Accident Summary
On May 2, 2017, about 0635 central daylight time, a Bell 407 helicopter, registration N457PH, operated by PHI Helicopters, Inc., made a precautionary landing at Grand Bay Receiving Station near Venice, Louisiana. The pilot reported detecting an in-flight vibration and chose to land. After landing, while shutting down the engine, the vibration increased, prompting an emergency shutdown using the rotor brake. The flight was a non-scheduled domestic passenger operation under 14 CFR Part 135, with a company VFR flight plan. Fifteen minutes prior, at 0629, the helicopter had departed Boothville (LS08), Louisiana, bound for Main Pass 311A in the Gulf of Mexico. Visual meteorological conditions prevailed. The five passengers and pilot were not injured, but the helicopter sustained substantial damage.
Post-Accident Examination
Inspection revealed that the tip block and weights had separated from one of the tail rotor blades. Cracks were found on the tail rotor gear box mounting hardware and the tail boom. The tail rotor hub and blade assembly, tail rotor gear box with two fractured studs, and tail boom support casting were sent to NTSB's Materials Laboratory for examination. Representatives from PHI, Inc., and Bell Helicopter were present.
Visual examination of the tail rotor confirmed the missing tip block and blade tip weights. According to PHI, the blade had a total service life of 2,658.65 hours, and a tip block replacement repair had been performed approximately 65 hours prior to the separation. The tip block separated along the adhesive interface, with most of the adhesive remaining on the blade skin. The adhesive showed a waffle pattern indicative of partial bonding and interfacial separation; about 50% of the adhesive surface had smooth, glossy areas consistent with voids and lack of contact with the tip block.
The tail rotor gearbox was detached from the tail boom support casting, and the two outboard attach studs were fractured. The entire support casting was fractured, and all but 2.7 inches of the skin and the four-inch wide cover were cracked. The casting fracture and skin crack were consistent with overstress separations. Both fractured left-hand studs exhibited reversed bending fatigue fractures, with features indicating multiple origin reversed bending fatigue initiating in the root radii on opposed sides of each stud. Fretting and rub marks were present on the support casting and gearbox where the attach studs were fixed; the alignment dowel pins were missing. The support casting had cracks at the two forward stud hole locations and elongation at the two aft stud hole locations, with a circumferential crack from the forward left stud hole along the left side.
Manufacturer Response
According to Bell Helicopter, after repairs to tail rotor blades, a 1,320-lb pull test was performed on the tip block, a tap test for voids, a peel test from skin patch material, and a water leak test. Bell reported that no blade had ever failed the pull test, and the facility performed approximately 25 tail rotor tip block crack repairs per year. Following the accident, the manufacturer revised its approved repair procedure, including changes to the cure cycle to use only positive pressure during adhesive curing, and expanded post-repair inspection procedures. Further details are available in the document titled "New Bell Helicopter Approved Tail Rotor Repair Procedures" in the public docket.