Using this new testing capability, OmniSeal[R] lip seals were recently qualified for a helicopter rotor head
and transmission retrofit program due to their great flexibility in creating a custom design with a precise fit in existing hardware.
Also the teetering rotor head
that holds the rotorblades to the rotor head
while allowing them to pivot and twist as required.
Investigators found metal fatigue in its gearbox cause a catastrophic failure and the rotor head
During post-flight inspection, we found nothing wrong with the rotor head
, rotor blades, or transmission assembly.
Item NSN Item Remarks Manager Main rotor head
1615-01-512-0889 BJA43 Main transmission 1615-01-532-9390 BJA42 Actuator support assembly 1615-01-527-3781 BJA46 Critical Signal data processor 1270-01-544-6370 BJA44 Main rotor blades All NSNs BJA61 Shock strut 1620-01-147-4775 BJA60 Shock strut 1620-01-465-9232 BJA60 Tail rotor gearbox 1615-01-507-5294 & BJA64 Trailing arm assembly related NSNs Trailing arm assembly 1620-01-147-4777 BJA67 Critical Trailing arm assembly 1620-01-147-4776 BJA64 Connecting link 3040-01-154-7056 BJA69 Critical Bell crank 1680-01-224-2263 BJA67 Bell crank 1560-01-263-9849 BJA67 Critical Quad control assembly 1680-01-375-0815 BJA67 Critical Cylinder assembly 1650-01-153-2314 BJA69
As a result, the blade-fold test set, aka the cheater box, was used to drive the lock pins against the micro switches to ensure a fully spread rotor head
Currently a minute number of cases have come forward of helicopters of the same model found to have cracks in the rotor head
, if anything is found concerning our helicopter then we will take the appropriate action.
The tower's 6,000-lb rotor head
will enable Sikorsky to spin blades weighing up to 500 pounds each, thereby easily accommodating blades flown by U.
During the subsequent startup, the air crewman noticed an unusual object hanging from the main rotor head
and alerted the helicopter aircraft commander (HAC).
The UK Air Accidents Investigation Branch has now issued the following information: "The investigation has determined that a failure within the epicyclic reduction gearbox module of the main rotor gearbox resulted in the rupture of the gearbox case, which allowed the main rotor head
to separate from the helicopter.
This resulted in the detachment of the main rotor head
from the helicopter and was rapidly followed by main rotor blade strikes on the pylon and tail boom, which became severed from the fuselage.
What makes this accident worth discussing is that both individuals knew that the mast nut, which retains the rotor head
in place atop the mast, had been removed two days earlier.