History of Flight
On November 15, 2011, at 0837 mountain standard time, a Williams Helicopter Corporation UH-1H helicopter (registration N502AW), operating under 14 CFR Part 91 as a business flight, lost main rotor transmission power during initial climb. The pilot, the sole occupant, performed a hard landing approximately 3 miles northwest of Valle Airport (40G), Grand Canyon, Arizona. The helicopter came to rest on its right side. The pilot reported flying at about 500 feet above ground level (agl) when the Master Caution warning illuminated, triggered by transmission low oil pressure. He turned left away from power lines and set up an approach. During descent, the helicopter yawed left and right at 50 and 30 feet agl. At about 10 feet agl with nearly zero airspeed, main rotor speed slowed and stopped, causing the helicopter to fall to the ground. The pilot cut himself free, called 911, and awaited rescue. The engine continued running for 10-15 seconds after impact. A witness heard a change in engine sound but did not see the accident.
Personnel Information
The 57-year-old pilot held a commercial pilot certificate with ratings for airplane single- and multi-engine land, helicopter, and instrument ratings for airplane and helicopter, as well as a helicopter instructor rating. He was issued a second-class medical certificate on January 11, 2011, with no waivers or limitations. He reported 27,000 total flight hours, with 450 hours in the preceding 6 months.
Aircraft Information
The helicopter, a restricted category UH-1H, was powered by a Honeywell T53-L-703 turbine engine (serial number LE10115Z), overhauled on August 30, 2005. A 25/50-hour inspection was performed on October 18, 2011, at total time 4,854.7 hours. The annual inspection was due in November 2011. In August 2011, the main rotor assembly, mast, and main transmission assembly were removed; new mounts and boots were installed, along with overhauled dampers. The assembly was reinstalled with no discrepancies noted after a ground run and leak check.
Wreckage and Impact Information
The helicopter impacted flat desert terrain, leaving a ground scar about 15 feet long. It came to rest on its right side heading approximately 350 degrees. The landing gear skid crossover tubes were shoved into the underside, crushing the lower fuselage and control rods. The aft crossover tube separated from the fuselage. All fuel bladders remained in place except the left aft bladder, which rested atop the belly; fuel leaked from the fuselage, but the separated bladder was half full. The tail rotor separated and came to rest 180 feet from the main wreckage; the tail rotor drive shaft between the 42- and 90-degree gearboxes separated. Main rotor blades, transmission assembly, and mounts separated but remained in their normal relative position; blades had ground damage but no leading edge damage. The main rotor transmission remained intact but separated from the fuselage; the drive shaft between engine and transmission separated, with fractured K-flex couplings at both ends. Flight controls were intact except for the collective rod and pitch horn on one blade. The tail rotor output quill coupling gear was exposed. The engine showed no obvious damage except a band of discoloration and peeling paint around the transmission oil jet area; a bolt was missing from an oil jet mounting flange, but no oil stains were observed.
Tests and Research
An engine inspection at Air Transport in Phoenix on May 8, 2012, revealed impact damage to the fuselage. The cockpit roof was crushed; transmission mounts separated. The oil tank had impact damage and contained no oil. The engine output shaft rotated freely. Debris was found in the engine inlet. The transmission was disassembled: large metal pieces were found in the cavity; oil pump was intact with some debris and scoring. Freewheeling unit was locked. Three oil jets each missing one retaining bolt. The swashplate mast had metal debris but no scoring. Molten metal was found in the upper planetary gear area. The sun gear showed metal transfer and smearing, indicating power at impact. The lower planetary gear assembly was significantly damaged. The main input quill housing cracked. A castellated nut and the lower planetary gear retaining cap nut were found in the lower housing. Oil lines and pressure regulator were debris-free. The transmission oil manifold and chip detector were examined by the NTSB Materials Laboratory; particles of various compositions (low alloy steel, magnesium alloy, brass) were found. CT imaging showed medium and high density materials in several locations but no completely blocked passages. A Bell Helicopter representative reviewed photos and stated the transmission seized due to over-temperature from lack of lubrication, noting that both main and tail rotor blades had stopped before impact. The UH-1H flight manual directs pilots to land as soon as possible upon Master Caution and transmission oil pressure/hot warnings, and perform an emergency shutdown after landing.