Date: 201910
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: S-76/S-76 Mark II
Operator: Air Taxi
Operating under: Part 135
Flight plan: VFR
Mission: Passenger
Flight phase: Takeoff / Launch
ATC / advisory: Tower ZZZ
Aircraft component: Tail Rotor
Component problem: Malfunctioning
Reporter organization: Air Taxi
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Rotorcraft; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Troubleshooting
Second reporter function: Captain; Pilot Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Regained Aircraft Control; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Winds were out of the east at 10-15 kts in VFR conditions; and the aircraft was oriented directly into the wind. The helideck of the platform is located on the south side of the superstructure; with obstacles to the north. Upon departure from the platform; the aircraft began an unexpected right yaw and began to drift in a southwestern direction. Once the aircraft began to rotate; I as the First Officer took control; believing the PIC (Pilot in Command) to be disoriented; as I had not heard a verbal acknowledgement after taking control. On the second or third spin; I was able to regain directional control through the application of left pedal and slight left cyclic while oriented to the east into the wind. I then lowered the nose in order to gain airspeed and was able to regain full control and recover the aircraft at roughly 50 feet AGL. After establishing a climb; I coupled the flight controls to the flight director; began a turn to the northwest; and relinquished controls back to the PIC.We then began an analysis of the aircraft; checking for any warning/cautions/advisories; any unusual vibrations in the flight controls; or any indications that an aircraft limit had been exceeded. None were present; and based on this information we continued our flight as planned. We made two more subsequent stops to drop off passengers and cargo; and terminated our flight. We conducted a normal shutdown; and then noticed we had used transient power; seven seconds into a two-minute power limit. Maintenance was notified; and we as a crew notified our Supervisor of what had taken place.


Second narrative: On takeoff; the helicopter began a right yaw. I continued to increase power to ensure we were clear of all structure. The helicopter continued to yaw to the right at which time the second in command said I have the controls. He was on the clear side away from the all structure. I relinquished command of the controls to the SIC (Second in Command) though I followed him through in all his inputs. The tail rotor seem to have lost all effectiveness. I received at least two revolutions and then the aircraft stabilized and started to fly. I saw torque values of 120% and the main rotor RPM somewhere below 100%. At that point I perceived we had not exceeded any transient limits since there were no caution or warning lights visible. The aircraft began to climb normally. We reduced power and flew away with no further incidents. From the beginning when the aircraft started to yaw I was holding right cyclic increasing collective pitch and adding left pedal prior to the SIC taking the controls. He continued with the same but said he added more left pedal. When in level flight; we checked all functions of the aircraft and found no problems; and still no warning or caution light. The aircraft acted normal in all modes of flight.


Synopsis: S-76 flight crew reported loss of tail rotor effectiveness on takeoff.