For all its' technical achievements, the Sikorsky S-55 series suffered from a design flaw which plagued the fleet for the life of its service and led to a redesign which was incorporated on some but, not all production S-55's. This flaw was the tendency of the main rotors to flex downward thus striking and often severing the tail boom from the aircraft whenever a hard landing was made.

Sikorsky engineers redesigned the tail boom to feature a downward slope of 3.5 degrees. This new design was incorporated on many USAF and Army S-55 variants. However, photographic evidence would strongly suggest that despite repeated problems with main rotor blade to tail boom contact, the USMC never opted for the redesign and stayed with the straight tail design.

BuNo127822 was nearly written off in an accident on the February 22, 1952 during the Lex Baker One amphibious exercise in Southern California. After the Marines had exited the aircraft, the pilot applied power to takeoff and was barely airborne when the main driveshaft broke. The aircraft came down hard with the resulting main rotor strike on the tail boom. Fortunately, there were no injuries to the two pilots.

Yankee November 11 is an unknown Bureau Number which while in service with HMR-361 at MCAF Santa Ana, California, came down hard on the beach for unknown reasons. Again, the resulting downward flexing of the main blades has severed the tail boom.

A self-locking nut which had been reused led to the crash of Bureau Number 130247 on October 17, 1960. After the nut had loosened, cyclic control was lost with the familiar results. There were injuries associated with this accident. See the article below: