Blue Hawaiian Helicopters Aerospatiale AS 355F1 accident

While operating under visual flight rules during an on-demand aerial sightseeing tour flight, the non-instrument-rated helicopter pilot encountered instrument meteorological conditions and impacted the 45- to 60-degree up sloping face of a 2,900-foot-high mountain, about 50 feet below the peak. The tour was intended to circumnavigate the west Maui Mountains with occasional close-up views of majestic locations. About 45 minutes before the accident, while returning from another tour flight, the pilot had flown near the accident site area. A videotape made during the earlier flight indicated that clouds were approaching the transition route into the valley, and the pilot elected to bypass it as did other tour pilots due to the clouds obscuring the mountain peaks in the Iao Valley. According to other company pilots, the weather conditions were typical for the area and included the tendency for rapidly changing conditions. When the search had begun for the overdue tour flight, the search pilots were unable to proceed up the valley due to the low height of the clouds. A witness in the Iao Valley State Park indicated that about 1000, he observed the Iao Needle (a vertical rock spire rising from the valley floor). The witness stated he noticed that a solid ceiling of clouds stretched from one side of the valley to the other (north to south). The cloud base obscured the upper 1/4 to 1/3 of the needle. (The Iao Needle's elevation at the top is about 2,250 feet msl, and it is located about 2 miles east of the accident site.) Three other tour flights were conducted within 2 miles of the accident site between 0950 and 1031. According to the pilots of these flights, the tours were modified to exclude the area flown by the accident pilot because of the weather conditions they observed in the area. Specifically, clouds obscured the Iao Valley ridgelines. Based on recorded radar data, about 10 minutes before completing the planned 30-minute-long tour, the pilot attempted to transition from the leeward to the windward side of the island via an established route into the Iao Valley. The pilot entered an area having multiple layers of clouds while climbing northward from 3,400 to 3,900 feet. Within 1 minute, the pilot reversed course and attempted to exit the valley. The pilot likely became disoriented regarding his location relative to the previously overflown ridgeline, and while in instrument meteorological conditions descended to 2,850 feet, whereupon the helicopter impacted nearly perpendicular to the face of the mountain.

Verbatim NTSB analysis and probable cause from the NTSB dataset