History of the Flight
Three days before the occurrence, a pilot and a company check pilot conducted practice autorotations and observed that the autorotation rotor speed (rpm) was 60 rpm lower than specified for the aircraft weight at the chosen altitude. On the day of the occurrence, an aircraft maintenance engineer (AME) from Héli Technik Inc., an approved maintenance organization, adjusted the collective low stop screw six turns to raise autorotation rpm and also removed, adjusted, and reinstalled the collective lock located on the floor.
The pilot and one AME then completed three uneventful flights to adjust main rotor blade alignment. The fourth flight, the occurrence flight, was intended to check rotor rpm during autorotation. The helicopter, an AS 350 BA (registration C-FPOO, serial number 2508) operated by Héli-Inter Inc., carried one pilot and two AMEs.
At 1200 feet above ground level (agl), the pilot performed an autorotation with the collective against the low stop at 80 mph, reducing drive power to idle; rotor speed was 365 rpm. After increasing power, the pilot noticed slight friction in the collective movement but, after checking travel, deemed it normal. He climbed to 1400 feet agl and initiated a second autorotation. The descent was normal until 800 feet agl. After reapplying power, the pilot observed that the collective locking plate was engaged and hindering lever movement. He unsuccessfully tried to disengage it with his thumb.
At about 40 feet agl, the pilot executed a flare and landed on Runway 36 at roughly 20 mph. After initial touchdown, the helicopter bounced and landed hard on its belly. The tail rotor drive shaft severed on the second impact, causing the helicopter to spin until an AME closed the throttle. The pilot held the collective lever down, concerned about sudden release. The helicopter came to rest, and the pilot completed shutdown before evacuation. The emergency locator transmitter activated at 1348 eastern standard time. The airport security officer arrived at 1350:50, and an ambulance arrived at 1405, directed to the site 17 minutes after the crash.
The Pilot
The pilot was certified and qualified for the flight, with about 4500 total helicopter hours, including 900 hours on the AS 350.
Helicopter Flight Manual
Section 4.1 of the AS 350 BA Flight Manual requires that the friction setting on cyclic and collective levers be adjusted during pre-flight to prevent unintended movement. During pre-flight, the pilot unlocked the collective control to adjust friction and could have noted any interference with the locking tab. The correct autorotation rotor speed range was 395-415 rpm. The procedure the pilot used—reducing power to check rpm—differed from the flight manual, which specified the check be done at full power and that the fuel flow control should not be returned to full power until the autorotation was complete and on the ground.
The Helicopter
The helicopter, an AS 350 BA (C-FPOO, serial number 2508, type certificate H83), had been repaired using structural parts from a damaged AS 350 D (serial number 1131). Héli-Expert, which owned both damaged helicopters, received Transport Canada permission to convert and repair C-FPOO into an AS 350 BA. Héli Fix Services Inc., an approved maintenance organization, completed the project. Eurocopter Service Bulletin 01-00-035, "Conversion AS 350 B Helicopter into AS 350 BA Version," was effective only if the AS 350 B was airworthy at conversion; Transport Canada approved the conversion without regard to that limitation. The project included 14 supplemental type certifications. Examination revealed that modification 350A07-1995 (blanking of upper cavity in collective pitch lever stop), from that SB, was not completed. Additionally, modification 350A07-0679 (replacing normal collective lever with a lever with a control box) was only partly completed; the collective lever low-pitch stop adjusting screw had not been inverted.
Transport Canada inspected the converted aircraft and issued a Certificate of Airworthiness on 08 June 2001. The helicopter had about 300 hours at the time of the occurrence.
Damage and Finding
After the occurrence, an AME examined the helicopter and noted the collective lever locking plate was not engaged; after engagement, it disengaged normally with light pressure. However, the space between the end of the collective lever and the electrical console was about 5 mm—11 mm less than the Eurocopter specification of 16 mm ± 0.5 mm. Witness statements indicated that before the accident, the space was larger and the locking plate did not interfere with collective travel.
Autorotation rpm is set by adjusting pitch links and rotor control links. Using the Eurocopter rigging tool, it was found that the adjustment of the pitch change links and control links exceeded manufacturer dimensions by 5 mm and 8.9 mm, respectively, leading to a lower collective lever position for a given blade pitch and low rotor rpm during autorotation.
Findings as to Causes and Contributing Factors
The collective lever locking plate accidentally engaged, and the pilot was unable to free the collective and slow his descent sufficiently before touchdown. The stop screw was in an inverted position, and the connecting rods were shorter than specified, allowing collective control overtravel down. This condition, combined with the down setting of the collective lever and the locking plate setting, contributed to the locking by reducing space between the electrical console and the collective lever.
Additional Observations
Transport Canada authorized the conversion without regard to the effectivity limitation of Service Bulletin 01-00-35. Deficiencies in maintenance work related to the repair and conversion were not detected by Transport Canada, and the Certificate of Airworthiness was issued when the helicopter was not airworthy.