LAX00LA193 · Sikorsky S61A

The twin engine helicopter experienced a dual loss of engine power while en route to the landing area during external long line logging operations and made a forced landing into trees. The flight crew noticed the low fuel caution lights began to flicker on and off just prior to the last logging run. The co-pilot indicated there was 225-250 pounds of fuel left in each fuel tank. The captain decided that they had enough fuel remaining in each fuel tank to finish the last log run, pickup an empty fuel tank on the long line, and return to their base to refuel with about 200 pounds of fuel in the tanks at landing. As the flight crew started the last log cycle, the number 1 LOW PRESSURE light illuminated, but the captain determined it was not an emergency situation and they continued with the flight. After the flight crew picked up the empty fuel tank, it swung toward some ground personnel. The captain pulled the nose up so that the tank would clear the ground crew. Shortly thereafter, the number 1 engine lost power. The captain initiated a landing to a field, but the number 2 engine lost power and the captain performed an autorotational landing to some soft pine trees. As part of the post accident helicopter recovery efforts, the salvage company drained the fuel tanks and found that approximately 167 pounds of fuel in the forward tank and 154 pounds in the aft tank (in his statement, the captain said that 10 gallons were drained first, set aside as the unusable fuel quantity and not counted in the totals reported by the salvage company). Post accident examination of the fuel system found that the aft fuel tank ejector pump, which fills the collector can that supplies fuel to the engine, was 90 percent blocked by a material that resembled old fuel tank sealant and/or disintegrating fuel bladder remnants. The forward fuel tank ejector pump was not obstructed. The helicopter's flight manual indicates that the low fuel caution lights will illuminate when approximately 210-280 pounds of fuel per tank remain while the helicopter is in a 3-degree nose down attitude, or between 170-200 pounds of fuel per tank remain when in a hover. A caution note is incorporated in the flight manual indicating that when the fuel low-level caution lights illuminate, attitudes in excess of 6 degrees nose up should be avoided due to the possibility of engine fuel starvation. The limitations section of the flight manual indicates that the minimum planned fuel on final landing shall not be less than 450 pounds total. According to the manual, the total unusable fuel is 17.75 pounds of fuel per tank. The captain said that the versions of the S61 that he had been flying have modified fuel tanks that reduce the minimum landing fuel to 200 pounds and he was unaware that the accident helicopter had the standard military fuel tanks with a higher 450-pound landing minimum. The captain also said that in the weeks before the accident he had found "dried up adhesive in the fuel samples" taken during preflight inspections. A former crew chief for the company said that the standard procedure the company used in response to fuel leaks was to "repaint" the fuel tanks with sealant and return the helicopter to service.

Verbatim NTSB analysis and probable cause from the NTSB dataset