Accident at New York International Airport, 14 Oct 1963 (N-6673D)

Accident narrative

On October 14, 1963, New York Airways Flight 600, a Boeing-Vertol 107-II helicopter (N 6673D), crashed and burned seconds after lift-off at New York International Airport (Idlewild) at 1233 e.d.t. The flight was regularly scheduled from Idlewild to Newark International Airport, with an intermediate stop at the Wall Street Heliport in Manhattan. All three passengers and three crew members were fatally injured, and the helicopter was destroyed by impact and fire.

### The flight

In order to effect a change of equipment, the helicopter was ferried from La Guardia Airport to Idlewild, arriving at 1213. The captain stated that nothing unusual was noted in the operation of the helicopter during this seven-minute flight. Company records indicated the crew was qualified for the flight, and computations showed the helicopter was loaded with a center of gravity and gross weight well within allowable limits.

The scheduled crew and passengers boarded, and the flight departed the ramp on schedule at 1230. The flight received clearance and took off at 1233. Ten seconds later, an unintelligible static or clatter effect was heard on the Idlewild Tower frequency. The local controller observed the separation of a rotor blade or blades and the subsequent impact of the helicopter with the ground. Tower personnel immediately initiated prescribed emergency procedures. A local weather observation at 1236 reported high scattered clouds, visibility 8 miles, and wind south-southwest at 12 knots.

Over 45 eyewitnesses to the accident were interviewed. A consensus of their accounts indicated that the flight climbed to an altitude of approximately 150 feet where structural failure occurred. Seventeen of the 25 witnesses who described this as a rotor failure indicated that it was the aft rotor which separated. Impact was described as tail first.

### What the investigation found

Examination of the wreckage indicated the helicopter crashed tail first in a left bank of 5 degrees, approximately 800 feet from the lift-off point. The major portion of the fuselage was consumed by fire. The aft rotor assembly, aft rotor drive shaft assembly, and aft pylon had separated in flight. The forward green rotor blade and the aft yellow and green rotor blades had collided and disintegrated in flight. There was no evidence of fatigue on any of the six rotor blades, and a detailed examination of the two jet engines found no evidence of pre-impact operational distress.

The entire drive system was taken to the manufacturer for teardown. This revealed that the quill shaft, which transmits the drive force from the mix box to the aft transmission, had failed in fatigue. Three stepped studs holding the mix box collector gear bearing retainer in place had also failed in fatigue. In addition, investigators discovered that the two jets designed to lubricate the quill shaft were plugged with metal shavings. These shavings were identified as AISI 4130 steel. The only parts in the mix box and aft transmission containing this grade of steel were the bearing liners.

Examination of the quill shaft disclosed that it met metallurgical design specifications, but wear steps had formed on the drive side of each of the rear splines. Fatigue cracks started at the wear steps and at a retainer pinhole, with one crack continuing into the central unsplined area of the shaft where ultimate overload failure occurred.

The Board concluded that the quill shaft fatigue was precipitated by a lack of lubrication following blockage of the jets by the metal shavings. The Board further concluded that the fatigue failures of the three stepped studs did not contribute to the quill shaft failure, but rather were the result of fatigue progression in the shaft.

The investigation traced the maintenance history of the specific aft transmission and mix box assembly. Metal shavings had been found in the mix box sump during an initial load run test by the manufacturer. Once in service, the assembly was removed multiple times for discrepancies, including a machining curl on the sump plug, broken gear teeth, and steel particles on the sump plug and strainer. The Board noted that shavings were introduced into the lubrication system as a result of boring operations on the liners by the manufacturer. Following the discovery of the plugged jets, procedures were changed to insert plastic plugs in oil passages during boring operations and to remove plug-type lubrication jets prior to flushing cases during overhaul.

Tests performed by the manufacturer demonstrated that operating a quill shaft with blocked lubrication jets at 50 percent torque produced fatigue cracks within 50 hours.

The Board also reviewed the Federal Aviation Agency (FAA) approved overhaul intervals. The Board believed that the number of premature removals of aft transmissions was excessive. Only one of the six assemblies operated by the carrier reached its initially scheduled overhaul without premature removal. Following an approved increase in the overhaul time to 600 hours, there were eight instances of early removals. The Board believed that an increase, without additional operating experience, was unwarranted. The investigation also noted that an FAA maintenance inspector had given verbal approval for revisions to the overhaul specifications, which was not in compliance with regulations requiring written approval from a supervising inspector.

### Probable cause

The Board determines the probable cause of this accident was fatigue failure of the drive quill shaft due to contamination of the lubrication system in the aft transmission assembly.