What happened
On 4 June 1998, a Sikorsky S76B, registration G-BWDO, was conducting a private training flight at Blackbushe Airport in Surrey. The flight involved two planned training sessions focused on vertical and oblique flight profiles. Following an initial successful exercise, a second detail commenced with the aircraft weighing approximately 9,48 to 9,480 lbs. This second maneuver was intended to consolidate the student's skills by simulating a single engine inoperative condition, with the number one engine selected for the simulation.
The weather conditions were favorable, characterized by good visibility, light winds, and an ambient temperature of +15°C. The exercise involved a simulated failure at an altitude of roughly 180 feet, with a designated Take-off Decision Point set at 200 feet. While the initial rejection of the takeoff was successful, the rotor speed dropped to approximately 101% due to excessive collective use during the later stages of the maneuver. As the aircraft descended toward 50 feet, the rate of descent increased, and the student applied a large amount of collective to arrest the descent. This resulted in a firm touchdown and a slight bounce. Following the impact, the aircraft yawed to the right and moved from the paved runway onto the grass at a speed of 10 to 12 kt. During this period, the student kept the collective lever raised to prevent the blades from flapping down and striking the tail boom while the rotor speed was low.
The investigation
Following the incident, an external visual inspection of the Sikorsky S76B showed no immediate signs of damage. However, the aircraft was returned to the operator's hangar for a detailed engineering assessment. This inspection identified that three of the four rotor spindles had been damaged. The investigation established that these components had made contact with the main rotor hub.
Findings
- The primary cause of the damage was the extended period that the collective remained raised after the aircraft had landed.
- The damage occurred while the rotor speed was low, causing the rotor blades to contact the hub.
- The manufacturer's assessment indicated that the contact was a result of the post-landing collective position rather than the impact of the landing maneuver itself.