Grand Prairie, TX, USA
N106LN
EUROCOPTER AS 350 B3
The instructor pilot reported that he and the pilot receiving instruction departed on a local night instructional flight to perform a simulated hydraulics failure maneuver in the helicopter. On shallow approach to the runway with hydraulic power off, the instructor told the pilot to fly the helicopter to a designated point on the airfield, at which point, the pilot was to perform a go-around. As the helicopter was "getting a little slow," the instructor again mentioned to the pilot that he needed to go around. As the pilot increased power, the helicopter's nose started rising, and the instructor told the pilot to get the nose down to increase the airspeed. The pilot remarked that it was hard to apply right pedal, so the instructor also manipulated the controls to assist him. At this point, the helicopter had started to turn left, and the instructor applied forward cyclic. The helicopter pitched nose down, and the instructor thought he might have overcompensated. The instructor felt the pilot applying aft cyclic, and the helicopter again pitched nose down, so he made an additional control input to level the helicopter. However, the helicopter started spinning left, developed extreme pitch attitude changes, and was not climbing. The instructor again attempted to level the helicopter, reduced the power to slow the rotation, and reapplied power to cushion the landing. The helicopter subsequently impacted terrain and rolled onto its right side. Flight control continuity was established, and all observed separations were consistent with overload. No evidence of any preexisting failures of the helicopter's airframe or engine were found that would have precluded operational control of the helicopter. The recorded vehicle monitor data were consistent with impact and rollover occurrences, and no preimpact failures or overlimit events were recorded. The flight manual notes that the hydraulic failure safety speed is from 40 to 60 knots and contains a caution to not attempt hover flight or any low-speed maneuver without hydraulic pressure assistance. The caution noted that the intensity and direction of the control feedback forces will change rapidly, which will result in excessive pilot workload, poor aircraft control, and possible loss of control. It is likely that the pilot receiving instruction failed to maintain adequate airspeed during the simulated hydraulics failure maneuver, which resulted in his loss of control of the helicopter and its subsequent impact with terrain.
HISTORY OF FLIGHTOn June 7, 2013, about 2140 central daylight time, N106LN, a Eurocopter AS 350 B3 helicopter, impacted terrain and came to rest on its side at the Grand Prairie Municipal Airport (GPM), near Grand Prairie, Texas. The two pilots sustained minor injuries. The helicopter sustained substantial tailboom damage. The helicopter was registered to CFS AIR LLC, Danbury, Connecticut, and was operated by Air Methods Corporation, Englewood, Colorado, under the provisions of 14 Code of Federal Regulations Part 91 as an instructional flight. Night visual flight rules conditions (VFR) prevailed for the flight, which did not operate on a VFR flight rules flight plan. The local flight originated from GPM about 2111. According to the instructor pilot, they were performing a "simulated" hydraulics failure maneuver. On shallow approach, he told the pilot under instruction to fly the helicopter to a designated point at which they would do a "go around." The instructor pilot, in part, stated: As the pilot got down to approximately 3-5 feet, we were getting a little slow I again mentioned that we go around. We were at that time, on the left side of the runway. As the pilot started increasing the power, the nose started coming up and I told him to get the nose down so the airspeed would increase. He also said it was hard to apply right pedal, so I came on the controls with him to assist because by this time, the aircraft was starting to turn left of runway heading. As I applied forward cyclic, I think that we may have overcompensated and when the nose started coming down past level attitude, I felt the pilot was applying aft cyclic feeling that he was going to be too much nose down, which we were. Again, I made an input to get the aircraft level. The aircraft started spinning more to the left, and we were experiencing more extreme pitch attitude changes and not climbing. I think that I had told him to turn the hydraulic switch back on and I don't know if he was able to do that or not. At some I point, I noticed that the aircraft was positioned in the water retention basin and I saw that we might be heading toward an rv park nearby. At this point, I just tried to get the aircraft level