inspected the rear bearing's magnetic plug strainer (TU208). During the 1200-hour check they removed and cleaned the oil scavenge tube. There was no record of either inspection results.

On July 25, 2016, a 600-hour periodic check was performed by the operator at 5,815 hours engine TSN, and 2,220 hours engine TSO on the engine's module 3. During the check, a rear bearing assembly permeability test was conducted. There was no record of the permeability test results or a trend analysis.

On June 23, 2016, a 400-hour periodic check was performed by the operator at 5,739 hours engine TSN, and 2,144 hours engine TSO on the engine's module 3. During the check they inspected the oil filter and the rear bearing's magnetic plug. There was no record of the inspection results.

On May 21, 2016, the oil level sight gauge was replaced by the operator at 5,637 hours engine TSN, and 2,042 hours engine TSO on the engine's module 3. The operator reported that the gauge was cloudy and dark and needed to be replaced. They also rinsed the oil system and conducted a rear bearing assembly permeability test; 100 milliliters of oil were collected during the test. A trend analysis was not completed.

The most recent gas generator rear bearing scavenge oil flow rate (permeability) check was performed 383 flight hours (FH) before the incident. The result of this test and the amount of oil collected was not recorded. The last rear bearing scavenge oil tube and in-line strainer maintenance was performed 209 FH before the incident. The lubrication system was serviced, the oil filter replaced, and engine oil change was last completed 51 FH prior to the incident. The rear bearing scavenge magnetic plug was inspected 12 FH prior to the incident. Oil change intervals during this period averaged 168 FH.

An oil system rinse and a permeability check were completed at 5,637 hours engine TSN. These tasks were unscheduled and were performed because of clouding of the oil tank's sight glass.

Prior to and during the incident the operator was using Mobile Jet II oil, which was acceptable per the engine maintenance manual (EMM). After the incident they switched to a high thermal stability Eastman 2197 turbo oil, per the oil options in the EMM. The high thermal stability oils provide better performance especially when stopping the engine quickly.

AIRPORT INFORMATIONMaintenance Information

On December 27, 2016, a 400-hour periodic check was performed by the operator at 6,146 hours engine time since new (TSN), and 2,551 hours engine time since overhaul (TSO) on the engine's module 3. During the check they inspected the oil filter and the rear bearing's magnetic plug. There was no record of the inspection results.

On December 14, 2016, a spectrometric oil analysis program (SOAP) was performed by the operator at 6,114 hours engine TSN, and 2,519 hours engine TSO on the engine's module 3. There was no record of the analysis results.

On October 22, 2016, an 800-hour and a 1,200-hour periodic check were performed by the operator at 5,988 hours engine TSN, and 2,393 hours engine TSO on the engine's module 3. During the 800-hour check they drained the oil system and inspected the rear bearing's magnetic plug strainer (TU208). During the 1200-hour check they removed and cleaned the oil scavenge tube. There was no record of either inspection results.

On July 25, 2016, a 600-hour periodic check was performed by the operator at 5,815 hours engine TSN, and 2,220 hours engine TSO on the engine's module 3. During the check, a rear bearing assembly permeability test was conducted. There was no record of the permeability test results or a trend analysis.

On June 23, 2016, a 400-hour periodic check was performed by the operator at 5,739 hours engine TSN, and 2,144 hours engine TSO on the engine's module 3. During the check they inspected the oil filter and the rear bearing's magnetic plug. There was no record of the inspection results.

On May 21, 2016, the oil level sight gauge was replaced by the operator at 5,637 hours engine TSN, and 2,042 hours engine TSO on the engine's module 3. The operator reported that the gauge was cloudy and dark and needed to be replaced. They also rinsed the oil system and conducted a rear bearing assembly permeability test; 100 milliliters of oil were collected during the test. A trend analysis was not completed.

The most recent gas generator rear bearing scavenge oil flow rate (permeability) check was performed 383 flight hours (FH) before the incident. The result of this test and the amount of oil collected was not recorded. The last rear bearing scavenge oil tube and in-line strainer maintenance was performed 209 FH before the incident. The lubrication system was serviced, the oil filter replaced, and engine oil change was last completed 51 FH prior to the incident. The rear bearing scavenge magnetic plug was inspected 12 FH prior to the incident. Oil change intervals during this period averaged 168 FH.

An oil system rinse and a permeability check were completed at 5,637 hours engine TSN. These tasks were unscheduled and were performed because of clouding of the oil tank's sight glass.

Prior to and during the incident the operator was using Mobile Jet II oil, which was acceptable per the engine maintenance manual (EMM). After the incident they switched to a high thermal stability Eastman 2197 turbo oil, per the oil options in the EMM. The high thermal stability oils provide better performance especially when stopping the engine quickly.

WRECKAGE AND IMPACT INFORMATION

The pilot landed the helicopter along the centerline of runway 3 at FSD, with a running landing distance of less than 100 ft. The helicopter did not sustain any additional damage during the landing.

A post-incident examination of the helicopter revealed fire damage limited to the aft outboard section of the No. 2 engine deck and the aft section of the engine compartment and cowling. The engine cowling, the central wall, and upper heat shield sustained thermal damage. Local blistering to the engine deck paint and oil splatter on the deck floor were observed. There was no evidence of a pool fire. The lower part of the engine was covered in oil residue with some thermal damage evident (Figure 1).

Figure 1 – Engine deck thermal damage and oil residue

The No. 2 engine oil tank was 1 to 1.5 quart...