Scottsdale, AZ, USA
N324PH
Schweizer 269C
The helicopter sustained substantial damage after experiencing a severe vibratory event during liftoff. The certified flight instructor (CFI) reported that the helicopter was positioned on a slope. The preflight and runup were uneventful. The engine was advanced to 3,100 rpm and the CFI instructed the student to bring the downslope skid level with the upslope skid. As the collective was raised, the helicopter began to vibrate. The CFI decreased engine power and control pressures. He then increased the engine speed to 3,100 rpm. As soon as pressure was placed on the controls, the helicopter began to "self destruct." The uphill skid did not leave the surface during either attempted takeoff. No unresolved mechanical discrepancies were noted with the helicopter prior to the accident. The helicopter was examined by an FAA airworthiness inspector. No preimpact discrepancies were noted with the main rotor dampers or the skid strut oleos. In the FAA Rotorcraft Flying Handbook (FAA-H-8083-21) it states that ground resonance is associated with fully articulated rotor systems. If a helicopter touches down on one corner, the blades may move out of their normal phase. If the rpm is in the normal operating range, the pilot should fly the helicopter off the ground, allowing the blades to automatically realign themselves. If not, the helicopter may self-destruct in a matter of seconds.
On April 14, 2002, at 0915 mountain standard time, a Schweizer 269C helicopter, N324PH, experienced a severe vibratory event during liftoff from the Scottsdale Airport (SDL), Scottsdale, Arizona. Scottsdale Helicopters was operating the helicopter under the provisions of 14 CFR Part 91. The certified flight instructor (CFI) and the student were not injured; the helicopter sustained substantial damage. The local area instructional flight was originating at the time of the accident. Visual meteorological conditions prevailed and no flight plan had been filed. In a written statement submitted by the CFI, he reported that the helicopter was parked on a sloped portion of the ramp, which allowed for water drainage. The preflight and runup were normal. The engine was advanced to 3,100 rpm. The CFI instructed the student to bring the downslope skid level with the upslope skid. The student moved the cyclic control to the upslope and raised the collective slightly. The helicopter began vibrating and the CFI took over the controls, reducing power and control pressures. The vibration ceased and the CFI increased the engine speed back to 3,100 rpm. As soon as the CFI placed pressure on the controls, the helicopter began to "self destruct." The CFI reduced control pressures and shutdown the helicopter. The uphill skid did not leave the surface during either attempted takeoff. The operator reported that the CFI was not one of the company pilots, but a renter who was allowed to give instruction. He said the helicopter was pulled out of the hangar and positioned on the ramp, which has a slight slope for water drainage, with the right skid downslope. The fuel tanks were 3/4 full and some fuel may have migrated from the left side to the right side due to the slope. After a preflight, the helicopter was powered to 3,100 rpm. The student lifted the helicopter from the ground and it began shaking. The helicopter was lowered to the ground and powered down to 2,100 rpm. The CFI then powered it back up and began to lift from the ground. The helicopter started to shake and he was in the process of putting it back firmly on the skids, when it began shaking violently. He was unable to get it to stop before major damage occurred. The operator reported the helicopter sustained extensive damage. The tail boom was severed in two places. One tail rotor blade was broken off at the hub and the other was bent. The tail rotor gear box separated from the boom. All three main rotor blades were damaged, the lead lag dampers were either pulled out or broken. The front and rear cross tubes were bent, and the bow was more pronounced on the right side. The upper canopy glass was broken, and the instrument console was broken off the cockpit floor mounts. All blade weights (main and tail rotors) were found in place. No mechanical anomalies were noted with the helicopter prior to the accident. The operator reported in 2001 there were a series of write-ups from company CFIs about the shock absorber oleos on the rear struts being soft. Those were replaced in July 2001, and since then there had been no further write-ups. The helicopter was examined by an Federal Aviation Administration (FAA) airworthiness inspector. No preimpact discrepancies were noted with the main rotor dampers or the skid strut oleos. In the FAA Rotorcraft Flying Handbook (FAA-H-8083-21) it states that ground resonance is associated with fully articulated rotor systems. If a helicopter touches down on one corner, the blades may move out of their normal phase. If the rpm is in the normal operating range, the pilot should fly the helicopter off the ground, allowing the blades to automatically realign themselves. If not, the helicopter may self-destruct in a matter of seconds.
The flight instructor's inadequate remedial action following the onset of ground resonance.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
