Date: 202102
Local time of day: 0001-0600
Location: ZZZZ.Airport, FO
Light: Night
Aircraft: B777 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Situational Awareness
Second reporter function: Captain; Pilot Flying
Anomaly: Ground Event / Encounter Loss Of Aircraft Control; Ground Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: Taxi
Result: Aircraft Equipment Problem Dissipated; Flight Crew Overcame Equipment Problem; Flight Crew Took Evasive Action; General Maintenance Action
Contributing factors: Airport; Weather
Primary problem: Airport

Narrative: While turning into Spot XXX on the cargo apron in ZZZZ; the plane was unable to stop in a timely manner due to what I believe was contamination on the apron. Due to the lack of braking ability the CA (Captain) briefly deployed the thrust reversers and the plane was then able to slow and we regained braking ability. I was not aware that there was difficulty braking until the CA deployed the reversers. We then proceeded to finish the turn into [spot] without issue. The entrance to the ramp was well cleaned and mostly free of contaminants; and according to the Captain; the braking condition was very good. However; further into the ramp; the contamination became present; although it was not very visible; almost like it was black ice on top of the pavement. When we exited the plane after shutting down and securing; the ramp and parking area was covered in a transparent; very slippery layer of ice with slush scattered sporadically throughout. I believe that this ice existed on the apron just outside of the parking spot as well. There was no active precipitation and all of the airport surfaces we had been on up until that point had had good breaking conditions. Thankfully the CA was able to control the aircraft without causing damage to the plane or surroundings. I do not have an exact recollection of the ground speed when we had the difficulty breaking; but I would estimate it to be in the range of roughly 5-7 knots. We notified the ground crew of the difficulty braking and hopefully they took actions to decontaminate that area of the ramp for the next aircraft.I believe the transition from well-cleared; contaminant free areas; to the contaminated area caused the braking issue. It was also night and the light did not reflect off of the ice on the contaminated areas of the ramp; making it difficult to see the contamination. I thought the Captain was maintaining a safe speed for the conditions and was surprised when the reversers were deployed.I would suggest that the entirety of the ramp is cleared to the same standard in the future if able. Crews should also be extra vigilant of contamination that is not easily visible in low light; or poorly lit conditions.


Second narrative: Normal arrival. While taxiing to Stand XXX we were following a company aircraft. Due to the light weight of our aircraft it kept accelerating while at idle thrust. When entering the cargo ramp; the pavement was bare and wet. The last 500 feet of taxi had thin frozen slush. The aircraft ahead slowed; and we were slowing to turn into our stand; when the Captain noted the aircraft was sliding. He applied full brakes to no effect; then deployed reverse thrust on both engines; slightly above idle. The aircraft slowed and stopped after sliding about 50 feet. The reversers were stowed and the aircraft turned into the stand and parked. As it approached the stop point it again slid about 5 feet in the attempt to stop. Reverse thrust was not used a second time. Less than 30% n1 in reverse.[The cause was] thin ice on the ramp. Taxi speed about 8-10 knots. Unnoticed change in braking effectiveness. Fatigue from a 15+ hour day.Reverse thrust was a last ditch effort to not scrape paint. Parking brake might have worked also. Even creeping to the stop point; the aircraft still slid about 2 feet past the stop point.


Synopsis: B777 flight crew reported temporary loss of directional control while taxing into parking spot due to contaminated ramp area.