Originally Posted by
212man
One area that puzzles me is there is no analysis of the different outcome in survivabilty if the landing gear had been down at impact...
They do, Page 126 from the report (my bold for emphasis):
Impact assessment
The helicopter manufacturer carried out an assessment of the deceleration loads experienced during the impact sequence using recorded and calculated data provided by the AAIB. The assessment considered the loads on the helicopter’s structure in the region of the fuel tanks and rear row of passenger seats. It also considered the possible differences had the helicopter’s landing gear been extended.
The assessment identified that with the landing gear extended, there was no significant decrease in the forces transmitted through the helicopter’s structure. The manufacturer stated that this was because the calculated rate of deceleration and the forces involved exceeded the landing gear’s ability to react, deform and dissipate the impact energy.
And to address this:
Originally Posted by
DOUBLE BOGEY
Maybe I misunderstood the report but I believed the TR Pitch went to FULL POWER. Which leaves no chance of a recovery as we saw in this event. No just loss of control . The worst scenario imaginable. Its odd that all other manufacturers fit a safety mechanism, or inherent blade aerodynamics, that would "center" the servo to a reasonable, hopefully survivable pitch setting. I also understand this latent failure event exists in 109/139/169 and 189. Are there any Leonardo techs on here that could confirm this.
The report states (page 27) that the forces experienced by the tail rotor control bearing in the axial direction (pitch changing direction) are all stabilising (centrifugal and aerodynamic loads seek 0 pitch, and the elastomeric loads seek 0 deformation on the elastomeric bearing). However, the hydraulic force on the tail rotor control rod was still present to overcome these forces and the tail rotor pitch continued beyond full 'non power pedal' deflection as the tail rotor control stops were no longer interacting with the tail rotor pitch control rod. Page 160 of the report (my bold for emphasis):
The actuator lever mechanism is designed to act as mechanical feedback for the hydraulic actuator, closing off hydraulic pressure once the movement of the control shaft matches the pilot’s pedal input. As the lever was now completely disconnected from the control shaft, the shaft continued to move under hydraulic pressure without restriction.