Date: 201905
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Dawn
Aircraft: Commercial Fixed Wing
Operator: Other OEM
Operating under: Part 91
Flight plan: None
Mission: Test Flight / Demonstration
Flight phase: Takeoff / Launch
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Training / Qualification; Time Pressure; Distraction
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed As Precaution; Flight Crew Overcame Equipment Problem; Flight Crew Returned To Departure Airport
Contributing factors: Aircraft; Human Factors; Incorrect / Not Installed / Unavailable Part; Procedure
Primary problem: Incorrect / Not Installed / Unavailable Part

Narrative: The aircraft was conducting a light-weight flaps 25 takeoff with simulated engine failure to determine pitch target marker data as part of a Part 25 certification flight test program. The test procedure required the SIC to pull the right throttle to idle at 85 KCAS and for the PIC to rotate at 109 KCAS. V1 (Takeoff Decision Speed) was coincident with Vr (Takeoff Rotation Speed); i.e. 109 KCAS. The original design intent of the aircraft was that flaps 25 was a landing flap and not a takeoff flap setting. Consequently the avionics were designed to trigger a 'CONFIG FLAPS' warning message if takeoff was attempted in flaps 25. During development flight testing it was decided that flaps 25 was going to be required for use as a takeoff flap setting. Therefore for this particular test point aural warnings were inhibited using the 'AURAL INHIBIT' push button and the takeoff run was initiated with a CONFIG FLAPS warning and AURAL INHIBIT advisory on the CAS (Calibrated Airspeed) stack. The right throttle was retarded to idle at 85 KCAS as planned. The SIC confirmed the left engine had correctly increased to the Automatic Power Reserve thrust setting and looked nominal; before returning his scan to the Primary Flight Display to make the 'rotate' call as the aircraft continued to accelerate rapidly due to its light weight. At 94 KCAS the 'FIRE ENG L' warning message initiated; flashed twice; came on steady for 2 seconds and occulted at 110 KCAS. By design new CAS messages flash twice as part of the alerting system's attention-getting function and all messages are persistent for a minimum of 4 seconds; so the indications were in accordance with the design for a momentary fire detection. The PIC's attention was focused mainly outside the aircraft; maintaining directional control for the simulated engine failure. The SIC's attention was possibly channelized on the PFD (Primary Flight Display) and he incorrectly attributed the 2 flashes of the CAS message as an intermittent fault. The normal aural warnings for an engine fire that could have alerted the PIC were muted; as planned; per the test point setup. The SIC called for 'rotate' at 109 KCAS; 4 seconds after the first indication of fire; which was when all fire indications disappeared. At approximately 400ft AGL the SIC highlighted his concern that there had been a momentary fire indication and onboard Flight Test Engineers were able to confirm that there had been 2 very short (approximately 1 second) exceedances of the parameter that would trigger the 'FIRE ENG L' warning. The right engine was brought back into use; the left engine was retarded to idle for the rest of the flight and the aircraft was landed immediately without further incident. In post-flight investigation it was determined that 2 of the left engine boroscope inspection ports had not had their plugs installed before flight. One was the high pressure turbine (HPT) inspection port; the other was to another slightly less hot part of the engine. There was significant damage to the thrust reverser thermal insulation adjacent to the 2 open inspection ports. The HPT port was adjacent to the 2 fire detection loops and it appeared as if hot gas from that port had impinged on the fire detection loops. A full boroscope inspection of the engine had occurred since the previous flight with all 9 inspection plugs removed. The 2 uninstalled plugs were found in the hangar; still in the tote used during the recent boroscope inspection maintenance activity. Preliminary investigation suggested that 7 of the plugs were placed on one side of the tote; and the other 2 plugs were put on the other side of the tote where they could not be seen from some angles. Re-installation of all 9 plugs had been signed off as being completed by both the maintainer who performed the work and an independent quality assurance checker.




Synopsis: Flight Test crew experienced engine fire warning after takeoff due to borescope plugs not being installed before flight.