and since the right pedal input to correct the left spin, I reduced the power to at least slow the rotation down. I saw the ground coming up rapidly and applied power again to cushion the landing as much as possible. We impacted the ground and rolled over on our right side. According to the pilot under instruction, the helicopter departed GPM's runway 35 and entered left closed traffic. The pilot under instruction, in part, stated: After a climb to 1200 [feet] and 80 [knots] the check airman initiated simulated hydraulics off, by depressing the hydraulic test switch. I slowed the [helicopter] to 60 [knots] and moved the collective hydraulic switch to the off position. I turned base to final for a low approach adjusting the airspeed and altitude as necessary arriving over the runway, intending to touch down at, or just above [effective translational lift]. The check airman asked if I thought I could land safely and I answered yes. He said, "Okay let's go around." When I applied power and pushed the nose over to gain airspeed the helicopter yawed approximately 45 degrees left and the nose tucked slightly. I added more right peddle but was unable to correct the yaw. As we proceeded to the left margin of the runway, I added right cyclic. This made the aircraft crab right, but the nose continued to yaw left. At about 90 degrees to the runway, the check airman got on the controls as we began a rapid series of turns to the left, each revolution faster and more violent than the last, until impacting sloping terrain just west of the runway. The aircraft landed left skid high on the slope, and rolled on its right side facing southeast. PERSONNEL INFORMATIONThe instructor pilot, age 64, held a Federal Aviation Administration (FAA) commercial pilot certificate with rotorcraft-helicopter and instrument helicopter ratings. He held a flight instructor certificate with helicopter and instrument helicopter ratings He held a second-class medical certificate with no limitations, which was issued on October 17, 2012. The operator's accident report indicated that the pilot accumulated 10,550 hours of total flight time and 1,851 hours of flight time in AS350 helicopters. The operator reported that the pilot accumulated about 75 hours of flight time in the 90 days prior to the accident, 32 hours within the 30 days prior to the accident, and 4 hours in the 24 hours prior to the accident. The pilot received his most recent flight review on January 14, 2013. Subsequent to the accident report, the operator further outlined the instructor pilot's flight time since April of 2008 to July 9, 2014, as: AS350 B 5+00 hours AS350 BA 10+26 hours AS350 B2 282+10 hours AS350 B3 205+05 hours The pilot under instruction, age 66, held a FAA commercial pilot certificate with rotorcraft-helicopter and instrument helicopter ratings. He held a second-class medical certificate with no limitations, which was issued on November 21, 2012. The operator's accident report indicated that the pilot accumulated 9,511 hours of total flight time and 76 hours of flight time in AS350 helicopters. The operator reported that the pilot accumulated about 18 hours of flight time in the 90 days prior to the accident, 1 hour within the 30 days prior to the accident, and 1 hour in the 24 hours prior to the accident. The pilot received his most recent flight review on June 8, 2012. Subsequent to the accident report, the operator further outlined the pilot's flight time since April of 2008 to July 9, 2014, as: AS350 B2 2+25 hours AS350 B3 119+31 hours AIRCRAFT INFORMATIONN106LN was a 1999 model Eurocopter AS 350 B3 helicopter with serial number 3251. It had a replacement FAA airworthiness certificate issued on March 28, 2000. According to the operator, the helicopter's most recent maintenance inspection was completed on June 6, 2013. The helicopter accumulated 7,682 hours of total time on that date. Its maximum gross weight was 4,961 pounds. The helicopter was powered by a Turbomeca Arriel 2B engine, serial number 22036, which was rated at 747 horsepower for takeoff and 728 horsepower for continuous operations. The operator reported that at the time of the accident, the helicopter's weight and balance was 4,355 pounds and its moment arm was at 135.9 inches from its datum, which were both within limitations. According to NTSB report LAX05LA025, on November 2, 2004, N106LN experienced a partial power loss after takeoff followed by a hard landing. The helicopter's tailboom was substantially damaged and a major repair and alteration form, dated April 1, 2005, approved its tailboom's repair. METEOROLOGICAL INFORMATIONAt 2135, the recorded weather at GPM was: wind 040 degrees at 4 knots; visibility 10 statute miles; sky condition clear; temperature 24 degrees