McDonnell Douglas 600N N959SD

Summary

On 23 October 2001 at about 00:00 local time, a McDonnell Douglas 600N registered N959SD was involved in an incident near Long Beach, California, United States. One person was on board and nobody was injured. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

23 October 2001 at 00:00

Classification

Incident

Location

Long Beach, California, United States

Nearest airport

Long Beach (LGB)

Coordinates

33.8195, -118.1101

Aircraft

McDonnell Douglas 600N

Registration

N959SD

Category

Helicopter

Engines

1

Operator

Not recorded

Operating rule

Public Use

Purpose of flight

Public Use

Phase of flight

Not recorded

Route

Long Beach → Unknown

Aircraft damage

Not recorded

Weather

VMC

Light

Day

NTSB number

LAX02IA013

Nobody was injured.

The fatigue failure of a 5/16-inch boom attach bolt was most probably caused by the angular misalignment between the tail boom bolt hole and the fuselage mounted nutplate.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

A MDHI 600N helicopter, operated by the Los Angeles County Sheriff's Department, was found to have a fractured tail boom attach bolt during a routine ground examination of the helicopter for evening ground standby duty. The pilot stated that as he pushed sideways on the tail boom it seemed loose. Subsequent examination by maintenance personnel found that the head half of the upper right 5/16-inch tail boom attach bolt was hanging loose by the safety wire. Examination of the bolt revealed that it had failed about three threads from the bolt shank. The remainder of the threaded portion of the bolt remained in the plate nut affixed to the fuselage. Fretting was observed on the fuselage and tail boom mating points in proximity to the fractured bolt. Areas of the bolt shank exhibited polishing. Subsequent examination for collateral damage revealed cracks were present at the aluminum attach fitting and associated angles. The operator examined two of their other 600N helicopters and found those with cracks at the same location. Two other local area law enforcement operators also found cracks in the same location. The tail boom is attached to the fuselage with four special OEM produced bolts. The helicopter tail boom is required to be removed every 300 flight hours for inspection, and, in addition is occasionally removed for other servicing procedures. Examination of the maintenance records disclosed that the bolts may have been through about 10 torque cycles. The bolts have no life limit. The failed 5/16-inch bolt, p/n HS5482-5-18, is torqued to 150-inch/pounds during installation. On November 2, 2001, MDHI issued service bulletin SB600N-036, which prescribes procedures for inspecting the upper right tail boom, attach bolt, and attach fitting assembly. "The Part 1 inspection requirements of this bulletin shall be accomplished within the next five (5) hours of helicopter operation after the receipt of this bulletin or within thirty (30) days of the issue date of this bulletin, whichever occurs first." "The Part 2 inspection and repair requirements of this bulletin shall be accomplished within the next twenty-five (25) hours of helicopter operation after the receipt of this bulletin or within ninety (90) days of the issue date of this bulletin, whichever occurs first." On November 28, 2001, the FAA issued Priority Letter Airworthiness Directive (Emergency AD) 2001-24-51, mandating compliance with the service bulletin 600N-036.

Quoted verbatim from the NTSB record.