Lessons Learned: The Risk of Ground Resonance
A shipboard helicopter accident likely due to ground resonance emphasizes the importance of proper pilot coordination in responding to abnormal situations.
An A109 helicopter accident on a bulk carrier after a marine pilot transfer highlights the risk of ground resonance, according to an ATSB (Australian Transport Safety Bureau) final report. The loss of control during marine pilot transfer operations involving Agusta A109E, VH-XUM and bulk carrier Star Coral occurred about 200 km north-east of Mackay, Queensland, on February 25, 2025.
As it was lifting off from the ship’s helideck, the helicopter developed severe vibrations. The takeoff was discontinued but control of the helicopter was lost.
The helicopter came to rest upright on the helideck, more than 90° counterclockwise from its original position, having sustained substantial damage. No injuries were reported.
The ATSB found that the vibration was likely the result of the helicopter entering ground resonance, a phenomenon that dissipates when airborne, while it was in the process of departing from the ship. “When the vibrations started, the pilot supervising perceived the pilot flying to be holding the cyclic in an abnormally aft position, and believed the main rotor may have struck the tail boom,” ATSB Director Transport Safety Stuart Macleod said.
In response, the pilot supervising, unannounced, took hold of the cyclic and collective in order to discontinue the takeoff, while the pilot flying was still attempting to lift off.
“In isolation, the immediate responses taken by each pilot following the sudden onset of vibration were understandable,” Mr. Macleod said.
“But discontinuing the takeoff after the onset of the vibration, with the rotor speed in the flight range, probably resulted in the loss of control and substantial damage to the helicopter.”
Mr. Macleod noted the accident was a good example of the potentially catastrophic nature of ground resonance.
“Typically, the onset of ground resonance is sudden and, if the pilot does not take immediate corrective action, loss of control can occur rapidly.”
After the accident, the helicopter operator added new guidelines on ground resonance to its procedures.
It has also developed an updated procedure for training and checking flight briefings that will include confirming the roles of each pilot, procedures for transferring aircraft control between pilots, and actions to be followed in the event of an actual emergency.
“Proper coordination between pilots is critical, particularly when responding to abnormal or emergency situations,” Mr. Macleod said.
“Pilot roles and responsibilities for emergency response and flying duties should be well-established prior to each flight.”
Read the final ATSB report: “Loss of control during marine pilot transfer operations involving Agusta A109E, VH-XUM and bulk carrier Star Coral, about 200 km north-east of Mackay, Queensland, on 25 February 2025,” publication date: 7/29/2025.
Content/image credit/source: ATSB, “A109 helicopter accident on bulk carrier after marine pilot transfer highlights the risk of ground resonance,” published July 29, 2025.
