History of Flight
On October 22, 2009, at approximately 2020 Pacific daylight time, an Agusta A119 helicopter, registration N119AH, sustained substantial damage during a forced landing near Blythe, California. The helicopter was operated by Tri state CareFlight LLC on an aeromedical flight under 14 CFR Part 135. The flight had departed Blythe Airport at about 1959, destined for a hospital in Palm Springs, California. Visual meteorological conditions prevailed, and a company flight plan was filed.
The pilot reported that after climbing to 4,500 feet and leveling off for 5 to 7 minutes, he heard a change in rotor system sound and felt an unusual vibration in the cyclic. He applied aft cyclic to slow down and observed rotor RPM decay. He reduced airspeed to about 90 knots and lowered collective to regain rotor RPM. After stabilization, he slowly raised collective to re-establish cruise power, but the low rotor warning system activated and the rotor tachometer confirmed the indication. Lowering collective silenced the warning. He then tried manual throttle mode but achieved no improvement, and the warning activated again. He lowered collective, returned throttle to normal, and initiated a descent toward Interstate Highway I-10. Using night vision goggles, he identified a landing area, turned on landing lights and night sun, and monitored rotor RPM. At about 200 feet radar altitude, he turned off the night sun, flared, and touched down with minimal forward speed, sliding 6–8 feet in soft dirt before stopping upright. The engine continued running for 5–7 minutes before being shut down.
In an addendum, the pilot noted he did not go fully through the "dead ban" and felt a delay in throttle response, suggesting the second low rotor RPM warning occurred before throttle engagement.
Aircraft and Personnel Information
The 45-year-old pilot held an airline transport pilot certificate with rotorcraft and instrument ratings, and a second-class medical issued September 22, 2009. He reported 3,866 total flight hours, including 3,162 rotorcraft hours and 278 hours in the Agusta A119. His most recent flight review was July 21, 2009.
The helicopter had accumulated 4,122 total hours. It was on a progressive manufacturer's inspection program, with the most recent inspection completed on October 5, 2009.
Meteorological Information
At 2052, the Blythe Airport ASOS reported calm winds, visibility 10 miles, clear skies, temperature 23°C, dew point -2°C, and altimeter 29.82 inHg.
Examination and Testing
On-site examination revealed the helicopter upright with tail section separated from the hard landing. Main rotor blades remained attached, and no post-crash fire occurred. The helicopter was recovered to a salvage facility in Phoenix, Arizona.
The engine, a Pratt & Whitney Canada PT6B-37A, underwent functional testing at the P&WC Longueuil Test Facility from November 10–12, 2009. Tests in Gas Generator and Power Turbine modes, with both electronic and mechanical engine control, showed normal behavior. Manual override functioned normally. An anomaly was noted during one acceleration maneuver where NG speed dropped 8%, but the engine recovered within 5.2 seconds. Further tests could not replicate the event. No non-recoverable loss of power was observed under steady-state conditions. During engine removal after the second test, the pressure regulator assembly on the fuel control unit (FCU) was found to rotate relative to the housing.
The FCU (model DP-F2, serial number C68105) bench tests at the supplier, Honeywell, showed it met acceptance test requirements but exhibited fuel flow instability at low p3-pressure (sub-flight idle), not at the higher pressure corresponding to the event. Manual manipulation of the Pr regulator caused an air leak and temporary fuel flow drop; two of three housing screws were loose (inadequate torque). After re-torquing, no anomalies were noted. Fine black powder (chromium and iron oxide) was found in the override section, but no abnormal wear was evident. The reason for the reported loss of engine power could not be determined.
The electronic engine control (EEC) was downloaded at Hamilton Sundstrand; only fault data and engine data were recovered, with no functional test performed. The electronic N2 governor unit (EGU) passed all acceptance tests at Woodward Governor Company. The rotary variable differential transformer (RVDT) was undamaged, and the linear variable differential transformer (LVDT) had a bent armature (0.008 inch) but still met acceptance parameters.
Probable Cause
No probable cause was determined by the investigation.