History of Flight
On August 22, 2010, at about 1819 Pacific daylight time, a Robinson R44 Clipper (registration N7186Z) operated by Point Zero Corporation under 14 CFR Part 91 made a forced landing in the water at San Diego, California. The private pilot sustained serious injuries, and the helicopter sustained substantial damage from impact forces. The flight was a local personal trip departing from a yacht. Visual meteorological conditions prevailed; no flight plan had been filed.
The pilot reported that he filled the fuel tank and departed Montgomery Field (MYF) at 1515 to his yacht at the Convention Center Marina. Around 1800, he prepared for the return trip to MYF, completed magneto and deicing checks, and planned to fly south over the Coronado Bridge. He contacted the Navy’s North Island air traffic control tower.
After lifting off the yacht, the pilot increased airspeed to 60 knots. As he approached the bridge, the engine lost power. He was above the bridge but the helicopter would not climb. He heard a screeching sound in his headset, airspeed decreased, the low rotor RPM horn sounded, and manifold pressure increased. He pulled up on the collective with no response. He began an autorotation and turned into the wind. The helicopter fell rapidly, and he could not get fully into the wind before touchdown. At about 100 feet above ground level, he deployed the floats and pulled the nose up into a flare. He could not determine if the tail boom hit the water first. He remembered releasing the carburetor heat tab.
All plexiglass shattered, and the pilot went underwater. He released his seat belt while evacuating and realized his back was badly hurt. He was sitting on floating wreckage when first responders arrived within 2 minutes.
A witness at a restaurant overlooking the water reported hearing a sputtering sound, saw the helicopter bank left and descend rapidly, and lost sight as it went below the tree line. She did not hear the helicopter warm up before departure.
An FAA inspector examined the helicopter after recovery. The carburetor heat tab had been released, but the carburetor heat knob in the center console was in the OFF (down) position.
Meteorological Information
The closest official weather observation station was San Diego (KSAN), 4 nautical miles northwest of the accident site. At 1751 PDT, a METAR reported wind from 310° at 7 knots, visibility 10 miles, sky 20,000 feet scattered, temperature 24°C/75°F, dew point 14°C/57°F, altimeter 29.87 inHg, and relative humidity 55 percent.
Tests and Research
On August 25, 2010, NTSB, Textron Lycoming, and Robinson Helicopters examined the wreckage at the Robinson factory in Torrance, California. Control continuity was established for the rotor head; tail rotor disconnects had jagged fracture surfaces. About 8.25 gallons of blue fluid (smelling like aviation gasoline) and 0.75 gallons of clear fluid were drained from the main fuel tank; from the auxiliary tank, about 3.5 gallons of blue fluid and 1.5 gallons of clear fluid were drained.
The engine crankshaft and accessory gears rotated freely. Thumb compression was obtained on all cylinders; valves moved freely with equal lift. Spark plugs appeared identical with no mechanical damage. Slight rotational scoring was noted on the cooling fan and upper drive belt sheave. Dried magnetos produced spark at each post when rotated. The carburetor heat cable was stretched and unreadable. No light bulb elements appeared stretched. Light blue fluid with aviation gasoline odor was found in numerous fuel system components.
Additional Information
The R44 Pilot Operating Handbook (POH) Section 4 directs pilots to apply carburetor heat when conditions conducive to ice are known or suspected, including high humidity or operating near water. It cautions that the governor may automatically increase throttle, maintaining constant manifold pressure and RPM, masking ice formation.
The accident helicopter had a carburetor heat assist device that correlated heat application with collective setting to reduce workload. Lowering collective added heat; raising collective reduced heat. A latch locked the control knob OFF. The POH recommended unlatching when OAT was between 80°F and 25°F and dew point spread less than 20°F, and adjusting heat after power changes.
The pilot stated he released the latch; the FAA observed it released at the accident site, but the carburetor heat knob was OFF.
Robinson Safety Notice SN-25 (1986, revised 1999) informed pilots about carburetor ice, noting that helicopters take off using only required power, making them vulnerable, especially with a cold engine and induction system. It recommended full carburetor heat during warm-up and as required during hover and takeoff.
FAA SAIB CE-09-35 (June 30, 2009) informed pilots of carburetor icing hazards, noting it can occur above freezing with visible moisture or high humidity. Vaporization and venturi cooling can build ice rapidly. A graph showed conditions at this accident (75°F, 55% humidity) were in the area of serious icing for glide power and icing for glide and cruise power.