N106LNEurocopter AS 350 B3 · 1999

On 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.

The 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

N106LN 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.

At 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.

N106LN 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.

The 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.

The 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.

The 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.

The 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.

The 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 required to cause the observed buckling damage.

Air Methods is a commercial on-demand air taxi operator specializing in helicopter emergency medical services (HEMS). The company was established in 1980 in Colorado, and currently operates in 42 states. Air Methods received its Title 14 Code of Federal Regulations (CFR) Part 135 Operating Certificate, number QMLA253U, on March 1, 1992.

In accordance with 14 CFR Part 135.21, Air Methods keeps current a General Operating Manual (GOM), which identifies management policies and responsibilities, training/currency policies, and the procedures under which flights are conducted.

Chapter 3 of the Air Methods Pilot Training Program revision 9 dated June 07, 2013 "Initial Equipment and Transition Training" addresses the recurrent training curriculum. The curriculum consists of 4 hours of ground training each for IFR and VFR operations, and recommends a minimum of 4 hours of flight training for IFR and 2 hours for VFR operations. However, an instructor can recommend a flight test before the completion of the recommended hours. The flight training is broken down into four modules. Each module addresses various normal, instrument, emergency procedures, and the fourth module addresses night operations. Autorotations are practiced in module 2, and hovering autorotations are practiced in module 3. Each module appears to be organized around 1 hour of flight time.

Annex 1 of the Pilot Training Program revision 8 dated January 31, 2012 delineates in detail all flight terms, definitions, and maneuver procedures for the Eurocopter AS350 helicopter. Sections 1-33 and 1-34 describe the procedures to practice simulated engine failure resulting in straight-in and turning autorotations. All practice autorotations are to conclude with a power recovery terminating in a 3- to 5-foot hover.

A flight proficiency check (FAR 135.293 check) is preceded by a training flight. The training flight consists of standard commercial maneuvers, normal, shallow, and steep approaches, sloped landings, engine failures, hydraulics off flight, basic instruments, and an instrument approach. Three to five practice autorotations are performed towards the end of the training flight and terminate in a 3- to 5-foot hover power recovery. If a pilot is not performing to standards, the check airman has the authority to provide extra training. Additionally, if a pilot feels they need extra training they can request additional training, which is coordinated through the appropriate chain of command and approved by the Chief Pilot or Aviation Training Manager. This policy is set forth in section 2.4 of the Air Methods General Operations Manual.

Air Methods has two dedicated training helicopters that are moved from base to base to conduct training and check flights. A training flight usually lasts 1-1.5 hours, and a check flight is usually 1 hour. On occasion, due to scheduling conflicts, the dedicated training helicopter is not available and the base's assigned helicopter is reconfigured to conduct training and check flights. In addition to dedicated training aircraft, Air Methods utilizes mobile and permanent advance aircraft training devices (AATD) as well as full-motion simulators in their training programs.