C; dew point 11 degrees C; altimeter 29.93 inches of mercury. AIRPORT INFORMATIONN106LN was a 1999 model Eurocopter AS 350 B3 helicopter with serial number 3251. It had a replacement FAA airworthiness certificate issued on March 28, 2000. According to the operator, the helicopter's most recent maintenance inspection was completed on June 6, 2013. The helicopter accumulated 7,682 hours of total time on that date. Its maximum gross weight was 4,961 pounds. The helicopter was powered by a Turbomeca Arriel 2B engine, serial number 22036, which was rated at 747 horsepower for takeoff and 728 horsepower for continuous operations. The operator reported that at the time of the accident, the helicopter's weight and balance was 4,355 pounds and its moment arm was at 135.9 inches from its datum, which were both within limitations. According to NTSB report LAX05LA025, on November 2, 2004, N106LN experienced a partial power loss after takeoff followed by a hard landing. The helicopter's tailboom was substantially damaged and a major repair and alteration form, dated April 1, 2005, approved its tailboom's repair. WRECKAGE AND IMPACT INFORMATIONThe helicopter came to rest on its right side in the grass infield on the west side of runway 35 about 1,000 feet from the runway's threshold. The main rotor blades exhibited varying degrees of damage consistent terrain impact. The cowling over the rotor mast was deformed and torn. The left side, as viewed from aft looking forward, fuselage and tailboom near their juncture exhibited areas of buckling. A semicircular opening was torn in the cowling covering the tail rotor driveshaft about a foot aft of the tailpipe exhaust heat shield. Skid-width indentations were noted in the grass infield surface near the wreckage. FAA representatives, party members, and technical advisers examined the wreckage on-scene and during follow-up examinations. The engine and its main rotor gearbox remained attached and were located within the fuselage structure. Flight control continuity was traced and all observed separations were consistent with overload. The hydraulic system was supplied hydraulic pressure and no leaks were noted. The hydraulic system, including the three main rotor servos, accumulators, and tail rotor servo and yaw load compensator, functioned when tested. ADDITIONAL INFORMATIONThe FAA Helicopter Flying Handbook described effective translational lift. The handbook, in part, stated: While transitioning to forward flight at about 16 to 24 knots, the helicopter goes through effective translational lift (ETL). ... Between 16 and 24 knots, the rotor system completely outruns the recirculation of old vortices and begins to work in relatively undisturbed air. The flow of air through the rotor system is more horizontal; therefore, induced flow and induced drag are reduced. The AOA is effectively increased, which makes the rotor system operate more efficiently. This increased efficiency continues with increased airspeed until the best climb airspeed is reached, and total drag is at its lowest point. The Eurocopter AS 350 B3 Flight Manual Supplement, Hydraulic Pressure Failure Training Procedure, in part, stated: To simulate a loss of hydraulic power, depressing the "HYD TEST" pushbutton on the central console produces the same effects as a real failure: The hydraulic pump pressure is by-passed The main rotor accumulators give limited time hydraulic assistance back-up. The red HYD light comes on, the Gong sounds one time. The simulation of a hydraulic failure is the same as a real failure with the exception that the tail rotor load compensator is depressurized and tail rotor pedal control feedback forces are higher than normal when pushing on the right pedal. ... CAUTION: Do not attempt to carry out hover flight or any low speed maneuver without hydraulic pressure assistance. The intensity and direction of the control feedback forces will change rapidly. This will result in excessive pilot workload, poor aircraft control, and possible loss of control. NOTE: The pilot must ensure that the "HYD TEST" pushbutton is selected off (upper position) prior to cutting off hydraulic assistance, or else the tail rotor load compensator will not be pressurized and right pedal force may be very high. The manual also noted that the hydraulic failure safety speed is 40 to 60 knots. FLIGHT RECORDERSThe helicopter was equipped with a vehicle engine multifunction display (VEMD), part number B19030MC05, serial number 1177, which is a dual screen display that provided vehicle and engine information to the pilot during flight (known as flight mode). The VEMD also has a maintenance mode, which stored non-volatile data for specified vehicle and engine exceedances and/or overlimits and VEMD-system-related