ORLANDO, FL, USA
N16705
BELL 206L
SHORTLY AFTER TAKEOFF, USING WATER/ALCOHOL INJECTION, THE PILOT NOTED THE N2 TURBINE SPEED INDICATION WENT TO THE TOP OF THE GAUGE. HE ROLLED OFF THROTTLE TO REDUCE THE N2 GAUGE READING; AT THE SAME TIME, HE LOOKED FOR A PLACE TO LAND. THE PILOT BELIEVED THERE WAS INSUFFICIENT ALTITUDE FOR AN AUTOROTATION. SUBSEQUENTLY, THE HELICOPTER TOUCHED DOWN HARD & CAME TO REST WITH EXTENSIVE DAMAGE. A POSTACCIDENT EXAM REVEALED NO PREIMPACT FAILURE OF THE AIRFRAME, FLIGHT CONTROLS, OR FUEL SYSTEM. TESTING OF THE WATER/ALCOHOL SOLUTION REVEALED 66.5% METHANOL & 33.5% WATER. SPECIFICATIONS REQUIRED 33.5% METHANOL & 66.5% WATER, BUT ALLISON ENGINE PERSONNEL SAID THE HIGH LEVEL OF METHANOL WOULD NOT HAVE AFFECTED ENGINE PERFORMANCE. DURING A POSTACCIDENT TEST, THE ENGINE OPERATED TO FULL POWER WITH NO EVIDENCE OF FAILURE OR MALFUNCTION. TESTING OF THE ENGINE INSTRUMENTS REVEALED THE N2 GAUGE WAS PROVIDING A FAULTY INDICATION. THE OTHER ENGINE INSTRUMENTS OPERATED NORMALLY AFTER THE ACCIDENT.
On March 25, 1994, about 1242 eastern standard time, a Bell 206L, N16705, registered to Universal Air Service of Florida, Inc., crashed while making an off-heliport landing at Orlando, Florida, while on a 14 CFR Part 91 sightseeing flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft received substantial damage. The commercial-rated pilot and one passenger received minor injuries. Four passengers received serious injuries. One passenger was not injured. The flight was originating at the time of the accident. The pilot stated that shortly after departure he activated the water-alcohol injection system and noticed an increase in engine performance and a reduction in turbine out temperature (TOT). A short time later he noticed that the N2 turbine speed was slightly above red line and rapidly swung to near the upper limit of the gauge. He reduced the throttle slowly to attempt to manually override the N2 overspeed, picked out a landing area, and began an approach to the landing area. He rolled the throttle to the idle detent, with no effect on the N2 overspeed and the engine quit shortly after this. He did not have enough altitude and airspeed to enter autorotation and the helicopter descended and touched down hard. Witnesses observed the helicopter flying from east to west at about 300 feet. The helicopter was making a high pitched squeal and was descending. The helicopter appeared to lose power and then crash in a construction area. Examination of the helicopter by FAA inspectors after the accident indicated that there was no evidence of precrash failure or malfunction of the aircraft structure, flight control systems, or airframe fuel system. A usable amount of uncontaminated fuel was found in the airframe and engine fuel systems. A water- alcohol solution was found in the water injection tank. After the accident the engine was removed from the aircraft and mounted in a engine test cell. The engine was started and operated to full power with no evidence to indicate precrash failure or malfunction. After the test run, the engine fuel control, governor, fuel pump, and bleed valve were removed from the engine and tested on a test bench. Each of the units operated normally. After the accident the N1, NR, N2, and TOT gauges and signal generators were removed from the aircraft for testing. The N1 gauge and generator, TOT gauge, and NR gauge operated within limits. The N2 gauge was found to read 10 to 15 percent low in the range above 90 percent. The N2 generator operated normally. See attached Bell Helicopter report. Laboratory testing of fuel and water-alcohol samples obtained from the helicopter after the accident was performed by Panair Laboratory, Inc., Miami, Florida. The fuel sample met specifications for aviation turbine fuel and no contamination of the fuel sample was reported. The water-alcohol sample was found to be a mixture of 66.5 percent methanol and 33.5 percent water. See attached laboratory report. Bell Helicopter and Allison Engine specifications require that water-alcohol fluid be mixed 33.5 percent methanol and 66.5 percent water. Allison engine personnel stated that the high level of methanol which was found in the accident helicopter would not have effected engine performance, for the engine controls would have countered any effect. See attached Allison Engine report.
THE PILOT'S FAILURE TO CROSS-CHECK A FAULTY ENGINE SPEED INDICATION WITH OTHER ENGINE PERFORMANCE INDICATIONS TO VERIFY WHETHER AN ENGINE MALFUNCTION HAD ACTUALLY OCCURRED, AND HIS FAILURE TO MAINTAIN ADEQUATE ROTOR RPM DURING AN EMERGENCY LANDING. THE PILOT'S REACTION TO THE PERCEIVED ENGINE MALFUNCTION LED TO AN UNNECESSARY REDUCTION OF ENGINE POWER AND SUBSEQUENT EMERGENCY LANDING.
Source: NTSB Aviation Accident Database
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