NYC96LA086

The pilot stated that while landing at an airport for fuel, the front of the landing skids touched down, followed by the rear area of the skids. The helicopter encountered ground resonance after touchdown. Also, the pilot stated that he attempted to liftoff; however, the helicopter remained on the ground. The passenger stated that the touch down was harder than they had experienced the previous day. According to witnesses, the helicopter remained on the ground, and continued to bounce up and down until the tail rotor struck the ground. Examination of the helicopter revealed no preimpact failure of the airframe or rotor system.

On April 19, 1996, at 1230 eastern daylight time, a Hughes 269A, a helicopter, was destroyed while landing at the Linden Municipal Airport, Linden, New Jersey. The airline transport pilot and passenger received serious injuries. Visual meteorological conditions prevailed for the observation flight that originated at Farmingdale, New York, about 1100. No flight plan had been filed for the flight conducted under 14 CFR Part 91.

In a written statement and telephone interview, the pilot stated that he decided to refuel at the Linden Municipal Airport (LDJ) after 1 hour of flying. In his written statement he said:

"...I attempted to land on the flight line...I touched the front skids down first and felt a gust of wind. I Iowered the rear skids and then experienced ground resonance. I then determined that I had adequate rotor speed and tried to lift off. The resonance continued and the aircraft became unstable and impacted the ground..."

In the passengers written statement, he said:

"As the helicopter approached the landing area, about 15 to 20 feet off the ground, the craft swayed back and forth. This was quickly corrected by the pilot. As we touched down (harder than we had the previous day), the aircraft began to hop, or bounce - more violently with each successive "hop."...After several seconds...the craft "exploded," tore itself apart actually, after which time it ceased hopping. At this time I noticed that the rotors were still spinning, but the glass bubble that encased the cockpit was gone, and the rotors were sagging..."

In a police officer's summarized report of witness statements, he stated:

"...The helicopter flew into the airport and landed, at which point the craft began to violently shake (a condition known as 'ground resonance'). Witnesses further state the crafts tail rotor then struck the ground and detached from the helicopter, at which point the main body of the helicopter 'shook itself apart.'..."

A Department of the Army Field Manual, Fundamentals of Flight, defined ground resonance. The manual stated:

"Ground resonance may develop in helicopters having fully articulated rotor systems when a series of shocks causes the rotor blades in the system to become positioned in unbalanced displacement. If this oscillating condition progresses, it can be self-energizing and extremely dangerous. Structural failure usually results...Ground resonance occurs when the helicopter contacts the ground during landing or takeoff...The oscillation severity increases rapidly and the helicopter may disintegrate unless one of the following immediate corrections is made. (1) Take off to a hover if the rotor RPM is in the normal range. A change of rotor RPM may also aid in breaking the oscillation. (2) Reduce power if the rotor RPM is below the normal range..."

Examination of the wreckage by a Federal Aviation Administration Inspector revealed no pre-impact failure of the fuselage or rotor system.