Helicopter Flight Information

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Landing and Taking off to/from a Hover

No more ground resonance Please!

In the last year there were far to many ground resonance accidents. These accidents are a result of poor technique, followed by poor technique.

Obviously those who are involved in helicopter flight already know that we are talking about multi-blade helicopters (those with more than 2 blades), and for those who are not yet involved in helicopter flight, now you know also.

There are only two causes of ground resonance; faulty equipment which could result in ground resonance during start-up (I know of only one case in the last several years), or a faulty pilot which results in ground resonance during landing (very common).  Since the faulty equipment issue is highly unlikely, we will first address the more common cause of poor pilot technique.

For ground resonance to occur during landing, the pilot must make two mistakes, the first mistake will set up the ground resonance, and the second mistake will ensure that the aircraft is completely destroyed. The first step in succeeding in a good level of aircraft destruction is for the pilot to be fearful of ground contact, which results in a pilot developing a bad habit of abrupt let down in the last 6 or so inches from the hover. The second step is to follow that initial case of poor ground contact with the failure to immediately execute the appropriate corrective action which ultimately should be picking the helicopter back up into a hover.

Avoiding Landing Ground Resonance

One would think that in most cases, the bad habit of poor landing technique could be traced back to the initial training; but lets not be to hasty to blame the instructor for a pilot who develops bad habits. I have found that most pilots/students develop bad habits after training because they fail to be self-critical and self-improving. As a student, you will be able to recognize an instructor who has poor technique if he or she has bad pick-up and set-down skills. If this is the case, attempt to discuss this with the instructor, or get a different instructor.

The most common error that pilots make which lead to poor technique during landing is that they fail to focus in the distance. Certainly at some point as a pilot gains skill, then he or she may look closer to the helicopter, or even down during landing, but never in the early hours of their career, and never if the helicopter begins to move around.

It is good to practice soft take-off and landings on/in a painted or chalk marked box on a hard surface taxiway or closed runway. Never should a low time pilot or student practice on soft surfaces. The helicopter will slide on a hard surface with improper control inputs, while on a soft surface, the helicopter will have a rolling tendency which could lead to dynamic rollover. The pilot or student as the case may be, must practice slow control inputs not permitting the helicopter to move around.

The take-off must begin with the controls centered; that is pedals neutral, and cyclic straight up and down laterally, with a very slight forward input. Any thing else is control leading, and absolutely unacceptable no matter how well you know the aircraft that you are flying. With the controls properly centered, begin raising the collective until the helicopter is light on the skids and some movement begins. Once the movement begins, stop increasing the collective pitch, and correct the movement by making the appropriate control input. Do not over-correct this movement with an excessive input. If the helicopter begins to move to much, abort the procedure immediately by fully lowering the collective and start the process over from the beginning. Anything else may lead to dynamic rollover. After successfully correcting any movement, then and only then continue increasing the collective, continuing the process of movement/input correction until the helicopter gently picks up, and then continue the collective increase until the helicopter has risen to a 3-foot hover (skid height above ground). Do not linger closer than 3-feet above the ground.

The landing must only commence from a stable 3-foot hover. Begin lowering the collective in the reverse of the above stated sequence. Do not continue down with the collective if the helicopter is moving about, and do not linger with the skids close to the ground. You must abort the landing if the helicopter begins to move to much, with the skids close to the ground by increasing the collective and bringing the helicopter back to a stable 3-foot hover.

I absolutely discourage any pilot from practicing this ground proximity maneuvering without an authorized instructor on board the aircraft. The dangers involved in this type of practice include dynamic rollover in all helicopters, and also ground resonance in multi-blade helicopters.

One must remember the simple rule that if you are picking up from a hover, and the helicopter becomes unstable, immediately fully lower the collective to prevent dynamic rollover, this must be accomplished without banging a skid on the ground, and therefore should be recognized before the helicopter becomes airborne. If you are landing, and the helicopter becomes unstable, you must take it back to a 3-foot hover and stabilize.

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Last modified: 01/19/08