NTSB Factual Report

HISTORY OF FLIGHT

On November 18, 2005, about 1430 central standard time, a Schweizer 269C helicopter, N400PD, operated by the City of Topeka Police Department, sustained substantial damage when it nosed over during a precautionary landing near Manhattan, Kansas, following an observed split in rotor/engine tachometer readings and an audible low rotor rpm alarm during cruise flight. Visual meteorological conditions prevailed at the time of the accident. The solo instructional flight was being conducted as public use under 14 Code of Federal Regulations Part 91. A visual flight rules flight plan was on file. The pilot was taken to the hospital for observation and he reported no injuries. The flight originated from the Philip Billard Municipal Airport, near Topeka, Kansas, about 1330 and was en route to the Emporia Municipal Airport, near Emporia, Kansas, at the time of the accident.

The pilot's accident report, in part, stated:

At or near 15 miles East of Manhattan, I descended to approx 2500

[feet above mean sea level] MSL after listening to [Automated

Surface Observing Systems] ASOS for current winds and runway

information for landing traffic at Manhattan airport. I recall the

surface winds were within 30 degrees of Runway 210 with winds

within my ability and not a concern. Pattern altitude at Manhattan for

light aircraft is 1900 MSL putting my position about 600 ft. [above

ground level] AGL directly East of the field inbound landing. The

traffic pattern was for left traffic with a restricted (hot) zone to the North

of the field. I expected Tower instructions to have me either report 45

degrees for left downwind runway 21, or left base runway 21. Having

flown to Manhattan in the past I recall the Kansas River being just

South of Runway 13/31 near the field.

When I passed 8 miles I was preparing to announce my position and

intensions e.g. (Manhattan Tower 400PD eight miles East inbound

landing, Stop and Go). The collective friction was not on, I maintained

level flight and I was enjoying the flight. I had crosschecked my GPS

position and heading and was on coarse 273 degrees as desired with

airspeed of 75 [knots] Kts. As I was looking for ground reference landmarks to

the airport, I heard the low rotor horn/alarm. I did not have any unusual

attitude or noted decrease in airspeed. When this occurred I checked the

RPM gage and expected it to be at the top of the green arc with a minor

power increase necessary to resolve the alarm (3,000 RPM to 3,100

expected). What was indicated however was a large split in the needles

(engine rpm vs. rotor speed) with the rotor rpm at the bottom of the green

arc. I did not understand why I had this reading but knew if correct, there

was a mechanical emergency. At this time I noted three indications of a

problem. The large split in needles engine rpm vs. rotor rpm), the audible

horn heard that alerted me initially, and now a high-low engine sound that

I had not heard in normal flight (Similar to the throttle corelator sound at

the end of the day after the rotor system has been disengaged, prior to

the engine mixture being pulled at 100 rpm). I did not induce throttle

and take it away and I could not explain what had happened causing the

readings and alarm. I recall lots of movement in the shared rotor/engine

gages, with the needles vibrating. At the same time I entered autorotation

with a full down collective and then concentrated outside of the aircraft. I

had Manhattan Tower in my #1 radio Manhattan ASOS in radio #2 and

was able to send a distress call to the control tower. I recall saying

something similar to "Mayday, Mayday, 400 Papa Delta 8 miles West

(meaning to say East)-unknown what direction was said to the tower. The

tower responded to me but I do not recall my reply. Days later Manhattan

Tower stated I repeated my distress and reported a mechanical.

The previous seconds and those following felt very fast with many things

happening at once. I recall them in fragments. Attitude ok. Pick a spot,

ok. Winds at Manhattan southwest, Airspeed (55-60kts ideal), ok. On

short final the terrain was not as flat as I had thought but I was committed

and did not feel I had the inertia (stored energy) or skill to try for an

alternate (more flat) spot South and West before touchdown. I was

mentally preparing for landing reminding myself to be ready on the

anti-torque pedals, that this was not a power recovery maneuver (which

we recover from at 50 ft during training) and my flare would be much

closer to the ground. The engine was making the same high low rpm

sound as I stated earlier and my landing point was a downhill slope. I

started my flare. The cyclic was brought back and slightly left into my Left

thigh. I remember the spot where the flight control touched my leg. I

also remember thinking my forward ground speed did not slow as much

as I expected but now it was time to pull all available power (raise the

collective) and contact was made.

Once I had touched the helicopter began to slide. The contact was hard

but not much harder than a high hovering autorotation. The ship was

intact. The terrain was rough, uneven, and rocky. My forward slide felt

fast. I felt an impact with something, slowed rapidly and flipped

forward. I do not remember seeing the limestone that caught the

searchlight or skid and could not have avoided it if I had. During the

forward roll/flip of the helicopter, it disintegrated. The next thing I

recall was being inverted in my harness and needing to get free and away

fearing a potential fire.

PERSONNEL INFORMATION

The pilot held a private pilot certificate with an airplane single engine land rating. His most recent Federal Aviation Administration (FAA) second-class medical certificate was issued on October 19, 2004, without limitations. The pilot reported that he had logged a total time of 236 flight hours. He indicated 56 of those hours were in the same make and model as the accident helicopter and of which 8 were as pilot-in-command of the same make and model as the accident helicopter.

