Helicopter Pilot’s Spatial Disorientation Detailed
Two crewmembers and five passengers aboard a Sikorsky S-92 operated in IMC by Cougar Helicopters were only 38 feet above the waters of the Atlantic Ocean when the pilot, having suffered a bout of spatial disorientation, regained control of the helicopter, according to a September 12 report from Canada’s Transportation Safety Board. The incident occurred on July 23, 2011, 217 miles southeast of St. John’s, Newfoundland.
During the IMC departure procedure from the Sea Rose oil platform, the captain made a large, rapid aft cyclic input just before the cyclic trim button was released and the autopilot’s go-around mode engaged. This caused the helicopter to enter a nose-high, decelerating pitch attitude that neither pilot noticed, possibly due to brightening within the cockpit that they interpreted as clear skies just above.
The airspeed of the helicopter continued to decrease, eventually to within 5 knots of the minimum control speed in instrument meteorological conditions (VMINI) when the captain momentarily pressed the cyclic force trim release button and made an aft cyclic input. This caused the helicopter’s airspeed to decrease below VMINI, and the helicopter to enter a 23-degree nose-high attitude followed by a descent toward the water.
“The captain, subtly incapacitated possibly due to spatial disorientation, did not lower the nose of the helicopter and apply collective to recover from the nose-high attitude,” concluded the report. “This contributed to the excessive amount of altitude that was lost during the inadvertent descent.”
The helicopter broke out of the clouds at 200 feet above sea level as full power was added to both engines, over-torquing both. The crew did not regain full control until the aircraft was 38 feet above sea level.
The helicopter eventually landed safely at St. John’s.