hardware or communication failures. The VEMD also recorded and stored flight reports, which can be found in the maintenance pages. A flight report begins when aircraft electrical power is applied and engine generator speed (NG) reaches 60 percent. The flight report ends when the NG decreases below 50 percent with aircraft electrical power still applied. During a normal landing and shutdown, the VEMD will display the flight report for the most recent flight when NG drops below 10 percent and main rotor rpm (NR) decreases below 70 rpm. The helicopter's engine was equipped with a single-channel digital engine control (DECU), part number 70BMB01020, serial number 1515, which monitors and controls engine operations. It incorporated a redundant electrical supply from the engine alternator and aircraft battery. The DECU was programmable and interfaced between the aircraft and system components. It was designed to capture and retain events that exceed certain pre-set parameters and store this data in its non-volatile memory. MEDICAL AND PATHOLOGICAL INFORMATIONThe pilot under instruction provided a test sample for postaccident toxicological testing. The report was negative for the tests performed. The instructor pilot was hospitalized, which precluded postaccident testing. TESTS AND RESEARCHThe VEMD initial examination was conducted on August 19, 2013, at American Eurocopter facilities near Grand Prairie, Texas, under FAA supervision. A follow-up examination under FAA supervision was conducted on August 20, 2013. The VEMD data showed the accident flight was about 20 minutes long. There were three failures recorded near the end of the data and two overlimits events. The first failure recorded was test reference code 122, which corresponds to a collective pitch potentiometer failure. The parameters associated with this failure are consistent with the parameters resulting from a main rotor blade ground impact. This failure was followed shortly afterwards by the fuel gage failures, which is consistent with fuel migrating away from its sensor during a helicopter rollover. The VEMD did not record any pre-impact failures or overlimits events. The DECU was examined and its data was downloaded by the engine manufacturer under FAA supervision on August 19, 2013, at Turbomeca facilities near Grand Prairie, Texas. Data from its non-volatile memory was recovered successfully when the unit was connected to a test bench. The DECU begins recording time as soon as the aircraft 28 volts is applied and since the VEMD does not start recording until the engine is started and reaches 60 percent Ng, it is probable for the DECU to show more time than the VEMD for a given flight. The first faults recorded by the DECU during the accident flight were 24 minutes 12 seconds after power up. The significant fault at that time was a collective pitch measurement that exceeded the applicable software parameters. The next and last faults recorded were 24 minutes 52 seconds after power up. The faults were recorded as raw torque measurement that exceeded the applicable software parameters and collective pitch measurement that exceeded the applicable software parameters. A real time check of the DECU was then performed and the DECU was found to be operating normally. The yaw load compensator was shipped to its manufacturer, Parker-Olaer, in Colombes, France, for examination under the supervision of the French aircraft accident investigation authority, the Bureau Enquetes-Accidents. The examination revealed that the accumulator was in good external condition and it held the precharge pressure. The core valve and bladder did not leak when it was pressurized during hydraulic testing. The core valve was in good condition. The compensator's bladder was in operational condition. The inspection further showed that witness marks were present, which were consistent with an accumulator operating at an undetermined time with very low, or nil precharge pressure. There was no other evidence found of any pre-existing anomalies of the helicopter airframe or engine. An engineer from the helicopter manufacturer examined details of the accident to include damage images and helicopter payload and subsequently calculated an estimate of the forces the helicopter tailboom sustained in the accident. The engineer estimated a load factor of approximately 10 Gs resulting from skid contact with the ground was req
The pilot receiving instruction's failure to maintain adequate airspeed during a simulated hydraulics failure training maneuver, which resulted in his loss of control of the helicopter and its subsequent impact with terrain, and the flight instructor's delayed and inadequate remedial action.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