AIRCRAFT INFORMATION

N400PD was a Schweizer 296C, serial number S1833, helicopter. The helicopter had a three-bladed, fully articulated single main rotor system and was powered by a Lycoming HIO-360-D1A engine rated at 190 hp at 3,200 rpm. Power was transmitted from the engine through a V-belt drive system and a tail rotor drive shaft transmitting power to two variable pitch tail rotor blades through a tail rotor transmission. The fuselage had a central, tubular steel, open frame construction. The canopy and door transparent areas were of cast acrylic construction. The seat structure was an assembly that included riveted aluminum beams, frames, bulkheads, and supports. The helicopter was reported to be configured with two seats. The landing gear was a non-retractable skid type with its crossbeams providing attachment for struts and oleo-type shock-absorbing dampers.

The aircraft's maintenance instructions, in part, stated:

The AES/STAR system consists of a solid state electronic control

unit, a special dual tachometer with electrical encoders, a special

clutch engagement switch, a weight on skids switch, a red ROTOR

LOW RPM Light, a warning horn, a TEST/MUTE HORN button, an

AUTO ENGAGE function switch, an AES/ROTOR WARN circuit

breaker and associated wiring. The system monitors engine and rotor

speed (RPM) at the dual tachometer and sends signals to the control

unit. Depending on operational mode the system provides three

separate functions. During engine startup, the limiter will ground the

magnetos at approximately 1800 RPM, to prevent an overspeed

condition that may damage the lower pulley coupling shaft. After

engine startup, the pilot may elect to initiate and monitor an automatic

rotor engagement. If rotor speed drops below approved RPM during

flight, the ROTOR LOW RPM light will illuminate and the warning

horn will sound, to alert the pilot. Pressing the TEST/MUTE HORN

button will silence the horn in flight and sound it on the ground. If the

system is disabled, if the control unit is removed, or if a standard

tachometer is installed, the aircraft may be operated normally but

without the features described above. The system monitors engine and

rotor RPM through two encoders in the dual tachometer. During

automatic engagement, the control unit senses the acceleration of the

rotor RPM and the deceleration of the engine RPM, to cycle electrical

power ON and OFF to the linear actuator, until the rotor and engine

tachometer needles are superimposed and the rotors are engaged. This

system automatically performs the pilot's manual task of moving the

CLUTCH switch from ENGAGE to HOLD and back to ENGAGE,

during rotor engagement.

During startup, the engine RPM signal is used to trigger transistors, in

the control unit, that ground (disable) the magnetos when the RPM is

at or above the set point (approximately 1800 RPM). The magnetos are

released to normal condition, as soon as the RPM falls below the set

point. Pilot action to retard the throttle is required to prevent repeated

cycling of the magnetos.

During flight operations, the rotor encoder signal is used to illuminate

the flashing red ROTOR LOW RPM light and sound the pulsing horn

when the RPM is below the bottom red line of the engine green arc.

The rotor encoder signal is used to activate the same light and horn to

a steady light and continuously sounding horn, when RPM drops to the

bottom of the rotor green arc (approximately 390 RPM). Pilot action to

increase throttle or reduce collective pitch and increase RPM above the

set points, will extinguish the light and silence the horn and is required

to return to safe flight conditions.

The last inspection of the helicopter was a 100 hour inspection on November 18, 2005. The aircraft's total time was reported as 2,253.4 hours.

The operator had reported that approximately 15 to 20 flight hours prior to the accident flight, the helicopter experienced a problem with the tachometer reading jumping in-flight. A precautionary landing was performed. The tachometer cable was inspected, lubricated, and reinstalled.

METEOROLOGICAL INFORMATION

At 1452, the recorded weather at the Manhattan Regional Airport, near Manhattan, Kansas, was: Wind 220 degrees at 12 knots; visibility 10 statute miles; sky condition clear; temperature 13 degrees C; dew point 0 degrees C; altimeter 30.14 inches of mercury.

WRECKAGE AND IMPACT INFORMATION

The helicopter came to rest about seven miles east of the Manhattan Regional Airport in a rough uneven field nearly inverted on its nose at latitude 39 degrees 6.451 minutes N and longitude 96 degrees 31.118 minutes W. Federal Aviation Administration inspectors examined the wreckage. No engine or airframe anomalies were detected. The wreckage was recovered back to the police helicopter unit. An end of the tachometer cable was rotated mechanically with a drill and the other end of the cable did not rotate at the same rpm.

TESTS AND RESEARCH

The operator reported that the tachometer cable was damaged and was cut to facilitate its removal. The airplane's tachometer, tachometer cable, and AES control box were shipped to Schweizer Aircraft Corporation for examination under FAA supervision. The Schweizer report, in part, stated:

The AES control box warning circuitry was not operational when

first checked at Schweizer, but operated after repair of an open

found on the circuit board. ... The pilot reported a warning light

prior to autorotation. The Flight Manual Supplement CSP-C-1 W

requires operational check of the warning system prior to flight and

there was no report the system was inop prior to flight.

The tachometer appears to be mechanically functional for needle

operation and electrically functional for warning light actuation. The

square drive bushing was compromised ... . Whether there was an

oversize drive bushing or under size cable prior to the failure could

not be established. The system is designed so that no malfunction

that may have been sensed by optical encoders in the dual

tachometer, nor any malfunction of the electrical system, could have

had a mechanical effect on the tachometer.

Visual exam of the cable exhibited indications of excessive wear and

possible binding with windup of the outer strands.

ADDITIONAL DATA/INFORMATION

The FAA and Schweizer Aircraft Corporation were parties to the investigation.

The aircraft wreckage was released to a representative of the Topeka Police Department.

NTSB Probable Cause

The binding of the main rotor blade's tachometer cable during cruise flight resulting in an observed split tachometer indication/aural alarm and perceived mechanical emergency and the unsuitable terrain the pilot encountered during the emergency landing. A factor was the rocky terrain.