Accident Summary
On the day of the accident, the pilot of an MD Helicopter 369D (serial number 370093D) was transporting cedar shake blocks in the Jordan River area of British Columbia. At approximately 1715 Pacific standard time, the pilot departed Jordan River for a 23-minute flight back to Lake Cowichan. The helicopter was reported missing at about 1800, and a search began at about 1845. An emergency locator transmitter signal was detected in the Mt. Modeste area. During the night, a ground search party found the destroyed helicopter, minus its tail section. The pilot, the sole occupant, was found in the wreckage and had been fatally injured. There was no fire.
Investigation
The weather was mostly clear, allowing for visual flight rules (VFR) flight, with light and variable winds. Sunset was at 1655 Pacific standard time, and it turned dark at 1728. The pilot had flown 4.9 hours that day, making 123 lifts, and had transported ground crews three times. A flight plan filed in the morning was to be closed by 1745, but since it was not, a search was initiated one hour later. The emergency locator transmitter activated upon impact. A Canadian Armed Forces search-and-rescue aircraft helped locate the main wreckage. The tail section was found two days later about one kilometer behind the main wreckage. The terrain was mountainous with second-growth trees and logged areas.
The helicopter struck the ground in a left-bank, nose-down attitude. Pieces of the helicopter and contents were scattered up to 500 feet away. The fuselage was severely crushed and skewered by two small trees. Only one other tree was damaged. The fuel cell had burst, but no fire occurred. Marks on the aft fuselage indicated that the main rotor blades had severed the tail section. All lead and lag blade dampers were torn apart.
The helicopter was fitted with five main-rotor blades identified by color. The red blade showed a clean break about one-third from its root, perpendicular to the leading edge, with the break in the spar recessed from the skin. The outboard two-thirds of this blade was not found. The white blade was missing completely along with its grip. The yellow blade was missing its end one-third and showed damage from hitting the tail section. The green blade was torn into two pieces after it had stopped turning. The blue blade was the only one in one piece. Damage to the main-rotor system was consistent with the rotor not turning or being driven at impact.
It was concluded that the red blade failed in flight and was the initiating event. The loss of a large section created an imbalance leading to damper failure and extreme vibrations. Two scenarios were considered: extreme vibrations compromising the tail-boom strength, causing it to flex into the rotor path, or the imbalance causing blades to strike the tail boom. Loss of the tail section caused loss of attitude control, spinning around the mast. The pilot likely attempted the emergency procedure for loss of yaw control, but spinning did not stop quickly. Circular distribution of pieces indicated spinning at altitude. Autorotation characteristics were destroyed, and the helicopter pitched nose-down uncontrollably.
The crack in the spar did not manifest through the outer skin due to lack of bonding, making it not visually identifiable. Tap inspections were not done on blades manufactured before 1999, and voids were found on early blades, suggesting susceptibility to corrosion and fatigue.
Findings
The Transportation Safety Board found that two-thirds of one main-rotor blade separated in flight, and one or two remaining blades struck and severed the tail section, rendering the helicopter uncontrollable. The lack of bonding on part of the skin allowed corrosion pits to form, from which a crack propagated, leading to fatigue failure. The crack was not visually identifiable before flight.
Safety Actions
After confirming a manufacturing flaw—lack of bonding in the area of blade separation—the blade manufacturer informed operators and issued a Mandatory Service Bulletin on 6 November 2000 to check bonding before the next flight. The US Federal Aviation Administration issued an Airworthiness Directive on 20 November 2000 requiring compliance. The directive called for a one-time tap inspection of all affected 369D main-rotor blades manufactured by the approved parts manufacturer and established new criteria for acceptable voids. Several affected blades exhibited voids and were removed from service.
This report concludes the Transportation Safety Board's investigation, with the report released on 24 May 2001.